I *think* my Fuzz Face is working correctly... or is it?

[bipedal]

Just built up my first Ge Fuzz Face, (PNP, positive ground), based upon the Tonepad's layout (http://www.tonepad.com/getFile.asp?id=82), trannies from Small Bear.  It works, but I'm not certain its "dialed in" and sounds as it should.

I made a few tweaks from the "stock" FF: Mayer's Hendrix mods and one of Fuller's suggestions:
- Replaced the 8k2 resistor at R5 with 18k.
- Added a 1K pot in series after R4 (470 ohm) and ahead of the traces to C3 (.01 uF) and R5, a la the "Contour" pot on GGG's '69 Boutique FF.
- Fuzz pot is now 2k instead of 1k.

Transistor measurements: Q1 = 89; Q2 = 136.

Sounds like?
I get reasonably smooth mild fuzz sounds in the lower half of the Fuzz pot's rotation.  As it's turned beyond the approx. 12:00 o'clock position -- where that rich sweet spot ought to reside, yes? -- the fuzz gets progressively "fizzier" & thinner and starts gating, i.e. initial fuzz note comes through, but is cut off as the string's volume fades.

Questions:
Is that just a feature of using a 2k fuzz pot -- higher settings will produce crazy, gate-y sounds more akin radio static than guitar fuzz? 
Or is this classic case of mis-biasing?  (Where to start?  Perhaps R5 should be adjusted down from 18K?)

I also haven't noticed any tonal changes so far as the the 1K "Contour" pot moves through it's range, but perhaps the issue noted above is masking the effect of this adjustment...


Thoughts?  Thanks in advance.

- Jay

[burnt fingers]

Sounds like mis biasing.  You should check your voltages with a multi meter and post them according to the "what to do when it doesn't work" thread.

This will help those in the know assess your situation.

Scott

[raulgrell]

burnt finger's suggestion seems right...

Anyways, check this out, http://www.geocities.com/sunsetstrip/studio/2987/britface.html, for some mods which could help your pedal's sound.

[bipedal]

Here are my voltages:

Fresh battery, currently reading 9.47 v.

Q1:
C = -0.53
B = -0.11
E = 0.0

Q2:
C = -0.35
B = -0.53
E = -0.35

I've already tried a quick swap of the 18K resistor at R5 with one approx. 9K, no significant change to what I'm hearing.

One build issue I was stuck on was the Tonepad layout's inclusion of pads for both a 9v - ("Black wire") and 9v + ("Red wire"); that stumped me a bit when wiring up a 3PDT for true bypass with an LED; the light seems to be working fine, but I'll take another look at this to see if I've routed this into the board incorrectly.

- Jay

[petemoore]

Fresh battery, currently reading 9.47 v.

Q1:
C = -0.53 {needs to be above base and emitter, about 1.15v is ballpark
B = -0.11
E = 0.0 And emitter is grounded.

Q2:
C = -0.35 Should be 1/2 of supply
B = -0.53  Is connected to Q1 base
E = -0.35
  They're all low, did you take a battery voltage reading when the circuit is connected? First I would check to have non-continuity between circuit +/-.

[bipedal]

Ah, figured it out.  I was looking for too complicated a fix and missing the basics.  D'oh!

That "Contour" variable resistor having no audible effect turned out to be the key -- found a missed trace between the 33k and 470 ohm resistors, which took that side of the loop completely out of the circuit.  A dab of solder and now it's good to go.  Hello, fuzz!

Thanks for the initial troubleshooting suggestions -- much appreciated.

Now to warm up the amp and make some racket...

- Jay

[burnt fingers]

Congratulatins.

Fuzz Faces are deceptive in that the circuit looks simple but everyone has problems. 

Glad you got it up and running.

Scott