Orange Graphic MkII 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 passive boost-and-cut stack of the James type, with independent bass and treble. It’s flat at noon, but it costs about 20 dB of level.
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 1 MΩ pot between two caps. It boosts and cuts the lows around a fixed middle.
- Treble
- A 1 MΩ pot between the two treble caps. It boosts and cuts the highs. With both knobs at noon the response is close to flat, unlike the Fender and Marshall stacks.
Parts
- C68n
- 68 nF, Coupling cap into the tone network.
- R100k
- 100 kΩ, Top resistor of the bass leg.
- Bass
- 1 MΩ, Bass, 1 MΩ log. Toward the top it boosts, toward the bottom it cuts.
- C2n2
- 2.2 nF, Across the upper half of the Bass pot. Above the bass it shorts that half.
- C22n
- 22 nF, Across the lower half of the Bass pot.
- R22k
- 22 kΩ, Bottom resistor of the bass leg.
- R100k
- 100 kΩ, From the Bass wiper to the Treble wiper, where the two legs meet.
- C1500p
- 1.5 nF, Top cap of the treble leg.
- Treble
- 1 MΩ, Treble, 1 MΩ log. Its wiper is the tone network’s output.
- C10n
- 10 nF, Bottom cap of the treble leg.
Source and load
Driven by: triode plate, 220 kΩ plate resistor. Driving: volume pot, 1 MΩ. Load: the 1 MΩ volume at full, then V1b’s grid. Its 330 pF bright cap is left out.
Values and wiring are the same as in the two-stage amp with passive baxandall tone and a six-way coupling switch 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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