This Week on the Breadboard: The Stupid-Simple Compressor

[fig]

I prefer the 1660 point ProtoBoards. Enough room to stretch out. Sometimes I build two different pedal circuits on one.

My ZIF sockets tend to pop out of the protoboard, I have to keep reseating them.

Oh yeah..I flung that one first time on the lever…(short memory I guess)..

I have two of the larger protoboards…they are really nice but I’d make a few changes / additions.

 

[swyse]

I just looked at the GL5516 datasheet. They do not define the test conditions of Rise Time and Fall Time, so to me those numbers are meaningless.
The LDRs I've tested respond very quickly to increasing light. Some respond almost as quickly to decreasing light, but the vast majority respond much slower to decreasing light. Slower response time is better in this case.

Best to socket or breadboard them and listen to the distortion level when playing low notes with SUSTAIN dimed.

The GL5516's resistance range is acceptable, but the sustain will be limited by the 500KΩ dark resistance. As a comparison, all of the Opto-Couplers I'm using have dark resistance over 2MΩ and most of them go well over 10MΩ. In this circuit, 5K - 10KΩ light resistance will work fine.

Sounds like there is one way to find out for sure, I'll check it out when they arrive if I get time and remember.

 

[BuddytheReow]

Reviving an older thread. Now that I’m working on my bass chops and setting guitar aside for a while is there a way I can tune this for bass? Should I simply alter C1 to something bigger such a 1uf or greater?

 

[Chuck D. Bones]

C1 rolls-off the low freq below 16Hz, so you don't need to change that one. C3 limits the bass response. Increasing that to 1uF extends the bottom end down another octave to 33Hz. One other consideration is the release speed of the optos. Most optical compressors detect the envelope and drive the opto with a filtered version of the peak amplitude. This one is like the SVDS (Closed Circuit Compressor), there is no filtering on the optos. A fast opto will not only follow the envelope; with a low-freq signal it will tend to follow the waveform as well which introduces a bit of distortion on the low notes. Not necessarily a bad thing, it's one of the contributors to the desirable tone of the SVDS. To make along story even longer, this effect is more pronounced with bass guitar. Fast optos will have more bottom-end grind and slower optos will have less. You might want to audition different optos on a breadboard. Or if you have a scope, test their release speed, the time it takes for the resistance to go up when the LED current drops.

 

[JamieJ]

Did you finalise the circuit with the treble and blend controls @Chuck D. Bones - I’d be very interested in building this!

 

[Chuck D. Bones]

I think so, here it is. I took my breadboard apart so I could build something else.
Try it and let me know what you think.

 

[JamieJ]

Thanks!