Help reading schematic - mod distortion to clean boost

[suprleed]

Hi all,

I built the Tweak-O from Small Bear a while back for my first build and I am now using it as a learning tool as I work out different mods to it.  I've already played around with different clipping arrangements and now am interested in converting it into a clean boost.  However, I need some help understanding a portion of the schematic (below):



The R5, R6, C6 group is the voltage bias network for the transistor (please correct me if I'm wrong).  So no messing with this section.

The diodes, C3 and R3 are the clipping section.  To make this a clean boost I switch out or pull out the diodes.  With the diodes gone would the R3 pot still do anything to the circuit?  Would it act as a clean gain boost?

I have no idea what R1, R2, and C4 do in the feedback loop?  Can someone please explain this to me?  Other single tranny distortion/boosts I've looked at (electra, trotsky) have really simple, bare-bones feedback loops.  What do these extra resistors/cap do?

R4 and C5 are the bypass resistor and capacitor (I think that's what they're called anyway).  Couldn't I alter the gain of the transistor by playing with these values?  e.g. reduce R4 to 1k for more gain?  Increase C5 to 4.7uf for more gain? or vice versa?

Finally, it seems to me that C2 is used to keep excess noise out of the circuit (once again, correct me if I' wrong here).  No changes needed here either.

Hopefully I haven't overloaded everyone with stupid questions, but I would appreciate any comments, explanations anyone has to offer.  Thx.

[jayp5150]

I have never built this myself, but I don't see why you can't omit the diodes and C3 and get a clean(er) sound. I don't know 100% about R3 acting as a gain, though.

Your question reminded me about Jack Orman's Muffer (it was my 2nd build), and he notes that you can omit the diodes and capacitor to get a clean boost.

Check this out http://www.muzique.com/schem/projects.htm It's down the page a bit (cool little dirt box, too--makes a good input stage to a bazz fuss...).

Anyhow... someone with more knowledge will jump in here for the more detailed questions, but I say try it and see what you get.

Experimenting is the fun part for me 

[suprleed]

Thanks JayP.  I think I will make the diodes switchable so I can go back and forth from dirty to clean.  Just not sure how that's going to affect R3 in clean mode or if I should just switch out the whole feedback loop including R1, R2, and C4.

Anyone else out there who can help shed some light on my questions...

[MikeH]

I could just be talking out of my ass, but I beleive that R1 R2 and C4 are for biasing, or something like that, and not for distortion.  I beleive ommitting c3, d1 and d2, and the 250K pot will make this behave more like a booster than a distortion.  Someone correct me if I'm wrong?