Ross compressor... clean blend... adding a send/receive loop?

[kvandekrol]

I got the chance to play a 70's Big Muff Deluxe recently. It's an opamp Big Muff with what I'm told is a Soul Preacher compressor, and a blend control between them. I got some really cool sounds out of it, especially with ratios like 80% clean and 20% fuzz, and it got me thinking of other ways to get the same effect.

Awhile ago I saw the Ross blend circuit daughterboard by Ben Milner here:
http://www.diystompboxes.com/smfforum/index.php?topic=40292.0

I never got around to playing with the blend, but I'm pretty partial to the Ross, and this seems like the best place to start. Is it easy to add a send/receive loop to this blend circuit? How would it be done? (Similar to an amp FX loop or a Tim, where if nothing's plugged in, signal just passes through clean.) If there was a way to put a Big Muff (or your drive pedal of choice) in the clean blend side, that would just about nail the sound I got from the BMP Deluxe.

[Processaurus]

It's a good mod!  I did that on that pedal in the thread you linked to.  Super compressed guitar mixed with distortion can be a more interesting sound then clean mixed with distortion, because the envelopes are more similar.



Referring to this schematic, I would insert the send / return jacks  between the Ross's Q1 emitter and C20.  To make the send, I'd add a 4.7 UF electrolytic cap in series between the Q1 emitter and the send, to filter the DC bias out of the signal (with a pulldown resistor after).  Then the return would just be the return jack to C20, with R28 on that side, it will be a high value pulldown resistor between the return jack and ground.  The pulldown resistors are so DC doesn't leak through the caps and cause pops if things in the loop are switched; they keep things referenced to 0v, rather than it drifting. 

That's pretty much the gist of how to add an effects loop to different points in any kind of pedal, find a low impedance, unity gain point (like Q1 here), break its connection to the rest of the circuit, and insert a send and return jack, with caps and pulldown resistors (like you see on the inputs and outputs of most all effects pedals) on either end.

You can be fancy and use a special jack for the return that when nothing is plugged in, has the tip normally connected to the send jack tip, that way it will work normally without anything plugged in the loop.

Make sense?

[kvandekrol]

Absolutely. Thanks for the explanation! This will be fun to experiment with.

[auden100]

I have a question related to the use of your schematic for a clean blend.

R28 (1M) is going to ground, but there's also a 10k resistor to ground coming off of Q1's emitter. That would make these two resistors in parallel, right? Are they both necessary? Or maybe should R28 and C20 be reversed?

[Mark Hammer]

Not that it is any sort of substitute for a compressor, but if your principal interest is blending of sustained fuzz sounds and clean, the Gretsch Controfuzz is an excellent platform to experiment with.  It provides a superdistorted tone that is blendable with the clean tone.  It earns its name because the clean tone is NOT compressed, such that it dies out faster than the fuzz, yielding a sound that starts out clean and gets fuzzier over time, where most distortions would start out fuzzy and get cleaner as the note decays.

Just a thought.

[Processaurus]

I have a question related to the use of your schematic for a clean blend.

R28 (1M) is going to ground, but there's also a 10k resistor to ground coming off of Q1's emitter. That would make these two resistors in parallel, right? Are they both necessary? Or maybe should R28 and C20 be reversed?

Hmmm, yeah, good eye, you don't need R28 for the normal, (effects loopless) Ross mod.  Extra part.

It earns it's keep as a pulldown resistor if you put in an effects loop like we're talking about here though.