Every guitar amp has a tone stack — a small circuit of resistors and capacitors that shapes the frequency response before the signal hits the power amp. Turn a knob, and resistor values change, and the EQ curve reshapes. But the curve at noon isn’t flat. It has a personality baked into the component values — and that personality is the difference between American and British, clean and dirty, thin and massive. These are the actual EQ curves hiding behind your knobs.
Key insight: Set all three knobs to 5 and look at the curve — it's NOT flat. There's a significant dip in the mids. This is Fender's signature. Now turn the mid knob to 10 — the scoop fills in and you get a much flatter, more 'Marshall-like' response. Most Fender players have never realized their amp is scooping mids by default.
Both amps, all knobs at noon. Same circuit topology, different character.
The Fender, Marshall, and Vox tone stacks are all passive circuits — networks of resistors and capacitors with no active gain stage. Passive circuits can only attenuate, never amplify. In practice, a Fender tone stack loses about 6–8 dB of signal, and Marshall and Vox lose a similar amount.
This doesn’t matter in the real amp because a recovery gain stage immediately after the tone stack makes up the loss. You never hear the missing decibels — the preamp just adds them back. But it means the tone stack isn’t boosting bass or treble in any absolute sense. It’s attenuating everything else less. “Turning up the treble” really means “cutting less treble.”
The curves above are normalized to 0 dB so you can focus on the shape — where the scoops, humps, and shelves are. In the real circuit, the whole curve sits 6–8 dB lower, and the gain stage lifts it back up.
For sixty years, the argument between Fender and Marshall players has been an argument about midrange. Fender scoops it. Marshall keeps it. Vox boosts it. The Tube Screamer pushes it. The Big Muff destroys it. These aren’t just tonal preferences — they’re circuit topologies, component values, physics.
The reason midrange matters so much for guitar is psychoacoustic. Human hearing is most sensitive between 1 and 4 kHz. Guitar fundamentals live between 80 Hz and 1.2 kHz, but the harmonics that give a guitar its “voice” — the ones that cut through a drum kit and bass guitar — live right in that 1–4 kHz sensitivity peak. Every tone stack is making a decision about how much energy to put in that critical range.
Now that you can see the curves, you can make that decision with your eyes and your ears. The knobs haven’t changed. But you know where they live.