Basic resonant peak and Q factor manipulation

[antigua]

I typed this up in a reply on another forum, and so I'm just reposting here since it might come in useful later, and some effort went into it. It's still rather quick and dirty, by no means comprehensive. 

-----

Before resorting to spending $100+ dollars on new pickups, you'll save a lot of money to realize that there is a good chance that you can get that 'new pickup' with a few cents worth of capacitors and resistors. 

The key ingredients are a resistor and a capacitor. The capacitor will move the resonant frequency, upwards if it's in series with the pickup(s), downward if it's parallel with the pickup. The resistor controls the Q factor, so that it doesn't get too out of hand.

So if you want more treble, you have the cap and resistor in parallel with each other, but in series with the pickup:



The exact values vary depending on the pickup, but since you'd choose the values by ear, it doesn't really matter. Realistic values are 47pF for the cap, and then the resistance will determine the degree of effect, so it can be anything from 1k to 100k ohms. The higher the value of the resistor, the brighter it will be. If you buy a box of assorted caps and resistors, you can just try values out until you find ones you like, then solder it in, or even hook it up to a push pull pot so that you can switch the mod on or off.

If you want more bass emphasis, you put the resistor and cap parallel to the pickup(s). For either of these mods, if you want the effect to only apply to one pickup, you do this between the pickup and the selector switch. If you want it to apply t the whole guitar, you just do it between the selector switch and the output jack.



With this mod, you'd use caps with values between 100 and 1,000pF, and resistors with values between 100k and 1 meg. The higher value the cap, the darker the pickup becomes. In general, as the cap value gets bigger, the resistor would need to be smaller to flatted the Q out. The screen shot above shows the balancing act, 500k ohms and 110pF capacitance, 400k ohms and 330pF capacitance, etc. Since you would choose the values by ear, you can just feel it out. These LTSpice models are nice because you can select values that are in the right ballpark, as I did above.

You can also see that the pickup much more readily becomes darker than brighter, so a bright, low wind pickup serves as a better platform for curve shaping.

[newey]

As a follow up, if you are applying a cap and resistor scheme to the entire guitar, you can do your testing external to the guitar, by sacrificing a piece of guitar cable. One can also build a "substitution box" with a variety of values to test, so that quick A-B comparisons can be made.

A potentiometer can also be used to "dial in" the resistor value, for testing purposes. Wire the pot in place of the resistor, turn it to suit your ears, then measure the resistance at that point on the rotation with your multimeter, thus giving you the resistance value you seek.

Somewhere deep in our archives here is further discussion of using a cap substitution box. I'll have to see if I can dig out that discussion.

Caps and resistors are cheap, so this sort of experimentation isn't going to break anyone's bank.

[antigua]

I'll usually expose the end of the guitar cable and hook up alligator clips to it. I use trim pots for variable resistance, or a full sized linear pot. Once I find values that are complimentary of the pickups, I solder them in.

The parallel bass mod is not much different than how a tone pot works, except that's series RC and this is parallel, and the treble mod can be done with a pot to function as a treble tone knob, so the concepts apply to either a usable control, or a hard wire permanent tone mod.

[ashcatlt]

I mean, there's no reason you can't put a resistance in series with the cap in either of those configurations. It would do...something...

There's some reference in this thread on Pickup Coil Response Tuning which I think might be what newey was looking for. ()


Edit - If you follow the link in that thread, things start to look pretty familiar.

[antigua]

I'm not saying you can't do series. In fact, for certain outcomes, it's necessary to do both.

Like I said, quick and dirty to get people started with experimenting. I also find that shorter narratives are more accessible, so it's a win win for someone with a sizable agenda. 

There's almost no limit to what can be done, the spice modelling makes it easy to try out concepts very rapidly. I tried modeling series RC, but it didn't have as dramatic of an effect as parallel, so I just went with parallel for the sake of demonstration. You see the same thing with RC treble bleeds; sometimes they're series, sometimes they're parallel, sometimes both. 

[stratotarts]

I found a great formula for loaded Q that takes both coil and load resistance into account. Credit to Manfred Zollner:

link

L = coil inductance
C = combined internal and external parallel capacitance
R1 = coil resistance
R2 = load resistance

Q = sqrt(L*C*(1+R1/R2)) / (R1*C + L/R2)

It can be useful in estimating physical losses, by subtracting the calculated peak that this Q produces from the actual measured peak.

[antigua]

Lately I've just been looking at the change in dB between the flat frequency response and the height of the peak, because it's just very easy to do and it has some correlation to what you'd actually hear. All it sacrifices is the band width, which tend to all be alike for, say a Strat pickup, then in the case of humbuckers and Filter'trons the eddy losses are so aggressive that Q factor seems to lose all meaning. 

[stratotarts]

Oct 22, 2016 11:59:21 GMT -5 antigua said:

Lately I've just been looking at the change in dB between the flat frequency response and the height of the peak, because it's just very easy to do and it has some correlation to what you'd actually hear. All it sacrifices is the band width, which tend to all be alike for, say a Strat pickup, then in the case of humbuckers and Filter'trons the eddy losses are so aggressive that Q factor seems to lose all meaning. 

Yes, I always record that in a column of my spreadsheet. The idea of my "Loaded Peak Loss" calculation is to obtain a rough figure-of-merit for losses that is more independent of pickup and load parameters. I keep such analytical figures in the right hand columns, as they are not as fundamental measurements. I also hide many columns because they are seldom directly relevant for an evaluation or comparison.

I use:

Loaded Peak Loss = 20*log(Q) - measured peak

[JohnH]

A couple of comments:

A guitar tone control is the easiest way we all have of adjusting Q. The upper half of the pot turn from 10 down to about 5 or 6 is all about the resistance and the tone cap value plays almost no part. It's main effect in this range is to flatten the Q peak. If we add the ability to put small parallel capacitances in addition, we can then tune the tones downward quite effectively. For example, taking a basic lively alnico single with minimal damping, I reckon you can bend its response to be within +/-1 db of a typical PAF, albeit at a lower output level, and without hum-cancelling (ie the original purpose of a humbucker)

But when we get more into detail though and look at the tests, we are seeing peaks that vary in height and in width, and these two parameters can vary more independently than is convenient. We can see a small but sharp peak, or a small but wide peak, and that is probably related to the extra reactive (ie not just restive) effects of the various damping mechanisms that are at play.

[antigua]

I should have prefaced this better, this was from a thread about buying new pickups, and this was presented as an alternative to wasting money on expensive pickups, so the idea is that you'd set the mod and forget it, like you might with a new set of pickups. I've added a line at the top.

[guitarnerdswe]

Oct 20, 2016 23:01:54 GMT -5 antigua said:

I typed this up in a reply on another forum, and so I'm just reposting here since it might come in useful later, and some effort went into it. It's still rather quick and dirty, by no means comprehensive. 

-----

Before resorting to spending $100+ dollars on new pickups, you'll save a lot of money to realize that there is a good chance that you can get that 'new pickup' with a few cents worth of capacitors and resistors. 

The key ingredients are a resistor and a capacitor. The capacitor will move the resonant frequency, upwards if it's in series with the pickup(s), downward if it's parallel with the pickup. The resistor controls the Q factor, so that it doesn't get too out of hand.

So if you want more treble, you have the cap and resistor in parallel with each other, but in series with the pickup:



The exact values vary depending on the pickup, but since you'd choose the values by ear, it doesn't really matter. Realistic values are 47pF for the cap, and then the resistance will determine the degree of effect, so it can be anything from 1k to 100k ohms. The higher the value of the resistor, the brighter it will be. If you buy a box of assorted caps and resistors, you can just try values out until you find ones you like, then solder it in, or even hook it up to a push pull pot so that you can switch the mod on or off.

If you want more bass emphasis, you put the resistor and cap parallel to the pickup(s). For either of these mods, if you want the effect to only apply to one pickup, you do this between the pickup and the selector switch. If you want it to apply t the whole guitar, you just do it between the selector switch and the output jack.



With this mod, you'd use caps with values between 100 and 1,000pF, and resistors with values between 100k and 1 meg. The higher value the cap, the darker the pickup becomes. In general, as the cap value gets bigger, the resistor would need to be smaller to flatted the Q out. The screen shot above shows the balancing act, 500k ohms and 110pF capacitance, 400k ohms and 330pF capacitance, etc. Since you would choose the values by ear, you can just feel it out. These LTSpice models are nice because you can select values that are in the right ballpark, as I did above.

You can also see that the pickup much more readily becomes darker than brighter, so a bright, low wind pickup serves as a better platform for curve shaping.

Necrobump!

Ok, I was thinking of trying the cap (or cap/resistor) to ground to shift the resonant peak of a bright pickup down a bit. The little red bit has my wondering though. If I put one end of the RC-network on the lug of a 5-way where the hot of pickup is connected, will it ONLY affect that pickup, even if that position on the 5-way has another pickup activated?

Like, if I put it on the bridge pickup of a strat, will the middle pickup be unaffected in the bridge/middle combo position? Or will the middle pickup also bleed through the RC-network to ground?

[antigua]

Dec 20, 2020 14:31:04 GMT -5 guitarnerdswe said:

Oct 20, 2016 23:01:54 GMT -5 antigua said:

Necrobump!

Ok, I was thinking of trying the cap (or cap/resistor) to ground to shift the resonant peak of a bright pickup down a bit. The little red bit has my wondering though. If I put one end of the RC-network on the lug of a 5-way where the hot of pickup is connected, will it ONLY affect that pickup, even if that position on the 5-way has another pickup activated?

Like, if I put it on the bridge pickup of a strat, will the middle pickup be unaffected in the bridge/middle combo position? Or will the middle pickup also bleed through the RC-network to ground?

The middle pickup would be affected also, since the RC is parallel to the bridge pickup. You'd have to use a "super switch" to make it such that the RC was only active with the first position. 

Solutions that are in series with the bridge pickup would only affect the bridge pickup regardless, so in that case, you would run an inductor in series with the bridge pickup, so, let's say you have a 2.5 henry bridge and a 1 henry inductor, that would result in 3.5 henries total, which would lower the resonant peak by something like 700Hz. The Bill Lawrence Q filter, or any other pot core inductor can achieve inductances over 1 henry without adding very much series resistance. The drawback is that you might have to wind an inductor yourself, it costs more than a cap, takes up more space and it's harder to conduct trial and error. 

If you want to retain a good "quack" in the bridge+middle position, a super switch is the way to go, and that's what people do with humbucker bridge pickups, they use the super switch to split the bridge pickup in the notch position, but get full humbucking in the first position. 

[guitarnerdswe]

Dec 20, 2020 15:22:36 GMT -5 antigua said:

Dec 20, 2020 14:31:04 GMT -5 guitarnerdswe said:

Necrobump!

Ok, I was thinking of trying the cap (or cap/resistor) to ground to shift the resonant peak of a bright pickup down a bit. The little red bit has my wondering though. If I put one end of the RC-network on the lug of a 5-way where the hot of pickup is connected, will it ONLY affect that pickup, even if that position on the 5-way has another pickup activated?

Like, if I put it on the bridge pickup of a strat, will the middle pickup be unaffected in the bridge/middle combo position? Or will the middle pickup also bleed through the RC-network to ground?

The middle pickup would be affected also, since the RC is parallel to the bridge pickup. You'd have to use a "super switch" to make it such that the RC was only active with the first position. 

Solutions that are in series with the bridge pickup would only affect the bridge pickup regardless, so in that case, you would run an inductor in series with the bridge pickup, so, let's say you have a 2.5 henry bridge and a 1 henry inductor, that would result in 3.5 henries total, which would lower the resonant peak by something like 700Hz. The Bill Lawrence Q filter, or any other pot core inductor can achieve inductances over 1 henry without adding very much series resistance. The drawback is that you might have to wind an inductor yourself, it costs more than a cap, takes up more space and it's harder to conduct trial and error. 

If you want to retain a good "quack" in the bridge+middle position, a super switch is the way to go, and that's what people do with humbucker bridge pickups, they use the super switch to split the bridge pickup in the notch position, but get full humbucking in the first position. 

For my particular situation, I was think of doing a bridge humbucker in parallel, that's in parallel with the middle single coil. And, a bridge humbucker in parallel, that's in parallel with a neck humbucker in series.

In both cases, I'd like to lower the resonance peak of the bridge humbucker into more typical single coil territory. Does a RC network have to be between the pickup and hot, or can it be placed between the pickup and ground?

[antigua]

Dec 20, 2020 17:02:53 GMT -5 guitarnerdswe said:

Dec 20, 2020 15:22:36 GMT -5 antigua said:

For my particular situation, I was think of doing a bridge humbucker in parallel, that's in parallel with the middle single coil. And, a bridge humbucker in parallel, that's in parallel with a neck humbucker in series.

In both cases, I'd like to lower the resonance peak of the bridge humbucker into more typical single coil territory. Does a RC network have to be between the pickup and hot, or can it be placed between the pickup and ground?

I'm not sure what you're doing exactly, it would help if I saw a summary of what the control layout would be all said and done, but the key thing is that to lower the resonant peak, either a capacitor has to be parallel with the pickup (hot to ground, the same as how a tone control works) or an inductor in series with the pickup (between pickup and hot, which is electrically the same as adding more turns of wire onto a pickup). I think whatever the case may be, you'd need a super switch, and then it's just a matter of figuring out the wiring for the super switch. 

[guitarnerdswe]

Dec 21, 2020 1:50:30 GMT -5 antigua said:

Dec 20, 2020 17:02:53 GMT -5 guitarnerdswe said:

For my particular situation, I was think of doing a bridge humbucker in parallel, that's in parallel with the middle single coil. And, a bridge humbucker in parallel, that's in parallel with a neck humbucker in series.

In both cases, I'd like to lower the resonance peak of the bridge humbucker into more typical single coil territory. Does a RC network have to be between the pickup and hot, or can it be placed between the pickup and ground?

I'm not sure what you're doing exactly, it would help if I saw a summary of what the control layout would be all said and done, but the key thing is that to lower the resonant peak, either a capacitor has to be parallel with the pickup (hot to ground, the same as how a tone control works) or an inductor in series with the pickup (between pickup and hot, which is electrically the same as adding more turns of wire onto a pickup). I think whatever the case may be, you'd need a super switch, and then it's just a matter of figuring out the wiring for the super switch. 

Let's take the HH superstrat as an example. In the middle position, I want the neck in series, the bridge in parallel. Kinda going for a Keith Richards telecaster tone.

The problem is, the bridge pickup in this scenario kinda dominates the neck pickup, making it disappear. The parallel bridge is almost hifi-like in its tone, and doesn't blend well with the neck. I think this is because parallel mode yields a tone that's way too bright, with its resonance peak at a higher frequency than a telecaster, or even when compared to a stratocaster bridge single coil.

Moving the peak a bit lower might give more pleasing results when combined with the series neck humbucker. Or simply when used by itself.

[antigua]

Dec 21, 2020 13:38:47 GMT -5 guitarnerdswe said:

Dec 21, 2020 1:50:30 GMT -5 antigua said:

I'm not sure what you're doing exactly, it would help if I saw a summary of what the control layout would be all said and done, but the key thing is that to lower the resonant peak, either a capacitor has to be parallel with the pickup (hot to ground, the same as how a tone control works) or an inductor in series with the pickup (between pickup and hot, which is electrically the same as adding more turns of wire onto a pickup). I think whatever the case may be, you'd need a super switch, and then it's just a matter of figuring out the wiring for the super switch. 

Let's take the HH superstrat as an example. In the middle position, I want the neck in series, the bridge in parallel. Kinda going for a Keith Richards telecaster tone.

The problem is, the bridge pickup in this scenario kinda dominates the neck pickup, making it disappear. The parallel bridge is almost hifi-like in its tone, and doesn't blend well with the neck. I think this is because parallel mode yields a tone that's way too bright, with its resonance peak at a higher frequency than a telecaster, or even when compared to a stratocaster bridge single coil.

Moving the peak a bit lower might give more pleasing results when combined with the series neck humbucker. Or simply when used by itself.

I think the reason for the problem is the fact of having the bridge in parallel. When two pickups are in parallel, each is a mutual load upon the other. The higher the load, the quieter the pickup. The series neck pickup has an impedance of, let's say 8k ohms (and beyond as the frequency rises) while the parallel bridge has an impedance of only 2k, so what happens is the voltage output of a bridge pickup is relatively unaffected, but the voltage of the neck pickup is severely reduced as a fact of it's being in parallel with a pickup that only has an impedance of 2k (again, that figure rises with the frequency). Does that make sense?   


The think about Keith Richard's Tele is that the bridge pickup is perhaps 7k ohms and the neck is maybe 8k, hard to say because it's authentic vintage hardware and not idealized modern recreations. The relative matching of the impedance means that the pickups will be relatively balanced, so the bridge + neck bell tone will become especially rich. If you split the bridge instead of running it in parallel, it would sound better, especially if you have a hot bridge, such as a JB or Super Distortion, since they have higher impedances for each coil. 

[guitarnerdswe]

Dec 22, 2020 15:52:36 GMT -5 antigua said:

Dec 21, 2020 13:38:47 GMT -5 guitarnerdswe said:

Let's take the HH superstrat as an example. In the middle position, I want the neck in series, the bridge in parallel. Kinda going for a Keith Richards telecaster tone.

The problem is, the bridge pickup in this scenario kinda dominates the neck pickup, making it disappear. The parallel bridge is almost hifi-like in its tone, and doesn't blend well with the neck. I think this is because parallel mode yields a tone that's way too bright, with its resonance peak at a higher frequency than a telecaster, or even when compared to a stratocaster bridge single coil.

Moving the peak a bit lower might give more pleasing results when combined with the series neck humbucker. Or simply when used by itself.

I think the reason for the problem is the fact of having the bridge in parallel. When two pickups are in parallel, each is a mutual load upon the other. The higher the load, the quieter the pickup. The series neck pickup has an impedance of, let's say 8k ohms (and beyond as the frequency rises) while the parallel bridge has an impedance of only 2k, so what happens is the voltage output of a bridge pickup is relatively unaffected, but the voltage of the neck pickup is severely reduced as a fact of it's being in parallel with a pickup that only has an impedance of 2k (again, that figure rises with the frequency). Does that make sense?   


The think about Keith Richard's Tele is that the bridge pickup is perhaps 7k ohms and the neck is maybe 8k, hard to say because it's authentic vintage hardware and not idealized modern recreations. The relative matching of the impedance means that the pickups will be relatively balanced, so the bridge + neck bell tone will become especially rich. If you split the bridge instead of running it in parallel, it would sound better, especially if you have a hot bridge, such as a JB or Super Distortion, since they have higher impedances for each coil. 

Thanks for your detailed response! Now it becomes clearer to me why the pickup in parallel tends to overpower the one in series in a dual humbucker guitar. The solution could be to run both in parallel and then filter out some of the highs (for me at least).

A question though: Is the impedance of a pickup directly tied to the resistance, or are they completely independent? I noticed your estimated impedance values also match the expected resistance from a vintage tele or a dual PAF guitar.

I do find it fascinating that a humbucker by itself loses output when wired in parallel, but gains perceived relative output when combined in parallel with a series humbucker.

[antigua]

Dec 22, 2020 16:24:11 GMT -5 guitarnerdswe said:

Dec 22, 2020 15:52:36 GMT -5 antigua said:

I think the reason for the problem is the fact of having the bridge in parallel. When two pickups are in parallel, each is a mutual load upon the other. The higher the load, the quieter the pickup. The series neck pickup has an impedance of, let's say 8k ohms (and beyond as the frequency rises) while the parallel bridge has an impedance of only 2k, so what happens is the voltage output of a bridge pickup is relatively unaffected, but the voltage of the neck pickup is severely reduced as a fact of it's being in parallel with a pickup that only has an impedance of 2k (again, that figure rises with the frequency). Does that make sense?   


The think about Keith Richard's Tele is that the bridge pickup is perhaps 7k ohms and the neck is maybe 8k, hard to say because it's authentic vintage hardware and not idealized modern recreations. The relative matching of the impedance means that the pickups will be relatively balanced, so the bridge + neck bell tone will become especially rich. If you split the bridge instead of running it in parallel, it would sound better, especially if you have a hot bridge, such as a JB or Super Distortion, since they have higher impedances for each coil. 

Thanks for your detailed response! Now it becomes clearer to me why the pickup in parallel tends to overpower the one in series in a dual humbucker guitar. The solution could be to run both in parallel and then filter out some of the highs (for me at least).

A question though: Is the impedance of a pickup directly tied to the resistance, or are they completely independent? I noticed your estimated impedance values also match the expected resistance from a vintage tele or a dual PAF guitar.

I do find it fascinating that a humbucker by itself loses output when wired in parallel, but gains perceived relative output when combined in parallel with a series humbucker.

Impedance is the combination of DC and AC resistance, also stated as "resistance" and "reactance", also stated as "real" and "imaginary" resistance. DC resistance is what is obvious, the spec listed for every pickup, and then you add to that the "resistance" that comes from the inductance of the coil when the electrical signal is alternating, which can be as high as 50k ohms at the resonant peak.

[ms]

Dec 23, 2020 3:59:59 GMT -5 antigua said:

Dec 22, 2020 16:24:11 GMT -5 guitarnerdswe said:

Thanks for your detailed response! Now it becomes clearer to me why the pickup in parallel tends to overpower the one in series in a dual humbucker guitar. The solution could be to run both in parallel and then filter out some of the highs (for me at least).

A question though: Is the impedance of a pickup directly tied to the resistance, or are they completely independent? I noticed your estimated impedance values also match the expected resistance from a vintage tele or a dual PAF guitar.

I do find it fascinating that a humbucker by itself loses output when wired in parallel, but gains perceived relative output when combined in parallel with a series humbucker.

Impedance is the combination of DC and AC resistance, also stated as "resistance" and "reactance", also stated as "real" and "imaginary" resistance. DC resistance is what is obvious, the spec listed for every pickup, and then you add to that the "resistance" that comes from the inductance of the coil when the electrical signal is alternating, which can be as high as 50k ohms at the resonant peak.

Let's look at this from the point of view of a meter, Extech or other.  If you set it up to measure inductance, you get two numbers.  One of them can be expressed as Q, D (dissipation) or R.  The last is what some people mean by "ac resistance": it is related to power dissipation, but at the frequency of measurement, rather than at dc.  The other number is the inductance, which is an impedance at the measurement frequency, but since the current is 90 degrees out of phase with the voltage, there is no dissipation of power, and it is better not to refer to it as a resistance, but as a reactance.

For a pickup at resonance, the effect of the inductance and capacitance cancel, and the resulting high value of ac resistance can be as much as several hundred thousand ohms.  But you might not measure such a high number unless you use a technique that removes (nearly) all the loading effect of the measuring instrument.

[guitarnerdswe]

So basically, for a noob like me: Impedance is somewhat equal to the resistance at low frequencies (from what I could gather by reading up a bit). But, then the impedance increases at higher frequencies.

Is there any rule of thumb on how much it increases? Does the impedance of a series humbucker increase more or less compared to the same pickup wired in parallel? 

[ms]

Dec 23, 2020 14:16:01 GMT -5 guitarnerdswe said:

So basically, for a noob like me: Impedance is somewhat equal to the resistance at low frequencies (from what I could gather by reading up a bit). But, then the impedance increases at higher frequencies.

Is there any rule of thumb on how much it increases? Does the impedance of a series humbucker increase more or less compared to the same pickup wired in parallel? 

Yes, the impedance of a pickup is just the winding resistance at very low frequencies.  It is a resistor in series with an inductance, and the impedance of the inductor starts to matter as you go higher than the lowest guitar frequencies.  The impedance of the inductor is the inductance value times the frequency times two times pi (3.14...).  But the impedance of the resistor and the inductor are different kinds of quantities, and so  you cannot just add them to get the total magnitude of the impedance.  You have to square them, add these squares, and then take the square root.  (Yes it is more complicated than we would like.)  At higher frequencies, the capacitance matters, too.  Antigua has a lot of plots of the frequency responses of various pickups on this site.  This is controlled by these impedances.

[guitarnerdswe]

I have to admit, things got complicated fast there. But looking at frequency plots, it appears that a series humbucker gets its resonance peak dampened a lot more than a parallel one, when measured with a load applied. Can one therefore assume that the impedance of a series humbucker rises more with frequency than a parallel one?

[antigua]

Dec 25, 2020 17:00:00 GMT -5 guitarnerdswe said:

I have to admit, things got complicated fast there. But looking at frequency plots, it appears that a series humbucker gets its resonance peak dampened a lot more than a parallel one, when measured with a load applied. Can one therefore assume that the impedance of a series humbucker rises more with frequency than a parallel one?

Series wiring results in both higher real resistance and higher inductance, so, yes, both the q factor and resonant frequency will both be lower, but its the latter difference that is mostly audible.

[roadtonever]

Related, but there's some overlap here, the parallel cap can be used to expand the tonal palette on a pickup that's already well tuned. Here's a demo by Lindy Fralin where he talks in the context of non-standard tone cap values:

[ekardscribner]

Hi all,

I know this is an old thread, but it seems appropriate to post this here. I've learned a ton about fine-tuning guitar controls from many of the posts on this forum, and I just wanted to share something I found interesting and useful.

By using a very small capacitor in series with the variable resistor of my tone control, the second resonant peak that is formed in the low range of the control falls in an actually usable range. By adding an additional series resistor, the Q-factor of this second resonant peak can be limited as desired (such as to match the Q-factor of the primary resonant peak of the circuit).

If for some reason the second resonant peak is not desired, a larger series resistor can be added. This configuration still provides better roll-off control than a simple variable resistor Q-factor damper, as the treble rolloff is limited to higher frequencies and can be carefully tuned by changing the capacitor's value.

I'm finalizing an Esquire build with a Seymour Duncan BG1400 pickup, and this tone control gives me huge versatility and usable sounds throughout the entire range. I know it's nothing groundbreaking, but it's pretty cool to have two "halves" of the tone control that work in different ways, rather than a range 10-6 that is used and 5-1 that is mostly ignored. And besides, it frees up a switch for other fun and games.

Cheers!

P.S. the pickup values were measured using a B&K 880 LCR meter. I'd be happy to share them elsewhere, along with measurements from a Fender Wide Range (CuNiFe) humbucker and Pure Vintage '77 Single Coil, if anyone is interested.

[antigua]

I like the sweep I get with a higher value tone cap. I sometimes even use .1uF caps. The lower peak is very bass-y, but the sweep range itself feels very usable. More recently I wired in a push pull with a 1nF to 3nF parallel cap in order to simply drop the resonant peak by some amount to get a more "humbucker" like cut-off. The main problem is mostly my forgetting to ever use that feature. I try lots of tone options but then find myself forgetting they exist, so I leave them out of future rewiring projects. 

[stateofepicicity]

Thank you so much for the explanation here.  I've been playing with resonant peak and Q manipultion using DuPont / breadboard jumper wires to test values quickly.  My bridge has a harsh pick attack, and I quickly was able to warm it with this method, ending up using 2nF||220k, but I may tweak to go a wee brighter than that.  I prefer emulating hum free Strat tones with my humbuckers in series, because parallel just looses too much bass with my guitar, so my goal is to create both warm Les Paul and Strat tones with a 5-way, keeping my humbuckers in series the whole time, so I created this diagram.  Here I have separate volume control for the LP and Strat emulations, no tone controls,and a 1.5nF||47k treble bleed for each, which I've found by ear to sound the most consistent for my tones.





I found it interesting that, if I understand it correctly, wiring for a bass cut circuit and for raising the resonant peak is the same, just with different component values.