Klon Centaur tone stack
Tone stacks and tone controls from amps and pedals, from their schematics, with the stage that drives each one and what it feeds. Turn the knobs and watch the curve. Pin a setting to compare, change any part, and listen through a speaker. Pickups and guitar knobs are on the Guitars page.
An inverting op-amp stage at unity gain in the mids. The pot swings the treble cap between the stage’s input and its feedback, so it’s a boost-and-cut treble control.
Swipe sideways for the whole drawing. Tap a part to change it. The source drives the end marked in, and the load hangs on the end marked out.
At this setting
0 dB is the source’s voltage with nothing hooked to it, so the curve shows what the stack cuts. A tube source changes the curve only through its output resistance, not its gain.
Pin this curve keeps what the graph shows, up to three pins in their own colors. Pins stay when you switch stacks, so you can lay a Marshall treble sweep over a Vox one. In a sweep, the lightest line is the knob at 0 and the darkest is 10.
Listen
You hear a picked string through a guitar on full, with 15 feet of cable. Play without it leaves the stack out.
Source and load
Driven by
Driving
The knobs
- Treble
- A 10 kΩ pot between 1.8 kΩ from the stage’s input and 4.7 kΩ from its output. Its wiper feeds the op-amp’s input through 3.9 nF. Toward the input end it lifts the treble, by about 16 dB at 10 kHz at full. Toward the output end it cuts, by about 8 dB. At noon the top is up about 2 dB.
Parts
- R22
- 100 kΩ, Tone stage input resistor.
- R21
- 1.8 kΩ, From the summing output to the treble pot.
- Treble
- 10 kΩ, Treble. It moves the C14 injection point between the input side (more treble) and the output side (less).
- R23
- 4.7 kΩ, From the treble pot to the tone output.
- C14
- 3.9 nF, Treble cap, from the pot wiper to the tone op-amp’s input.
- U2B
- Tone stage (inverting, unity gain in the mids) on the charge-pump rails.
- R24
- 100 kΩ, Tone stage feedback resistor.
Source and load
Driven by: op-amp buffer. Driving: volume pot, 10 kΩ. The op-amp runs on the pedal’s charge-pump rails, about −8.6 V and +16.2 V from a 9 V battery. Source: the summing amplifier before it. Load: 560 Ω into the 10 kΩ Output pot at full, then the 100 kΩ pulldown. The 4.7 µF coupling cap is left out.
Values and wiring are the same as in the blended op-amp overdrive with germanium diodes circuit on the bench, so the two always match.
Warnings. The summary above the graph turns red if the stack can’t be solved as set, usually from a part at zero or a shorted pot track.
How this tool works. We solve each stack with the circuit bench’s engine: the source stage’s operating point first, then every part at 161 frequencies from 20 Hz to 20 kHz. A stack that’s also in a bench circuit is built from that circuit file, so the two always match.
The curves are small-signal. They don’t show clipping or grid current in the next stage. For the stage before or after a stack, try the gain stage tool.
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.
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