Fender 6G6-A Bassman 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 bass control of the Fender 6G6-A Bassman, 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
- Bass channel bass, 25 kΩ linear on the layout, a variable resistor between the two .25 µF caps’ far ends.
Parts
- R2
- 27 kΩ, From the volume’s top to the bass pot’s top, 27 kΩ on the 6G6-A (56 kΩ on the 6G6, 10 kΩ on the 6G6-B). With the bass pot it sets how much the lows come up.
- 1 MΩ
- From the follower’s cathode, 1 MΩ to the two .25 µF caps. Most of the mids and lows reach the volume through here and the caps.
- 250 nF
- .25 µF from the 1 MΩ to the bass pot’s top.
- 250 nF
- .25 µF from the 1 MΩ to the bass pot’s foot. With the pot turned up, the lows go through it around the pot.
- Bass
- 25 kΩ, Bass channel bass, 25 kΩ linear on the layout, a variable resistor between the two .25 µF caps’ far ends.
- 820 Ω
- The network’s foot, 820 Ω to ground.
Source and load
Source: 660 Ω, the output resistance of the stage before it on the bench at 1 kHz. Load: 250 kΩ with 120 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 6G6-A Bassman 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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