Fender 5C8 Twin 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 Treble and Bass controls of the Fender 5C8 Twin, with every part as on the bench.
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
- Treble
- Treble, 1 MΩ, its wiper on the inverter’s grid. Clockwise moves the wiper toward the 250 pF from the plate. Counterclockwise toward the .005 µF to ground, which bleeds treble off the grid. The drawing marks no taper or direction. Audio taper, clockwise brighter.
- Bass
- Bass, 2 MΩ as a variable resistor across the bass cap, its wiper on the 47 kΩ’s foot, one end to ground and the other free. Clockwise adds resistance, so the cap does the shunting and the bass comes up against the treble. Counterclockwise shorts the cap and the 47 kΩ lowers everything evenly. The drawing marks no taper or direction. Audio taper, clockwise more bass.
Parts
- 250 pF
- Treble cap, 250 pF (.00025 µF), from the 6J5’s plate to the treble pot. It carries the top end around the bass ladder.
- Treble 1M
- 1 MΩ, Treble, 1 MΩ, its wiper on the inverter’s grid. Clockwise moves the wiper toward the 250 pF from the plate. Counterclockwise toward the .005 µF to ground, which bleeds treble off the grid. The drawing marks no taper or direction. Audio taper, clockwise brighter.
- 5 nF
- From the treble pot’s far end to ground, .005 µF 600 V.
- 50 nF
- Coupling cap from the 6J5’s plate into the bass ladder, .05 µF 600 V.
- 1 MΩ
- 1 MΩ to ground at the ladder’s input. It keeps the coupling cap’s far end at ground for DC.
- 250 kΩ
- The bass ladder’s first 250 kΩ.
- 47 kΩ
- From the middle of the ladder down to the bass cap and pot, 47 kΩ. With the pot turned all the way down it’s a plain 47 kΩ to ground, which cuts every frequency about 16 dB.
- 5 nF
- The bass cap, .005 µF 600 V to ground. With the pot’s resistance across it turned up, it shunts the treble and lets the bass through.
- Bass 2M
- 2 MΩ, Bass, 2 MΩ as a variable resistor across the bass cap, its wiper on the 47 kΩ’s foot, one end to ground and the other free. Clockwise adds resistance, so the cap does the shunting and the bass comes up against the treble. Counterclockwise shorts the cap and the 47 kΩ lowers everything evenly. The drawing marks no taper or direction. Audio taper, clockwise more bass.
- 250 kΩ
- The bass ladder’s second 250 kΩ, into the inverter’s grid.
Source and load
Source: 11 kΩ, the output resistance of the stage before it on the bench at 1 kHz. Load: 2 MΩ with 60 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 Fender 5C8 Twin 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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