"Body pot" for gain shaping or harmonic enhancing or presence

[roberto]

Hi,

I've just sketched this schematic that can be used as a pre-shape for the gain control (to substitute the classic Marshall 470k//470p or VHT 1M//680p or Soldano 470k//2n2 CAE 1M//1n, etc...), or even as a harmonic enhancer on the following stages (between 2nd and 3rd or even between 3rd and 4th).

On the right there's a plot of what the pot does, and the schematic shows the option to be used before the gain pot, but as said it can be used also later on the circuit.
Used before the volume pot, can be used as a presence. It is needed to change frequencies and the ratio between the volume pot and the stereo presence pot to match the frequencies and the gain of the presence.

The good thing compared to other circuits is that the load seen by the source (the coupling cap) is the same for every position of the pot, so it can be used to get a stable high pass filter due to the coupling cap (useful in earlier stages to cut lows and get more defined overdrives, and in final stages not to cut lows while changing midrange gain).

[Colossal]

Very cool, Roberto! An interesting idea... it makes me remember that Trainwreck Dirty Little Monster control labeled "Harmonics"...always wondered what that might have been. I'm sure it was not your idea, but it's fun to speculate.

Cheers

[roberto]

Just wondering that a simple pot, used like an old Marshall presence, does the same thing with less complicate wiring:
- bypass fully the pot with the smaller cap;
- bypass one side to the wiper with the bigger cap;

That's it.

[roberto]

it makes me remember that Trainwreck Dirty Little Monster control labeled "Harmonics"...

This could be the control, as it’s exactly what it does.

I'm sure it was not your idea, but it's fun to speculate.

I was not even aware of that control nor that amp, but I would like to know if it’s something similar.

[roberto]

A guy on sloclone has simulated the circuit:

[Colossal]

Very good!

[roberto]

I have a three channel preamp where I will implement this control on both crunch and lead channels:
- "body" control before the gain potentiometer (placed on the left of the gain pot);
- "harmonics" control before the CF of each channel (placed on the left of the eq).

[roberto]

Something like this

[roberto]

This is another possible evolution, where one pot is as I've already shown before.
The added one can give shape from full bright switch, to less abrupt bright switch (sometimes the bright effect is too much when the gain is low, but the sound is too dull when the bright is switched out), to a full cut of lows (so a bandpass, together with the previous control) that can increase the versatility of the amp.