Filtered Tone Control

[frets]

Happy Sunday Guys,
March Madness Rules!!

Anyway, this circuit has been around but I don't think it has been applied to guitars.  Its actually a very nuanced tone pot that gives the impression of a steady roll in of tone as opposed to one capacitor shunting.  It really is worth a try if your unhappy with your tone control.  Don't be put off by the 100nF, the way the circuit is configured it never gets that dark.  I was putting in a customer's guitar and thought you guys would like to see it.

[reTrEaD]

Mar 20, 2022 13:46:43 GMT -5 frets said:

Anyway, this circuit has been around but I don't think it has been applied to guitars.

Hey Cindi,

I think you'll want to install this with a switch to interrupt at least the blue and yellow wires from the CW of the volume pot, so that you can evaluate the effect of loading.

At 1kHz, the 10nF capacitor has an Xc of 16k ohm. Combined with the 39k resistor, that gives you an impedance of 42k in the blue circuit. Less as the frequency increases.

The yellow circuit isn't quite as bad, but still basically just a bit more than the 100k resistance at 1kHz. But the two circuits together load the pickups with roughly 30k at 6kHz. This is gonna suck a lot of treble regardless of setting of the tone pot.

A circuit like this might be useful in an amplifier or even with active pickup, but I predict you (and more importantly your customer) won't like what it does with passive pickups.

[frets]

Hi Retread,

It sounds okay to me on an HSS; but, I trust you. So guys, let’s forget this one for guitars. Like Retread said, maybe for amplifiers.

Thanks!😸😸😸
Go Kansas!!

[sumgai]

I didn't analyze it in terms of frequency response like reTrEaD did, but what I'm wondering is why.... why did you complicate the Treble Bleed circuit so much? 'Cause that's all this is, a variable TB circuit - it shunts across the two Vol pot terminals just like any other TB, with an added twist of sending some part of the signal to ground. May not sound "bad" to the ears, but at what cost in components, soldering time, etc.

You're right, we've seen this before, but usually with a gain stage. Active circuit guitars have used this, often calling it a 'Contour' control. I'll bet that MattB plots a SPICE curve for you, and you'll see what we're talking about. Matt?


HTH





sumgai

[frets]

I am chagrined. It was just an experiment to get a more steady roll in of tone. My bad so to say. Never mind. I’ll come up with something else. Right angellahash? Ha!😸😸😸

Go Kansas!

[sumgai]

Mar 21, 2022 12:48:58 GMT -5 frets said:

I am chagrined.

Don't be. Remember, absolutely everyone who came before you had to start somewhere. I hope you don't think that such people as Edison, Marconi, and even earlier in time, that they all had a classic education in electricity such that they could just simply sit down at a work bench and come up with their inventions... do you?  IOW;

Invention, thy name is Experimentation.

And I'll bet that you didn't know that 3/4 fo the current crop of boutique amp/guitar builders are not in any way, shape or form, electrical engineers as earned by a college education.  No, they are experimenters who happened to stumble on something that sounded good, and they capitalized on it.  You're heading in that direction, and in fact, you are already making a living by doing exactly that - experimenting.  Building better instruments/equipment is putting food on your table, no?  Well, you're young enough that the trend will only continue to grow, so long as you don't give up from continual chagrin.   Trust me on that one.

HTH



sumgai

[reTrEaD]

Mar 21, 2022 12:24:33 GMT -5 sumgai said:

I didn't analyze it in terms of frequency response like reTrEaD did, but what I'm wondering is why.... why did you complicate the Treble Bleed circuit so much? 'Cause that's all this is, a variable TB circuit - it shunts across the two Vol pot terminals just like any other TB, with an added twist of sending some part of the signal to ground.

I think this is (or at least is trying to be) much more than that.

The yellow circuit is a high pass filter. The blue circuit is a low pass filter. The tone pot is bridged across the output of those two filters. Evaluating the signal at the tone pot wiper: When the wiper of the tone pot has about 60% of its resistance toward the blue circuit and 40% toward the yellow circuit, there's roughly 5dB insertion loss and a subtle mid scoop. Rotate the tone pot toward the blue circuit and there's less loss on the low frequencies but a strong rolloff of higher frequencies. Rotate the tone pot toward the yellow circuit and the lows (up to about 400Hz) have about 8dB of loss and the highs (above 2kHz) have almost no loss.

This is quite similar to the Big Muff (sorry thetragichero ) Supro Thunderbolt one-knob tone control. However the way it's wrapped around the volume control with the 100nF makes analysis of what this actually does, rather complicated. With volume on ten, it's impossible to give any preferential treatment to the treble. Only treble-cut. And as I mentioned earlier, I believe the loading on the pickup(s) will be too much.

I reckon if one was interested in doing a tone control that was interactive with the volume control, better results might be had using the tweed (5F2-A) Princeton circuit as a starting point.

[Deleted]

Got to say I like circuits like this.
Having to look deep In to them and figure out what they will do.

What drives me NUTz is the binary switching and talking about it!
____________


I don't think there is much new we can design. It's all a type of circuit done before or made a bit more smoother/robust so it does more.



I do like Fretz ideas and designs
Love MattB and JHNG circuits
Also John's circuits and debate
It was John who talked to me about treble bleeding to get my head around it. Tell me 1nF was good but around 6 it gets a bit flipped up. So I converted a wafer with paint on silver to make a pot wafer in to a two way Switch and later a third one 1nF..610pF..200pF
Till I got a comment on the forum "Why bother" (did find it strange for a wiring guitar forum) but if I recall John stood up for me and felt encourage to do other things.

I would sooner show Fretz what is wrong and how to improve if . Let her fall over and say why . For if she does great things , then I would be proud of pushing her to gain that.
----
________

[Yogi B]

Mar 21, 2022 16:16:19 GMT -5 reTrEaD said:

This is quite similar to the Big Muff (sorry thetragichero) Supro Thunderbolt one-knob tone control. However the way it's wrapped around the volume control with the 100nF makes analysis of what this actually does, rather complicated.

Complicated to the point where ashcatlt's, adage of "everything's a voltage divider" looks pretty challenged — there are multiple components which would seemingly be part of the upper (series) part of the divider and the lower (parallel) part of the divider. (A bridged-T filter is probably the simplest circuit for which this is true.) However, we don't quite need to reach for SPICE (or, more generally: nodal analysis) just quite yet — not if we state: "everything (when subjected to sufficiently many Δ-Y transforms) is a (or a series of) voltage divider(s)".

(Also, on a practical note, my GuitarFreak-esque Jupyter notebook works by assuming that guitar wiring is a sequence of voltage dividers, thus the above is necessary to facilitate my use of it to produce the fancy (animated) plots below.)

I'm simulating using Texas Special (middle) pickup model from GuitarFreak, 250k pots, 500pF cable capacitance & 1Mohm input impedance.

First off, each coloured line is frets's circuit at 10% rotation increments of the (idealized 10% log taper) volume pot. The tone pot (with the same taper) is swept over time — with a colour change at every 10% (i.e. red = 100%-91%, orange = 90%-81%, etc.). The static grey line is the regular wiring fixed at maximum vol & tone, for reference purposes, and illustrates the reduction of treble caused by the new circuit (even at maximum tone) due to the excessive loading.

Secondly, with the mention of the Big Muff Pi, here's a more focused look at frets's circuit in a region where it better acts as a 'tilt' control. The volume control has been set to 50% rotation (225k + 25k voltage divider) — I've also swapped the taper of the tone pot to linear: this matches the taper used in the aforementioned fuzz/distortion pedal and (in this reduced-volume scenario) better spreads out the adjustment range. (The reference line remains at maximum tone, but has similarly had it's volume reduced.)

Finally, and although (briefly) shown in the first plot, the below is meant to give a better idea of how this circuit performs as a treble bleed versus standard wiring (no treble bleed). Unlike the previous plots, now the volume is varied over time, whereas the tone is fixed at maximum.

[reTrEaD]

Yogi B each of us can only apply one like per post, else I'd apply at least ten for that one.


Would it be a bother to run a sim on a variation of the tweed Princeton tone circuit, using the same pickup, cable, etc?  I'm thinking 250k audio volume, 500k linear tone, 2nF boost and 20nF cut.



It looks interesting, although I'm less sure of how useful or clumsy it might be.

[frets]

Thanks Yogi for the amazing analyses. The loading effect is quite surprising when one sees it; although, Retread saw that right from the get go. I still have an interest in developing a filtered slope (if that’s the correct term) across the sweep where the pot changes from light tone to medium or standard tone to deeper tone. But the problem of the upfront load is one I can’t seem to get around. I hope some finagling with Retread’s circuit will reap a solution. But I will wait for Yogi’s input.

I wish I were more proficient with Guitarfreak. I can never figure out how to produce the multistringed plots. If someone could tell me how to do that, I could do my own analyses on these circuits I build. I do appreciate it😸😸😸

[reTrEaD]

Mar 23, 2022 12:08:30 GMT -5 frets said:

I hope some finagling with Retread’s circuit will reap a solution. But I will wait for Yogi’s input.

What I expect we'll see with that adaptation of the Fender (tweed) Princeton tone circuit:

When the volume control is fully CW, the tone control will function much the same as the typical treble-cut tone control (modern wiring) and no boost in treble will be available.

When the volume control is somewhere of the middle of it's rotation, there will be some treble boost at one extreme, little effect somewhere in the middle of the rotation, and treble cut at the other extreme. The amount of "treble boost" will be dependent on the setting of the volume control. Lower volume settings will allow greater treble boost.

---

I also see the possibility of flipping the structure around a bit, more like '50s wiring. The boost cap would connect to the CW lug of the volume control and the wiper of the tone pot would connect to the wiper of the volume control. But I'm hesitant to ask Yogi B to invest the time to do a sim on a second circuit. It's already a big ask to do one on the first circuit I presented.

[frets]

Retread😻😻😻,
I understand. I’ll research the circuit some more. But I don’t want Yogi to do a big analysis either. I wish I could understand the whole “loading” concept. I’ve got a lot of reading to do!!

[Yogi B]

Mar 23, 2022 10:39:56 GMT -5 reTrEaD said:

Would it be a bother to run a sim on a variation of the tweed Princeton tone circuit, using the same pickup, cable, etc?  I'm thinking 250k audio volume, 500k linear tone, 2nF boost and 20nF cut.
...
It looks interesting, although I'm less sure of how useful or clumsy it might be.

I already had the Princeton circuit (and a variation thereon) implemented for examining a difference purpose: with both pots turned to about midway, a standard treble bleed (parallel 1nF + 220k, or similar) overcompensates. (The tone pot cuts less treble, in comparison to the same setting at full volume.)

500k linear tone

While a linear taper does give better performance for frets's circuit at mid-volume settings, that's mostly due to the inclusion of the other resistors. Without them something like the S-curve of a W-taper pot would be better, but whatever single gang pot we use at maximum volume the HPF is shorted and we're left with the standard LPF tone control but with the poor performance offered by a linear/W taper.

My solution to this (in my case of better marrying treble-bleed & tone control) was a dual-ganged pot 250k log no-load in series with the tone cap and 500k lin in series with the treble-bleed cap. Depending on the setup 'upping' the taper of the HPF gang to reverse log might be preferable?

On the other hand I can see the logic of going for 500k linear, whereby the 50% will be equal to 250k, thus the middle will always be 'flat' with respect to two 250k pots. (As opposed to the my treble bleed version where the tone at maximum in 'flat') Therefore, perhaps, a TBX pot might make a good starting point for a dual gang version?

---

As it stands (exactly as you specified), the below is the result:

You can see the midpoint by observing when the top coloured line passed the grey reference line (alternatively it's when the colour shifts between light blue and purple) and at this point we can see the settings at lower volumes are relatively flat. However between say 70% and 20% there's really little change going on.

[JohnH]

Mar 23, 2022 12:08:30 GMT -5 frets said:

I wish I were more proficient with Guitarfreak. I can never figure out how to produce the multistringed plots. If someone could tell me how to do that, I could do my own analyses on these circuits I build. I do appreciate it😸😸😸

If you'd like to describe more of what you'd like to do, maybe I can add some clarification?

[reTrEaD]

Mar 23, 2022 23:07:04 GMT -5 Yogi B said:

As it stands (exactly as you specified), the below is the result:

You can see the midpoint by observing when the top coloured line passed the grey reference line (alternatively it's when the colour shifts between light blue and purple) and at this point we can see the settings at lower volumes are relatively flat. However between say 70% and 20% there's really little change going on.

First of all, I can't even begin to tell you how grateful I am for the time and effort you invested on this.

At first I was puzzled by why the 100% volume peaked slightly higher than the grey reference line. Then I realized the 500k pot was presenting a lighter load than the standard 250k tone pot.

Regarding taper, I'm not sure exactly what a W taper looks like but from context it sound like it's 50% resistance at the midpoint and the rate of change is fast in the middle and slow at both ends? That seems appropriate to me, although I reckon those would be harder to find.

It seems 2nF was a bit big for the "boost" cap. I think 1nF (or maybe 500pF) would be a better choice.

I've been told '50s wiring presents less loading on the pickup(s) as the volume is rotated counter-clockwise, and this slightly lessens the loss of treble when the volume is reduced. I think we can afford to reduce the value of the tone pot to 250k so at the midpoint it loads the pickups a bit more when the volume is full CW and take greater advantage of the reduced loading as the volume is rotated CCW. I'm not a big fan of '50s wiring but this might be a case where the dimples will outweigh the warts.

[Yogi B]

Mar 24, 2022 11:13:36 GMT -5 reTrEaD said:

At first I was puzzled by why the 100% volume peaked slightly higher than the grey reference line. Then I realized the 500k pot was presenting a lighter load than the standard 250k tone pot.

I thought that your intention, but I also realised while trying out some ideas I'm not precisely sure what the specific goals are.

At lowered volumes we want some kind of tone control that can both cut and 'boost' treble — okay, but when this control is at 50% should that be: as close as possible to the response with a regular tone control at maximum; have a mild amount of treble bleed, to better match the full volume tone; or have some treble rolled off, in order to be a better midpoint between the extremes offered by the new control?

Additionally what should happen at maximum volume? If we say 50% should be 'flat' (match the tone of full volume), what should turning from 50% upwards do: absolutely nothing; reduce the loading; or cut bass?

Also, something that the default wiring of a TBX control does is adds loading (an 82k resistor) — essentially removing the natural resonant peak — providing a flatter baseline to work from and thus allowing for more treble 'boost' even at full volume.

Regarding taper, I'm not sure exactly what a W taper looks like but from context it sound like it's 50% resistance at the midpoint and the rate of change is fast in the middle and slow at both ends? That seems appropriate to me, although I reckon those would be harder to find.

Yep, and Yep. Potentiometer manufacturers so inclined categorise it under their B family of tapers (Alpha and a few others call it "4B", bourns "B4"). Panasonic call it "G". Additionally, while "S" would make sense though I've not seen it on a manufacturers datasheet (more on this point in a moment). The below image is from Alpha ("4B(W)" is the second outermost curve):

A handful of stompboxes use pots with this taper, probably most famously the Tube Screamer with 20k W pot for its tone control.

Widely available for purchase I've only seen 10k, 20k, 50k & 100k, but higher values could exist. Peavey's T-60 guitar / T-40 bass used what are labelled as "250k S" pots on their schematic as tone/spin-a-split controls — I don't have any confirmation that these are the same taper, but I struggle to see what else they could be.

It seems 2nF was a bit big for the "boost" cap. I think 1nF (or maybe 500pF) would be a better choice.

When I said "exactly as you specified", that wasn't 100% accurate — I neglected to say that whenever I read something like 2nF I automatically translate that as a nearby standard value so in this case 2.2nF (likewise for the 20nF LPF cap), so the cap I used is a little bigger. Nevertheless, you're right 2nF is still too big, even without the extra 10% I added.

I've gone with 680pF, as at max tone control that keeps the resonant peak in roughly the same place as the volume is rolled down. I've also upped the other cap to 47nF as is more typical for single coils. The following plot incorporates these changes with the W250k pot but retains modern wiring.

I'm not a big fan of '50s wiring but this might be a case where the dimples will outweigh the warts.

This is the same as above, but '50s-ised — it's still pretty warty:

[frets]

John,
You know me, I’m gonna take a big chunk and try to get you to explain how you did it.

Remember eons ago when you analyzed a concentric tone pot I came up with? You generated some really informative graphs and I have no clue how you did it.  Here are some of the graphs.






Maybe this broad type of example is beyond a simple explanation.  But I would really like to be able to set the parameters of some of my tone controls and come up with some of the graphs like the ones above.

How about I do up a circuit and maybe you could walk me through how to analyze it it Guitarfreak.  I think it would not only help me but also, help a lot of us numbskulls on here😸😸😸.

[reTrEaD]

Mar 24, 2022 21:57:27 GMT -5 Yogi B said:

I'm not a big fan of '50s wiring but this might be a case where the dimples will outweigh the warts.

This is the same as above, but '50s-ised — it's still pretty warty:

I'd say VERY warty. Thanks for running that. Now, I know that's path not worth taking.

Mar 24, 2022 21:57:27 GMT -5 Yogi B said:

Regarding taper, I'm not sure exactly what a W taper looks like but from context it sound like it's 50% resistance at the midpoint and the rate of change is fast in the middle and slow at both ends? That seems appropriate to me, although I reckon those would be harder to find.

Yep, and Yep. Potentiometer manufacturers so inclined categorise it under their B family of tapers (Alpha and a few others call it "4B", bourns "B4"). Panasonic call it "G". Additionally, while "S" would make sense though I've not seen it on a manufacturers datasheet (more on this point in a moment). The below image is from Alpha ("4B(W)" is the second outermost curve):

A handful of stompboxes use pots with this taper, probably most famously the Tube Screamer with 20k W pot for its tone control.

Widely available for purchase I've only seen 10k, 20k, 50k & 100k, but higher values could exist. Peavey's T-60 guitar / T-40 bass used what are labelled as "250k S" pots on their schematic as tone/spin-a-split controls — I don't have any confirmation that these are the same taper, but I struggle to see what else they could be.

Good information. It sounds like a 250k pot with the desired taper will be hard to acquire. That's unfortunate. Linear will be more touchy at the areas of interest.

Mar 24, 2022 21:57:27 GMT -5 Yogi B said:

I've gone with 680pF, as at max tone control that keeps the resonant peak in roughly the same place as the volume is rolled down. I've also upped the other cap to 47nF as is more typical for single coils. The following plot incorporates these changes with the W250k pot but retains modern wiring.

Yes, you steered this in the right direction. For the benefit of anyone following this, here's the updated circuit:

Mar 24, 2022 21:57:27 GMT -5 Yogi B said:

I also realised while trying out some ideas I'm not precisely sure what the specific goals are.

Since I rained on her parade regarding the HPF/LPF concept, I was hoping to present frets with a lesser but still interesting and useful tone circuit. Goals:

• Simple circuit. Low parts count, readily available parts
• Allow for a sweep from treble-cut, through "normal" to treble-boost at reduced volume
• Not be a massive tone-suck at the midpoint
• Have a reasonable track of flat frequency response when the volume is adjusted with the tone at the midpoint

If the midpoint of tone rotation in your animation is represented by the last frame of blue, just before the traces are turn purple ...

This is neither great nor horrible. Tolerable.

Looking at the boost end of the rotation ...

With the volume reduced by 12dB, the boost end just starts to become interesting. Below that, it's more interesting.


If 250kW pots were readily available, I think this might worth trying. Since a linear pot for tone would be rather twitchy at the ends of the rotation, I reckon that would be sort of a deal-breaker. But at least we have a better idea of how it would perform. And I thank you sincerely for your help.

[frets]

Hi Guys,

I am going to build this circuit. I have the W tapered 250k. So what I’m seeing in this circuit is a 2 pot interaction. Is that correct? The 250W and the 250A? Thanks guys. Just needed that clarification.

[reTrEaD]

Yeah frets, the 250kA is the volume control and the 250kW is the tone.
What I neglected to mark is which is the CCW connection on each.
For the volume, the CCW is at the bottom. (obvious)
For the tone, the CCW is at the top. (less obvious) The W taper is the same in both directions but connecting the CCW at the top makes the boost happen at the CW end of the rotation.

[frets]

Okay Retread, thank you and Yogi so much. I’m excited about this. I’ll report back. Maybe I’ll know how to use Guitarfreak better. I owe John a circuit so he can help get started using it.

[JohnH]

Hi frets , On GFreak, getting the multiple traces is done with the three buttons Reference, Save and Clear at lower right. They engage macros like short sequences of keystrokes to do what they do. So the first thing is to see if macros are enabled in your Excel program (or other if you don't use excel) Macros are often disabled by default so that nefarious guitar nerds don't make your pc do dodgy things. There may be a message when you start GF, or maybe near the top of the screen.

When working, you can copy up to 10 traces to the chart, setting the controls as you wish for each one. 'Reference' copies the live Red trace to the blue dashed trace. 'Save' copies Red to up to 10 new traces. 'Clear' will clear all but the reference trace.

The origin of that was for comparing treble bleed ideas.eg Reference allowed a full volume setting to be stored, then compared to a range of others

Does any of that work for you? If so, there's a few more tricks.

But, just to note that GF is set up to analyse lots of variations within the context of quite a wide range of guitar circuits that are hard-wired into it. Sometimes a new idea can be created from what is already there. But some of the great new ideas that we talk about in threads like this may not fit into what's already coded there in GF. Sometimes I can add something to it, but other times, a more general simulation software is better.

[newey]

JohnH and frets-

We sort of have two simultaneous discussions going at once in this thread. On the one hand, we're discussing a particular tone control; on the other, John is helping frets with Guitarfreq.

Before this gets too disjointed, let me suggest that either:

- You two move the tutorial of guitarfreq to PMs.

- Or, better yet, John, if you start a Guitarfreq tutorial thread, so that we all can learn us a thing or two . . .

[Yogi B]

Mar 25, 2022 10:13:45 GMT -5 reTrEaD said:

Good information. It sounds like a 250k pot with the desired taper will be hard to acquire. That's unfortunate.

I didn't actually think to search for which company uses the "W" designator — I've since found out that it's ALPS. That lead me to this eBay listing for some W 250k pots though they're not exactly in a guitar friendly format. frets: where'd you get yours?

If the midpoint of tone rotation in your animation is represented by the last frame of blue, just before the traces are turn purple ...

Actually it's the very next frame, the first purple. That's close enough though, especially considering component tolerances.

Mar 24, 2022 21:57:27 GMT -5 Yogi B said:

I also realised while trying out some ideas I'm not precisely sure what the specific goals are.

Since I rained on her parade regarding the HPF/LPF concept, I was hoping to present frets with a lesser but still interesting and useful tone circuit. Goals:

• Simple circuit. Low parts count, readily available parts
• Allow for a sweep from treble-cut, through "normal" to treble-boost at reduced volume
• Not be a massive tone-suck at the midpoint
• Have a reasonable track of flat frequency response when the volume is adjusted with the tone at the midpoint

This is useful. For instance, the fourth point helps rule out a variation that acts identically to a normal tone control at max volume, but gradually shifts the tone's midpoint towards flat as the volume is reduced.

Though for the dual-gang version I've been testing out, I am going to have to give the first point a liberal reading of "the necessary components can be constructed from parts of readily available components". This is the circuit:

The 100k load of the 1Meg pot at half way isn't ideal, as it pulls the total load under the 125k of two 250k pots, I've somewhat compensated for that by upping the volume to 500k. This increase also helps the circuit have more upwards adjustment particularly at max volume: for a 250k volume the load varies from about 71k at 50% tone to 200k at max; a 500k volume gives an increased range of 83k to 333k. (The 1Meg wafer could also be modified to go no-load at max, though this doesn't offer all that much — raising the resonant peaks by only around 1dB to 1.5dB. The plots below shows it unmodified.)

The reduction in loading also comes with a negative consequence ... for my graphs. The peak at maximum volume is 6.9dB, above the 6dB max I've used thus far. For consistency I've kept the scale the same, even though the cropping is unfortunate. Anyway, below is said graph:

Something you may notice with this circuit is the increase is a decrease in volume reduction at lower tone settings — this was present in frets's original circuit, and I think an interesting idea worthy of duplicating. Attempting to keep the perceived volume equal by offsetting the loss of the treble frequencies. The amount demonstrated by this circuit was chosen on a whim and would be better determined by ear. (Also, while I don't think this explicitly contradicts the four goals you stated, it is an extra variable to balance — therefore possibly inflicting compromises upon those goals.)

Another difference from the W-taper variant, and something that may not be as immediately obvious in the above graph, is that even at maximum treble the taper of the volume pot is altered: slightly increasing the taper towards linear from the regular 10% to around 15%. (Whereas, with no purely resistive path in parallel with volume pot, the W-taper variant preserves the pots intrinsic taper.) The below graph serves as a means of comparison between the dual-gang variant with a regular 10% taper volume (coloured traces) and the W-taper variant with an actual 15% taper volume (grey traces). The three plotted volume pot positions are 100%, 50%, & 10%.

---

Finally, having now looked at both the TBX control and a regular 1 Meg tone pot in quick succession, I have to wonder what Fender were thinking. The following is a plot of the resistive load of the both gangs of the TBX and 82k resistor (plotted in red) versus a CTS log taper scaled to 1Meg (in yellow). While this doesn't quite tell the full story, it is pretty representative of how close the two circuits are.

[frets]

I got mine from Tayda but I just looked at it and it’s only a 100k. But it is an Alpha Taiwan. I will continue to look for a 250k version.

As far as the Guitarfreak conversation, it’s up to John. We could just make a new thread.

[reTrEaD]

Mar 26, 2022 1:35:29 GMT -5 Yogi B said:

Though for the dual-gang version I've been testing out, I am going to have to give the first point a liberal reading of "the necessary components can be constructed from parts of readily available components".

Yeah, unlikely to find a dual gang pot that has a 1Meg log element and a 500k linear element. Otoh, taking one 1Meg log dual gang and one 500k linear dual gang will have all the pieces necessary to Frankenstein two dual gang pots with the desired elements.

For the less adventurous, the required Franking would be a deal-breaker. For others, nbd.

Mar 26, 2022 1:35:29 GMT -5 Yogi B said:

Something you may notice with this circuit is the increase is a decrease in volume reduction at lower tone settings — this was present in frets's original circuit, and I think an interesting idea worthy of duplicating. Attempting to keep the perceived volume equal by offsetting the loss of the treble frequencies. The amount demonstrated by this circuit was chosen on a whim and would be better determined by ear. (Also, while I don't think this explicitly contradicts the four goals you stated, it is an extra variable to balance — therefore possibly inflicting compromises upon those goals.)

I see it as a bonus feature. And I think the added treble boost at the CW end of the rotation in your circuit is also plus.

Speaking of adding more boost ...

I reckon even more boost could be available by introducing some resistance between the wiper of the volume pot and the output node. But I fear that might create other problems as the tone control is rotated CCW. idk.

[swirling]

Mar 23, 2022 15:09:02 GMT -5 frets said:

Retread😻😻😻,
I understand. I’ll research the circuit some more. But I don’t want Yogi to do a big analysis either. I wish I could understand the whole “loading” concept. I’ve got a lot of reading to do!!

"load", as an engineering term, has a few meanings, but in this case it refers to damping the resonance of the pickup.

You probably realise that a guitar pickup has a resistance, capacitance and impedance, so it is self-filtering and thus produces a resonance of several orders in the mid treble region.

Or not.

Anyway, when you connect a resistor across the coil it reduces the output overall and squashes the resonant peak quite a bit. This resistor is the volume pot, of course. We then add another resistor but block it with a capacitor so only high frequencies see it and now, without changing the volume, we can raise or lower that peak to change the guitar's tone!

Sure, a cap causes a -6dB rolloff, but that effect is lost in the wide range of the pickup's resonance. Your tone pot is damping the pickup to turn the treble down.

Remember, ALL guitar pickups are active. If you want to add a filter to a guitar, you have to buffer the generator coil first.

[reTrEaD]

Mar 26, 2022 21:58:17 GMT -5 swirling said:

Remember, ALL guitar pickups are active. If you want to add a filter to a guitar, you have to buffer the generator coil first.

Uh ... not really.

"Active" is a term reserved for devices that require an external source of power to control or modify signals. (Transistors,tubes, integrated circuits, etc). It's a bridge too far to view a guitar pickup (transducer) as an active device.

Passive pickups are reactive, meaning the internal impedance is more complex than simply resistance. It also has inductive and capacitive components.


Also, it's not strictly necessary to buffer the signal from a passive pickup to add a filter. However, since passive filters are lossy, we need to consider the insertion loss and/or how the passive filter will work in concert with internal impedance of the pickup.

[frets]

Guys,

I can’t find W250’s.  So I bought 10 W100’s at 50 cents a piece from Tayda and am going to increase their resistance doing the scrape method.  I figure with 10, I’ll hit it right by the third or fourth pot.  But let me know if you see anything wrong with my plan.