Big Muff Bass & Treble

The passive bass and treble tone stack from the Big Muff, in the two-knob form designed by the legendary Jack Orman of AMZ-FX. See exactly what every part does.

fbass = 1 / (2π·R1·C2)
ftreble = 1 / (2π·PT·C1)
Click any value and type your own: 4k7, 0.22u, 220n, 1M, 75%. Enter commits, Esc cancels.
R1 · Series Resistor
nearest E12:
C2 · Bass Path Cap
nearest E12:
BASS · Pot Value & Position
Pot Position
0% = bass off · 100% = full bass
C1 · Treble Path Cap
nearest E12:
TREBLE · Pot Value & Position
Pot Position
0% = treble off · 100% = full treble
MIX RESISTORS
R3 · Bass Side
R2 · Treble Side
standard values · they sum the two paths and keep the pots from fighting
▬ Exact values▬ ▬ Nearest-E12 build⋮ bass corner fb, treble corner ft
Low Path Corner (R1·C2)
—
Where R1 against C2 stops letting treble down the bass path. The stock 33k / 10n pair lands near 482 Hz.
High Path Corner (C1·Pot)
—
Where C1 into the treble pot starts letting highs through. Figured with the full pot value, so the exact knee drifts a little with the knob and the mix resistors.
Tilt (100 Hz vs 10 kHz)
—
Level at 100 Hz minus level at 10 kHz. Positive means the stack is set dark, negative means bright. At noon this stack leans a few dB bright.
Big Muff bass and treble passive tone stack schematic, Jack Orman AMZ-FX two-pot version

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How this tone control works

      
This is the bass and treble control from the Big Muff, in the two-knob passive form designed by the legendary Jack Orman of AMZ-FX. There is no op-amp and no power here: just two filters running side by side from the input, each with its own volume knob, summed back together at the output. That simplicity is the whole appeal. Drop it after any gain stage and you get a real two-band tone control for a handful of parts.

    
The bass path runs through R1 into C2, which shunts treble to ground: a plain low-pass filter. The stock 33k / 10n pair puts that corner near 482 Hz, so everything below passes and everything above fades. The bass pot then works as a volume control for that filtered low half, and R3 carries the result to the output.

    
The treble path is the mirror image. C1 blocks lows and starts conducting around the corner it makes with the treble pot, near 568 Hz at the stock 5.6n / 50k. The treble pot sets the level of that high half, and R2 carries it to the output. The two mix resistors matter more than they look: they let the two halves sum without the pots shorting each other out, and their values set how much the two knobs interact. Bigger mix resistors mean less interaction but more overall loss.

    
At noon on both knobs the stack actually leans a few dB bright, with the level around -15 dB at 100 Hz and -11 dB at 10 kHz. Turn both knobs up full and the two corners pull apart into the classic scooped shape: a dip near 420 Hz sitting about a dB below the shoulders on either side. And that headline number is the honest cost of going passive: this stack eats 6 to 15 dB depending on the knobs, which is exactly why the Big Muff follows its tone control with a recovery gain stage. Plan for one.

    
Two assumptions sit under all of these curves. The input is assumed to come from a buffered, low-impedance source: feed it from a 10 kΩ source instead and that impedance adds to R1, pulling the stock bass corner from 482 Hz down to about 370 Hz and shifting levels with it. The output is assumed to drive a high-impedance stage: hang a 100 kΩ load on it and the whole stack sags by close to 3 dB. The dashed curve shows what you would actually hear if you built it with the nearest standard E12 parts.