Hiwatt DR103 Custom 100 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.
Hiwatt’s stack, fed from a 220 kΩ plate resistor. It has separate treble and bass feeds and a bridged mid pot.
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
- A 220 kΩ linear pot between the treble cap and the mid network.
- Middle
- A 100 kΩ pot bridged by 1 nF, in series with the bass return. It shapes the upper mids more than a Fender mid control does.
- Bass
- The bass path runs through its own 100 kΩ and two 47 nF caps. It’s fed from the plate separately from the treble.
Parts
- C10
- 1 nF, Feeds the treble and middle legs of the tone network. It passes little below a few hundred hertz.
- C11
- 220 pF, Treble cap, to the top of the Treble pot.
- R17
- 220 kΩ, From the same point to the bottom of the Treble pot, the path for the middle frequencies.
- Treble
- 220 kΩ, Treble, 220 kΩ linear. Its wiper is the network’s output.
- R18
- 22 kΩ, From the bottom of the Treble pot to the Middle pot.
- Middle
- 100 kΩ, Middle, 100 kΩ linear, wired as a variable resistor between the treble leg and the bass leg.
- C12
- 1 nF, Across the Middle pot. Above a few kilohertz it shorts the pot, so Middle leaves the top end alone.
- R19
- 100 kΩ, Feeds the bass leg straight from V2’s plate.
- C13
- 47 nF, With the 100 kΩ a low-pass at about 34 Hz, so only the bass gets through this leg with any strength.
- C14
- 47 nF, Couples the bass leg to the Bass and Middle pots.
- Bass
- 470 kΩ, Bass, 470 kΩ log, wired as a variable resistor to ground. Turned down it shorts the bass leg.
Source and load
Driven by: triode plate, 220 kΩ plate resistor. Driving: volume pot, 220 kΩ. Load: 22 kΩ in series into the 220 kΩ master at full, then the next grid.
Sources
- Mark Huss, redrawn Hiwatt preamp schematics
Values and wiring are the same as in the four-input amp with master volume circuit 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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