Circuit bench

What this is

Each circuit is a real, well-documented schematic from a classic pedal or tube amp. Every resistor, capacitor, transistor, tube and diode is simulated, and the whole circuit is solved again for every sample of audio, so what you hear and see comes from the parts, not from a recording or a curve fit. Each circuit’s notes say which sources it follows, where versions differ, and what is left out. Tube amps are modelled from the input to the phase inverter; the power stage is not included.

Getting around

Pick a circuit from the menu; pedals and tube preamps are listed separately. The buttons beside it switch between versions of the circuit and turn switches and mods on and off. Room temperature matters for germanium parts. Reset circuit puts every part back.

The front panel has the circuit’s own knobs and the guitar’s volume. Choose what drives the input: a Guitar (a pickup with its inductance and resistance, the guitar’s volume pot and the cable) or a bench Generator with an output resistance you set. Pick the note, add intervals for chords, and set the level.

The schematic

Tap a part to change its value, swap a transistor, tube or diode, or edit its model. Tapping either half of a dual triode selects the whole tube. Tap any wire to move the probe there. The rust-coloured numbers are the DC voltages at each node, recalculated whenever something changes.

The graphs

Input compares the pickup’s unloaded voltage with what actually arrives at the circuit, so you can see how hard the circuit loads the guitar. Output is the signal at the amp input (for a pedal) or at the phase inverter’s grid (for a preamp). Probe shows the node you tapped, with DC or AC coupling. Spectrum shows the harmonics at the output or the probe: the fundamental in ink, even harmonics in orange, odd in blue, and with chords, intermodulation in rust.

Frequency response shows the gain from the generator to the probe. The ink curve is the small-signal response, what a very quiet signal sees; it follows every knob and the probe instantly. Measure with noise adds a blue curve measured with pink noise at the level you set, and a grey coherence line: where coherence drops below 1, clipping has taken over and no single curve describes the circuit.

Below the graphs, the readouts give the output level, distortion and harmonic balance, and the bias point of every transistor and tube.

Listening

Play the string plays the pickup alone. Play through the circuit renders the same note through the circuit, heard at the output or at the probe; listening at the probe lets you hear what each stage does. Match loudness evens out the levels so you compare tone rather than volume.

Limits

Part presets are representative values for their type; real parts spread, sometimes widely. The simulation is only as good as its models and the schematic it follows, so treat it as a close study of the circuit rather than a copy of any one unit.