Tonepad Ross Compressor Questions

[sevenisthenumber]

1) What does the .05 cap off of the 10k and volume lug 3 do? What would putting an .01 in there do?
2) What exactly does the trimmer do? Is there an actual name like "release, attack"?
3) What is the BEST way to add a clean blend to this circuit?

Schematic and Layout:
http://www.tonepad.com/getFile.asp?id=9

Thanks!

[jacobyjd]

1. I'm not sure, but the rule of thumb (ought to be the rule of the wrist? :-P ) I use is to make sure I have SOME capacitance, even if it's not the right amount (I just built a resonant LPF and tried to sub a .01 for a .1uf and paid dearly for it with my hearing...nothing like untamed self-oscillation from an op-amp). Anyway. give it a whirl. If it gives you any trouble, then get the right value in there.

2. Honestly, I'm not sure. I set mine in the middle and it sounded great from the start. I'll be assembling it in a week. I'll try to remember to reply to this with results of fiddling with it if nobody else chimes in.

3. I'm no expert, but I'd suggest a buffered splitter, then an opamp mixer to put it all back together (check out GGG's take on the geofex design).

Good luck I couldn't believe how great mine sounded when I ran it through testing on my breadboard. I'd highly suggest implementing the attach mod from fuzz central.

[BAARON]

1.  The 0.05µf cap is the output coupling cap.  If you make it smaller (0.01µF, for example), you'll lose some bass at the output of the pedal because the 0.05µF is cutting is pretty close already (and shaving a minute amount of bass off as it is).  http://www.muzique.com/schem/filter.htm might be a useful tool for you, though you'll probably want to look up high-pass and low-pass filters to see what they are/how they work.
Also, you probably won't find a 0.05µF cap in real life.  You'd usually use a 0.047µF instead.

2.  The trimpot sort of adjusts the bias on the op-amp, I think?  I haven't looked too closely.  On the Keeley Compressor (a modded Ross, btw), it's hardwired to the very middle of the trimpot.

If you want an attack control, the mod from here is very useful.  http://fuzzcentral.ssguitar.com/ross.php  You can also accomplish roughly the same thing by replacing the 150k pot with a 250k Audio taper pot and wiring across the center and right lugs (when viewed from the back of the pot), but I like the option with the switch better: it takes less space on your enclosure, and the knob offers more tweakability than is useful anyway.
Also, I found that the attack was too harsh when I turned my attack knob down, so I ended up removing the pot and sticking with the stock 150k resistor for the smoother attack it offered.

3. The best way to add a clean blend and an attack knob to a DIY Ross clone is to start by buying the 5-knob compressor from BYOC instead of trying to add a clean blend to a PCB that doesn't support it by default, I'd say.  The second best way is probably to study their schematic (it's in the instructions for their kit, downloaded from this page http://www.buildyourownclone.com/5knobcompressor.html) and take a hint from what they're doing.  

[R O Tiree]

1. It removes the DC bias from the output signal (from Q2's emitter). 0.05µF is large enough to pass the frequencies of interest. Put a smaller cap in there and the bass frequencies will be more attenuated.  (BAARON said the same thing while I was typing).

2. The trimmer ensures that the currents flowing into the + and - inputs of the CA3080 are the same.

3. You get a buffered clean signal from the emitter of Q1 already. Have a look at this article at GEOFex. On page 1, half way down you'll see a circuit fragment inside a box for a constant power cross-fader. Does the trick very nicely.