Tone Bender MKIII, 100k fuzz pot vs 250k

This is in response to a question I saw that asked on Facebook regarding reducing the minimum amount of fuzz available on a Tone Bender MKIII / MKIV.

With the fuzz pot at full, there's almost no resistance between the first stage and Q3.  The fuzz pot acts as a variable resistor, so even at the lowest fuzz setting (highest resistance), the signal still makes it through to Q3.  In the case of a stock Tone Bender, this is 100k.   So increasing the resistance reduces the amount of signal reaching Q3, meaning less fuzz.

TONE BENDER MKIII FUZZ POT VALUE COMPARISION

100k fuzz pot - the lowest setting

Total harmonic distortion - 39%

Level is -16.9dB

 

250k fuzz pot - the lowest setting

Total harmonic distortion - 28%

The level is -18.7dB  (close to 2dB lower)

It's easy to see a lot less in terms of harmonic content in the spectrum analyser window compared to the 100k pot - less fuzz.

 

There's definitely less gain using a larger pot, if you would like a bit more range on the fuzz.  Sometimes the lowest setting can still be pretty intense on a stock MKIII / MKIV.  

Dropping back the 10k resistor to 4k7 on the collectors of Q1 & Q2 also helps, but not as much as the pot.   You get slightly less clipping from the first stage this way.