Treble bypass cap affecting fuzzface/volume pot clean up?

bbill335

I have a tele that was loaded with a fairly standard wiring loom. 2x250k pots, a .22 tone cap and another 22 treble bypass (treble bleed) cap across lugs 2 and 3 of the volume pot. I swapped a 4-way switch for 3-way.

When I played through my pedals, I found that the guitar's volume pot didn't make my fuzzface cleaner when rolled back. In fact, both tone and volume pot seemed to do very little until the extreme end of the sweep. 

I switched the volume-tone pot connection to the 50s/Fezz Parka style (which I tend to do on most of my guitars) and it was still largely the same until I also removed the treble bypass cap. Then, the guitar's controls and their interaction with the fuzzface worked as expected.

What I don't understand is why did the treble bypass cap affect the fuzzface cleanup interaction so drastically? I know that the fuzzface/vol pot cleanup is related to the impedance of the fuzz input and the impedance of the guitar's output but I don't know enough to say how/why the cap changes things.

With that cap installed, the guitar was very midrange-heavy and had a nice, fat grunt but the controls were basically useless. With it removed, it's much more trebly with vol/tone maxed and the controls have a much more noticeable effect on the sound.

ICBM

Your treble pass cap is far too large a value - by a factor of 20 to 200 times. It isn't a treble pass cap, it's a treble and all of the midrange pass cap .

The useful value range for it is usually 100pF (.0001uF) to 1000pF (.001uF). For what it's worth, unless that .22uF is a typo your tone cap value is also a factor of ten too large, in which case the treble-pass is actually 200 to 2000 times too large and is essentially bypassing the taper entirely, so you will only hear a difference when the pot gets close to zero. Tone caps should usually be in the .01uF to .1uF range.

Even with the right cap value the Fuzz Face tends to not clean up as well with a treble-pass, so I would completely expect it to not do at all with that size of cap.

But that said, unless you've also wired something else up wrong, the treble pass cap should have no effect on the tone with both the volume and tone up full.

bbill335

ICBM said:

Your treble pass cap is far too large a value - by a factor of 20 to 200 times. It isn't a treble pass cap, it's a treble and all of the midrange pass cap .

I did mean to put 0.022 for the bypass cap and tone cap values (I often get the decimals in my capacitance measurements mixed up ), which is within the useful range you mentioned. I'm pleased it's gone, it's just confirmed that normal 50s wiring is best for me. I may try a .047 cap on the tone control because it's still quite trebly, and I know you like that value for strats.

ICBM said:

Even with the right cap value the Fuzz Face tends to not clean up as well with a treble-pass, so I would completely expect it to not do at all with that size of cap.

Is the reason for this simple enough that you could explain it to a simpleton like myself? 

ICBM

bbill335 said:

I did mean to put 0.022 for the bypass cap and tone cap values (I often get the decimals in my capacitance measurements mixed up ), which is within the useful range you mentioned. I'm pleased it's gone, it's just confirmed that normal 50s wiring is best for me. I may try a .047 cap on the tone control because it's still quite trebly, and I know you like that value for strats.

I much prefer .047/.05uF or even .1uF with Fender-type single coils - .022 is too middy when turned right down, for me. It's the right value for humbuckers with 500K pots though.

bbill335 said:

Is the reason for this simple enough that you could explain it to a simpleton like myself? 

I'm not totally sure, although it's something I have noticed. I assume it's because the input impedance of the Fuzz Face is quite low, in parallel with the lower part of the pot track, and so the pot is effectively 'turned down' further than it physically is and the effect of the cap is then exaggerated.

I have to admit I'm not a fan of Fuzz Faces and that overly-touchy interaction with the guitar. For me there is only one good setting, which is both the pedal knobs and the guitar volume up full...

bbill335

ICBM said:
I assume it's because the input impedance of the Fuzz Face is quite low, in parallel with the lower part of the pot track, and so the pot is effectively 'turned down' further than it physically is and the effect of the cap is then exaggerated.

I have to admit I'm not a fan of Fuzz Faces and that overly-touchy interaction with the guitar. For me there is only one good setting, which is both the pedal knobs and the guitar volume up full...

Thanks for that. Yes, lower-gain germanium ones can be very touchy, but they are far more forgiving when they're stacked into something overdriven/compressed to even out the differences. Higher gain and/or silicon ones are less touchy IME, like a meathead/black acid or similar.

Next time I do a part order, I'll grab a couple of .047 caps to try out.