Reverend Style Bass Contour wiring?

[Embenny]

If I'm not mistaken, the main reasons for using a "C-type" reverse audio taper pot is so that the knob of the bass cut responds intuitively in the same direction that a guitar tone pot does, and that it gives a little finer control throughout its range with the majority of the bass cut happening at the end of the rotation. I think if you use a regular "A-type" audio taper pot, or a "B-type" linear pot, most of the bass cut effect will occur rapidly at the beginning of the rotation.

You're half-right. I put the true statement in bold and the incorrect one in italics.

You can reverse the "direction" of a pot by swapping the connections on the two outer lugs. If you take a multimeter and measure from the centre lug to either side as you turn the knob, you'll see the resistance of one side approaching 0 as the other approaches the full value of the pot, and vice versa.

However, the taper (audio, linear, reverse audio) affects the rate at which those changes happen as you turn the knob. The reason G&L specs a reverse audio taper doesn't directly have to do with getting the knob to give full bass on 10 and full cut on 0 - you can do that with any pot. But Leo found the usability of the pot's sweep to be ideal with a reverse audio taper, and from the G&Ls I've played and the PTB circuits I've wired DIY, I kinda get why.

I personally don't worry about the taper at all, because I tend to use the bass cut in one of two ways - either finding a spot I like on the pot and leaving it there, or simply as an on/off type of deal like a Jaguar's strangle switch. I don't ride the pot like I do a volume knob. On Jags and JMs, I like to wire the rhythm circuit as a volume and bass cut with two 1M rollers, and pre-set the amount of cut I want for the neck pickup that I can just switch to it when needed. For single-circuit guitars, I find I just do all-or-none. Yeah, that means I could just wire the cap to a switch on a push/pull, but I find those annoying compared to just turning a knob.

[JackFawkes]

Thanks so much for sharing your knowledge on this mbene085!
I find the various Passive Tone & Bass control schemes very interesting, but the details of them to be poorly explained in most of the posts around the internet.

Jack

[bodhi]

It's fundamentally a pretty simple thing. The bass capacitor will need to be in line with the signal to cut bass, whereas the treble pot is a parallel path to ground. Any way you achieve that will end up with a similar two-band eq.

In my own experimentations, I found that the C1M pots are essential (ordered directly from G&L, but any will work technically) to get a completely useful range for the control. I recall trying with a 500k pot, but the range wasn't as useful, but this might have been with the exact same value capacitor as the 1M pot, so perhaps that wasn't the correct approach.

If you can solder even a little bit, I'd just suggest ordering the correct parts and trying out the alternatives for yourselves. I don't know if having the volume pot after the bass and treble will have that significant of a difference, but in any case the bass pot is useful as a gain/distortion control if you have that kind of sound dialed in. It's also good for fixing issues with some amps that can't handle bass that well, typically smaller speakers.

[sciuri]

[EDIT: I found out later my tele doesn’t have a C1M pot but a CTS 500k left handed pot, so I’ve corrected the original post below.]

Wanted to loop back to confirm for me, the reverse audio taper is essential. Today I got to briefly A/B a Reverend 3-knob bcc against my newly modified tele deluxe 4-knob (volume, volume, treble, bass). This is not apples to apples, was clean tones only, and not anything scientific, but it confirmed the things you all described!

The Reverend’s bcc was certainly usable, but the 500k regular audio taper was not great for fine tuning — turning the knob from 10 to 8 rapidly cut the bass by about 60%, with a more gradual cut between 8 to 5, but then with an almost imperceptible effect from 5 to 0. It was almost like switching between 3 settings rather than turning a knob. Useful, but not satisfying when half the sweep it doesn’t feel like it’s doing anything.

The reverse audio taper on my tele deluxe was much smoother and perceptually actually felt more linear. Turning the knob from 10 to 8 was subtle, with a very gradual and linear feeling cut from 8 to 2, and then a noticeable cut below 2. It felt much more intuitive and more like continuous control rather than switching between plateaus.

Thanks for all the advice, and I hope this helps someone else in the future. For 3 knobs the diagram seems well established, but it was harder to figure out what to do for 4 knobs. The Premier Guitar Diagram 1c and Kyle Shutt diagram do indeed work, but the bass has to use a reverse audio taper to achieve any sense of control over the amount of bass cut.

[bodhi]

It's good to get more validation to the core idea

Which pots did you end up going with? The thought crossed my mind that the pots that I've been using directly from G&L might have a slightly custom taper compared to regular reverse audio pots, since they're very likely to be the exact ones they use themselves on the guitars and have maybe dialed them in properly for this particular use case... This is completely unfounded and I haven't checked, but the thought crossed my mind since Fender have historically used so called J-taper pot variants instead of audio taper sometimes, and this might have an effect on especially tone controls and amp EQs...

[sciuri]

Hi, this was all ordered by my tech but I’m glad you asked because it turns out they’re not what I expected.

The pots are CTS 450G 1meg for volume volume treble and CTS 500k left handed for the reverse audio taper bass contour. (I’m assuming a left handed pot is the same as a reverse?… shows how little I know!).

I thought we were going to order a G&L C1M pot for the bass contour, but the current pots work well for me so I’m not going to change anything (other than wondering whether 1meg would allow even broader control of the sweep). If 500k left handed works well, perhaps the reverse audio taper is the most critical aspect, more so than the pot value, in order to achieve a usable sweep.

[JackFawkes]

The pots are CTS 450G 1meg for volume volume treble and CTS 500k left handed for the reverse audio taper bass contour. (I’m assuming a left handed pot is the same as a reverse?… shows how little I know!).

Yes, my understanding is that a "left handed" audio taper pot is the same thing as a "reverse" audio taper pot (C-type).
And for completeness sake, a "left handed" linear taper pot is still just a regular linear taper pot (B-type), but wired "backwards".

I thought we were going to order a G&L C1M pot for the bass contour, but the current pots work well for me so I’m not going to change anything (other than wondering whether 1meg would allow even broader control of the sweep).

I'm not sure... I think on-paper, using a larger value bass-cut pot just allows for more bass to be cut at its maximum setting. Which sort of implies to me that as long as your C500K is cutting enough to satisfy you, it's probably giving more precise control over that specific range than a C1M would.

If 500k left handed works well, perhaps the reverse audio taper is the most critical aspect, more so than the pot value, in order to achieve a usable sweep.

That's seeming like a reasonable observation to me!

Jack