Fender 6G7-A Bandmaster 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 6G7-A Bandmaster (vibrato channel), with every part as on the bench. The Fender 6G4-A Super (vibrato channel) 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
- Bass
- Bass, 250 kΩ audio, a variable resistor between the treble pot’s tap and the bass cap. Turned down, it ties the tap to the 6800 Ω through the bass cap, and the bass drains away. Turned up, it puts more resistance in that path.
- Treble
- Treble, 350 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 .003 µF. No taper is marked, so it’s assumed to be linear.
Parts
- 250 pF
- Treble cap, from the plate to the top of the treble pot. There’s no coupling cap ahead of the tone network: every path from the plate to ground goes through a cap.
- 100 kΩ
- The low path, from the plate down to the two caps below.
- 100 nF
- Carries the lows and mids on to the treble pot’s tap.
- 20 nF
- Bass cap, to the bottom of the bass pot and the 6800 Ω.
- Bass
- 250 kΩ, Bass, 250 kΩ audio, a variable resistor between the treble pot’s tap and the bass cap. Turned down, it ties the tap to the 6800 Ω through the bass cap, and the bass drains away. Turned up, it puts more resistance in that path.
- 6.8 kΩ
- From the bottom of the bass pot to ground.
- Treble
- 350 kΩ, Treble, 350 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 .003 µF. No taper is marked, so it’s assumed to be linear.
- 3 nF
- From the treble pot’s bottom lug to ground. With the wiper below the tap it cuts the highs.
Source and load
Source: 40 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 6G7-A Bandmaster (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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