Eureka moment regarding increasing "Compression Quotient" of distortion pedal

[Vivek]

Lately I have been thinking about some arbitrary scale to measure level of dynamism of a distortion pedal.

Currently the idea is :

Input sine wave at 1000 Hz, 600mv peak
Measure RMS of output

Input sine wave at 1000 Hz, 60mv peak
Measure RMS of output

Calculate ratio of the two to get a kind of metric that gives you an idea of the amount of dynamics to expect from a distortion design.

Then a user asked for a method to get both gain and clipping from the same one Opamp. I suggested scaling resistors at output of Opamp.

Eureka moment ?

I realised that if we place a waveshaper (multiple diodes with resistors) in R4 position, one of the SCALING RESISTORS, we can have dynamically variable gain.

And it might be possible to independently control shape of output wave and RMS value of output wave.






I'll put in some time on LTSPICE soon, and publish some graphs if I manage to make it work.

[Vivek]

Here is an attempt to dynamically adjust one of the gain resistors in an attempt to increase dynamics of the distortion.

I hope its not just equivalent to statically inserting compliance resistors to soften the clipping and hence increase dynamics.

[Vivek]

Without the diodes on the R4 leg



Peak of 600mv input signal = 3.52V
Peak of 60mv input signal = 2.46

Compression quotient considering peaks = 1.43



With the diodes on the R4 leg



Peak of 600mv input signal = 5.90V
Peak of 60mv input signal = 2.52

Compression quotient considering peaks = 2.34


I hope this is sufficiently different than just plonking in compliance resistor to soften the clip and therefore increase dynamic range.