Gibson GA-77RVT Vanguard 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 2 and Bass 2 controls of the Gibson GA-77RVT Vanguard, 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 2
- Channel 2’s Treble, 250 kΩ reverse audio as marked. Its wiper is the network’s output. Turned up, the wiper moves toward the treble cap and the treble comes up.
- Bass 2
- Channel 2’s Bass, 250 kΩ audio, its far end grounded. Turned up, its wiper moves toward ground, so more of the track sits between the 100 kΩ and ground and more bass gets through. Turned down, the .01 µF and 10 kΩ pull the bass down.
Parts
- 250 pF
- Channel 2’s treble cap, into the top of the Treble pot. Only the treble gets through it.
- Treble
- 250 kΩ, Channel 2’s Treble, 250 kΩ reverse audio as marked. Its wiper is the network’s output. Turned up, the wiper moves toward the treble cap and the treble comes up.
- 100 kΩ
- From the network’s input to the bottom of the Treble pot and the top of the Bass pot. The bass and mids come this way.
- Bass
- 250 kΩ, Channel 2’s Bass, 250 kΩ audio, its far end grounded. Turned up, its wiper moves toward ground, so more of the track sits between the 100 kΩ and ground and more bass gets through. Turned down, the .01 µF and 10 kΩ pull the bass down.
- 10 nF
- From the top of the Bass pot to its wiper. It passes the mids and treble around the bass part of the track.
- 10 kΩ
- From the Bass wiper to ground. It sets how far the bass can be cut.
Source and load
Source: 48 kΩ, the output resistance of the stage before it on the bench at 1 kHz. Load: 45 kΩ with 100 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 Gibson GA-77RVT Vanguard 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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