Enclosure not stated · 4 knobs
Fred Briggs Pharmacy Fuzz
Based on the Fred Briggs Pharmacy Fuzz
From the vendor
The blog author's own Fuzz Face-type design, with each of the two transistors replaced by a Darlington pair made of a germanium device (about 50 hFE, low leakage) driving a silicon device (about 250 hFE), and a variable resistor between them to set each pair's gain. An Aggression control in the feedback loop acts as an overall gain control, and a Bass Cut control is the familiar Fuzz Face input tone blend. Ferrite beads on the input and a suppression choke in the supply reduce noise and radio interference.
Use a 100k trimmer for the first pair's gain (T1) and a 100k pot for the second pair's gain (T2), since the second pair is where most of the clipping happens. For simplicity the first Darlington pair can be replaced by a single low- or medium-gain transistor. Set the 10k bias trimmer for about half the supply voltage (4.5-6V) on the second pair's collector, or wherever it sounds best. Without the parts, replace the suppression choke with a 100 ohm resistor and leave out the ferrite beads.
Schematic
The schematic is in the post. Open it at Revolution Deux. No KiCad fragment has been drawn for this circuit yet.
Parts list 26 rows
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Check before you build · 1 value the reader of this schematic was not sure of
- The feedback capacitor across the second pair is drawn as a range, 100-470p.
| Ref | Value | Normalized | Type | Notes |
|---|---|---|---|---|
| Resistors 6 | ||||
| R1 | 15K | 15k | input; read from the schematic by eye | |
| R2 | 1M | 1M | input pulldown; read from the schematic by eye | |
| R3 | 15K | 15k | first pair collector; read from the schematic by eye | |
| R4 | 22K | 22k | feedback; read from the schematic by eye | |
| R5 | 1.8K | 1.8k | second pair collector; read from the schematic by eye | |
| R6 | 1K | 1k | second pair emitter; read from the schematic by eye | |
| Capacitors 7 | ||||
| C1 | 4.7n | 4.7n | input; read from the schematic by eye | |
| C2 | 1u | 1u | electrolytic, Bass Cut leg; read from the schematic by eye | |
| C3 | 2.2n | 2.2n | across Aggression; read from the schematic by eye | |
| C4 | 470p | 470p | feedback, drawn 100-470p; read from the schematic by eye | |
| C5 | 47u | 47u | electrolytic, second pair emitter bypass; read from the schematic by eye | |
| C6 | 100n | 100n | output; read from the schematic by eye | |
| C7 | 220u | 220u | electrolytic, supply filter; read from the schematic by eye | |
| Transistors 4 | ||||
| Q1 | germanium | GERMANIUM | first pair, about 50 hFE, low leakage; read from the schematic by eye | |
| Q2 | silicon | SILICON | first pair, about 250 hFE; read from the schematic by eye | |
| Q3 | germanium | GERMANIUM | second pair, about 50 hFE, low leakage; read from the schematic by eye | |
| Q4 | silicon | SILICON | second pair, about 250 hFE; read from the schematic by eye | |
| Inductors 3 | ||||
| L1 | suppression choke | SUPPRESSION CHOKE | supply, 50-100 ohm; or a 100 ohm resistor; read from the schematic by eye | |
| FB1 | ferrite bead | FERRITE BEAD | input; read from the schematic by eye | |
| FB2 | ferrite bead | FERRITE BEAD | input; read from the schematic by eye | |
| Potentiometers 6 | ||||
| T1 | 100K | 100k | Potentiometer | trimmer, first pair gain; read from the schematic by eye |
| Bias trim | 10K | 10k | Potentiometer | trimmer, drawn 10KB, set 4.5-6V; read from the schematic by eye |
| Bass Cut | B100K | B100k | Potentiometer | read from the schematic by eye |
| Aggression | B100K | B100k | Potentiometer | read from the schematic by eye |
| T2 | B100K | B100k | Potentiometer | second pair gain; read from the schematic by eye |
| Level | B100K | B100k | Potentiometer | read from the schematic by eye |