Alternatives to Coil Tapping

[thedirestrat]

Hello there,

We all know the benefits of coil tapping, it could give two sounds in one. Going from vintage sweet clear outputs, to thicker and louder hotter outputs, simply with a flick of a switch. What if you have a hot pickup you liked, but that's not tapped, and you want lower output capabilities? Rewiring and tapping the pickup is quite arduous, you even need to drill a hole for an extra eyelet for the tap wire. If you're a winder, then it's not too hard, but if not, it's probably expensive-- at least where I live (170+ in Canadian dollars). 

And then I learned about the venerable Mr. Bill Lawrence's Q-Filter (thank you gckelloch!), which I'm sure you wiring aficionados know about. Usually its used as a "Q-Tone", variable inductance control, so you can reduce the inductance of a select pickup by rolling down the knob.

However, I'd like to simulate a coil tap. These are not gradual, but rather are immediate. I think its useful having an immediate "tap like" inductance drop. For example, I have a hot "S-90" pickup in the bridge position, which is beautiful on its own, but for the position 2 when in parallel with the middle pickup, the sound is darker and louder (gets dirtier quicker) than the traditional setting. I'd like to have that traditional setting lol... 
If the Q-Filter was *fixed* on the bridge pickup, only in position 2, to have a certain low inductance, then that sound should more or less be achieved. Of course, it's gonna be a little different with the different pole pieces, but close enough for me at least. Those of you with regular hot Strat pickups, this shouldn't be an issue for you. Of course this should work for any guitar-- in a certain positon, the Q-Filter comes on immediately, and drops the inductance of the pickup you wired it to, just like a tap. Even should work as a coil split, for Humbuckers, you flick a switch (probably push pull) and then your Humbucker is a much lower inductance, with hopefully a resonant frequency vaguely similar to a single coil at least.

Now, here comes the question: how do we do this? 

Let the discussion begin! Thank you once again everyone for making this such a fun place to be a part of.

[thedirestrat]

This is my current, albeit basic, idea on how to do it. 

You first wire the Q-Filter like a variable control, get it working only on the bridge pickup in position 2 (my specific application, the example you guys could use to illustrate this general topic), and roll down the knob until you get the sound you like. Then make note of the resistance on the pot, and then when trying to make it "fixed", you put a resistor of equal (or approximate) value of such resistance to simulate the pot rolled down at your preferred position, and then theoretically it should work! I just don't know how you would wire the Q Filter in the guitar circuit per se. Is it in parallel to the bridge pickup, etc. gckelloch helped me with coming up with this idea when we were talking about q filters.

[gckelloch]

Jul 14, 2022 14:45:00 GMT -5 thedirestrat said:

This is my current, albeit basic, idea on how to do it. 

You first wire the Q-Filter like a variable control, get it working only on the bridge pickup in position 2 (my specific application, the example you guys could use to illustrate this general topic), and roll down the knob until you get the sound you like. Then make note of the resistance on the pot, and then when trying to make it "fixed", you put a resistor of equal (or approximate) value of such resistance to simulate the pot rolled down at your preferred position, and then theoretically it should work! I just don't know how you would wire the Q Filter in the guitar circuit per se. Is it in parallel to the bridge pickup, etc. gckelloch helped me with coming up with this idea when we were talking about q filters.

I'll try to cover all the related aspects of your wiring idea here. First, wiring the Q-filter in parallel with one pickup will be in parallel with any other parallel wired pickups. I have two hand-drawn wiring schemes you might be interested in that don't involve a Q-filter. The blend can be switched to the middle or outer pickups with or without a cap in series and in or out of phase:

drive.google.com/drive/folders/0Bx0CnqsQz_uYd1VsTG1CY0RnWFk?resourcekey=0-cruyLuYHK6nPyzYQ4kvkfw&usp=sharing

The "GCK (Shrd T1 Knb) Blend+Swap=Xover,HOoP - 3xMC's & 5PosSS & 2xPP" scheme blend knob can't be wired to do both full and half freq range blending, and I haven't tested it out. I have successfully wired the other 3 pickup scheme on two guitars.

Neither scheme can blend the bridge and neck pickups, but you could sacrifice one of the switch functions or add another switch to get that option. You can also change whichever cap values if you want a lower blend crossover point or tone knob peak. HOoP schemes recommend a much higher cap value. I was trying to cancel the harsh ~3kHz range. It actually cancels a bit lower range for some reason I don't grasp, but it sounds fine. You might need to go down to ~1nF to cancel the ~3kHz range, but it will still cancel lower than that range when the middle pickup is half blended with your S-90. I really like the 1.5~2kHz tone knob peak on all pickups, but it sounds quite different than the standard values below 7 on the tone knob.

You may not need a Q-filter with either of those schemes. Blending the middle pickup HOoP with the bridge pickup will give your guitar a typical Strat bridge pos sound with the highs from the middle pickup. It's very close in tone to a lower inductance bridge pickup by itself. You'll need to use the scheme that offers both half and full freq blending to get that option along with octave blending options. You might try that scheme b4 ordering a Q-filter.

[thedirestrat]

Wow those are some cool mods gckelloch! Honestly, for this thread, I'm focusing all on that position 2. I'd like to find a way to lower the inductance of the bridge pickup *immediately* when on position 2, when the bridge pickup is in parallel with the middle pickup. That blending stuff is super cool, but I'd rather have something fixed and fast. Like a coil tap! I just would like my position 2 to be like (very similar) to a Strat middle and bridge in parallel sound, so I can get some Robert Cray tones without sacrificing the S90 in the bridge pickup.

Thanks for telling me that the Q-Filter works on *both* bridge and middle pickups in parallel. I think that works fine, I'll just use my ears to see whatever sounds best. I just need to know how to used it "fixed".
Now, if there are better methods to get an immediate drop in inductance and more classical middle+bridge in parallel on position 2, I'm all ears. I know there's some combinations you can do with capacitors and resistors to manipulate the resonant frequency of a pickup, but I'm quite confident that it's for more subtle changes. The Q-Filter should be shedding quite a bit of inductance, and thus, a lot of midrange.

For the out of phase blend, I was discussing it in my other thread as a mod, another degree of functionality, so I can get some out of phase blending and more tones-- from two neck and middle pickups in parallel and in phase to gradually some out of "phaseness" being added to them. Please, whoever wants, go on that thread and shoot your ideas! I'd love to hear.

[gckelloch]

Jul 14, 2022 18:11:13 GMT -5 thedirestrat said:

Wow those are some cool mods gckelloch! Honestly, for this thread, I'm focusing all on that position 2. I'd like to find a way to lower the inductance of the bridge pickup *immediately* when on position 2, when the bridge pickup is in parallel with the middle pickup. That blending stuff is super cool, but I'd rather have something fixed and fast. Like a coil tap! I just would like my position 2 to be like (very similar) to a Strat middle and bridge in parallel sound, so I can get some Robert Cray tones without sacrificing the S90 in the bridge pickup.

Thanks for telling me that the Q-Filter works on *both* bridge and middle pickups in parallel. I think that works fine, I'll just use my ears to see whatever sounds best. I just need to know how to used it "fixed".
Now, if there are better methods to get an immediate drop in inductance and more classical middle+bridge in parallel on position 2, I'm all ears. I know there's some combinations you can do with capacitors and resistors to manipulate the resonant frequency of a pickup, but I'm quite confident that it's for more subtle changes. The Q-Filter should be shedding quite a bit of inductance, and thus, a lot of midrange.

For the out of phase blend, I was discussing it in my other thread as a mod, another degree of functionality, so I can get some out of phase blending and more tones-- from two neck and middle pickups in parallel and in phase to gradually some out of "phaseness" being added to them. Please, whoever wants, go on that thread and shoot your ideas! I'd love to hear.

Problem is: Someone might know better, but I think the middle pickup output will still dominate when in parallel with the much higher inductance S-90 and the Q-filter. You might get a better "quack" if you add 10~20k of resistance to the middle pickup in pos 4. I'd guess the total inductance should still drop enough to get more high-end from the bridge pickup, but you would need the Q-filter to drop the bridge pickup inductance in pos 1. Add whatever resistor you decide on to the filter if you just want the inductance drop. Wire that in parallel with the bridge pickup. Add the supplied cap in parallel with the resistor if you don't want any bass reduction, so it creates a mid dip.

[ashcatlt]

Assuming you don’t need to use the second half of the Strat switch for T pot switching (just wire them across the pickups directly instead, or use master T). You’d ought to be able to connect the top end of the inductor where the bridge hot is and the bottom of it to that same position on the other side of the switch. Connect the middle position lug on that side of the switch to ground. That should make the inductor disconnected except in the bridge+middle position. In bridge-only position, it would kind of be hanging from hot, but idk how much of an issue that would be.

[Yogi B]

Jul 14, 2022 14:40:42 GMT -5 thedirestrat said:

Usually its used as a "Q-Tone", variable inductance control, so you can reduce the inductance of a select pickup by rolling down the knob.

To expand on what gckelloch has already said, the Q-filter does not "reduce the inductance of a select pickup", it presents a load to one or more pickups that is somewhat similar to the impedance of the pickups themselves. It's kinda similar to what happens when you put two pickups in parallel: each pickup intrinsically puts out the same voltage as it would alone but each pickup is also loaded by the other, nearly identical, pickup — because of the laws of voltage dividers this (roughly) halves each pickup's output voltage, but adding these two halved voltages together gives a similar output level to either lone pickup. The Q-filter has a similar loading effect, the difference being that it isn't a pickup thus does not contribute its own voltage, thereby we only get the reduced output from the actual pickup(s).

For example, I have a hot "S-90" pickup in the bridge position, which is beautiful on its own, but for the position 2 when in parallel with the middle pickup, the sound is darker and louder (gets dirtier quicker) than the traditional setting. I'd like to have that traditional setting lol...

If the Q-Filter was *fixed* on the bridge pickup, only in position 2, to have a certain low inductance, then that sound should more or less be achieved.

For the reason discussed above, you can't have the Q-filter affect only one pickup of a parallel pair (at least not with the standard wiring) — it'll affect both the bridge & middle alike. True, that will lower the combined output, and that might be good enough, but it won't actually fix the underlying imbalance.

Normally what happens with pickups of a similar construction is that the output voltage and (resistive) impedance scale roughly proportionally so parallel combinations are, to some extent, 'self-balancing'. The overwound pickup's larger output voltage is reduced to less than half due to the voltage divider formed from it's own larger impedance and the smaller impedance of the underwound pickup — whereas the underwound pickup's lesser output voltage isn't reduced by as much, due to the same albeit 'mirrored' voltage divider.

With vastly dissimilar pickup construction this 'self-balancing' property ceases to be, however we can try to restore it by attempting to (re-)match the pickups' voltage/impedance ratios. At it's most basic this can be done by adding series resistance to the hotter pickup (like a parallel blender, just to a lesser extreme). However, with just resistance this will disproportionally cause a reduction in the bass contribution of the pickup being tamed (though in practice this may not be a problem). To get a more even reduction across all frequencies we'd also add some amount of series inductance (e.g. the Q-filter), though the ideal amount will vary between different pickups.

[gckelloch]

Jul 14, 2022 19:10:01 GMT -5 Yogi B said:

Jul 14, 2022 14:40:42 GMT -5 thedirestrat said:

Usually its used as a "Q-Tone", variable inductance control, so you can reduce the inductance of a select pickup by rolling down the knob.

To expand on what gckelloch has already said, the Q-filter does not "reduce the inductance of a select pickup", it presents a load to one or more pickups that is somewhat similar to the impedance of the pickups themselves. It's kinda similar to what happens when you put two pickups in parallel: each pickup intrinsically puts out the same voltage as it would alone but each pickup is also loaded by the other, nearly identical, pickup — because of the laws of voltage dividers this (roughly) halves each pickup's output voltage, but adding these two halved voltages together gives a similar output level to either lone pickup. The Q-filter has a similar loading effect, the difference being that it isn't a pickup thus does not contribute its own voltage, thereby we only get the reduced output from the actual pickup(s).

For example, I have a hot "S-90" pickup in the bridge position, which is beautiful on its own, but for the position 2 when in parallel with the middle pickup, the sound is darker and louder (gets dirtier quicker) than the traditional setting. I'd like to have that traditional setting lol...

If the Q-Filter was *fixed* on the bridge pickup, only in position 2, to have a certain low inductance, then that sound should more or less be achieved.

For the reason discussed above, you can't have the Q-filter affect only one pickup of a parallel pair (at least not with the standard wiring) — it'll affect both the bridge & middle alike. True, that will lower the combined output, and that might be good enough, but it won't actually fix the underlying imbalance.

Normally what happens with pickups of a similar construction is that the output voltage and (resistive) impedance scale roughly proportionally so parallel combinations are, to some extent, 'self-balancing'. The overwound pickup's larger output voltage is reduced to less than half due to the voltage divider formed from it's own larger impedance and the smaller impedance of the underwound pickup — whereas the underwound pickup's lesser output voltage isn't reduced by as much, due to the same albeit 'mirrored' voltage divider.

With vastly dissimilar pickup construction this 'self-balancing' property ceases to be, however we can try to restore it by attempting to (re-)match the pickups' voltage/impedance ratios. At it's most basic this can be done by adding series resistance to the hotter pickup (like a parallel blender, just to a lesser extreme). However, with just resistance this will disproportionally cause a reduction in the bass contribution of the pickup being tamed (though in practice this may not be a problem). To get a more even reduction across all frequencies we'd also add some amount of series inductance (e.g. the Q-filter), though the ideal amount will vary between different pickups.

Ah, so two would generally balance if of the same construction. I'd assume the higher wound of the two would still contribute less high-end, which may reduce the "quack" factor? That might still be a problem if the S-90 has a strong magnet as well as the Steel screws = is more efficient. Adding resistance to it would reduce highs even more, no? I suppose he could try using a Super Switch and wiring pos 4 without the tone knob, and not connecting the open lug of the blend knob (if incorporated). That would bring back some high-end. Would adding resistance to the middle pickup then be useful, or is it time to consider replacing the S-90 with something like the middle pickup?

[thedirestrat]

Yogi B, gckelloch, ashcatlt,

Thank you so much for your invaluable information. I know know how to install the Q Filter more or less, the problem is what resistor to put in front of it to control how much of it works, and getting those pickups "self balanced", even though those pickups aren't the same at all. I also *really* don't want Position 1 to be tampered with, I'd like the full S90, no inductance cuts or whatnot. Luckily, I'm using a Super Switch and my positions 2 and 4 are wired so that there is no tone pot on those positions. This should help with quack and brightness. 

I'd like to get close to a coil tapping result but I'm not sure if we can do it. Is it worth it to wind it yourself? I was thinking of rewinding the pickup and making it tapped, but then I found out about the Q-Filter, I knew I had at least had to try it out.

[Yogi B]

Jul 14, 2022 20:39:49 GMT -5 gckelloch said:

Ah, so two would generally balance if of the same construction. I'd assume the higher wound of the two would still contribute less high-end, which may reduce the "quack" factor?

Compared to the other pickup, yes. However, in terms of that pickup's resonant peak, it will be shifted by the loading of the quieter pickup such that it's taller & at a higher frequency than the hotter pickup alone — so it mightn't be as bad you expect. To be fair, I'm just usually more concerned with overall level or low frequencies (for the sake of hum-cancellation), than quack.

Though now I'm putting more thought into it, the reason for the comparatively lesser treble contribution is due to the inductance of the hotter pickup rising more quickly than resistance or voltage (ideally at a square of that rate, but off the top of my head it's usually lower, maybe around a power of five-thirds) — this 'extra' inductance could very well make redundant my earlier suggestion of wiring the Q-filter in series with the pickup, meaning only the resistor would be required.

Adding resistance to it would reduce highs even more, no?

To a small degree, but with the (primarily inductive) loading of the middle pickup, any extra resistance is mainly forming an R/L high pass filter, so bass gets reduced at a much faster rate than the loss of treble.

That might still be a problem if the S-90 has a strong magnet as well as the Steel screws = is more efficient.

Ideally you would want a more efficient pickup, where the hotter pickup produces the ratio of the two pickups' inductances times the voltage of the quieter pickup — rather than (approximately) the ratio of resistances, as you'd get by simply overwinding. In this ideal case, upon adding enough external series resistance to the hotter pickup, such that the ratio of resistance to inductance is equal between the pickups, then by extension the ratio of voltage to impedance would also be equal and thus both pickups would contribute equally. (That's probably clearer written as math, and I should also do that to double check I have it right, but for now that'll have to wait until later.)

---

Jul 15, 2022 0:54:20 GMT -5 thedirestrat said:

I know know how to install the Q Filter more or less, the problem is what resistor to put in front of it to control how much of it works

If you're going with my plan then you mightn't need the Q-filter (see above), but the idea is you'd put both that and the resistor in series with the bridge pickup. The way you'd wire that is to hook the bridge to the position-1 terminal as normal, but rather than using a wire jumper between that and the adjacent position-2 terminal that's where you'd insert the resistor/Q-filter.

Is it worth it to wind it yourself? I was thinking of rewinding the pickup and making it tapped, but then I found out about the Q-Filter, I knew I had at least had to try it out.

In this day & age I see only a few reasons to actually want a rewind on a fully functional pickup, back in say the '70s where pickup parts were presumably harder to acquire, sure I can see rewinds being a necessity. But nowadays, that's a less common problem. If one were to have a rare/obsolete (but not especially sought-after) pickup, whereby that limitation on parts still exists, then it could make sense; and obviously a rewind might be the only way to fix certain dead pickups. However, with a fully working pickup I'd expect its sale offsetting the cost of a new pickup would often work out cheaper or at least pretty close to the price of a rewind.

[thedirestrat]

Jul 15, 2022 3:50:59 GMT -5 Yogi B said:

n this day & age I see only a few reasons to actually want a rewind on a fully functional pickup, back in say the '70s where pickup parts were presumably harder to acquire, sure I can see rewinds being a necessity. But nowadays, that's a less common problem. If one were to have a rare/obsolete (but not especially sought-after) pickup, whereby that limitation on parts still exists, then it could make sense; and obviously a rewind might be the only way to fix certain dead pickups. However, with a fully working pickup I'd expect its sale offsetting the cost of a new pickup would often work out cheaper or at least pretty close to the price of a rewind.

Just what I thought. And that's why I don't wanna cut into my S90 pickup and change its windings, I like the way it sounds by itself. I'd just like to get something close to having it coil tapped for position 2, so I can get classical Strat quack out of it, instead of the "mud" that I'm getting now. So is there anyway to do this? I know you and gckelloch were talking about possible solutions, but I'm not sure I fully comprehended, sorry...

1. I believe you said a possible solution is to add series (external) resistance to the S90 hotter pickup. Doing so would make the "self balancing" equal between the two pickups, thus this will make the impedance/voltage ratios equal on both pickups, like a normal conventional Strat? Thus, it should be more normal Pos. 4 sounding? If so that is great. I know that a resistor can also increase Q factor, and that when in parallel, the S90 (hotter) pickup should have a resonant frequency that is taller and high in freq more so like a normal Strat pickup-- so thus, emphasizing this peak, the Q, via a resistor, this will add some of that treble back in too? Basically, I'd like to know absolutely why having the self balancing parallel position (equal loading on the two of them) is essential to having a more normal sounding Pos. 4.

2. Why no Q-Filter? Because the hot S90 already has extra inductance, so no need for the Q-Filter. But why these need for extra inductance? I know you originally said we needed the Q Filter for the bass frequencies-- this would emphasize the bass, or lower the bass? In sum, what's the problem with the bass? Too much or too little with these extra added series resistors?

3. Shouldn't we be focusing on the resonant frequency of the S90 pickup, and manipulating it so that it resembles a normal Strat pickup? I heard you can do this with capacitors and resistors. I'm thinking I would have a capacitor and high ohm resistor in parallel with each other, and that little combo in series with the bridge pickup (S90), so that it is more Strat like. Thus no need for Q Filter-- but there are problems. I think this combo would affect both pickups in parallel too right? Or else, if I make it only affect the bridge S90 pickup, then by itself, that combo will still be there, which is not ideal at all obviously. Maybe adding the series resistance to the S90 like you mentioned Yogi B is manipulating the resonant frequency to a normal Strat reso freq? Maybe having them in parallel already makes the reso peak of the S90 like a Strat pickup, and adding the series resistors just emphasizes this peak along with aiding in equal ratios of Voltage/impedance on the two pickups?



4. Lastly... how is quack caused between two pickups? Since I want to emphasize that quack as much as possible, à la Robert Cray (I can't get enough of this guy!), I think knowing what controls it is a good start to wanting to later emphasize it. It can't just be voltage dividers, the stuff you explained before Yogi, right? I heard it had to do with comb filtering too, or something like that. Anyways, if there's something I can do to emphasize the "quack", other than equally balancing those ratios between the pickups and a Q Filter, I'll do it. Also, gckelloch, I am going to have a wiring with a super switch so that the tone knobs get disconnected in the 2 and 4 (in-between) positions to "maximize the quack". So maybe treble isn't that much of an issue.

Thanks guys, I'm learning so much

[ashcatlt]

The comb filtering comes from the fact that the harmonics are in different phases at different points in the string, so that some will reinforce between pickups while some cancel out to some degree. In order to get the strongest effect, the various harmonics want to be as close to the same level between pickups as possible. But the slope of the harmonic series is different at different spots along the string which is like the whole reason we have more than one on so many guitars. There’s no good electronic way to even out that slope. I think you’d want to target one or a couple of the out of phase harmonics and balance things so that their levels were roughly equal between pickups. Just matching the fundamentals is not going to maximize the phase cancellation. The middle pickup will probably need to be louder than the bridge and probably by a fair bit.

But honestly idk a damn thing about quack. I think there’s more to it than that kind of comb filtering. Honestly the best way to maximize it is probably the old fashioned way. Use three very similar pickups and adjust their heights by ear until you get what you want.

[gckelloch]

I think Robert Cray uses pos 4 a lot, and he picks very hard. You simply may not be able to get that tone with the S-90 in the bridge. A cheap way to solve this dilemma would be with an ~$80 set of Tonerider pickups. Off hand, I'd say the Surfari set would be closest to the Cray sound. The AIII poles allow to set the pickups close to the strings to maximize the punch and note fundamentals. I like the sweet tone of those the most in the clean video demo, and those who have tried other Tonerider sets generally prefer them. The Pure Vintage set sounds thinner and more metallic, but they might work for you. The bridge pickup in the other sets seems too high inductance for a good quack tone. You might be able to use just the Surfari bridge pickup with your other two pickups if they are not full strength AV poles, but mixing pickup sets can be a crap shoot.

To get the tone of your S-90 with either of those pickups, you can use a 1.5~2nF cap on the bridge tone knob to get a 1.5~2kHz peak with the knob below 7. The cap value and peak freq being the same is purely coincidental. It works well. I have that on 3 guitars, and I ground the outer lug so the peak isn't too strong. You can then wire up a blend knob for pos 2 & 4 as you like. I'd add a ~250k R to ground on 2 & 4 if you don't connect the open lug to ground, but you might like it without it. You won't need a Q-filter either.

[roadtonever]

That would probably compromise on the solo tone of the S90 though. Because it has a steel loaded core that imparts its own attack characteristic vs Alnico rods.

[gckelloch]

Jul 16, 2022 13:31:07 GMT -5 roadtonever said:

That would probably compromise on the solo tone of the S90 though. Because it has a steel loaded core that imparts its own attack characteristic vs Alnico rods.

One of the more knowledgeable members here pointed out that permeability only increases efficiency to a point, beyond which it doesn't make a difference. AIII is generally more permeable than AII or AV, and I think the difference can be heard. Not as Permeable as Steel, but the total magnetic power would determine how the poles affect string timbre. Chances are the S-90 will have a more aggressive attack character at the same string distance, and raising the Surfari pickup to compensate will increase the transient punch and the lower harmonic strength. It won't be quite the same sound, but it's one possible inexpensive solution. A Steel baseplate would increase warmth and output at a given height without much affecting the high end. Same goes for the Pure Vintage model, which would then probably have better quack than the Surfari. I've already recommended a set of MicroCoils, but they are 2x the price and there's the issue with the stock pole screws. The AlNiCo MC's might be good, but the inductance is much lower than usual at only 1.4H.

[Yogi B]

Jul 15, 2022 3:50:59 GMT -5 Yogi B said:

That might still be a problem if the S-90 has a strong magnet as well as the Steel screws = is more efficient.

Ideally you would want a more efficient pickup, where the hotter pickup produces the ratio of the two pickups' inductances times the voltage of the quieter pickup — rather than (approximately) the ratio of resistances, as you'd get by simply overwinding. In this ideal case, upon adding enough external series resistance to the hotter pickup, such that the ratio of resistance to inductance is equal between the pickups, then by extension the ratio of voltage to impedance would also be equal and thus both pickups would contribute equally. (That's probably clearer written as math, and I should also do that to double check I have it right, but for now that'll have to wait until later.)

(As well as easier to spot what potentially dubious assumptions I'm making.)

SPOILER: Click to show

If we have two pickups A & B with intrinsic outputs of V_A & V_B and (series) impedances of Z_A & Z_B, connected in parallel the voltage contribution (V_a & V_b) of each pickup loaded by the other's impedance is given by:
\begin{aligned}
V_a &= {V_A Z_B \over Z_A + Z_B}
\\[1.5em]
V_b &= {V_B Z_A \over Z_A + Z_B}
\end{aligned}Note, I'm ignoring the parallel impedances such as the pickups' capacitance & damping inductance/resistance. If purely combining the two pickups all these are in parallel and their effects can be added by a further calculation. In our case we're adding an external series resistance to one of the pickups so this isn't perfectly true, but despite this the simplification should still yield a reasonably good approximation because the parallel impedances are typically significantly larger than the series impedances.

If we then define a ratio of the two pickups' inductances and duplicate this ratio also between the resistances via addition of an external resistor (here I'm choosing pickup A as the hot pickup and assuming L_A > L_B, thus adding resistor R_x, to the intrinsic resistance of pickup A, R_a). We get:
\begin{aligned}
L_A &= x L_B
\\[1.5em]
R_a + R_x &= {L_A \over L_B} \cdot R_B = x R_B = R_A
\end{aligned}So, looking at the impedances and substituting equivalents for L_A & R_A, we have:
\begin{aligned}
Z_B &= R_B + \omega j L_B
\\[1.5em]
Z_A & = R_A + \omega j L_A
\\[1.5em]
&= x R_B + \omega j x L_B
\\[1.5em]
&= x (R_B + \omega j L_B)
\\[1.5em]
&= x Z_B
\end{aligned}Since we're interested in when are loaded voltages are equal we'll, equate our equations from earlier:
\begin{aligned}
V_a &= V_b
\\[1.5em]
{V_A Z_B \over \cancel{Z_A + Z_B}} &= {V_B Z_A \over \cancel{Z_A + Z_B}}
\\[1.5em]
V_A Z_B &= V_B Z_A
\\[1.5em]
V_A \cancel{Z_B} &= V_B x \cancel{Z_B}
\\[1.5em]
V_A &= x V_B
\end{aligned}If however we had a pickup that were simply an overwound version of pickup B, and since (all else being equal) output voltage is approximately proportional to the number of turns, thus approximately proportional to resistance, we'd have:
\begin{aligned}
V_{OW} &\approx R_a \cdot {V_B \over R_B}
\\[1.5em]
&\approx \left({L_A \over L_B} \cdot R_B - R_x\right) \cdot {V_B \over R_B}
\\[1.5em]
&\approx \left({L_A \over L_B} - {R_x \over R_B}\right) \cdot V_B
\\[1.5em]
&\approx \left(x - {R_x \over R_B}\right) \cdot V_B
\\[1.5em]
\therefore V_{OW} &\lesssim V_A &\left(\text{since ${R_x \over R_B} > 0$}\right)
\end{aligned}Thereby, for the almost ideal balancing of the two pickups, pickup A must be more efficient (in terms of volts per ohm) than pickup B, by a factor of L_A × R_B / L_B / R_a. (This factor being greater than one being essential to the validity of the whole of this analysis).

---

Jul 16, 2022 1:30:47 GMT -5 thedirestrat said:

1. I believe you said a possible solution is to add series (external) resistance to the S90 hotter pickup. Doing so would make the "self balancing" equal between the two pickups, thus this will make the impedance/voltage ratios equal on both pickups, like a normal conventional Strat? Thus, it should be more normal Pos. 4 sounding?

Not exactly like a conventional Strat (wherein I'd say all the pickups are close enough in output/impedance to be almost negligible), but hopefully closer, yes.

I know that a resistor can also increase Q factor, and that when in parallel, the S90 (hotter) pickup should have a resonant frequency that is taller and high in freq more so like a normal Strat pickup-- so thus, emphasizing this peak, the Q, via a resistor, this will add some of that treble back in too?

Though there will be some amount of it, it's not exactly about adding back treble, but instead cutting the bass & mids in order to form a new resonant peak.

Basically, I'd like to know absolutely why having the self balancing parallel position (equal loading on the two of them) is essential to having a more normal sounding Pos. 4.

Because equal loading is the normal sound for position 4, as you'd typically have nearly identical pickups. I'll admit that I slightly misspoke earlier, the self-balancing property is intrinsic any parallel combination, but combinations of overwound/underwound pickups of similar construction automatically have proportional (resistive) loading, whereas combinations with differing pickup designs this is unlikely to be the case. Proportional loading (of which equal loading is a special case), means that both pickups contribute electrically equally (i.e. excluding effects of pickup height & string harmonics), as I said this is the default case with a regular Strat so attempting to force your pickups to adhere to it should get you closer.

2. Why no Q-Filter? Because the hot S90 already has extra inductance, so no need for the Q-Filter. But why these need for extra inductance? I know you originally said we needed the Q Filter for the bass frequencies-- this would emphasize the bass, or lower the bass? In sum, what's the problem with the bass? Too much or too little with these extra added series resistors?

In a parallel combination, adding more & more series resistance to a pickup predominantly lowers its bass & mids contributions to the overall mix, whereas adding series inductance mainly cuts mids & treble, so it's a balancing act. If the S-90 is so loud that we need a particularly large resistor in order to reduce its overall volume we might end up cutting more of its bass that we'd like, so we can offset that by reducing the extra resistance and adding inductance.

This also goes back to proportional loading, ideally we'd have both the resistances and the inductances of the pickups share the same ratio.

3. Shouldn't we be focusing on the resonant frequency of the S90 pickup, and manipulating it so that it resembles a normal Strat pickup?
...
Maybe having them in parallel already makes the reso peak of the S90 like a Strat pickup, and adding the series resistors just emphasizes this peak along with aiding in equal ratios of Voltage/impedance on the two pickups?

Bingo! With the typical Q-filter wiring we're placing a series inductor & resistor (& relatively large cap, which I'm ignoring because its purpose is to emphasise the mid-scoop) in parallel with the affected pickup(s) — a pickup, is itself a series inductor & resistor and so adding another in parallel results in a similar effect.

Also since you mentioned it, in an isolated circuit adding a capacitor in series and adding an inductor in parallel (and vice-versa) give largely the same results — this is because inductive impedance is the reciprocal of capacitive impedance. Which is 'best' for a given situation depends upon how the surrounding components will affect (or, will be affected by) this choice — though capacitors are also usually greatly preferred due to being cheaper, more available, and generally closer to ideal.

4. Lastly... how is quack caused between two pickups? Since I want to emphasize that quack as much as possible, à la Robert Cray (I can't get enough of this guy!), I think knowing what controls it is a good start to wanting to later emphasize it.

You might struggle in that regard, I don't know of any attempt to quantify quack, so you're unlikely to "control" it, only influence it. My view is that that the comb filtering, due to the sensing aperture of each pickup, is the single underlying source of quack — other factors such as pickup height and electrical interaction between pickups can't add quack, just do a better/worse job of maintaining what is already there. My focus on the electrical side is in attempt to get the situation close to that of a regular Strat and thus hopefully minimize one of those variables.

[gckelloch]

Again, someone else might know more, but to follow up about the effect of different pole magnets. Assuming the Tonerider clean video samples were recorded with the same amp settings, it sounds like the output of these three sets from strongest to weakest is: Classic Blues, Pure Vintage, Surfari. That should have much more to do with magnetic power than the respective inductance differences, but the Classic Blues set may also have thinner wire insulation = denser coils which may audibly affect the lower harmonic strength. The bridge pickup also has 43AWG wire, so there may be a slight increase in lower harmonics (and maybe midrange clarity), even if the bobbin height has not been shortened to increase efficiency -- I doubt it has been.

It should be noted that stronger pole magnets do not "produce more bass", as is a common misconception. As mentioned b4, the harmonics are affected by increased string pull so the attack and note timber is usually harsher and thinner sounding, and the total signal output is higher. The Surfari's do sound like they have less bass and highs in the video, but that is likely to do with how a stronger signal affects the amp gain structure. The real test would be to listen to DI recordings of each set adjusted to the same output level, or if one runs a clean boost pedal b4 a guitar amp, or through an amp model with a level adjustment b4 the first gain modeled stage. That's how we could really hear the differences in pickup character at the same string distance (with the exception of the inductance & internal capacitance differences).

Yikes! If you can wait a month for delivery, this looks worth a shot for a ~3H Strat bridge pickup with a Copper-plated Steel baseplate:
www.aliexpress.com/item/3256803865932460.html?spm=a2g0o.detail.1000014.26.46b84734T7Hp9F&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.14452.226710.0&scm_id=1007.14452.226710.0&scm-url=1007.14452.226710.0&pvid=a392c72e-8bd2-4e4c-8989-8f4f39e9f1ba&_t=gps-id:pcDetailBottomMoreOtherSeller

It also has a modern stagger like the Toneriders. Might have full strength AV poles, but they can be de/re-Gaussed with a strong permanent magnet if desired. I may be thin insulation poly wire, but potentially harsher midrange can be countered via magnetic strength and/or Aluminum pickguard shielding. You may just need to order a bobbin cover for it. Those are really cheap.

My guess is it's the bridge pickup from this set, but with HF or Poly wire:

www.aliexpress.com/item/3256804066778942.html?spm=a2g0o.detail.0.0.45b23f08UTk2Wy&gps-id=pcDetailBottomMoreThisSeller&scm=1007.13339.274681.0&scm_id=1007.13339.274681.0&scm-url=1007.13339.274681.0&pvid=08964782-6cf4-4459-afa2-e3ca2668e07d&_t=gps-id:pcDetailBottomMoreThisSeller

Look at the printing on the bobbin bottom? I wouldn't be surprised if those are just like the actual Suhr V70 pickups with the weaker AV poles.  Maybe get the full set and the bridge pickup with the Steel baseplate to try which you prefer. I'd go for them myself if I didn't already have all Wilde NF and MC pickup sets.

[gckelloch]

I forgot that you said your S90 has AII magnets. That would mean the output would be even that much lower at the same string distance when combined with the middle AlNiCo pole pickup. Judging from the average Gauss level of only ~250 at the screw tops in a PAF with an A5 magnet, it might be even lower than that. The tops of full strength AV measure ~1000! AII is ~1/2 that, and AIII is a little lower still. Considering that, the higher inductance (4~5H?), and the reduced high-end from the high impedance Steel core, even after accounting for the efficiency of higher permeability, the problem is likely that its output is considerably lower when in parallel with your middle Strat pickup. BTW, does it have a 42AWG coil at 10k, or?

This leads me to believe that even a (weakened) AV, AII or even AIII pole 2.5~3H Strat pickup with a Steel baseplate will have at least as much punch and bite as your S90. and essentially the same tonal quality with a 1.5~2nF cap on a tone knob set somewhere below 6.

BTW, Yogi: doesn't the fact that the Steel core S90 has much higher impedance in the high-end than an AlNiCo pole pickup mean the high-end from it will be that much more reduced when in parallel?

[Yogi B]

Jul 18, 2022 20:40:39 GMT -5 gckelloch said:

I forgot that you said your S90 has AII magnets.

Where? As far as I can see, thedirestrat has mentioned the pickup here & in the cocked wah thread but don't see a mention of magnets in either thread. (Obviously it doesn't necessarily have to be true in all cases, but on single-coil sized P90s I've typically seen ceramic magnets — they seem more readily available in the reduced width as required by the design.)

Judging from the average Gauss level of only ~250 at the screw tops in a PAF with an A5 magnet, it might be even lower than that.

Not knowing the pickup I don't know if the pole pieces are the same as a typical PAF or if they, as some are, are thicker. (Some use what are essentially only very lightly threaded slugs and, despite personally not recommending these, may contribute to higher flux density.) Plus, even if they are the regular fillister screws, I assume the coil is at least the typical Strat height — taller than a standard PAF bobbin — meaning there'll be less screw length protruding out the rear. antigua has previously shown this can increase flux density at the poles, perhaps by even more so in the S90, since the screw won't be trimmed. Additionally, doesn't the opposing dual (though admittedly reduced in size, compared to actual P90s) magnet arrangement usually result in higher gauss than a PAF?

Considering that, the higher inductance (4~5H?), and the reduced high-end from the high impedance Steel core, even after accounting for the efficiency of higher permeability, the problem is likely that its output is considerably lower when in parallel with your middle Strat pickup.

Given that thedirestrat stated that the combination of middle & bridge is "darker and louder ... than the traditional setting" (and described the S90 as hot, so presumably has more volume than the lone middle) I don't think that's the problem.

BTW, Yogi: doesn't the fact that the Steel core S90 has much higher impedance in the high-end than an AlNiCo pole pickup mean the high-end from it will be that much more reduced when in parallel?

To some extent, yes. However, the plan to add the resistor would raise the impedance for the S90 at lower frequencies, thereby evening out the response. This does leave the S90 with significantly reduced output across the board, but it sounds like that needs to happen anyway. Though whether the (comparatively) flat frequency response & matched volume levels coincide is basically pot luck when combining arbitrary pickups, so is likely to need further help via adjustment of pickup height(s).

[gckelloch]

thedirestrat mentioned the S90 AII magnets in a PM discussion we had b4 he started this thread. Yeah, I guess it would be too hard to determine the Guass at the top of the screws with all considerations, but I would strongly doubt it is near as high as the top of an AlNiCo V Strat pole. A guy over at WGS speakers measured the top of pole/screw Guass for a bunch of pickups. The AII-powered P90 was only ~300, and the magnets would be much shorter on the S90. The AII pole Strat pickups he measured were higher than I expected, up in the 700-800 range. Here: wgsusa.com/blog/exactly-what-guitar-pickup-gauss-magnetic-charge-level-means-and-why-its-important-tone

The darkness of the pos 2 sound could be the lack of added bridge pos upper-harmonics and/or how the lower combined output of the S90 pickup affects cancelations? Maybe there's a lack in the 2~4kHz range, yet there's still some highs from the middle pickup, but somewhat stronger lows if the two very different sounding pickups are close in output only below ~2kHz?

The question is whether to spend time and money experimenting with resistors and a passive coil or to just replace the bridge pickup with something more likely not to cause a dark pos 2 sound, and use a cap on the tone knob to emulate the S90 tone. That Alibaba pickup with the Steel baseplate is the best deal I could find, and deGaussing if desired is not a difficult or "destructive" task...and Heckubis, the baseplate alone might cost that much. If not having adjustable pole screws is not an issue, I'd go for it. It even comes in flat poles or modern stagger. I prefer the clarity of the middle strings the modern stagger would offer, and there'd probably be better quack on those strings when combined with the middle SC. BTW, just judging from the color of the coil wire, I think it's actually HF wire. I think there is a bit less fundamental than PE or Poly insulation 42AWG, but the Steel baseplate should at least compensate for that effect.

[thedirestrat]

Yogi B gckelloch

Sorry for the late response guys, I finally have the chance to discuss this. 
I've thought about it, and I decided: "hm, let's play the Strat in question again, and let's see how it sounds" Position 1, the S90 by itself, sounded great. Quite P90ish and different than the rest of the pickups, and I really like that. Position 2 honestly wasn't even too bad. It felt like that "classic quack" was in there somewhere, but was being choked and buried and muffled... so darker maybe a bit louder. Its in there somewhere though, we just have to rescue it!

gckelloch, I really appreciate you being the source of reason around here, telling me that it is a better idea to just simply buy a classic Strat bridge pickup for that classic quack, and then approximating the P90 tone from there, in order to get closer to that Cray tone. But you know what I realize? Even with the quackiest setting ever, I'm still not going to sound like Cray, because I can't play like Cray. I need to focus on practicing, and buying new pickups, albeit relatively inexpensive ones, is something that I don't want to go for now. It's great to know that there are great inexpensive pickups out there, and a AlNiCo 3 pickup with a baseplate sounds very tempting. Yet, I'd rather get some resistors for cheap locally or even use the ones I have and try from there. Yes, I know it would take some time to find which setting yields the best sound, so if it just takes too much time, I probably will be happy with I already have. But I'm going to do it though, for I'm quite excited to try out this resistor method! 

I went into this thread with the idea of simulating a coil tap without having one. I'm pretty sure that with a tapped S90 pickup, lowest tap being like 6.4 kOhms, in parallel with my 6.3 kOhm middle pickup, I'm quite sure that would yield some serious quack. Now if we can get close to that using other means that "do the same thing" as a tap of 6.4 kOhms, then that's interesting, so I thank you all for the info and wisdom!


Before I start asking questions, I think I should answer some. I think I should provide you guys some info on my pickups.

Middle Pickup: 
6.3 kOhms, around 2.5 Henries, it got bevelled Alnico 5 pole piece magnets, and has 42 AWG Formvar wire. Classic (60's) Strat pickup when it comes to construction.

Bridge S90 Pickup
10 kOhms, 4 something-ish henries, I think 4.66 H, it got steel slot head screw slugs, powered by two Alnico 2 bar magnets. I'm pretty sure the wire is 42AWG, and I know for sure it is enamel wire. If I recall, the screws are phenolic core, or something like that. The producer of the pickup doesn't make em anymore, so I can't look up the specs of its construction any more. All I know is that core thing is an attempt to stay as true as possible to a real P90 pickup.

Sorry for not mentioning earlier, and thanks for the reminder gckelloch!

Ok now the electrical side of things.

Jul 14, 2022 19:10:01 GMT -5 Yogi B said:

With vastly dissimilar pickup construction this 'self-balancing' property ceases to be, however we can try to restore it by attempting to (re-)match the pickups' voltage/impedance ratios.

This is the goal, we're going to try and get the two pickups "the same", for the lack of better words. Obviously they won't be completely the same, but hopefully this ratio will be close. This is what Mr. Kinman of Kinman Pickups has to say about quack: "It's produced by 2 identical high-peak Fender type pickups running in parallel and in-phase. When one of the pickups is different in some way the quack gets compromised to varying degrees. The greater the difference the less quack." I believe the series resistor route follows through with Kinmans words, so that's good.

Jul 15, 2022 3:50:59 GMT -5 Yogi B said:

the reason for the comparatively lesser treble contribution is due to the inductance of the hotter pickup rising more quickly than resistance or voltage

Jul 16, 2022 17:37:29 GMT -5 Yogi B said:

If the S-90 is so loud that we need a particularly large resistor in order to reduce its overall volume we might end up cutting more of its bass that we'd like, so we can offset that by reducing the extra resistance and adding inductance.

What I'd like to talk about is the treble and bass frequencies.

Treble
I understand that the S90 naturally has a bit less treble based off its construction (high inductance and steel screw pole pieces), but treble isn't too much of a problem since I'm going to be using the no tone pot position 4 super switch mod, and adding series resistance cuts bass (and mids) not treble anyways. Of course, the whole reason to add this series resistance is to emphasize the new reso peak in the parallel setting and aiding in equal ratios of voltage/impedance on the two pickups-- that reducing in bass and mids is an extra (well it's part of the whole reso peak thing). You also mentioned Yogi B that the reason why the S90 has less treble is because the the inductance rising more quickly than resistance or voltage. So here adding more inductance won't help. So what do I do if there's somehow not enough treble? I don't think this will be a problem though.

Bass
I understand the bass may be a bit of an issue. Series resistance, which we need, cuts bass, so there might not be enough. How do I get it back? Reducing the resistance and adding inductance to cut some treble (bring in bass) you say. My question is: How do I add inductance to cut treble to emphasize bass? I add an inductor? What exactly is that? A little coil that has a fixed henries amount? Just like there's a typical resistor with a fixed resistance amount? That seems hard to find, so are there any alternatives, like a capacitor for example?

Jul 19, 2022 1:08:00 GMT -5 Yogi B said:

This does leave the S90 with significantly reduced output across the board, but it sounds like that needs to happen anyway. Though whether the (comparatively) flat frequency response & matched volume levels coincide is basically pot luck when combining arbitrary pickups, so is likely to need further help via adjustment of pickup height(s).

I really don't want the tone and sound to be changed in position 1, the S90 by itself. The only thing I'm ok with happening here in position 1 is the output lowering. The output of this pickup is simply mean, and overpowers the other pickups. Kinda cool, but yeah there's a jump in volume. I thought of fixing this with pickup heights, but maybe I don't have to if the output will be reduced due to these series resistances. But why would the series resistance affect the output even in position 1, where the whole series resistance thing shouldn't be present (it should only be present in position 2)?


Lastly... what is the value of the resistor? I understand I'd have to do some trial and error, but with the specs I gave above about my pickups, is there some way of knowing at least the general range of resistor values I should aim for when purchasing/finding resistors? Also, I don't think I need the Q Filter unless I need to cut some highs for preserving the bass-- but I really don't want to spend 34 dollars USD just for this sole purpose! There must be another inductor out there or another means necessary just in case I need to add series inductance.

Ok Lastly for real now: Yogi B, thanks for that excellent math in your previous post. Reading through it was quite fun, and your wisdom and skill never ceases to impress. 

[gckelloch]

Glad to hear back, thedirestrat. I'm not trying to push any one solution, but merely offering options. BTW, since the middle pickup is AV, the Steel baseplate AV pickup on Alibaba would likely be a better choice than an A3 pickup. Not sure how it works, but the Steel baseplate may actually draw some of the total magnetic power away from the other side of the pole so it sounds less spikey, and the thicker coil from the HF wire insulation might even give it more of a P90 character -- midrange cancelation?

I don't think the S-90 pole screws could be phenolic. That's a type of plastic fiber used as circuit boards. The volume increase compared to the middle pickup could be somewhat of an illusion. I'd be surprised if a 10k 42AWG wire Steel core Strat size pickup is only 4.6H, but I don't know the whole story. The increased efficiency of the Steel core combined with the midrange emphasis and output increase from the higher inductance might make it sound louder than it is, but the Steel core might increase output more than I'd expect. I don't know all the specifics.

To keep it simple for now, you could just try wiring one of the pots as a blend on the middle pickup in pos 2. See if it has the tone you want at a given setting and then measure the resistance. If that doesn't work. Try the blend pot on the bridge pickup in pos 2, and measure where it sounds good to you. Make sure your pickups are adjusted to the height you want b4 doing all that.

The Q-filter is pricey, so you'll want to find something like it so as not to reduce the high end too much. The Q-filter has a very low wind count coil inside a structure that clamps it under high pressure to increase inductance, but not significantly increase noise. Antigua may know of something like it. Hopefully you won't need to bother with that.

[thedirestrat]

Jul 25, 2022 1:35:15 GMT -5 gckelloch said:

I don't think the S-90 pole screws could be phenolic. That's a type of plastic fiber used as circuit boards.

Ah that's it then! The guy who made the pickup proudly announced that it *wasn't* phenolic core then. I don't know why it would ever be, but whatever, he claimed it's as close to a P90 as you can get, and I'm good with that. I like the sound!

Jul 25, 2022 1:35:15 GMT -5 gckelloch said:

The volume increase compared to the middle pickup could be somewhat of an illusion.

You are right-- I tried using a decibel meter (phone app) on the amp, and yeah, the bridge pickup is only a few decibels higher than the rest of the positions. So then, I really hope the bridge pickup's output doesn't get killed by the series resistance!

Jul 25, 2022 1:35:15 GMT -5 gckelloch said:

I'd be surprised if a 10k 42AWG wire Steel core Strat size pickup is only 4.6H, but I don't know the whole story.

You'd be right again! I did the quick way of doing things, connected my LCR meter on the guitar cable (which was connected to the guitar) and it read about 6.7 Henries. Seeing how the neck and middle measured 2.15 and 2.26 respectively (dropped by ~0.3 each), the bridge pickup is probably close to 7 Henries, which makes sense. 

Jul 25, 2022 1:35:15 GMT -5 gckelloch said:

To keep it simple for now, you could just try wiring one of the pots as a blend on the middle pickup in pos 2. See if it has the tone you want at a given setting and then measure the resistance. If that doesn't work. Try the blend pot on the bridge pickup in pos 2, and measure where it sounds good to you. Make sure your pickups are adjusted to the height you want b4 doing all that.

Would this be simulating adding series resistance? Wiring a pickup to a blend pot is adding the potentiometer in series with the pickup? Or would it be parallel? 

Jul 25, 2022 1:35:15 GMT -5 gckelloch said:

The Q-filter is pricey, so you'll want to find something like it so as not to reduce the high end too much. The Q-filter has a very low wind count coil inside a structure that clamps it under high pressure to increase inductance, but not significantly increase noise. Antigua may know of something like it. Hopefully you won't need to bother with that.

I really don't want to buy the Q-Filter especially if it's not going to do what I want in a coil application. If the only reason why I may need an inductor is to add series induction to cut highs if there is too much, then I'd like to use something else-- the Q Filter is not meant for that application, even though it could do it. If I could have the "resistor" equivalent of an inductor, that's optimal! antigua, if you ever heard of an inductor like this, made for adding series inductance, please share if you can!

But also, can't I just do something with a capacitor to lessen highs, instead of using an inductor? Thanks for all the help gckelloch! 

[antigua]

If you want a specific inductance, it's probably best to make one, I made one guitarnuts2.proboards.com/thread/8288/bill-lawrence-filter-analysis , and that's cost effective if you want to have a few of them on hand, but if you only need one, it might be worth it to just by a "Q Filter" and save the time and hassle. Some people buy a small high ratio transformer on Mouser and use the high inductance side of the transformer as an inductor, but it has a non-negligible series resistance, and really doesn't work well at all. The Q Filter and homemade versions use a large ferrite ceramic enclosure, which enables a high inductance for a small length / higher gauge of wire.

I only use them for mid scoops, which is what the Q Filter diagram achieves, or a high pass filter, I've never used one as a low pass since you can do the same with a capacitor in parallel to the pickup. An inductor in series with the pickup should have a similar effect as a cap in parallel, although it will have a lower Q factor, since the ratio of inductance to capacitance becomes higher rather than lower. There might be some other benefits to using an inductor, if taking the whole circuit into consideration. For example, putting a cap in parallel with the pickup changes the phase of the pickup, altering the tone when two or more pickups are all used together at once, whereas, AFAIK, adding series inductance will mostly preserve the pickup's phase, or at least not change it by as much, with respect to the other pickups. I almost always have my tone controls "global" to all of the pickups, like a Telecaster, so phasing issues between pickups, as a result of tone mods, isn't something I ever have to worry about.

[Yogi B]

Jul 25, 2022 10:18:01 GMT -5 thedirestrat said:

Jul 25, 2022 1:35:15 GMT -5 gckelloch said:

The volume increase compared to the middle pickup could be somewhat of an illusion.

You are right-- I tried using a decibel meter (phone app) on the amp, and yeah, the bridge pickup is only a few decibels higher than the rest of the positions. So then, I really hope the bridge pickup's output doesn't get killed by the series resistance!

I'd prefer a measurement direct into an interface so we can be sure that there is no compression from the amp. Also I can't be sure how the app is determining the volume, is it measuring at a single specific frequency or averaging across multiple? But in any event it sounds as though some of my assumptions were a bit off...

Jul 25, 2022 1:35:15 GMT -5 gckelloch said:

I'd be surprised if a 10k 42AWG wire Steel core Strat size pickup is only 4.6H, but I don't know the whole story.

You'd be right again! I did the quick way of doing things, connected my LCR meter on the guitar cable (which was connected to the guitar) and it read about 6.7 Henries. Seeing how the neck and middle measured 2.15 and 2.26 respectively (dropped by ~0.3 each), the bridge pickup is probably close to 7 Henries, which makes sense.

Hmm, that's actually quite a bit closer to a P90 than I'd been thinking — so gckelloch's likely correct that at higher frequencies the bridge will contribute less signal than the middle. With the ratio of inductances being 7 / 2.5 = 2.8, in order for the S90 to be louder even at treble frequencies it'd need to be 2.8 times (approx. 9 dB) louder than the middle pickup which does seem a little unlikely.

Jul 25, 2022 0:51:58 GMT -5 thedirestrat said:

Treble
...
You also mentioned that the reason why the S90 has less treble is because the the inductance rising more quickly than resistance or voltage. So here adding more inductance won't help. So what do I do if there's somehow not enough treble? I don't think this will be a problem though.

Now I've got some rough numbers to play around with, it seems quite likely that there would be a lack of treble from the S90, but the answer is pretty simple: add the inductance in series with the middle pickup instead.

Bass
...
My question is: How do I add inductance to cut treble to emphasize bass? I add an inductor? What exactly is that? A little coil that has a fixed henrys amount? Just like there's a typical resistor with a fixed resistance amount?

Yep, though not necessarily that little...

That seems hard to find, so are there any alternatives, like a capacitor for example?

They are pretty expensive/hard to find at the values appropriate to our use, as well as having pretty wide tolerances. As such, in electronics they're generally avoided in favour of capacitors — but we're talking powered electronics with a passive circuit we're pretty much stuck wanting an inductor. (Unfortunately, as with any sort of manufacturing at scale, it's basically a self-fulfilling prophecy that niche products become more niche.)

Jul 19, 2022 1:08:00 GMT -5 Yogi B said:

This does leave the S90 with significantly reduced output across the board, but it sounds like that needs to happen anyway. Though whether the (comparatively) flat frequency response & matched volume levels coincide is basically pot luck when combining arbitrary pickups, so is likely to need further help via adjustment of pickup height(s).

I really don't want the tone and sound to be changed in position 1, the S90 by itself. The only thing I'm ok with happening here in position 1 is the output lowering. The output of this pickup is simply mean, and overpowers the other pickups. Kinda cool, but yeah there's a jump in volume. I thought of fixing this with pickup heights, but maybe I don't have to if the output will be reduced due to these series resistances. But why would the series resistance affect the output even in position 1, where the whole series resistance thing shouldn't be present (it should only be present in position 2)?

By "across the board" I meant 'across the entire frequency spectrum', not 'all positions'. And even if the resistor were present in position 1, it would have much less on an effect because the output of the bridge pickup is being loaded by only the volume/tone controls, not by the middle pickup.

Lastly... what is the value of the resistor? I understand I'd have to do some trial and error, but with the specs I gave above about my pickups, is there some way of knowing at least the general range of resistor values I should aim for when purchasing/finding resistors?

You want a value roughly in the range of your pickups' DCR so I'd say a maximum of around 10k — though instead of a handful of resistors you could get a single 10k trim pot.

Also, I don't think I need the Q Filter unless I need to cut some highs for preserving the bass-- but I really don't want to spend 34 dollars USD just for this sole purpose! There must be another inductor out there or another means necessary just in case I need to add series inductance.

The Q-filter may have more or less inductance than what we need — as antigua mentions, the advantage of winding your own is that you can tune the inductance to fit. Hammond are a potential alternative for low resistance inductors, which may be cheaper than the Q-filter depending on the specific model — though do take note of the dimensions & weight. Another option, depending upon required value, might be to use a wah inductor or two, these are typically around 500 mH and less than 100 ohms.

---

In addition to the above, I figure it would probably help to show some plots of roughly what would be happening with additional resistance & inductance. I've used 6-part pickup models based on the parameters you've given: 10k & 7 H for the bridge; 6k3 & 2.5 H for the middle — but substituted the rest of the values with those from similar pickups. The biggest unknown is exactly how much louder the bridge pickup is than the middle when each is selected alone. I've plumped for 6 dB, this may be a little on the high side based on your description, but hopefully not too unrealistic. Remember: the pickups apparently share the same wire gauge, and if the S90 was as efficient as the SC in terms of volts per ohm we'd expect it to be about 10 / 6.3 = 1.6 times (4 dB) louder — however we're expecting greater efficiency due to the steel core.

First we have the outputs when the pickups are subjected to only the standard load 200k (250k volume & 1Meg amp input impedance) & 470 pF cable capacitance (i.e. selected individually). The red trace is the bridge S90, and the yellow is the middle single coil:

The next plot shows how the two pickups load each other when selected in parallel. Note that — despite its lower frequency & height when selected alone — the bridge's resonant peak is shifted to closely match the shape of the middle's, albeit at a lower amplitude.

Next the effect of adding series resistance to the bridge pickup is shown, with a maximum of 10k being added (linearly). The two lines cross when the resistance is approximately 2k7 ohms. Additionally note that at a larger resistance, around 6k8 ohms, the two lines are basically parallel (separated by around 2.5 dB at all frequencies) — thus if you wanted to avoid using an inductor you could, by either: raising volume of the bridge by 2.5 dB; or lowering the volume of the middle by 2.5 dB (this would need to be done by altering pickup heights).

Lastly, building on the previous result of matching bass levels with 2k7 added to the bridge, the following plot shows the effect of that plus adding series inductance to the middle pickup. Again we're sweeping linearly up to and additional 2 H, and the point where the two traces are almost equal is around 850 mH. Note that I'm assuming that the inductor's series resistance is negligible and that I'm modelling a 100k damping resistor in parallel with the inductor to help eliminate an additional resonance caused by interaction with the pickups' winding capacitance (this otherwise has virtually no effect upon the frequency response — an imperceptible reduction of the peaks).

As a final note, the above animated plots illustrate that for whatever change we make to one pickup the opposite (but not necessarily equal) effect applies to the other pickup. I don't think I explicitly pointed this out previously, and once again is the self-balancing nature of parallel combinations at work. This means that the overall summed output doesn't greatly vary: in particular, when talking about too much / too little bass or treble, I've been referring to the output of one pickup relative to the other — not the combined tone.

[thedirestrat]

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

I'd prefer a measurement direct into an interface so we can be sure that there is no compression from the amp. Also I can't be sure how the app is determining the volume, is it measuring at a single specific frequency or averaging across multiple? But in any event it sounds as though some of my assumptions were a bit off...

Thanks for this extremely informative reply Yogi B! I'll be sure to plug my Strat into my computer and see the (more) approximate decibel values there.

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

Now I've got some rough numbers to play around with, it seems quite likely that there would be a lack of treble from the S90, but the answer is pretty simple: add the inductance in series with the middle pickup instead.

Sounds great! That makes sense and it works with the whole self balancing thing-- your last animation made it clear, when one goes down in treble, the other pickup goes up! So bring the middle pickup down and the bridge pickup peak will go up in treble.

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

They are pretty expensive/hard to find at the values appropriate to our use, as well as having pretty wide tolerances. As such, in electronics they're generally avoided in favour of capacitors — but we're talking powered electronics with a passive circuit we're pretty much stuck wanting an inductor. (Unfortunately, as with any sort of manufacturing at scale, it's basically a self-fulfilling prophecy that niche products become more niche.)

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

The Q-filter may have more or less inductance than what we need — as antigua mentions, the advantage of winding your own is that you can tune the inductance to fit. Hammond are a potential alternative for low resistance inductors, which may be cheaper than the Q-filter depending on the specific model — though do take note of the dimensions & weight. Another option, depending upon required value, might be to use a wah inductor or two, these are typically around 500 mH and less than 100 ohms.

I found some of those Dunlop Fasel wah wah pedal inductors on amazon, and one guy in the comments claims they measured the inductance to be around 630 mh. If we need around 850mh this is not enough. Also, these little fellas are 30 bucks CAD each... 

I also found some Hammond "choke" inductors of various inductances, but always the same size: too darn big! 2 cm in width, 2 cm in height, 4 cm in length. I don't think that's going to fit in a Strat cavity....

But then I found some small tiny inductors on Mouser.ca with relatively high inductances for their size: 
This one is 960 mH!
This one is 370 mH!

I thought I found the jackpot, but then I faced it... 3.7 kOhms for the 960 mH, 2.15 kOhm for the 370 mH. It makes sense... they are like tiny pickup coils with hair like strands of copper to compensate for their small size to get a high inductance. But that's too much series resistance to be negligible. Is the non negligible series resistance of an inductor such a problem though? Can we reduce this resistance, or rather re-use it as series resistance on the bridge pickup?

If not I'll go for the Dunlop one, but it doesn't seem right to get two just to have enough, quite expensive (60 dollars CAD). They are small though. Also, that reminds me, is it better to overshoot the inductance on an inductor for our application? So basically, I should go for the inductor that has more? Let's just say I have an inductor of 2 H, and I only need 0.850 H. Can we make it so that we can use only 0.850 H? 

Maybe *making* an inductor of 850 mH that is small with negligible resistance is a good idea-- the thing is though, is such a thing even possible? I don't see how I can make an inductor of such relatively high inductance with such small dimensions so it can fit in a Strat control cavity. At least it's not a Tele we're dealing with here, and I do have a swimming pool route Strat. Phew! antigua, o inductor master, maybe you have some insight for this. Thank you for your previous post.

Oh and that reminds me, you also said I could bypass the need for an inductor by raising and lower pickup heights. I like to have generally balanced pickup positions, but I understand I'm going to have to compromise. Also, by having no tone pot load on the in between positions (superswitch mod), does that make my situation better for the whole inductor fiasco?

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

You want a value roughly in the range of your pickups' DCR so I'd say a maximum of around 10k — though instead of a handful of resistors you could get a single 10k trim pot.

Excellent. I'll just adjust the trim pot to get the sound that's best then. According to your theoretical numbers, this should be around 2

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

Next the effect of adding series resistance to the bridge pickup is shown, with a maximum of 10k being added (linearly). The two lines cross when the resistance is approximately 2k7 ohms. Additionally note that at a larger resistance, around 6k8 ohms, the two lines are basically parallel (separated by around 2.5 dB at all frequencies) — thus if you wanted to avoid using an inductor you could, by either: raising volume of the bridge by 2.5 dB; or lowering the volume of the middle by 2.5 dB (this would need to be done by altering pickup heights).

You know, raising the volume of the bridge by 2.5 db doesn't sound all too bad! Maybe I don't need an inductor after all.

Also, when you say that the lines cross, do you mean this: 

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

Lastly, building on the previous result of matching bass levels with 2k7 added to the bridge, the following plot shows the effect of that plus adding series inductance to the middle pickup.

So, again, the whole point of series resistance on the bridge pickup is to cut bass and mids to create a new resonant peak for the bridge pickup so that it could be more like a Strat pickup in parallel with the middle pickup, and their voltage/impedance ratios would be the same. So does that look like this:



This is what we're aiming for right? After the series inductance (or pickup height change) and series resistance additions, the two peaks should be on top of each other, almost synonymous, or congruent, to one another? I'm assuming this is how a "normal" Strat would look under a oscilloscope on position 2 or 4, is this correct?

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

resistance is negligible and that I'm modelling a 100k damping resistor in parallel with the inductor to help eliminate an additional resonance caused by interaction with the pickups' winding capacitance (this otherwise has virtually no effect upon the frequency response — an imperceptible reduction of the peaks).

Ok so I'll purchase a 100kohm resistor for the inductor, correct?

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

By "across the board" I meant 'across the entire frequency spectrum', not 'all positions'. And even if the resistor were present in position 1, it would have much less on an effect because the output of the bridge pickup is being loaded by only the volume/tone controls, not by the middle pickup.

I'm sorry Yogi I'm not quite sure about what you mean here exactly-- on position 1, bridge S90 pickup by itself, would the sound be the same after doing this mod? If not, what changes? Thanks!!

I love the animations, they helped me understand so much, and I thank you Yogi for spending your time making those for me-- and others of course wanting to properly learn what this is all about!

[thedirestrat]

Jul 26, 2022 16:45:02 GMT -5 antigua said:

If you want a specific inductance, it's probably best to make one

Hey antigua, thanks for your reply about inductors! From Yogi B's calculations, it seems I need an inductance of 850mH. I think it's best for me to make one, it's cheap and doesn't seem too difficult. I'll get into this more a bit later.
My first question is, if I have an inductor of 1.5 Henries, and I only need 0.9 H of it for example, can I use only 0.9 H of the coil? If so, how? So is it better to overshoot the inductance? This helps a lot with my calculations. 

Jul 26, 2022 16:45:02 GMT -5 antigua said:

Some people buy a small high ratio transformer on Mouser and use the high inductance side of the transformer as an inductor, but it has a non-negligible series resistance, and really doesn't work well at all.

Yeah... I found some inductors that are relatively high inductance (1 to 7 H), but they are either small and non negligible series resistance, or have very low (relatively) resistance, but are big and clunky and won't fit in a Strat cavity at all. 

Jul 26, 2022 16:45:02 GMT -5 antigua said:

The Q Filter and homemade versions use a large ferrite ceramic enclosure, which enables a high inductance for a small length / higher gauge of wire.

This is the jackpot, and thanks to your post antigua about the Q Filter, I have a plan if I don't want to jack up the bridge pickup by 2.5 db (see Yogi's post for context--2.5 db louder than the middle pickup prevents me from using the inductor altogether). 


Here's the ferrite core pots I found that go for around 10 dollars CAD with shipping and should arrive quite fast (based in Canada):
www.digikey.ca/en/products/detail/fair-rite-products-corp/5678261721/8599614
Here's a picture if the link doesn't work:




The only problem I see with this is that they don't seem to include a bobbin. But I don't think that's a big problem, I can just use some paper or use a "thread spool" you use to sow. Of course I'll probably need to reshape it (easy).


The thing I will try to build will look something like this:




When the windings are all done, I'll have two ends, and I think I'll put some copper tape on the edge of a ferrite core pot cap, and solder the winding edges there. Then I'll solder two normal hook up wires to the copper tape and then its ready to be installed in front of the middle pickup!


Here's the magnet wire spool I'm thinking of using that I wound on Amazon:


It's 0.1 mm diameter wire, so 28 AWG, which is not quite 38 AWG that you recommended antigua in your post, but it seems to work just find for the calculations (coming up)


And these are the inductance calculations:




I put 0.8 inches for the diameter, because that's a little less than the ferrite pot core encasing. The ferrite pot cores are apparently 2300 for their relative permeability, according to the Digikey website). Only 150 windings and I got like 1.4 H. Not many windings, and I could do it by hand. I'll test everything with my LCR meter to see how much inductance I get.


So in all it comes out to just under 20 bucks CAD with shipping and all that. And I have excess wire too. Is this feasible? Are parts good, especially the ferrite pot casing? Thanks! The Q-Filter is 43 dollars Canadian, and that's without shipping...

[Yogi B]

I'll get around to responding to the rest later, but for now:

Jul 28, 2022 1:14:32 GMT -5 thedirestrat said:

I'll be sure to plug my Strat into my computer and see the (more) approximate decibel values there.

Something that I forgot about yesterday is that a measurement taken from playing is obviously going to include differences due to the (longitudinal) position of the pickups, thus the results are somewhat meaningless without either attempting to eliminate or correct for those differences. For instance, swapping a pickup from the middle position to the bridge position and keeping the same pickup-to-string distance will still reduce its (overall) output simply because there is reduced vibration closer to the ends of the string. Basically any in-situ measurement of volume difference will include the effects of both electrics & mechanics, whereas I have been talking in terms of purely electrical differences. Separating out the two would be critical to reducing the need for trial and error — unfortunately I can't think of an easy and reliable way of doing that, so if anyone has an idea, please speak up.

Additionally, speaking of trial and error...

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

Lastly... what is the value of the resistor? I understand I'd have to do some trial and error, but with the specs I gave above about my pickups, is there some way of knowing at least the general range of resistor values I should aim for when purchasing/finding resistors?

You want a value roughly in the range of your pickups' DCR so I'd say a maximum of around 10k — though instead of a handful of resistors you could get a single 10k trim pot.

That was the answer I'd had in my head from a while back, but I forgot that since we have some numbers and a general methodology we can at least make an approximation. Recall that we're attempting to equalize the ratio of voltage-to-resistance for the two pickups and also the ratio of voltage-to-inductance. Here I'll be using the assumed 2 times (approx. +6dB) voltage from the bridge pickup, as in my previous post. (This gives us the opportunity to compare the results.)

Firstly voltage-to-resistance, for the regular single coil we have a resistance of 6k3, so for V/R to be equal with the S90 we'd want double the resistance, 12k6. But the actual resistance is only 10k, therefore we want an additional series resistor of approximately 2k6. (This is almost exactly in agreement with the 2k7 I got from the more advanced calculation in my previous post.)

As for voltage-to-inductance, the single coil clocks in at 2.5H and the S90 at 7H. For V/L to be equal for both, again we want the inductance of the S90 to be double that of the SC. In this case it's already more than double therefore we need to add extra inductance to the SC instead, 7H / 2 = 3.5H, one henry more than the intrinsic inductance (compared to the 850mH = 0.85H, this isn't as accurate, but only 15% out isn't too bad either).

To get a sense of how much these values could vary depending upon the volume difference between the pickups I'll include two further situations, both of which I've already mentioned in passing. The first is if the voltage-to-resistance ratio of the two pickups were already equal i.e. the S90 is only 10/6.3 = 1.6 times (+4dB) louder: obviously we'd need no extra resistance in this case, but the extra SC inductance needed is 7H / 1.6 − 2.5H = 1.875H. The second case is if the voltage-to-inductance ratio of the pickups were already equal, this would be if the S90 is 7/2.5 = 2.8 times (+9dB) louder: no extra inductance needed, but the extra resistance needed in series with the S90 would increase to 6.3k * 2.8 − 10k = 7.64k.

[thedirestrat]

Jul 28, 2022 14:56:30 GMT -5 Yogi B said:

I'll get around to responding to the rest later, but for now:

Jul 28, 2022 1:14:32 GMT -5 thedirestrat said:

I'll be sure to plug my Strat into my computer and see the (more) approximate decibel values there.

Something that I forgot about yesterday is that a measurement taken from playing is obviously going to include differences due to the (longitudinal) position of the pickups, thus the results are somewhat meaningless without either attempting to eliminate or correct for those differences. For instance, swapping a pickup from the middle position to the bridge position and keeping the same pickup-to-string distance will still reduce its (overall) output simply because there is reduced vibration closer to the ends of the string. Basically any in-situ measurement of volume difference will include the effects of both electrics & mechanics, whereas I have been talking in terms of purely electrical differences. Separating out the two would be critical to reducing the need for trial and error — unfortunately I can't think of an easy and reliable way of doing that, so if anyone has an idea, please speak up.

Additionally, speaking of trial and error...

Jul 27, 2022 12:36:45 GMT -5 Yogi B said:

You want a value roughly in the range of your pickups' DCR so I'd say a maximum of around 10k — though instead of a handful of resistors you could get a single 10k trim pot.

That was the answer I'd had in my head from a while back, but I forgot that since we have some numbers and a general methodology we can at least make an approximation. Recall that we're attempting to equalize the ratio of voltage-to-resistance for the two pickups and also the ratio of voltage-to-inductance. Here I'll be using the assumed 2 times (approx. +6dB) voltage from the bridge pickup, as in my previous post. (This gives us the opportunity to compare the results.)

Firstly voltage-to-resistance, for the regular single coil we have a resistance of 6k3, so for V/R to be equal with the S90 we'd want double the resistance, 12k6. But the actual resistance is only 10k, therefore we want an additional series resistor of approximately 2k6. (This is almost exactly in agreement with the 2k7 I got from the more advanced calculation in my previous post.)

As for voltage-to-inductance, the single coil clocks in at 2.5H and the S90 at 7H. For V/L to be equal for both, again we want the inductance of the S90 to be double that of the SC. In this case it's already more than double therefore we need to add extra inductance to the SC instead, 7H / 2 = 3.5H, one henry more than the intrinsic inductance (compared to the 850mH = 0.85H, this isn't as accurate, but only 15% out isn't too bad either).

To get a sense of how much these values could vary depending upon the volume difference between the pickups I'll include two further situations, both of which I've already mentioned in passing. The first is if the voltage-to-resistance ratio of the two pickups were already equal i.e. the S90 is only 10/6.3 = 1.6 times (+4dB) louder: obviously we'd need no extra resistance in this case, but the extra SC inductance needed is 7H / 1.6 − 2.5H = 1.875H. The second case is if the voltage-to-inductance ratio of the pickups were already equal, this would be if the S90 is 7/2.5 = 2.8 times (+9dB) louder: no extra inductance needed, but the extra resistance needed in series with the S90 would increase to 6.3k * 2.8 − 10k = 7.64k.

Thank you Yogi B for replying to these messages, they contain a lot of information and questions, so I know it can't easy to take time out of your day to answer them, and for that, I appreciate and thank you indefinitely. 

Since there's still more stuff to reply to, I won't add more questions, because I don't want to give you more to reply to, but mostly because I don't have any other additional questions. 
I take it that knowing the volume difference between both pickups is very important. What I could do, is first put the middle pickup at the middle pickup position on the pickguard, put it at a set height and remember that height, and then plug it into the computer to see how loud it is. Then I put the bridge pickup in the middle position spot, put it at the same height, and then record the decibel loudness levels there too. 

With the realistic volume difference range being from +4dB louder to +9dB, I get a range of values I need for the added series resistance and inductance. 
For +4dB
Series Resistance for the S90: 0 ohms
Series Inductance for the SC: 1.876 H

For +9dB
Series Resistance for the S90: 7.64 kOhms
Series Inductance for the SC: 0 H

So the resistance range is: 0 to 7.64 kOhms, which is covered by the 10k trimpot.
So the maximum inductance I need is: 1.9 H basically, and this is assuming I could only a portion of this amount, if need be (like 0.85 H instead of 1.9 H without needing to rewire the inductor).

[frets]

Dire,

Just make sure the pot cores come with the bobbin. I could not get the product sheet to load on my phone but I did not see a bobbin in the product photo.