Fender 5E6-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 Treble and Bass controls of the Fender 5E6-A Bassman, with every part as on the bench. The Fender 5E8-A Twin 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
- Treble
- Treble, 1 MΩ. Its wiper is the driver’s grid. One end has the 250 pF from the follower, the other goes to ground through .01 µF. Up moves the wiper toward the 250 pF, so more treble.
- Bass
- Bass, 1 MΩ, its wiper on the bass path. One end goes straight to ground, the other through .005 µF. Down shorts the bass path to ground. Up leaves only the .005 µF there, which removes the treble and lets the bass through to the driver.
Parts
- 250 pF
- Treble cap, 250 pF (.00025 µF on the drawing), into the bright end of the treble pot.
- Treble 1M
- 1 MΩ, Treble, 1 MΩ. Its wiper is the driver’s grid. One end has the 250 pF from the follower, the other goes to ground through .01 µF. Up moves the wiper toward the 250 pF, so more treble.
- 10 nF
- From the far end of the treble pot to ground, .01 µF 400 V. With the pot turned down it bleeds the treble path’s top end to ground. The 5E6 has none: its treble pot’s far end is on the bass pot’s .005 µF.
- 100 nF
- Coupling cap from the follower into the bass path, .1 µF 200 V.
- 220 kΩ
- From the bass path to ground, 220 kΩ. It holds the node at 0 V for the 10 MΩ and loads the follower lightly.
- 10 MΩ
- Feedback, 10 MΩ from the bass path back to V2a’s grid. V2a turns the signal over and the follower doesn’t, so this feeds back out of phase. It cuts V2’s gain about 3 dB.
- 220 kΩ
- From the bass path to the bass pot’s wiper, 220 kΩ (the 5E7 and 5E4-A have 100 kΩ here).
- Bass 1M
- 1 MΩ, Bass, 1 MΩ, its wiper on the bass path. One end goes straight to ground, the other through .005 µF. Down shorts the bass path to ground. Up leaves only the .005 µF there, which removes the treble and lets the bass through to the driver.
- 5 nF
- From the bass pot’s far end to ground, .005 µF 600 V.
- 220 kΩ
- From the bass pot’s wiper to the driver’s grid, 220 kΩ. The bass path and the treble wiper mix here.
- V2a grid
- 150 kΩ, A resistor from this network feeds back to V2a’s grid. Here that grid is a resistor to ground, about 150 kΩ. The feedback loop isn’t on this page.
Source and load
Source: 750 Ω, the output resistance of the stage before it on the bench at 1 kHz. Load: 2 MΩ with 60 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 5E6-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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