Fender 6G8 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 Bass and Treble controls of the Fender 6G8 Twin (vibrato channel), 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
- Bass
- Bass, 1 MΩ reverse audio, wired as a divider: its top on the 180 kΩ, its foot on the 10 kΩ, its wiper on the treble pot’s tap. Up, the wiper sits at the top and passes the whole signal, lows included. Down, the wiper sits near the 10 kΩ and the tap gets the top through the .001 µF only, so the lows drop away. The drawing marks it 1M-D: reverse audio.
- Treble
- Treble, 350 kΩ, tapped 70 kΩ from its bottom lug. The highs reach the top and the bass pot’s wiper the tap, and the wiper mixes the two. Below the tap it slides toward the .005 µF. No taper letter on the drawing, so it’s assumed to be linear.
Parts
- 50 nF
- Coupling cap, .05 µF, from the plate into the tone network.
- 250 pF
- Treble cap, 250 pF, to the top of the treble pot. The highs go this way.
- 180 kΩ
- Down to the top of the bass pot. The lows and mids go this way.
- Bass
- 1 MΩ, Bass, 1 MΩ reverse audio, wired as a divider: its top on the 180 kΩ, its foot on the 10 kΩ, its wiper on the treble pot’s tap. Up, the wiper sits at the top and passes the whole signal, lows included. Down, the wiper sits near the 10 kΩ and the tap gets the top through the .001 µF only, so the lows drop away. The drawing marks it 1M-D: reverse audio.
- 1 nF
- From the bass pot’s top to its wiper. It carries the mids and highs past the upper part of the track.
- 10 nF
- From the bass pot’s wiper to its foot. It drains the highs from the wiper toward the 10 kΩ, so with the bass up the tap leans toward the lows.
- 10 kΩ
- From the bottom of the bass pot to ground.
- Treble
- 350 kΩ, Treble, 350 kΩ, tapped 70 kΩ from its bottom lug. The highs reach the top and the bass pot’s wiper the tap, and the wiper mixes the two. Below the tap it slides toward the .005 µF. No taper letter on the drawing, so it’s assumed to be linear.
- 5 nF
- From the treble pot’s bottom lug to ground. With the wiper below the tap it cuts the highs.
Source and load
Source: 45 kΩ, the output resistance of the stage before it on the bench at 1 kHz. Load: 490 kΩ with 15 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 6G8 Twin (vibrato channel) 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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