The Fuzz potentiometer of a FuzzFace?

[ribolovec2]

Hello,

I have a question regarding the pot. In the original schematic its value is 1k. However, i'd like my clone to have a little more fuzz, so it needs to be 1.5k - 1.6k. The problem is that there is no such standard value. The closest is 2.2k and it is too much.. way too much - the pedal sometimes goes into oscillation and it's really unpleasant. I was wondering, if I put a resistor across the left and the right pin of the pot, would that do the trick? Would that change the response of the fuzz control?

Thanks in advance.

(here is a link to the original schematic http://fuzzcentral.ssguitar.com/fuzzface/fuzzfacenpnschematic.gif )

[Mark Hammer]

Actually, no.

The Fuzz control on a Fuzz Face varies the resistance between a cap between the emitter and ground.  The lower that resistance, the greater the gain for AC voltages (bass rolloff dictated by the value of that cap).  Max gain occurs at that point where the wiper is essentially connected with the emitter.

If it should be the case that your unit is TOO fuzzy, and lighter grind is harder to achieve, then yes a higher-value pot would be helpful.  But for the time being, you have it backwards.  There are other strategies to try i order to increase the fuzziness.  One is to play with the value of the feedback resistor, normally 100k.  Another is to play with the hfe vaues of the transistors involved.  Finally, as a number of highly-prized have done, stick an additional transistor gain stage at the input of the pedal so the Fuzz Face circuit is goosed a little.

[ribolovec2]

Thanks for the explanation, I'll see what could be done.

[LucifersTrip]

yet, before you do anything...did you take the transistor voltages to make sure they're close to what they should be?

edit:
typical voltages for ge FF averaged from numerous good sounding ones:


e   b    c
Q1:    0, -.1, -.6
Q2:  -.4, -.6, -4.5

[Gus]

A schematic that has been at this site for years

I make the bias control an external potentiometer

[ribolovec2]

I have another question - in some schematics I've seen that what is R3 in gus's schematic is a 10k pot which is used as bias control. If such a pot is installed in the position of R3, should it be linear or logarithmic?

[nocentelli]

Linear

[Mark Hammer]

That will depend on your tastes, your transistors, and how you intend to use it.  Some people may elect to use a 10-turn trimpot, in which case taper is largely irrelevant; taper being a "strategy" for being able to dial in intended results with a device that can only be rotated once some 240 degrees.

Working on a buddy's BYOC Fuzz Face the other day, I noticed that there was a sweet spot where output level and distortion were optimized.  Turning it a little more yielded more output level, but not as much sizzle.  If you want to work with that AS a panel-mount control, then you can probably use linear or log.  Same thing likely goes for set-and-forget trimpots.

By the way, while there is nothing wrong with Gus' labelling of R1 as a bias control (and maybe even something a little more accurate in some estimations), what you will see labelled as bias control on a great many other FF circuit diagrams is the functional equivalent of R3.