Feedback loop help?

[add4]

Hello all,
I was looking at the schematic of the madbean cherrybomb and i have a few questions for those who understand what's going on.
link for reference: http://www.madbeanpedals.com/projects/Cherrybomb/docs/CherryBomb.pdf

Is R25 a feedback loop to tame the first gain stage?
This is how i imagine it works:

in this configuration: emitter and collector of a transistor are out of phase with the base. so if i want a feedback loop for one single gain stage, i can take the output from the collector and feed it back to the base, with some reduction (resistance), frequency selection (cap high frequencies are tamed, not the bass) or clipping (diodes, so if the difference between the base and collector voltages is above the conducting limit, the collector output goes back to base, out of phase, effectively canceling it; 'squareish wave'. This is in the case of a single stage feedback loop as in a gain stage of a big muff for instance

So here are the corollary questions :
- if i want my feedback loop for 2 gain stages like on the cherry bomb, i still want out of phase signal so  i have to take the output of the collector of the second transistor, and feed it, not to the base because then it's in phase, but to the emitter. Then, out of phase signal? right? Then why not feed it back to the collector and have a 'more direct' cancellation?
- Then what's the purpose of R3? which seems to do exactly the opposite? feeding the emitter of the second transistor to the base of the first one?
What's happening then? i prevent the ... voltages from feeding the first transistor ? like starving it from juicy electrons?
- If i wanted, i could also put caps and diodes i guess?
- Also, how is it different from, say, a feedback look for each stage as in a big muff ? (i guess the same effect could be reached with two different stages, but here it's controlling both at the same time and it's easier to get the result you want?
- It's still taming the first stages, but with a dependency with the second one, right ?

Thanks !

[PRR]

I do not see a "R25".

R4 and R3 provides DC feedback to set operating points. The Base of Q1 is likely near 0.9V (0.55V in the B-E junction and 0.4V in R2). Drop in R3 due to Q1 base current is probably small. So to be happy, Q3 emitter must be near 0.9V-1.0V. This forces R4 current to be about 2mA. Q2 collector will sit about 2mA*R6 or about 4V down from 9V, near 5V.

The audio path through R3 is nominally broken by C2 bypass. (However to really KILL the audio requires much more than this, which with R3 C1 turns this topology into an unintended and unpredictable sub-bass-bumper.)

This topology is key to many-many 1970s small-signal amplifiers (and their modern children in stomp-land). Worth getting to know.

R5(??) is audio feedback. Ignoring the knob, gain is almost 3. With the knob all the way, gain appears to go to infinity (but of course it won't).

> why not feed it back to the collector and have a 'more direct' cancellation?

You can. Now write the overall gain equation. R2 is still in the math. I don't see how this is any more "direct", or why we care. (Actually this form is useful for VERY high frequency amplifiers where we find much stray capacitance.)

In this case we can't use a C-B resistor as small as the 12K used here, because it would greatly increase the bias current in Q1. But if that resistor is larger then to get the same gain R2 must be larger, which with higher q1 current causes huge DC drop.