Bass-cut and the G&L PTB system

[axedoctor]

well, I'm betting it wasn't a mistake 

some quick searching didn't yield any simple info about the reason, but it likely had to do with providing a desirable tonal range for the pickup sets used with the guitars equipped with PTB

note that the S-500 which uses the custom MFD pickup set included a 0.001uF capacitor in parallel with the 500k treble tone control to further shape the tone whereas the Legacy with AlNiCo V single coils does not - clearly, the sound intent for these two models was somewhat different, hence the name "Legacy" for the more "stratty" version

selecting capacitor and potentiometer value for treble control will be always be a "this sounds like what I want" matching effort as to some degree will be the capacitor used with the bass cut portion of the PTB ... seems that maintaining the 4:1 ratio between the bass cut and volume control potentiometers is needed to provide effective operation, so 1M & 250k are likely to prevail

let's see what others have to say about this

[thetragichero]

Dec 15, 2018 5:18:02 GMT -5 Ro_S said:

The original G&L 'PTB' scheme was for single coil pickups.

Why do suppose that Leo Fender elected to use a 500k value pot for the treble-cut tone control rather than a 250k pot one given that the latter was the norm for his earlier Strat and Tele designs?

Do you suggest a different capacitor value than 0.0022uf in respect of the bass cut control would be better suited for humbucker pickups? 

thanks

the guitar nuts approved(tm) answer would be to download the guitar freak spreadsheet and play with values until you see something that looks like it'll work, or install everything except the ptb capacitor and swap values using clip leads until you've found something that sounds good to your ears on your setup

that being said, using my signal chain with the humbucker in the bridge of my blacktop jazzmaster the standard values work for my ears. if I had a desire to free up the pot, a jaguar strangle switch would suit my needs just fine (bass cut really cleans up atmospheric delay stuff)

I find experimenting works best for me, so that I can hear the difference component changes make... I'm much more of a tinkerer than an understanding theory EE type at this point of my journey (not that I wouldn't love to learn the how and why... just scratching the surface of RC filters has done wonders for my understanding of fx and amp schematics)

[JohnH]

I like the idea of the PTB system, but I still cant claim to have actually tried it myself. But I think it is likely that if you pick a value for some component based on theory only, then when you try it, you can sometimes find that you prefer one a bit higher or lower.

But just based on theory, the system seems to give the nicest and widests spread of results with a 250k pot and either as high a treble pot as you can get, or preferably, a no-load pot so you can then use a smaller value.

So for anything from a vintage single to a moderate humbucker (say 8.5k), Id use a 250k volume pot and a 250k no-load tone pot, with 1M bass cut pot. And Id throw a 120k//1nF parallel treble bleed on the volume. When all pots are at max, this has the same pickup loading as a guitar with two 500k pots, so appropriate for an Hb. As you turn down treble, you have the same nice spread of tones that a 250k treble pot gives, and with the 250k volume, you have a more consistent lower impedance output than with a 500k. My starting value for the bass cut cap would be 2.2nF, but if I had this, Id want to experiment with other values, particularly lower ones just to see what happens (see earlier posts above).

[Ro_S]

Dec 15, 2018 13:35:20 GMT -5 JohnH said:

So for anything from a vintage single to a moderate humbucker (say 8.5k), Id use a 250k volume pot and a 250k no-load tone pot, with 1M bass cut pot. And Id throw a 120k//1nF parallel treble bleed on the volume. When all pots are at max, this has the same pickup loading as a guitar with two 500k pots, so appropriate for an Hb. As you turn down treble, you have the same nice spread of tones that a 250k treble pot gives, and with the 250k volume, you have a more consistent lower impedance output than with a 500k. My starting value for the bass cut cap would be 2.2nF, but if I had this, Id want to experiment with other values, particularly lower ones just to see what happens (see earlier posts above).

But if a no-load pot was not an option, what value pots would you suggest for volume and treble tone re: vintage style humbuckers in the 'PTB' scheme?  Both 500k?

thanks

[Ro_S]

JohnH -

Another quick question...

Re: the value and taper of the bass cut pot -
Are you still of the view that if a 1meg pot with reverse taper (as specified in the G&L scheme) - or normal 1 meg pot ? - is not available then the next best option is a normal 500k audio taper pot (but wired backwards for better taper use) ?   

I can't find a reverse taper 1meg pot.  But I can just about find a 1meg pot, but only in mini pot size.

thanks

[JohnH]

My second choice after a no-load treble pot, would be to make one. Very easy job, starting with a full-sized 250k audio.

If you have to use all 500k audio, then that's what you have to use. Test a few bass cap values, but I can't speak from having tried it.

[Ro_S]

JohnH -

I've managed to source a few reverse audio taper 1 meg pots.  I want to implement the PTB scheme to a few of my guitars.

I've struggled to find a reliable wiring diagram for the PTB scheme; all the ones I've found are all different to one another.    So I've prepared the draft diagram below.   
Please can you check my diagram, thanks.  

SPOILER: Click to show

[Yogi B]

Dec 31, 2018 11:04:54 GMT -5 Ro_S said:

I've struggled to find a reliable wiring diagram for the PTB scheme; all the ones I've found are all different to one another. So I've prepared the draft diagram below.
Please can you check my diagram, thanks.

Swapping between a log taper and reverse-log taper (to keep the same apparent taper but reversing the direction of rotation) is a mirroring operation, i.e. if you could somehow pull the reflection of a log pot out of a mirror it would be a reverse-log pot. Bourns, for one, at least partially acknowledge this on their datasheets, by referring to the terminals of reverse-taper pots in reverse (mirrored) order, though personally I think that's potentially just more confusing.

In general one needs to swap the connections to the 1 and 3 terminals, between the normal and reverse taper versions.

However, since the bass cut is only using the potentiometer as a variable resistance, the assignment of the two utilised terminals can be freely swapped, all that matters is which pair of terminals are used: 2 & 1 for the non-reverse taper (as seen below); or 3 & 2 for reverse taper.


So, going back to your previous post for the non-reverse bass cut:

Mar 20, 2018 1:40:39 GMT -5 Ro_S said:

You could either: move the cap to go between terminals 3 & 2 and move the purple wire from terminal 1 to terminal 3; or leave the everything else alone and just move the pot itself about 57 pixels to the right. 

Also, vis-à-vis grounding the bass cut pot, although grounding any of the terminals isn't required (and would interfere with its operation), I would still ground the pot's casing.

[Ro_S]

Dec 31, 2018 13:02:50 GMT -5 Yogi B said:

You could either: move the cap to go between terminals 3 & 2 and move the purple wire from terminal 1 to terminal 3; or leave the everything else alone and just move the pot itself about 57 pixels to the right.

Also, vis-à-vis grounding the bass cut pot, although grounding any of the terminals isn't required (and would interfere with its operation), I would still ground the pot's casing.

Thankyou for your post.

I've revised my diagram - see below. Please could you verify whether if it now correct? Thanks.

Re: the treble tone control- have I definitely shown this wired correctly? In another diagram I've seen lugs 2 & 3 being used instead of, as in my diagram, lugs 1 & 2.

SPOILER: Click to show

[newey]

Re: the treble tone control- have I definitely shown this wired correctly? In another diagram I've seen lugs 2 & 3 being used instead of, as in my diagram, lugs 1 & 2.

It differs if one is looking at the rear of the pot or at the shaft end. Your diagram says it's looking from the rear, and the lug assignments are correct from that perspective.

I always get confused, so I posted this.

[Ro_S]

Jan 1, 2019 20:44:23 GMT -5 newey said:

Re: the treble tone control- have I definitely shown this wired correctly? In another diagram I've seen lugs 2 & 3 being used instead of, as in my diagram, lugs 1 & 2.

It differs if one is looking at the rear of the pot or at the shaft end. Your diagram says it's looking from the rear, and the lug assignments are correct from that perspective.

I always get confused, so I posted this.

Thanks, but that doesn't seem to account for the variation I'm seeing?  For example, see this version here, which also has the pots viewed from the rear.  Same for this other one too.

[JohnH]

Hi RoS

There sure is some confusion around the net on this. There may be other things on the internet that are wrong! Who knew?


I think yr last drawing is right. I look at it in these ways:

The two lugs used by the treble pot in PTB, should be the same two as on any standard treble-cut tone control.

Given that you have taken the trouble to source reverse log pots for bass-cut, then the two lugs used for bass cut should be middle and the other outer one, opposite to that of the treble pot.

I always have to imagine reaching around the front and twistng both knobs up to 10. Then, with max bass and max treble, the treble pot resistance will be at max and the bass-cut resistance is zero.

[sumgai]

Ro_s,


John has it correct above... for most players.  Indeed, except for the Vol pot, how a control works is up to the needs/desires/taste of the individual player.  Some do indeed like it backwards, meaning that "0" represents "least cut" or full bass.  Your diagram shows it as John describes, "10" on the knob is full bass.

Where it all goes South (or in John's explanation, someone on the Internet is wrong! ), is in the fact that more than a smattering of wiring diagrams show the controls as if the mounting plate were invisible... meaning, you're intended to think of it as seeing the controls through the plate (or through the wooden top of the body, for a rear-mounted assembly).  This is well-intentioned, but makes things miserable for the rest of us.  Indeed, I'd like to meet the guy who can solder a control in the exact same "real world matches the paper diagram" scenario, that would be an astounding feat of physical dexterity!

After all, one simply must translate from paper to the real world as they work in order to get the job done.  Where wiring diagrams are supposed to make this easier is to remove all doubt by baldly stating "do it exactly like this, and all will be well".  By showing the controls as if you were using your X-ray vision to look through the top of the axe and directly down on to the controls, that just forces yet another translation upon the builder/modder.  I say, Bah! Humbug!  A pox upon those infidels!!

But that's just me, I'm from the old school.  (When I was born, the transistor was still a dream in the Bell Labs.  Is that old enough for you? ).  Since we don't all think alike, I have to maintain a certain level of tolerance for those who suffer from lack-of-thinking-of-the-ramifications-itis.  But Hell, even I have been known to eschew the KISS principle, once in awhile.

tl;dr:

Build it like you drew it, and I'll bet that you're a happy camper.

HTH

sumgai

p.s. To my fellow long-time Nutz: Note that I did not once mention schematics, or go off on a rant of any kind.  That new prescription for Prozac is reeeaaaly working out, juuuuussst fine.

[Yogi B]

Jan 2, 2019 13:54:58 GMT -5 sumgai said:

By showing the controls as if you were using your X-ray vision to look through the top of the axe and directly down on to the controls, that just forces yet another translation upon the builder/modder.  I say, Bah! Humbug!  A pox upon those infidels!!

But that's just me, I'm from the old school.

I'd like to think these people suffer from their own version of being old school, where the mirroring isn't an issue because one could place an actual printed physical copy of said wiring diagram face down upon a light box/table.

In the new school, I use a image viewer browser extension picked mostly due to the ease at which it mirrors & rotates images. Though I don't recall using it for a wiring diagram, usually PCBs, but there's gotta be a first for everything.

Also re PCBs, without the existence of air-wires within layout programs, it'd only be a matter of time before I got confused when flipping components between the faces of the board.

[skern49]

Hello. If I have a 500k log pot, can I wire it so that it behaves like reverse log? How would I do that?

[JohnH]

Hello and welcome to GN2

There's no way to convert a log to a reverse log in terms of the direction that you turn it. Best to just use it as it is for your bass-cut pot in a PTB system. Use the same two lugs as a normal tone pot and become used to the max bass, or minimum bass cut, being at knob = 0.

[skern49]

Feb 21, 2014 22:30:56 GMT -5 JohnH said:

The plots go down to 40Hz, in case this is put in a bass guitar. The traces are in half-step increments, then 1 then 2 then 3 steps. This does seem to confirm that in fact, a log or anti-log taper is most suitable.

This part confuses me. I can understand why reverse log is most suitable, but that would imply to me that log is least suitable. Worse than linear, I mean. With a linear taper, based on the graph, you get half of the effect from 10-8. So a reverse log would make this initial period more gradual (good) and a log would make it even more sudden (bad), right?

[reTrEaD]

May 8, 2019 3:34:07 GMT -5 skern49 said:

Feb 21, 2014 22:30:56 GMT -5 JohnH said:

The plots go down to 40Hz, in case this is put in a bass guitar. The traces are in half-step increments, then 1 then 2 then 3 steps. This does seem to confirm that in fact, a log or anti-log taper is most suitable.

This part confuses me. I can understand why reverse log is most suitable, but that would imply to me that log is least suitable. Worse than linear, I mean. With a linear taper, based on the graph, you get half of the effect from 10-8. So a reverse log would make this initial period more gradual (good) and a log would make it even more sudden (bad), right?

On an audio taper pot, the 'sudden' change is at the clockwise extreme of rotation.

On a reverse-audio taper pot, the 'sudden' change is at the counter-clockwise extreme of rotation.

---

What's 'desired' is to have the gradual change occur when the 'bass' control is set for minimum cut (minimum resistance) and the rapid change occur when the 'bass' control is set for maximum cut (maximum resistance).

---

Use an audio taper pot and connect the wiper and CCW lug across the capacitor for the bass control. Maximum cut will be at the clockwise end of the rotation.

OR

Use a reverse-audio pot and connect the wiper and CW lug across the capacitor for the bass control. Maximum cut will be at the counter-clockwise end of the rotation.

[Deleted]

I tried this, with C1M and B500K felt around the 250K low end it had no effect, also the C1M cost a bit for what it was £3 
so tried 500K with a B500K in Series, also using a switch that added another 500K resistor to the one i have lowering it down to 250K

500k-1M or 250k-750K to catcher what a C1M would do 
also cheated with a Dual Pot and used the second one with a CUT so when at 0 it short circuited the Other pot, lowering it to ZERO

500K-1M becomes 0-500K-1M and 250K-750K becomes 0-250K-750K ... a Bypass for the bass





cut at the being of one of the legs to make a short circuit to make the Pot come down to Zero after adding the Resisters to boost it up

[sci4us]

Jan 2, 2019 0:41:22 GMT -5 JohnH said:

Hi RoS

There sure is some confusion around the net on this. There may be other things on the internet that are wrong! Who knew?


I think yr last drawing is right. I look at it in these ways:

The two lugs used by the treble pot in PTB, should be the same two as on any standard treble-cut tone control.

Given that you have taken the trouble to source reverse log pots for bass-cut, then the two lugs used for bass cut should be middle and the other outer one, opposite to that of the treble pot.

I always have to imagine reaching around the front and twistng both knobs up to 10. Then, with max bass and max treble, the treble pot resistance will be at max and the bass-cut resistance is zero.

Here is a DIY Layout of the pots for a strat:




Note: Treble has 0.0xx µf and bass has 0.00xx µf caps.  Treble pot is no-load.

Is this "correct" in its wiring scheme?  Any notes or corrections are welcome!  

[JohnH]

hello sci4us and yes I think that wiring is all good
J

[carlsoti]

I recently ordered parts to put the PTB tone system on the late 80s MIJ strat I recently bought. I thought I had a good handle on the whole thing until I stumbled on this thread. While I'm fully capable of the installation, and doing it well, doing the math to understand the relationships between all the components is beyond my comfort level right now. When I started reading about issues with compatibility with certain pedals and amps, I figured it's time to ask for some help from people that know what they're talking about. 

To start, the 5-way switch started acting up. I've now completely copper shielded the cavities and pick-guard while deciding on, ordering, and waiting for parts. 6-way switch and gibson-style shielded single conductor cloth push-back wire from Stew-mac. Pots an a pile of caps are coming from Mouser.  I got Bourns DPDT push-pulls, all with audio taper, in 250K, 500K, and 1M. The bass pot will turn backwards from how I want it to work, but it's hard enough to find an anti-log 1M pot suitable for guitar, let alone one with a P/P switch. The idea is that I want to put two different caps on each tone pot. The ones that tend to be "more" will be on the pull. For example, I REAALLLYY like the sound that Fralin gets with his "magic cap." It's like being able to turn down the "presence" control of the pick-up, without losing the treble. The downside is that it really only does it's thing on the bridge pick-up. Barely noticeable on the neck. Push/Pull solves that.  The pull on the Volume pot will be a treble bleed, pushed in will be "normal", with nothing set to that position.

Does that all seem to be viable? FWIW, the pups are ceramic singles, typical strat config. I'm uncertain as to whether they're original 80's MIJ, or just something thrown in. The guitar is modded from floyd rose to hartail, but the neck and body appear legit and in alignment with the serial number, so it could go either way. They're not "hot" by any means, but I haven't played enough different pickups to describe the "flavor" accurately, but they seem the polar opposite of the Texas Special singles in my '97 Lonestar strat. 

The last question I had was regarding pedal compatibility, in particular, fuzz face circuits. Before having to re-wire the guitar, I was actually waffling over buying and modding or building a fuzz face style circuit with some added flexibility. The most important thing is the touch sensitivity. Dynamic control over the amount of fuzz. Is the PTB system going to handicap that right off the bat? I understand there there are different impedances in different circuits, but I just don't understand how they interact.

Any guidance would be greatly appreciated.

Thanks.

Tim.

[newey]

carlsoti-

Hello and Welcome to G-Nutz2!

We'll be happy to help, and yes, I think that what you're after here is feasible. But I have a number of questions:

To start, the 5-way switch started acting up

Acting up, how?

waiting for parts. 6-way switch

What sort of 6-way switch did you order? Is it replacing the 5-way switch? If so, what will the extra position be doing?

The idea is that I want to put two different caps on each tone pot. The ones that tend to be "more" will be on the pull.

So, both the treble cut and bass cut will have a choice of values, values to be determined, right?

I don't have an answer to your questions about the fuzzface or other pedals. I would think if the pedal in question has a buffer, it wouldn't matter. But that's just a guess. Someone else will be along . . .

Are you wanting a diagram of all this?

[JohnH]

hi carlsoti and welcome,

Fuzzface circuits do interact in interesting quirky ways with the guitar circuit, and its part of their appeal. I have a germanium fuzzface clone which is a lot of fun, being a thick and soupy fuzz with the guitar volume at max and cleaning up nicely at lower guitar volume.

Id think the PTB circuit will join in that interaction, in ways yet to be discovered. But, with the bass control at max, it defaults to being no different to a standard tone and volume circuit, so no tonal options are lost.

[carlsoti]

Newey, thanks for the warm welcome and reply to my comment. 

The standard 5-way strat switch that's in the guitar started making noise while switching. It would randomly bip, boop, and pop while switching, or leave a pick-up sounding "brokenly anemic", which would sometime go away on it's own, other times I'd have to futz with the switch to get the regular tone back out of it. It's a Japanese "potted" 5 way, so there wasn't any diagnosing going on with that.

It's possible that it wasn't the switch at all, but some weird static buildup on the pick-guard, which I've heard is sometimes an issue.  That's what lead me to do the full shielding.

The 6-way switch is an Oak Grigsby coming from from stew-mac, to replace the 5-way.

www.stewmac.com/electronics/components-and-parts/switches/oak-grigsby-6-way-lever-switch.html

I'll most likely end up putting the "tele-option" on the 6th position, bridge and neck pups, only, and most likely it will be "past" the "neck only" position.

Both tone pots will initially have two different caps on them. At some point, I'd like to put an anti-log bass pot on it, so all three knobs "turn the same direction", so to speak. Since I can't find 1M Reverse taper pots with push/pull, I'll have to settle on one value, or add a separate dpdt switch for the caps.  That's all down the road, though. I don't feel I need a wiring diagram for this one, but if you're bored and like to do that sort of thing, I'm not going to stop you! I have read that the widely circulated premier guitar PTB circuit is "incorrect", I was likely going to look at that in comparison to the partial diagram posted here, just above my first post. If I don't like the way one sounds, it's literally only a few minutes to change it. It'll take longer for my iron to heat up that it will to  swap wires around, at that point, and the longest part of the whole thing will tuning the guitar pack up to pitch.

JohnH, Thank you for your input, as well. This thread is freakin' phenomenal! The modeling you've done will be invaluable in helping select caps for this project. I guess the only thing left do is to find something to do while waiting on parts!

[newey]

Sept 9, 2020 9:18:38 GMT -5 carlsoti said:

I'll most likely end up putting the "tele-option" on the 6th position, bridge and neck pups, only, and most likely it will be "past" the "neck only" position.

Ah, yes, the Oak-Grigsby 6-way lever switch. I bought one for a project a while back, but ended up not using it. What I found, at least on the guitar I was going to use it on, was that it required cutting the slot longer to get the 6th throw; with the stock slot for a 5-way, the lever hit the end of the slot before the switch got to the sixth position. However, the guitar I was doing wasn't a Strat-type guitar, so maybe it will work OK in your application.

This is an oddball switch in terms of how the internal connections are made. I started a thread on it when I bought the switch, I'll look for that and link to it if I can find it. But it is specifically made so as to give you the N + B option, so if that's what you want, no problem. However, you may not have a choice of which selections are at which positions- it's not at all like a Superswitch.

I don't feel I need a wiring diagram for this one, but if you're bored and like to do that sort of thing, I'm not going to stop you!

I have plenty to do, thanks! But if you do a diagram, we'll vet it.

Since I can't find 1M Reverse taper pots with push/pull, I'll have to settle on one value, or add a separate dpdt switch for the caps.

Not sure if it can be done, but you might be able to take the anti-log resistance track out of a 1M "C" pot and swap it into a P/P pot. Seems to me we had someone around here report that they had successfully switched one pot's innards for another, although I don't recall if a P/P pot was involved.

EDIT: Here's the skinny on the 6-way switch: guitarnuts2.proboards.com/thread/7948/new-6-lever-switch

[ashcatlt]

FF circuits are unusually low impedance, and that is the bulk of what causes the “quirky” interaction.

When all the controls on the guitar are on 10, connecting to that low impedance is very much like turning the T knob way down. The pickup is the “top resistor” in a voltage divider where the pedal is the “bottom”, and since the pickup is an inductor, that “top resistor” looks bigger to higher frequencies, so those higher frequencies are divided down(attenuated) much more than the lower ones. The fuzz circuit gets mostly low frequencies - the fundamentals” of the strings. This is what causes that characteristic warm, singing kind of sound, and is actually part of why they tend to fart out and get wonky with polyphonic inputs and chords. You really can get a “fuzz” sound out of a “distortion” pedal like a Rat or whatever just by turning the T pot on the guitar down.

When you turn the V pot on your guitar down, it introduces a static resistance in series. When our load is high impedance, we usually end up seeing a loss of treble here because there is the other voltage divider where the pickup and V pot are the top and the capacitance of the cable is the bottom, and that capacitance looks smaller to higher frequencies so that as the series resistance of the V pot gets bigger, more treble is divided down. In this case of a low impedance this still happens, but from the perspective of the pickup, that series resistance from the V is actually part of the “bottom resistor”, so that less treble is dropped across the inductor, so more treble comes out. The FF cleans up when you dial back the V just because the input is overall smaller, so it’s not driven as far past it’s limit, but it also brightens up or doesn’t sound quite so muddy because of this thing where inductor is isolated or protected from the low-Z input by the series resistance of the pot.

Turning down the (treble cut) T pot on the guitar won’t make a whole lot of difference until it’s way down because the resistance of the pot is parallel to that already low impedance, and parallel Rs are dominated by the smaller of the two until they start to get relatively close to one another. But that T pot is normally also isolated behind the series resistance of the V pot, so that as you roll back the V, the T will start to act more like you’d normally expect.

The bass cut when turned...ummm...off (no cut) is just straight wire, and has no impact either way. Turned the other way, it’s a capacitor which gets big at low frequencies in parallel with a big resistor which mostly just stops it from getting quite so big as the top resistor with the pedal as the bottom. Lower frequencies are divided down more than higher frequencies. Well, but actually the bottom is the parallel combination of the pots in the guitar and the load impedance, and “normally” the load itself is bigger than the pots, but in an FF, it’s smaller, so makes the whole thing look smaller, so you’ll end up with a less low frequencies, or more properly, you’ll have more noticeable loss at a point higher in the spectrum. Since we’re already losing a bunch of treble, I’d expect this to dry quickly start to act more like a full-range volume loss, or at least the useful range of the B pot will be severely limited. Again, though, this will be “isolated” as you turn down the V pot, so much like the T pot, it should act more normal as you roll back the V.

But wait! You’ve got a treble bleed on your V pot? Well that works by allowing the higher frequencies to “bypass” the series R of the pot. Normally, this means the divider with the cable doesn’t drop as much treble, but in this case it means that the inductance of the pickup isn’t so much isolated from the too low input Z, so that I would expect it to have almost the opposite of its intended function. It won’t let the thing “unmuddy” as you dial back the V.

Now of course, this is all kind of “napkin scribbling”, and actual values matter, so basically mileage will vary.

[Yogi B]

Sept 9, 2020 12:05:40 GMT -5 ashcatlt said:

But wait! You’ve got a treble bleed on your V pot? Well that works by allowing the higher frequencies to “bypass” the series R of the pot. Normally, this means the divider with the cable doesn’t drop as much treble, but in this case it means that the inductance of the pickup isn’t so much isolated from the too low input Z, so that I would expect it to have almost the opposite of its intended function. It won’t let the thing “unmuddy” as you dial back the V.

I want to only point out that a bass control is just a cap-only treble-bled volume, just without the other half of the pot reducing the resistance to ground: that should be enough to ring a few bells.

A wise person once postulated:

"Everything useful is a voltage divider." 

Well I'd like to suggest a modification: everything is part of at least one voltage divider.  Irrespective of it being useful, whether or not your looking for one, or to what other components it may be connected.

It's true enough that the treble bleed capacitor allows higher frequencies to bypass the resistance of the upper half of the pot, however that cap, itself, is also not impervious to the effects of the low input impedance. To an extent these two effects cancel out, more specifically the centre frequency of an RLC bandpass filter does not vary with R.

---

The bass cut
...
Since we’re already losing a bunch of treble, I’d expect this to dry quickly start to act more like a full-range volume loss, or at least the useful range of the B pot will be severely limited.

I'm not going to disagree that there will be quite a noticeable loss of output, but what is should be quite a narrow 'slice' of upper mid range -- not too dissimilar to a rangemaster or a parked wah -- which, situationally, can be very useful.

[ashcatlt]

@yogi B - Ah good point on the treble bleed! I knew I was oversimplifying...

Waaaaay back in the day there was a discussion around here about bass cut circuits in which a long lost member named fobits put forward the idea that it might be useful or at least more pronounced if the “extra lug” was grounded. That of course makes it exactly the same as V with TB.

[carlsoti]

Life has gotten in the way of this project just a bit.... I do better with the parts on the bench and a meter in hand. ...