Two-stage fuzz with a starved third transistor and an active tone stage, 2000s 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 Electro-Harmonix Ripped Speaker.

An op-amp buffer, two transistor gain stages with Fuzz between them, and a third transistor whose base bias is a knob, Rip. Turned down, it starves Q3 and the note sputters. An op-amp tone stage follows.

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. IC1A buffers the guitar. R4 drops it about 10 times into Q1, and Q1 and Q2 each bring it up about 20 times, so the note leaves Q2 clipped. Q3’s base has no bias of its own: Rip sets it. At 4 Q3 idles with its collector near 7.3 V. Turned down, Q3 turns off and passes only the tops of the wave, which gates and sputters a quiet note. Turned up past about 5, Q3 saturates, and at full only a few millivolts get through. Tone is an active control around IC1B, from more bass at 0 to more treble at full.

Download.

Parts and what they do

Stock values. Tap a part on the schematic to change it.

R102, 16 kΩ
Top of the Vref divider.
R103, 22 kΩ
Bottom of the Vref divider.
C102, 100 µF electrolytic
Filters the divider.
Q4, 2N5088
Emitter follower. Its emitter is Vref, about 4.6 V, at a low impedance.
R104, 10 kΩ
Q4’s emitter resistor.
C103, 100 µF electrolytic
Filters Vref.
C104, 100 nF
Filters Vref at the top of the range.
R1, 2.2 MΩ
From the input to ground.
C1, 1 µF
Input coupling cap.
R2, 2.2 MΩ
Holds the input at Vref and sets the input impedance near 2.2 MΩ.
R3, 1 kΩ
Series resistor into the buffer.
C2, 1 nF
With R3, a low-pass far above the audio range, for radio.
D1, 1N914 / 1N4148
1N4148 from the buffer’s input to 9 V. It conducts only on an input over the supply.
D2, 1N914 / 1N4148
1N4148 from ground to the buffer’s input. It conducts only on an input below ground.
IC1A, OPA1678
Input buffer, an op-amp follower.
R4, 47 kΩ
Into Q1. With Q1’s input it drops the level about 10 times.
C3, 10 µF electrolytic
Coupling cap into Q1.
R5, 430 kΩ
Top of Q1’s base divider.
R6, 43 kΩ
Bottom of Q1’s base divider, about 0.8 V.
Q1, 2N3904
First gain stage.
R7, 10 kΩ
Q1’s collector load.
R8, 390 Ω
Q1’s emitter resistor, unbypassed. With R7 it holds the gain near 20.
C4, 10 µF electrolytic
Couples Q1 to the Fuzz pot.
Fuzz, 10 kΩ pot, linear taper
Fuzz, a 10 kΩ linear pot. It sets how much of Q1’s output reaches Q2.
R9, 390 Ω
Under Fuzz.
C5, 10 µF electrolytic
Coupling cap into Q2.
R10, 430 kΩ
Top of Q2’s base divider.
R11, 43 kΩ
Bottom of Q2’s base divider.
Q2, 2N3904
Second gain stage, the same as Q1.
R12, 10 kΩ
Q2’s collector load.
R13, 390 Ω
Q2’s emitter resistor.
C6, 10 µF electrolytic
Coupling cap into Q3.
R14, 11 kΩ
Above the Rip pot.
Rip, 100 kΩ pot, audio taper
Rip, a 100 kΩ audio pot whose wiper is Q3’s only base bias. Turned down, Q3 gets less bias and starves.
R15, 2.7 kΩ
Below the Rip pot.
Q3, 2N3904
Third gain stage, biased by Rip.
R16, 10 kΩ
Q3’s collector load.
R17, 390 Ω
Q3’s emitter resistor.
C7, 1 µF electrolytic
Couples Q3 to Volume.
Volume, 100 kΩ pot, audio taper
Volume, a 100 kΩ audio pot returned to Vref, ahead of the tone stage.
R18, 22 kΩ
From Volume into the tone stage.
Tone, 50 kΩ pot, linear taper
Tone, a 50 kΩ linear pot. Its wiper is the op-amp’s minus input, so it slides between the input side and the feedback side.
R21, 22 kΩ
From the Tone pot to the output.
C8, 18 nF
With R20, a treble path from Volume to the feedback end of Tone.
R20, 4.7 kΩ
In series with C8.
R19, 4.7 kΩ
With C10, a treble path from the input end of Tone to the output.
C10, 18 nF
In series with R19.
IC1B, OPA1678
The tone stage, inverting, plus input on Vref.
C9, 150 pF
Across the tone stage. It keeps it stable at the top of the range.
C11, 10 µF electrolytic
Output coupling cap.
R22, 100 kΩ
Holds the output side of C11 at ground.
R23, 100 Ω
Output series resistor.

About this version

2N3904, OPA1678
Negative ground, 9 V. 2N3904 transistors and an OPA1678 dual op-amp, as the kit drawing has them.

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.

Spot an error, or want a circuit added? Email info@swellamps.com. A schematic or a clear photo of one helps. Anything you send may be used to improve these models and our desktop app.

© 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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