Colorsound Overdriver 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.
A Baxandall bass and treble network wrapped around one common-emitter transistor. The network is both the stage’s input path and its feedback path, so the controls boost as well as cut.
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
- Bass
- A 100 kΩ pot between 4.7 kΩ from the input and 4.7 kΩ from the transistor’s collector. 0.1 µF sits across the whole pot, so it only works on the lows. Toward the input end it boosts. Toward the feedback end it cuts.
- Treble
- A 100 kΩ pot between 10 nF from the input and 10 nF from the collector. Its wiper goes into the center node through 5.6 kΩ. Toward the input end it boosts the highs, and toward the feedback end it cuts them.
Parts
- R7
- 4.7 kΩ, Input end of the bass leg.
- Bass
- 100 kΩ, Bass. Toward the input end it boosts, toward the feedback end it cuts. Linear taper assumed.
- C6
- 100 nF, Across the whole bass pot, so above a few hundred hertz the pot is shorted out and has no effect.
- R8
- 4.7 kΩ, Feedback end of the bass leg.
- R9
- 39 kΩ, From the bass wiper to the center node.
- C7
- 10 nF, Input end of the treble leg.
- Treble
- 100 kΩ, Treble. Toward the input end it boosts, toward the feedback end it cuts. Linear taper assumed.
- C8
- 10 nF, Feedback end of the treble leg.
- R10
- 5.6 kΩ, From the treble wiper to the center node.
- C9
- 100 nF, Couples the center node to Q3’s base.
- R11
- 150 kΩ, Top of Q3’s base divider.
- R12
- 33 kΩ, Bottom of Q3’s base divider, about 1.6 V at the base.
- TR3
- The tone stage’s amplifier. Its collector feeds back to its base through the tone network, so the network sets its gain at each frequency.
- R13
- 1.8 kΩ, Q3’s collector load. The drawing shows 5 V here.
- R14
- 470 Ω, Q3’s emitter resistor.
- C10
- 25 µF, Bypasses R14.
- C11
- 25 µF, Couples Q3’s collector to the feedback end of the tone network.
Source and load
Driven by: ideal. Driving: cable and amp, 1 MΩ. The transistor is solved at its bias point first (about 1.5 V at the base and 5.8 V at the collector, from 9 V), then for small signals, so this is the response below clipping. Source: ideal. The gain pair before it drives the network from its 1.8 kΩ collector through 6.4 µF, and its feedback pulls that resistance down further. Load: the output cap into a cable and a 1 MΩ amp input. The 0.22 µF cap is left out.
Values and wiring are the same as in the three-transistor overdrive with active tone controls 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.
© 2026 Swell Amplification LLC. All rights reserved. The simulator and tools, their 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.
From Swell Amplification, swellamps.com.