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 Normal treble and Normal bass controls 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
- Normal treble
- Normal treble, 250 kΩ tapped 70 kΩ from its bottom lug. The lows reach the tap and the highs the top, and the wiper mixes the two. Below the tap the wiper slides toward the .05 µF. No taper is marked, so it’s assumed to be linear.
- Normal bass
- Normal bass, 250 kΩ audio, a variable resistor.
Parts
- 250 pF
- Treble cap, 250 pF, straight off the plate.
- Treble
- 250 kΩ, Normal treble, 250 kΩ tapped 70 kΩ from its bottom lug. The lows reach the tap and the highs the top, and the wiper mixes the two. Below the tap the wiper slides toward the .05 µF. No taper is marked, so it’s assumed to be linear.
- 50 nF
- From the treble pot’s foot lug to ground, .05 µF.
- 100 kΩ
- Slope resistor, 100 kΩ.
- 100 nF
- Bass cap, .1 µF, to the treble pot’s tap and the bass pot’s top.
- CM
- 50 nF, Middle cap, .05 µF (.02 µF on the 6G6).
- Bass
- 250 kΩ, Normal bass, 250 kΩ audio, a variable resistor.
- RM
- 6.8 kΩ, The network’s foot, 6800 Ω, as on the 6G6 and 6G6-B.
Source and load
Source: 37 kΩ, the output resistance of the stage before it on the bench at 1 kHz. Load: 1 MΩ, 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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