Help me understand the purpose of a few components in the following circuit

[m4j0rbumm3r]

Hi all,

I've just built my first stompbox, basically following the tips of alex frias and jimi photon in this thread http://www.diystompboxes.com/smfforum/index.php?topic=70080.0.
The pedal works, and it's very cool, but I don't yet understand all of the components' purpose.

I have carefully read this, which has been a great help: http://geofex.com/circuits/what_are_all_those_parts_for.htm

However, could you please shed light on the purpose of the following components in the schematic given below:
* the 0.022uF cap to ground, on the left. Is this part of a RF low-pass filter?
* the 56pF cap in parallel with the 18K resistor connecting the second transistor emitter to base. What is it good for?
* the 0.0022 uF cap right before the output. Is this perhaps intended as a treble cut to take the ice-pick sound out of the clipped signal?
Would it be somehow risky (e.g. for the trannies) to leave any of the above out, or tinker with their values?



Note that I'm not criticizing a great circuit, just trying to understand what I've built a little better. I'm planning to (even after the build) do a little experimenting with this circuit on a breadboard, but it would help if I somewhat know what I'm doing.

Thanks guys!

p.s. Any more good links to circuits and their components explained would also be very welcome! It's easy to find pages explaining components in very general terms, not so easy to find pages explaining their functions and interactions within in an audio effect circuit.

[R.G.]

* the 0.022uF cap to ground, on the left. Is this part of a RF low-pass filter?

Yep. Keeps RF feedback from getting into the input by way of the power supply.

* the 56pF cap in parallel with the 18K resistor connecting the second transistor emitter to base. What is it good for?

Cuts off the high frequency response of the transistor to a certain degree. Purpose is largely the same as above.

* the 0.0022 uF cap right before the output. Is this perhaps intended as a treble cut to take the ice-pick sound out of the clipped signal?

Yes.

Would it be somehow risky (e.g. for the trannies) to leave any of the above out, or tinker with their values?

No, excepting if they would be damaged by RF oscillation. The boss tone this was taken from readily oscillates at RF. I'm guessing these are here for helping prevent that, especially in the face of that 100K 'bender' pot.

p.s. Any more good links to circuits and their components explained would also be very welcome! It's easy to find pages explaining components in very general terms, not so easy to find pages explaining their functions and interactions within in an audio effect circuit.

You might try the circuit analysis talks in the "Technology of..." articles at Geofex.

[m4j0rbumm3r]

Thanks a lot R.G., very helpful!

For other beginners reading this thread: In addition to the "Technology of..." articles at Geofex, which were well worth checking out indeed, I also found out there is some very relevant info at: http://www.diystompboxes.com/wiki/index.php?title=Simple_mods