Op-amp overdrive with a mid boost before the clipper, 1983 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.
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.
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.
3Press Play
Press Play through the circuit to hear a picked note or chord. Play the string is the guitar by itself.
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.
5Tap a wire
Tap a wire to put the probe there. The Probe graph and the spectrum show the signal there.
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
- Not sure what a control does? Hover over it, or hold a finger on it, for a short note.
- For step-by-step walkthroughs, open Start here at the top of the page.
- To put together a pedal or preamp of your own, use the Builder tab.
- Your switches stay where you left them the next time you open that circuit, in this browser only.
- A tube amp opens whole, with its power amp. Pick Preamp only in the Power amp menu to hear the preamp alone, or another power amp to try this preamp on it.
- The graphs use a steady test tone. Play sounds a picked note that dies away.
- Part values are typical of their type. Each circuit’s notes say which schematic it’s based on.
Modeled after the Ibanez ST-9 Super Tube Screamer.
The Tube Screamer’s clipper and tone stage, with an op-amp input buffer and a fixed mid boost ahead of the clipper. Bite moves the boost’s frequency.
Try this
Common mods
Changes people often make to this circuit. Try it plays the note before and after, at the same loudness. Keep it adds the mod to Your changes, where it can go on a switch.
Input
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.
Your build
Stack blocks from the guitar down to the output. Tap + Add a block wherever you want one. The coupling caps and the supply are wired in for you.
Your blocks. These are blocks you saved with Save block, values and part changes included. Add one to any build of the same kind with + Add a block. They stay in this browser.
Your builds stay in this browser, on this device, and 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 to a file to keep a copy. Open a file, or drop the .bench file on the page, brings it back on any device.
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.
Tap where each leg goes. Tap both ends of a part to put the new one across that 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.
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.
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.
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. IC1B is the mid stage: its gain is one at the bass and treble and about 7 dB at the Bite frequency, which runs from about 200 Hz to 2.5 kHz. The manual quotes 25 dB, and the model agrees with the 8 dB others have worked out. That boosted band then reaches the Tube Screamer clipper, so it clips first. Tone and Level work as on a TS9. The later STL Super Tube moves the mid stage after the clipper. That order isn’t modeled.
Download.
Parts and what they do
Stock values. Tap a part on the schematic to change it.
- R18, 10 kΩ
- Top of the 4.5 V reference divider.
- R19, 10 kΩ
- Bottom of the reference divider.
- C13, 47 µF electrolytic
- Filters the 4.5 V reference.
- C1, 47 nF
- Input coupling cap.
- R1, 1 kΩ
- Input series resistor.
- R2, 510 kΩ
- Biases the input buffer at 4.5 V and sets the input impedance near 510 kΩ.
- IC1A, JRC4558D
- Input buffer, an op-amp follower with a gain of one.
- C2, 1 µF
- Coupling cap into the mid stage.
- R3, 220 kΩ
- Biases the mid stage’s plus input at 4.5 V.
- IC1B, JRC4558D
- The mid stage. Its gain is one at the bass and treble and rises around the Bite frequency.
- C3, 27 nF
- From the mid stage’s output to its minus input. With C4 it sets how high the boost goes and how wide it is.
- R5, 1.5 kΩ
- From the output toward the Bite common point.
- Bite, 20 kΩ pot, reverse audio taper
- Bite, one half of a dual 20 kΩ reverse-audio pot, used as a variable resistor. Turned up, both halves drop and the boost moves up in frequency.
- R4, 1.5 kΩ
- From the minus input toward the Bite common point.
- Bite (second half), 20 kΩ pot, reverse audio taper
- The other half of Bite, turned by the same knob.
- C4, 68 nF
- From the Bite common point to ground. Around the Bite frequency it pulls the feedback down, so the gain rises there.
- C5, 1 µF
- Coupling cap into the clipper.
- R6, 10 kΩ
- Biases the clipper’s plus input at 4.5 V.
- IC2A, JRC4558D
- The clipper, as in a Tube Screamer: a non-inverting stage with diodes across its feedback.
- C7, 47 nF
- In series with R8 to ground, so the clipper has full gain only above about 720 Hz.
- R8, 4.7 kΩ
- Sets the gain with R7 and Drive: 1 + (51 k + Drive) / 4.7 k.
- R7, 51 kΩ
- Least feedback resistance, so the gain stays over about 12.
- Drive, 500 kΩ pot, audio taper
- Drive, a 500 kΩ audio pot used as a variable resistor in the feedback.
- C6, 51 pF
- Across the feedback. It rolls off the top of the clipped signal.
- D2, D3, 1N914 / 1N4148, one each way
- One 1N914 each way across the feedback.
- R9, 1 kΩ
- With C8, a low-pass ahead of the tone stage, about 1.6 kHz.
- C8, 100 nF
- The low-pass cap, 100 nF on the drawing.
- R10, 10 kΩ
- Biases the tone stage’s plus input.
- IC2B, JRC4558D
- Tone stage.
- Tone, 20 kΩ pot, linear taper
- Tone, 20 kΩ, modeled linear. It slides R11 and C9 from the plus input, where they cut treble, to the minus input, where they lift it.
- R11, 220 Ω
- Tone network resistor.
- C9, 220 nF
- Tone network cap.
- R12, 1 kΩ
- Tone stage feedback resistor.
- C10, 1 µF
- Coupling cap toward Level.
- R13, 1 kΩ
- Series resistor to Level.
- Level, 100 kΩ pot, linear taper
- Level, a 100 kΩ linear pot.
- C11, 100 nF
- Coupling cap into the output buffer.
- R14, 510 kΩ
- Biases the output buffer from the 4.5 V reference.
- Q1, 2SC1815
- Output buffer, an emitter follower.
- R15, 10 kΩ
- Output buffer emitter resistor.
- C12, 1 µF
- Output coupling cap.
- R16, 10 kΩ
- Holds the output side of C12 at ground.
- R17, 470 Ω
- Output series resistor.
About this version
- JRC4558D
- Negative ground, 9 V. JRC4558D op-amps and a 2SC1815 output buffer. One 1N914 each way across the clipper.
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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