Three-transistor germanium fuzz, 1962 style

Pedal and tube amp circuits, solved part by part the way SPICE (the circuit simulator engineers use) does it, while you listen and watch. Turn the knobs, change any part, or tap a wire to put a probe on it.

How to use the bench

Every part is simulated. Nothing you hear is a recording.

  1. 1Pick a circuit

    Choose one from the menu, or type a name, maker or year in Find a circuit. The buttons under the menu switch between versions.

  2. 2Set the knobs and the input

    Turn the circuit’s knobs on the front panel. In the Input box, choose Guitar or Signal generator, and the note or chord.

  3. 3Press Play

    Press Play through the circuit to hear a picked note or chord. Play the string is the guitar by itself.

  4. 4Tap a part

    Tap any part on the schematic to change its value, or swap the transistor, tube or diode. The red numbers are DC voltages, and they update as you go.

  5. 5Tap a wire

    Tap a wire to put the probe there. The Probe graph and the spectrum show the signal there.

  6. 6Try a change

    Press Try it on a card under Try this to hear one change, before and after. Modify this circuit, below the schematic, adds or removes parts.

Good to know

Modeled after the Maestro FZ-1 Fuzz-Tone.

The first commercial fuzz. An emitter follower feeds two germanium stages that each clip one side of the wave, then a tiny output cap turns the square wave into spikes. It runs on 3 V, and two of its three transistors have no bias network at all.

Input

Add

Peak voltage from the pickup for each note. Strum hard and a single coil puts out a few hundred millivolts. When you play a chord, its strings share this level.

How it’s played
Tap a part to change its value, or a wire to probe it. To add or take out parts, open Modify this circuit, below. Red numbers are DC voltages to ground, not warnings. Scroll or drag sideways to see the whole circuit.
Modify this circuit Add parts, take them out, or put one in series with another, then hear what it does. Tap to open.

Pick what to do, then tap the schematic. Your changes show in purple. Any change can go on a switch beside the knobs, from the menu in its row under Your changes.

Add a part

Tap where each leg goes. Tap both ends of a part to put the new one across that part.

Change a part

With Remove a part on, tap any part of the pedal or amp to take it out, and tap it again to put it back. Tapping a purple part you added deletes it.

Turn on Add in series with a leg and tap a part. In that part’s box, below the schematic, pick which leg to lift and what goes in the gap, such as a resistor between a cap and ground or a stopper in front of a grid.

Change a wire

With Cut into a wire on, tap any wire. Pick a part from the menu and it goes in the gap, wired in. Volume pot puts a pot there with the input on one end, the output on the wiper and the other end to ground.

With Run a wire on, tap a leg, then where the wire goes. Drag any piece of a wire you ran, or of an added part’s lead, to square it up or move it.

Keep and share

Your changes stay in this browser, on this device, for your next visit. Nothing is sent to us. Anyone using this browser can see them. They’re lost if you clear your browsing data or use a private window, so save a file to keep a copy. A shared link carries the circuit after the #, a part browsers never send to a server.

Test tone for the graphs
The graphs use a steady tone. Play sounds a plucked string that dies away.

Input

pickup, unloadedat the pedal input

Output

at the amp input

Probe

Spectrum

Frequency response

What the curves mean

The ink curve is the response to a very quiet signal, from the generator to the probe. The blue curve is measured with pink noise at the level you set, like an audio analyzer. When stages clip, the blue curve pulls away from the ink one and the gray coherence line (right-hand scale) drops below 1. Then no single curve tells the whole story. Both use the signal generator, whichever Input tab is picked.

Output

Bias

every voltage and current at rest

What to listen for. The thin, buzzy fuzz on mid-1960s records. It lets very little bass through. The 3.3 nF output cap into 56 k passes almost nothing below about 860 Hz, so what reaches the amp is the edges of a square wave. Attack raises the resistance under Q2’s base, letting more signal and bias reach it. At minimum the note gates and sputters, and at maximum it saturates into a steady buzz. Q1 and Q3 run on their own leakage, so warming up the pedal does much what turning up Attack does.

Download.

Parts and what they do

Stock values for the FZ-1, 1962 version. Tap a part on the schematic to change it.

R14, 100 kΩ
Input series resistor. With R20 it sets the input impedance near 1 MΩ, and with the pickup it cuts some treble.
C15, 10 nF
Input coupling cap. With R20 it passes everything above about 16 Hz.
R20, 1 MΩ
Q1’s only bias, a resistor from base to ground. Q1’s leakage current flows out through it and pulls the base to about −1.5 V.
Q1, 2N270 (leaky)
Emitter follower, the patent’s impedance transforming stage. No voltage gain. It drives the low-impedance clipping stage without loading the guitar.
R19, 10 kΩ
Q1 emitter load.
C24, 20 µF electrolytic
Coupling cap into Q2. 1 µF on the FZ-1A.
R26₁, 470 kΩ
Bias from the battery to Q2’s base. The patent prints 470 Ω, which would saturate Q2, but real units have 470 kΩ. The patent says it keeps the pedal from dying in the cold, when the leakage currents shrink.
R29, 2.2 kΩ
From Q2’s base to the attack network.
R30, 22 kΩ
In parallel with the attack pot, so the network never goes above 15 kΩ.
Attack, 50 kΩ pot, linear taper
Attack, a variable resistor to ground under Q2’s base. More resistance shunts less signal and bias away from Q2, so it clips harder and sustains longer.
Q2, 2N270 (leaky)
First clipping stage, biased near cutoff (collector close to the full battery voltage) so it clips one side of the wave.
R26, 1.5 kΩ
Q2 collector load. It went up to 10 kΩ on the 1965 FZ-1A.
C31, 20 µF electrolytic
Coupling cap into Q3. 1 µF on the FZ-1A.
R33, 10 kΩ
Q3’s only bias, a resistor to ground. Like Q1, Q3 idles on its leakage.
Q3, 2N270 (leaky)
Second clipping stage. It squares off the other side of the wave.
R35, 10 kΩ
Q3 collector load.
C37, 3.3 nF
Output cap. With R38 and the volume pot it makes a high-pass near 860 Hz, which the patent calls a differentiating circuit, turning the square wave into spikes. This one part is most of the Fuzz-Tone sound.
R38, 56 kΩ
The resistor of the differentiating network.
Volume, 500 kΩ pot, audio taper
Volume. Its value isn’t in the patent. Real units have 500 kΩ. The FZ-1A has 50 kΩ.

Versions

FZ-1, 1962
Positive ground on two 1.5 V cells, 3.1 V fresh as in the patent, so every voltage reads negative. The 2N270 preset puts this circuit near the patent’s bias voltages at 77 °F, the bench’s default temperature. Real parts spread widely.
FZ-1A, 1965, modeled after the Maestro FZ-1A Fuzz-Tone
One 1.5 V cell. 1 µF coupling caps, 10 kΩ on Q2’s collector, no 56 kΩ at the output and a 50 kΩ audio Volume. The drawing lists 2N2613 or 2N2614 transistors. The 2N270 preset stands in for them. Its leakage alone holds Q2 near saturation, its collector about 0.07 V from ground, so the drawing’s parts may idle differently.

Sources

How this tool works. Every part is an equation, and the whole circuit is solved several times per audio sample: 192,000 samples a second while you drag a knob, 384,000 once you let go. Transistors use Ebers-Moll with gain, leakage, Early effect, base resistance, junction capacitance and temperature. Their charge storage is set at the bias point, close for small signals and rough while they switch hard. Tubes use Koren’s equations fitted to each datasheet, plus grid current. Diodes are exponential junctions with series resistance. Presets are typical of each type. Caps are ideal, and the battery or HT is a voltage behind a resistance.

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© 2026 Swell Amplification LLC. All rights reserved. The simulator, its circuit models, drawings, presets and text are the property of Swell Amplification LLC and may not be copied, reproduced, redistributed or used to build another product without written permission. The original circuits are historical designs documented in public sources, and no claim is made to them. Everything here is provided as is, without warranty of any kind, for study and personal use. Results are simulations of typical parts, not measurements of any real unit. Don’t rely on them for the safety of any build or repair. Tube amplifiers carry lethal voltages.

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