Marshall tone stack help

[Jaymz77]

Good morning all, how are we?

I'm posting this in the hope that someone with more knowledge than me can assist.

Long story short... I have a schematic that shows a 2 knob eq for the clean channel, see attached, and I want to add a mid pot. However I want the end result to be in the same ball park as the 2 pot setup, just adjustable. I don't want to change the tone too much.
Is this even possible?
Essentially I just want to add control of the mids, I don't really want to revoice the eq at this point in time.

I have downloaded the tone stack calculator but this is a section of circuitry that I am only just starting to learn about. So some assistance would be much appreciated.

Cheers

[HotBluePlates]

... I want to add a mid pot. However I want the end result to be in the same ball park as the 2 pot setup, just adjustable. I don't want to change the tone too much. ...

See R42 (10kΩ) in your schematic fragment? That is like a midrange pot, with the setting fixed at 10kΩ.

If you'd like some room to adjust mids above and below what you have now, replace R42 with perhaps a 25kΩ linear pot. Now a setting at a little under halfway is the same at what you have now.

Your could use a 10kΩ pot, but it would be the stock setting at max, and only allow for less mids than you already have.

[Jaymz77]

Ha ha legend!
Thanks heaps HBP!
I was thinking/ hoping it would be that simple.

I just got a bit concerned when I started playing with the Tone stack calculator and none of the curves really looked the same. That is, the 2 knob eq has a much more pronounced mid dip. The 3 band eq, while the curve looks similar, it doesn't have that same pronounced mid dip, or should I say its operational window starts and finishes at lower points. Do I make any sense at all?

That tone stack calculator really shows how the knobs interact with each other doesn't it?