Marshall JCM800 2205 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 Lead treble, Lead middle, and Lead bass controls of the Marshall JCM800 2205, with every part as on the bench. The Marshall JCM800 2210 has the same network.
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
- Lead treble
- The lead channel’s treble, 220 kΩ linear. Its wiper is the stack’s output.
- Lead middle
- The lead channel’s middle, 100 kΩ log, a variable resistor from the mid cap to ground. Turned down, it shunts the mids from the slope node.
- Lead bass
- The lead channel’s bass, 1 MΩ log, a variable resistor. Turned up, it lifts the bottom of the treble pot further from ground, so more bass gets through.
Parts
- R28
- 10 kΩ, Series resistor from V3a’s plate to the tone stack.
- C17
- 470 pF, Treble cap.
- Lead treble
- 220 kΩ, The lead channel’s treble, 220 kΩ linear. Its wiper is the stack’s output.
- R23
- 56 kΩ, Slope resistor.
- C19
- 22 nF, Bass cap, to the bottom of the treble pot.
- C21
- 22 nF, Mid cap, on its own branch to the mid pot.
- Lead middle
- 100 kΩ, The lead channel’s middle, 100 kΩ log, a variable resistor from the mid cap to ground. Turned down, it shunts the mids from the slope node.
- R33
- 4.7 kΩ, In series with the bass pot.
- Lead bass
- 1 MΩ, The lead channel’s bass, 1 MΩ log, a variable resistor. Turned up, it lifts the bottom of the treble pot further from ground, so more bass gets through.
- C20
- 2 nF, From the bottom of the treble pot to ground. It holds the bottom of the treble pot down for high frequencies at any bass setting.
- R22
- 100 kΩ, From the treble wiper to the master node.
Source and load
Source: 34 kΩ, the output resistance of the stage before it on the bench at 1 kHz. Load: 68 kΩ with 98 pF across it, the input of what follows it on the bench, from its impedance at 1 and 10 kHz.
Values, wiring and drawing are taken from the Marshall JCM800 2205 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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