Marshall Tonestack sounds weird

[JackSkellington]

Hello guys. New projects, new questions.

I'm playing around a booster with a Marshall Tonestack. As you can see is a LPB-1 in front with the eq and another LPB-1 as recovery stage.



It's clear enough, I hope. This is a simplified version of my whole schematic that has just a low pass filter in the end with an hard clipping, even if this doesn't sound so good.
The 4.3k before the eq is to avoid too much signal in the second stage, else it distorted. I want it pretty clean.

Hard clipping aside, I like it, it works, but the eq is not so good in this configuration, and I don't know why. The schematic is correct, but how I can see in in the emulation of the software and in my built prototype, indeed I tried it, the Treble pot doesn't cut treble; I got a kind of flat response of the high frequency; I can get a pretty sparkle sound even with the Treble at minimum.
Bass pot has just a little range.
Mid pot make a flat response of the mid at maximum and a treble cut at minimum. Depends from the Treble setting.
My intention is to use the Marshall Tonestack, so I don't want to change it. Anyway, I guess it never will sound good.

Did you ever tried something like this?

[Scruffie]

Your new 4k3 resistor isn't cutting signal, it's forming a high pass filter with C8. You'd need a resistor in series with it to create a voltage divider to do what you're intending but if you want to lower the gain in to the stack, I'd increase R10.

Also, people generally scale these tone stacks by a factor of 10 for guitar pedal use.

[JackSkellington]

Thank you.
The 4.3k forms a high pass filter, but I tried it and it really cut volume/distortion, too. I tried 1k, but was too much volume cut, a 4.3 k leaves just a little bit distortion to the peak.
Anyway, I have to try a voltage divider adding a resistor in serie to the C8, creating a sort of gain pot. Right?
I didn't want to change R10 because with a switch (not in the schematic) I bypass the eq and its recovery stage to link directly to the Volume pot, for a more transparent mode of the boost. I have to try to keep about the same output between with and without eq.

What do you mean about the eq?
I emulated different compoents values of the eq, basic on the Protone Body Rot II. It could be better. I'd like the idea to build a kind of Marshall EQ Boost, but, I don't know why it doesn't work right.

[Scruffie]

Thank you.
The 4.3k forms a high pass filter, but I tried it and it really cut volume/distortion, too. I tried 1k, but was too much volume cut, a 4.3 k leaves just a little bit distortion to the peak.

That may be, but it's cutting all the bass below something like 350hZ which is going to give you a brighter sound (as you found) and give the tone stack less to work with in the bass frequencies (as you also found).
Yes, the voltage divider would be like a gain pot, you'd need larger resistor values or a larger cap though to reduce the bass cut.

Could you not decrease gain in the recovery stage then if you don't want to cut it up front?

By scaling I meant multiply all the caps by 10 and divide the pots/resistor by 10, impedance and all that business.

[JackSkellington]

I'll work on a gain pot or similar configuration using a voltage divider resistors after the first stage.

It' a bit difficult try just the recovery stage but I'd say it sounds clean. It's almost the same of the first stage, maybe with a slight difference impedance because the two resistors 43k/430k in the first stage and 100k/1M in the second.
When I pass through the whole schematic I don't have any attenuateion of the signal after the first stage, probably was this to caused the distortion.

What you said about the EQ and the factor 10 has sense to me! ProTone Body Rot II has 330nF instead 22nF (well a bit bigger) and 4,7nF instead 470pF. a 2.2k resistor instead a 33k (again, a bit too smaller), and 20k for Treble, 2k for Mid (those are pretty), and a 50k for Bass pot (this is smaller).
Pots value doesn't help too much, but if I scale the eq value parts like you tell me early, do you think I can still talk of Marshall Tonestack?

(I see some pedal use the same Marshall or Fender eq. The Krank Distortus Maximus is the same circuit of the Body Rot II, but it has the orignal values of a Marshall Tonestack.)