Boss DS-1 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.
The four-transistor fuzz’s low-pass and high-pass blend, scaled down to low impedance: 6.8 kΩ resistors and a 20 kΩ pot, fed from the op-amp through 2.2 kΩ with 10 nF at the clipping diodes.
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
- Tone
- Blends a low-pass (6.8 kΩ and 100 nF, about 234 Hz) with a high-pass (22 nF and 6.8 kΩ, about 1 kHz) through a 20 kΩ linear pot. The corners sit well apart. So at noon, with its source and load, the mids are down about 6 dB near 650 Hz.
Parts
- C9
- 470 nF, Output coupling cap.
- R14
- 2.2 kΩ, Feeds the diodes and, with C10, filters above about 7 kHz while they are not conducting.
- C10
- 10 nF, Across the diodes. It rounds the edges of the clipped wave.
- C11
- 22 nF, Tone high-pass cap. With R17 the corner is about 1 kHz.
- R17
- 6.8 kΩ, Tone high-pass resistor.
- R16
- 6.8 kΩ, Tone low-pass resistor. With C12 the corner is about 234 Hz.
- C12
- 100 nF, Tone low-pass cap.
- Tone
- 20 kΩ, Blends the low-pass and high-pass sides. In the middle, both are down around 500 Hz. That’s the scoop.
Source and load
Driven by: op-amp buffer. Driving: volume pot, 100 kΩ. The clipping diodes are left out, so this is the tone control at small signals. Load: the 100 kΩ Level pot at full, then the output buffer’s input, about 330 kΩ, its 1 MΩ and 1 MΩ bias divider in parallel with the emitter follower. The 47 nF coupling cap between them is left out.
Values and wiring are the same as in the transistor-boosted hard-clipping distortion 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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