Boss BD-2 Blues Driver 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 fixed low-pass (5.6 kΩ and 5.6 nF, with 5.6 nF across the resistor), then a tone pot between two 18 nF caps.
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
- A 10 kΩ linear pot between two 18 nF caps, one from the signal and one to ground. The wiper is the output, so turning it moves between a brighter blend and a darker one. Which way is clockwise is assumed. Here, up is brighter.
Parts
- R26
- 5.6 kΩ, Tone-shaping network: series resistor.
- C17
- 5.6 nF, Across R26. It passes the treble around it.
- C19
- 5.6 nF, Tone-shaping network: cap to ground. With R26 a low-pass near 5 kHz, partly bypassed by C17.
- C100
- 18 nF, Tone network: series cap to the top of the Tone pot.
- Tone (VR2)
- 10 kΩ, Tone, 10 kΩ linear (VR2). Its ends go to C100 from the signal and C101 to ground, and the wiper sets a brighter or darker blend. The direction is assumed: clockwise brighter.
- C101
- 18 nF, Tone network: cap from the bottom of the Tone pot to ground.
Source and load
Driven by: ideal. Driving: volume pot, 100 kΩ. Source: ideal, the second discrete op-amp’s output, whose feedback keeps its output resistance low. Load: the 100 kΩ Level pot at full, then the output op-amp’s 470 kΩ bias resistor. The 47 nF coupling cap between them is left out.
Values and wiring are the same as in the two discrete-op-amp overdrive with one gain knob for both stages 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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