General Tso’s Compressor

manfesto

Member
Hi! For a drill template did you just use a 4-knob template and drill the bottom-left hole smaller for the switch?
 

manfesto

Member
Just noticed that there’s a pad labeled “mute” with the footswitch wiring, what’s that for (I’m assuming muting the circuit input)?

Haven’t seen it on other buffered bypass PCBs
 
I just finished my General Tso and I like that it seems to be more subtle than the non-optical pedal. Also, it puts a noticeable and pleasant fatness in the signal. As a single coil guy this is great, particularly when playing clean The only thing that bugs me is that when in Blend mode I can't blend in a much of a heavily squashed signal without the volume getting out of hand. Is there something I'm missing about the way this thing works?
 

Chuck D. Bones

Well-known member
The only thing that bugs me is that when in Blend mode I can't blend in a much of a heavily squashed signal without the volume getting out of hand. Is there something I'm missing about the way this thing works?

That's how it works. You can have either a Blend control or a Volume control, depending on the Mode switch. Have you tried the other mode?
 
Just came back to dealing with this issue. . .maybe its my ears, but after listening to several YouTube demos it seems that mine is not getting the same level of compression (that chickin' pickin' snap) that the demos produce. I checked all of the component values (except for the pots) and the only thing that's different is that the LDR's that PPCB offered were out of stock so I went with the attached. Is something wrong with the LDR spec or installation? I also checked the LED's in a dark room and get modest, but discernible glow when fed a guitar signal (but nothing like the intensity of a the LED power indicator).
 

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Chuck D. Bones

Well-known member
A Youtube demo is not the same thing as having the real pedal in you home or studio for comparison. All sorts of things can happen in the recording or playback process to change the sound.

I'll qualify my statements by saying that everything I know about the General Tso is based on analysis. I have never built one or heard one live. The Tso is not capable of large amounts of compression, so you may be chasing a ghost. The biggest variable in optical compressors is the LDR. LDRs vary widely and that will affect circuit performance. Let's see what we can learn about your LDRs. Do you have any spares? If so, measure their dark resistance, and by that I mean in total darkness. Put the LDR in cardboard box (with test leads attached) and close it up tight. Next, measure the light resistance in normal room light. Report the results and we'll go from there.
 

jubal81

Active member
Chuck's spot on.
After building this and monkeying around with the circuit a bit, I have a couple tips.
To get closer to what you want, you need a different LDR. Look for one with the lowest possible ON resistance. The GL5516 goes down to 300R-ish, so that's a good target. This will get you the subtle optical style with longer sustain - working as intended. If you want ridiculous chicken-pickin', try a superbright LED. The sustain knob will be pretty much useless and the sustain isn't right, but it will give that crazy squish attack. It sounded 'broken' but I had a fun afternoon with it like that.
 

jubal81

Active member
Got a more specific update.
Look for an LED with luminous intensity of 100 mcd, point it directly at the GL5516 LDR and make it as light-tight as you can (this is important because even the tiny amount of light from an indicator LED inside the box can affect the LDRs).

Buy this LED from Mouser or Arrow or Newark or an actual, reputable new-component seller. HINT: Not Tayda.
 
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