Op-amp distortion with treble, mid and bass, 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.
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 MT10 Mostortion.
A Tube Screamer style clipper with two diodes each way, then a passive tone network with Treble, Mid and Bass, and a second op-amp stage to bring the level back.
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. Q1 buffers the guitar. The clipper’s gain runs from one with Drive at 0 to about 186 at full, and two diodes each way hold its output near 1.2 V either way. Below about 270 Hz its gain falls toward one, so the bass clips least. The tone network after it is passive. Bass and Mid are variable resistors to the reference, and Treble fades between the network and a 330 pF path straight from the clipper. The second op-amp stage, a gain of about 5.7, makes up the level the network drops. Every knob at noon leaves the response within about 1 dB from 400 Hz to 2 kHz.
Download.
Parts and what they do
Stock values. Tap a part on the schematic to change it.
- R101, 10 kΩ
- Top of the 4.5 V reference divider.
- R102, 10 kΩ
- Bottom of the reference divider.
- C101, 47 µF electrolytic
- Filters the 4.5 V reference.
- R1, 2.2 MΩ
- From the input to ground.
- C1, 22 nF
- Input coupling cap.
- R2, 1 kΩ
- Input series resistor.
- R4, 510 kΩ
- Biases the input buffer from its divider and sets the input impedance near 510 kΩ.
- R5, 9.1 kΩ
- Top of the input buffer’s divider, about 6.3 V.
- R6, 22 kΩ
- Bottom of the input buffer’s divider.
- C2, 10 µF electrolytic
- Filters the divider.
- Q1, 2SC1815
- Input buffer, an emitter follower.
- R3, 10 kΩ
- Input buffer emitter resistor.
- C3, 1 µF
- Coupling cap into the clipper.
- R7, 220 Ω
- Series resistor into the clipper’s plus input.
- R8, 1 MΩ
- Biases the clipper’s plus input at 4.5 V.
- IC1A, CA3260 (BiMOS)
- The clipper, a non-inverting stage with diodes across its feedback.
- R9, 2.7 kΩ
- Sets the gain with Drive: 1 + Drive / 2.7 k, up to about 186.
- C5, 220 nF
- In series with R9, so the gain falls toward one below about 270 Hz.
- Drive, 500 kΩ pot, audio taper
- Drive, a 500 kΩ audio pot used as a variable resistor in the feedback.
- C4, 51 pF
- Across the feedback. It rolls off the top of the clipped signal.
- D1 to D4, 2 × 1N914 / 1N4148, one each way
- Two 1N4148s in series each way across the feedback, so the clipper swings about 1.2 V either way.
- R10, 47 kΩ
- From the clipper into the tone network.
- C8, 68 nF
- Mid: in series with the Mid control to the reference.
- Mid, 50 kΩ pot, audio taper
- Mid, a 50 kΩ audio pot used as a variable resistor. Turned down, C8 and C9 pull more of the mids to the reference.
- C9, 15 nF
- Across Mid.
- C7, 33 nF
- From M to the bass end of the Treble pot.
- R11, 10 kΩ
- In series with Bass to the reference.
- Bass, 250 kΩ pot, audio taper
- Bass, a 250 kΩ audio pot used as a variable resistor to the reference.
- C6, 330 pF
- Treble path: from the clipper straight to the treble end of the Treble pot.
- Treble, 250 kΩ pot, audio taper
- Treble, a 250 kΩ audio pot. Its wiper fades from the network at C7 to the treble path through C6.
- R12, 1 MΩ
- Biases the second stage’s plus input.
- IC1B, CA3260 (BiMOS)
- Second stage, a gain of about 5.7 to make up for the tone network.
- R13, 47 kΩ
- Second stage feedback resistor.
- C10, 1 nF
- Across R13. It rolls off above about 3.4 kHz.
- R20, 10 kΩ
- Sets the second stage’s gain with R13.
- C15, 1 µF
- In series with R20 to the reference.
- C11, 1 µF
- Coupling cap toward Level.
- R14, 1 kΩ
- Series resistor to Level.
- Level, 100 kΩ pot, linear taper
- Level, a 100 kΩ linear pot returned to the reference.
- C13, 100 nF
- Coupling cap into the output buffer.
- R16, 510 kΩ
- Biases the output buffer.
- Q2, 2SC1815
- Output buffer, an emitter follower.
- R17, 10 kΩ
- Output buffer emitter resistor.
- R18, 470 Ω
- Output series resistor.
- C14, 10 µF electrolytic
- Output coupling cap.
- R19, 100 kΩ
- Holds the output at ground.
About this version
- CA3260, 2SC1815
- Negative ground, 9 V. A CA3260 dual op-amp and 2SC1815 buffers. Two 1N4148s 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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