Sourcing pots for Rothstein PTB Tone Stack and Dual Vol Mods

[Peckhammer]

I’m assuming you’ve wired this like a two volume Gibson. When you use the middle position of the 3-way switch, backing down just one of the volumes to zero shuts off the entire guitar because the pickups are wired together in parallel and the pickups are engaged. Because the two volume controls are not decoupled, they interact. With a passive circuit like this, it's just the nature of this type of wiring. It can be wired differently, but you may need to install a treble cut filter (cap and resistor on each volume pot).

[Augs]

OK I have done some research on this, apparently you can just swap the connections between the 3-way and the hot wire on the potentiometer. However I have heard that this means that lowering the volume will also roll off the treble, so I need a treble bleed(resistor and capacitor in series). But I have a few questions:

How come this setup requires a treble bleed but the dependent controls don't?

What values should I use for the resistor and capacitor? If the answer is "it depends", then what does it depend on? How could I go about calculating reasonable values?

Finally, has anyone tried this with a jazzmaster and what values did you use? Did it work out or is this not worth trying?

[HarlowTheFish]

OK I have done some research on this, apparently you can just swap the connections between the 3-way and the hot wire on the potentiometer. However I have heard that this means that lowering the volume will also roll off the treble, so I need a treble bleed(resistor and capacitor in series). But I have a few questions:

How come this setup requires a treble bleed but the dependent controls don't?

What values should I use for the resistor and capacitor? If the answer is "it depends", then what does it depend on? How could I go about calculating reasonable values?

Finally, has anyone tried this with a jazzmaster and what values did you use? Did it work out or is this not worth trying?

Can't speak as to why you wouldn't need this with the traditional wiring (because I sure as heck would), but as far as values, "it depends".

Depends on whether you want to mitigate the treble rolloff, negate it completely, or make it so that rolling down actually cuts lows before highs (bigger treble bleed = more treble left over when you roll down the volume), and whether you're more willing to compromise on the brightness, the taper, or your time (parallel vs. series resistor or a combination of the two). On my parts Mustang (which is 25.5" with JM pickups and trem) I went with the Ibanez-style (a single 330pf cap, no resistor) and on my Vintera Mustang I went with the PRS-style (180pf cap, no resistor) because if anything I'd rather it get brighter than darker as I roll off the volume, but these are both pretty even to my ear. Adding resistors can start messing with taper/effectiveness, and the values of both the cap and resistor(s) can be pretty dependent on your specific pickups, pot values (higher pot values, like the 1M in a standard JM circuit, roll off a ton of treble as you bring the volume down), cable length/capacitance, and whatever the input impedance of the first thing in your chain is.

IMO, get a 180pf cap and a 330pf cap for each volume to try, because they're super simple and easy to snip if you don't like the sound, and try a couple of different values from there. If just a single cap isn't doing it for you (and do keep in mind that if you have two volumes you can have different pot/treble bleed values for each pickup) then consider one of the cap/resistor combinations.

[Peckhammer]

I’d suggest a 150K-ohm 1/4-watt resistor in parallel with a .001uF capacitor. Wire it between the input and output lugs of the guitar volume control pot.

[Augs]

I found this great video:

https://www.youtube.com/watch?v=NzYwuYG1Ls0

Seems like the costs aren't worth the benefits here. I think I'll stick with the dependent controls. Although I might still get a volume mod.

[devanbumstead]

If you're stateside, Small Bear has a pretty nuts selection of oddball components, including mini reverse-log pots, so they'll probably have what you're looking for.

Just to pick this back up, would these pots from Small Bear work for the PTB mod? Assuming I buy the roller knobs with larger 6mm holes and ream them a bit (Allparts MK-3155-003 seem to be the right rollers)

1 Meg Reverse Audio Taper (Bass Cut)
https://smallbear-electronics.mybigcomm ... der-terms/

1 Meg Audio Taper (Treble Cut)
https://smallbear-electronics.mybigcomm ... dio-taper/

[bodhi]

If you're stateside, Small Bear has a pretty nuts selection of oddball components, including mini reverse-log pots, so they'll probably have what you're looking for.

Just to pick this back up, would these pots from Small Bear work for the PTB mod? Assuming I buy the roller knobs with larger 6mm holes and ream them a bit (Allparts MK-3155-003 seem to be the right rollers)

1 Meg Reverse Audio Taper (Bass Cut)
https://smallbear-electronics.mybigcomm ... der-terms/

1 Meg Audio Taper (Treble Cut)
https://smallbear-electronics.mybigcomm ... dio-taper/

Sure, but it might be a lot easier to get metric 6mm pots directly instead of trying to enlarge the knobs. I tried it at some point and the hole became too large (a bit off-centered, loose and wobbly), so ditched the attempt for parts that were already machined to fit. You might be better at it than me, of course

[devanbumstead]

Sounds fantastic! Haha. You have a link to those parts? Haven’t been able to find anything myself.

[bodhi]

Sounds fantastic! Haha. You have a link to those parts? Haven’t been able to find anything myself.

... err, where are you located? There's always Digikey or Mouser or the like if nothing else...

[devanbumstead]

Sounds fantastic! Haha. You have a link to those parts? Haven’t been able to find anything myself.

... err, where are you located? There's always Digikey or Mouser or the like if nothing else...

California.

[bodhi]

Anyone with better local knowledge want to chip in?

If nothing else, make a selection of 16mm body size pots from Mouser : https://eu.mouser.com/c/passive-compone ... rt=pricing

... though not sure if there are reverse audio pots in that selection... You might need to work with something else than solder lugs to get those from Mouser...

[ThePearDream]

FYI, 500K Reverse pots can work great for bass cut controls too, but are far easier to find.

FWIW, I've done the thing where you ream out the roller knob to fit a1/4"shaft pot and it was a relatively simple procedure. You just need to be sure the roller is positioned securely.

[devanbumstead]

FYI, 500K Reverse pots can work great for bass cut controls too, but are far easier to find.

FWIW, I've done the thing where you ream out the roller knob to fit a1/4"shaft pot and it was a relatively simple procedure. You just need to be sure the roller is positioned securely.

Pretty sure this the route I’m going. Good to know it can be accomplished.