Op-amp overdrive, 1986 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 Ibanez TS10 Tube Screamer.

The TS9 circuit with a 220 Ω into the clipper, the input buffer on its own bias divider, and two coupling caps into the output buffer. An op-amp with two diodes in its feedback, then an active tone stage.

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. U1’s gain is 1 plus the Drive pot and 51 kΩ over 4.7 kΩ, and the 47 nF in series with the 4.7 kΩ means full gain only above about 720 Hz. The diodes hold the clipper’s output within about 0.6 V of its input, so the clean note rides under the clipped part. The tone stage then rolls the top off. The input buffer idles near 6.3 V on its own 9.2 kΩ and 22 kΩ divider, where the TS808 and TS9 bias it at 4.5 V. The model leaves out the electronic bypass and its LED.

Download.

Parts and what they do

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

10k, 10 kΩ
Top of the 4.5 V reference divider.
10k, 10 kΩ
Bottom of the reference divider.
C20, 47 µF electrolytic
Filters the 4.5 V reference, so everything returned to it sits at a quiet AC ground.
C1, 20 nF
Input coupling cap. Against the input impedance, about 480 kΩ, it sets a corner near 17 Hz.
R1, 1 kΩ
Input series resistor.
R4, 510 kΩ
Biases the input buffer from its divider, and sets most of the input impedance.
R2, 9.2 kΩ
Top of the input buffer’s own bias divider, about 6.3 V. 9.2 kΩ as drawn on the trace.
R3, 22 kΩ
Bottom of the input bias divider.
C2, 10 µF electrolytic
Filters the input bias divider.
Q1, 2SC1815
Input buffer, an emitter follower, with a gain of one and a high input impedance.
10k, 10 kΩ
Input buffer emitter resistor.
C3, 1 µF
Coupling cap into the clipping stage, a 1 µF non-polar.
220, 220 Ω
In series into the clipper’s plus input. The TS808 and TS9 have none.
10k, 10 kΩ
Biases the clipper’s plus input at 4.5 V.
IC1A, JRC4558D
Clipping stage. A non-inverting amp with its gain set by the Drive pot and the diodes across its feedback.
4.7k, 4.7 kΩ
With the 51 kΩ and the Drive pot it sets the gain: 1 + (51 kΩ + Drive) / 4.7 kΩ.
47n, 47 nF
In series with the 4.7 kΩ to the 4.5 V reference, so the stage has full gain only above about 720 Hz.
51k, 51 kΩ
Least feedback resistance, so the gain never drops below about 12.
Drive, 500 kΩ pot, audio taper
Drive, a 500 kΩ audio pot wired as a variable resistor in the feedback. More resistance means more gain before the diodes conduct.
51p, 51 pF
Across the feedback. It rolls off the top of the clipped signal, more as Drive goes up.
Diodes, 1N914 / 1N4148, one each way
Two 1N914s back to back across the feedback. Past about 0.6 V either way they pull the gain down.
R12, 1 kΩ
With C8, a low-pass at about 720 Hz ahead of the tone stage.
C8, 220 nF
The low-pass cap, a 0.22 µF tantalum.
10k, 10 kΩ
Biases the tone stage’s plus input. The trace shows it to 9 V, the other drawing to 4.5 V (followed here).
Tone, 20 kΩ pot, linear taper
Tone, 20 kΩ. Slides the 220 Ω and 0.22 µF from the plus input, where they cut treble, to the minus input, where they boost it.
220, 220 Ω
Tone network resistor.
.22µ, 220 nF
Tone network cap, a 0.22 µF tantalum.
IC1B, JRC4558D
Tone stage.
1k, 1 kΩ
Tone stage feedback resistor.
1µ, 1 µF
Coupling cap to the Level pot, 1 µF non-polar.
1k, 1 kΩ
In series to the Level pot.
Level, 100 kΩ pot, linear taper
Level, 100 kΩ linear, returned to the 4.5 V reference.
C11, 1 µF
Coupling cap from the Level wiper, 1 µF non-polar.
R17, 510 kΩ
Holds the bypass switch at 4.5 V. The switch, closed with the effect on, is drawn as a wire.
R24, 510 kΩ
The other side of the same switch, also to 4.5 V.
.1µ, 100 nF
Coupling cap into the output buffer.
R19, 510 kΩ
Biases the output buffer at 4.5 V. The trace shows it to ground, which would leave Q2 off. The other drawing has 4.5 V.
Q2, 2SC1815
Output buffer, an emitter follower.
R20, 10 kΩ
Output buffer emitter resistor.
10µ, 10 µF electrolytic
Output coupling cap.
R21, 470 Ω
Output series resistor, 470 Ω as on the TS9. The TS808 has 100 Ω.
R22, 100 kΩ
Output pulldown, 100 kΩ as on the TS9.

About this version

TS10
Values from a trace of one TS10, checked against a drawing that lists the TS10’s differences from the TS9. NJM4558 op-amp, the library’s JRC4558D.

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.

Product and company names are trademarks of their owners. They are used here only to identify the circuits these models are based on; this site is not affiliated with or endorsed by any of them.

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