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I have finally finished a pedal based on the Vox Tonebender (precursor to the Fuzz Face) using a PUFF board. Got interrupted by babysitting my granddaughter who gave me a really nasty URI as well as Hurricane Ian (we were on the northern eyewall). This delayed the build for a few weeks.
I did my research on this one finding schematics, which differ a little, and inspected gutshot pictures posted on the internet to confirm component values. What I found, as in many of the early fuzzes and other pedals, that component values differed slightly from pedal to pedal. I found that the Input Cap could be 0.15uF or 0.22uF, the Output Cap 3.3nF or 4.7nF and R3 could be 1.0K or 2.2K, as seen below in the schematic I used. The Emitter Bypass Capacitor could be 25uF or the more common nowadays 22uF. The TB Mk1.5 also uses slightly different component values. Other component values that differ from the FF are the R3 of 1.0K or 2.2K compared to 330-470R, R2 of 10K instead of 33K in the FF, and R4 of 47K instead of the FF value of 100K.
Reading up on biasing the circuit I found that the Collector Voltage of Q1 should be 0.5V-0.7V (negative) and ideally -0.7V. Using the stock 10K resistor on the collector side of Q1 gave a Q1 Collector Voltage of -0.80V. I then used a trimmer to dial in the -0.7V getting a value close to 14K. Using a 15K resistor gave a Q1 Collector Voltage of -0.68V, which I could have used, but instead I decided to keep the trimmer at R2 like some of the boutique pedal builders do.
The Q2 Collector bias should ideally be at -4.5V to -7.0V for the best sounding fuzz and that is why the 20-30K trimmer is prescribed for the resistance for the Collector side of Q2 – to dial in the proper or desired voltage. However, I converted this to a 25K external pot, like I do for all my Germanium fuzzes because playing with the bias settings dials in different variations of fuzz and tone, and is quite fun to me to me to do this. As you can see from the gutshot picture below, the Q1 trimmer is mounted on the left inside side of the box and the Q2 bias control is located beneath the PUFF PCB. For transistors I used a unknown PNP Ge with an HFE of 85 and leakage of 47, and for Q2 I used an old PNP OC75 I had laying around that has an HFE of 136 and leakage of 181.
For the cover graphics I went with a simple Vox scheme of a blue classic diamond grill pattern (the Valvetronix series used this) with Gold lettering and accents.
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