Cesar Diaz Square Face Fuzz

This is my hand-built clone of the famous Cesar Diaz Square Face fuzz. I have built it using the schematic below. The only differences from the classic fuzz face circuit is the R2 resistor which has been increase to 1.2 k Ohms and the Fuzz control potentiometer which was also increased to 2k Ohms.

In my build, I have used for R3 a combination of a 5.6k Ohm resistor with a 10k Ohm trimmer potentiometer to be able to adjust the Q2 collector bias to 4.5 V. With the 8.2k Ohm resistor the bias will normally around 5.5-6.0 V, which I found to be too much for my taste. You can replace R3 with a 12k Ohm resistor if you want to get to 4.5 V but this also depends on the gains for the 2 transistors.

The plot below shows the output of the circuit with the Volume control full on for an sine-wave input with 50 mV amplitude. As you can see this is a very loud pedal compared to the classic fuzz face circuit.

For transistors, I got nice sounding results using either a pair of 2N3705 with hfe gains of ~165 or using a pair of BC547A with hfe gains of ~195. The clean up was better with the 2N3705 types but not as good as GE based fuzz faces. I have also tried an AC127 Ge transistor for Q2 with good results. The AC127 really warms up the sound but you loose on those "glassy" tone when you roll off the guitar volume.

In addition to replacing R3 with a resistor and a trimmer potentiometer, I have added a small (47pF) capacitor between the collector and basis electrodes of Q1 to avoid receiving radio stations if it happen a strong one is close by.

This is one of my builds with an AC127 npn Ge transistor for Q2 and an NTE123AP for Q1. This combination is the best of both worlds. Q1 gives temperature stability while Q2 gives Ge warmth and character.

Some measurements: Input = 1 kHz sinewave with amplitude 50 mV

VOL = Max and FUZZ = Max