Fender Bassman tone stack

[Tommy Boswell]

Question for the tube amp gurus here on the Forum. I have a Fender Bassman 70 head, ultra linear, and want to know how to set the EQ (treble and bass) as flat as possible. I'm using a Sesh.400 pedal in front of the amp, and want the pedal to handle the EQ function as much as possible.

[Mike Auman]

Tommy, for the flattest response on a Fender Bassman 70:
- Use the Normal input jack
- Bright switch off
- Treble knob all the way down
- Bass knob just a hair above all the way down (below 2)

This will cut treble and bass to match the built-in midrange cut, and give you a nearly linear (flat) frequency response, although at a lower volume level.

If you download the Duncan Tone Stack Calculator, you can turn the knobs and see a graphic of the resulting response for yourself. https://www.duncanamps.com/tsc/

Here's a Tone Stack Calculator screen shot with the knobs halfway up, which gives you the normal midrange notch that most amps have.




And here's a screen shot with the settings I described, you can see how flat the response gets.


(For both simulations, I've set the Mids knob to match the actual 6.8k fixed mids resistor in your Bassman.)

[Tommy Boswell]

Thank you Mike, I'll try that setting.

I do have that Duncan Amps app, but I didn't know what to do with the Mid slider, since my Bassman doesn't have a midrange control. But what you said makes sense, so thanks again.

[Mike Auman]

On the Duncan app, change the Mid pot value from 10k ohms to 6.8k ohms, then push the slider all the way to the right, and that will match your Bassman's mids circuit.