Gain between clipping stages in Big Muff Pi.

[Kesh]

Sorry to bore you all with YET ANOTHER BMP TWEAKING THREAD. I have searched and read extensively, but looking for confirmation.

I'm thinking that if you want to play with different diodes in the BMP, because of there being two diode stages, it's necessary to control the gain between Q2 and Q3, else either one or the other stage's clipping will dominate. Is this correct?

My understanding of electronics is somewhat limited, but it seems I can do this by playing with R12? Replacing with a pot to a ground resistor like the sustain control? Or could I play with the emitter resistor of Q2? (All numbering as per this schematic.)



I would also like to keep these changes of gain flat, if that is even possible. I mean flat in and of itself. Driving the next stage differently is obviously going to change tone.

Here's another schematic you may enjoy, this time a Russian BMP, with military spec components no doubt.

[Pyr0]

Check out this article from kitrae for tweaking big muffs

[Kesh]

Thanks, but I have that article, and have read it and the links on it. It's mostly about cap values around the diodes.

As I said, I have already searched and read extensively.

I have found almost nothing on gain between the two diode stages.

[Mark Hammer]

What takes place in the BMP is partly a function of relative gain, but it is also a function of the frequency content one stage feeds another.  Keep in mind that any clipping stage will necessarily feed the subsequent stage with an "unfaithful" copy of the original input signal.

This is why folks noodling around with the BMP not only play with the values of the emitter and collector resistors, but also the cap between base and collector and the cap in series with the diodes.

You may or may not be aware the Colorsound Jumbo Tonebender was essentially a BMP with no clipping diodes across the 2nd transistor.  That is, there were two largely similar gain stages prior to a single clipping stage.  each of those stages used a cap to shape the tone prior to clipping, so as to elicit a particular quality to the distortion.  Of course, because there was no clipping provided by Q2, that also impacted on the overall amplitude of signal being fed to Q3, conceivably producing a harder clipping in that stage when the Sustain control was maxed.

rather than playing with the gain of the stages, or diodes, one of the simpler things you can do is make the Q2 stage a little more like the Q1 stage.  So, stick an additional 100k pot and 0.1uf cap after the 0.1uf  output cap, so that you could dime the first Sustain control and push the first clipping stage hard, and then adjust how hard you want the 1st clipping stage to push the 2nd one.

[Kesh]

Rather than playing with the gain of the stages, or diodes, one of the simpler things you can do is make the Q2 stage a little more like the Q1 stage.  So, stick an additional 100k pot and 0.1uf cap after the 0.1uf  output cap, so that you could dime the first Sustain control and push the first clipping stage hard, and then adjust how hard you want the 1st clipping stage to push the 2nd one.

Thanks, this is what I had in mind when I mentioned replacing R12 with a pot to a ground resistor like the sustain control.