DOD 280 Compressor

[patrick398]

Just boxed up a build for a friend which is an attempt to approximate the instant lo-fi junky by zvex. I've mentioned this elsewhere but it's basically a pt2399 chorus, stomp lfo for multiple waveshapes, pot to blend between chorus and vibrato and all running into a dod 280 compressor.
It sounds great but i'm struggling with the compressor a bit. I stupidly just grabbed a LED/LDR i had laying in the draw and threw it in.
Even with the trimpot wound all the way back it's super inconsistent. Hit a chord hard and it just sucks the life out of everything and takes a while to recover. I'm guessing this is to do with the LDR i used and it's dark resistance and recovery time?
It's also using a super bright 3mm LED so perhaps too bright.
I'm not sure what the LDR is but probably either a 5516 or GL5539.

What's the best thing to change here? A more compatible LDR or try a standard brightness LED first?
This is my first run in with a compressor so i'm a little clueless.

Cheers all

[pinkjimiphoton]

did you do it like a homemade vactrol? ie, encased in something to keep the light out? if not, that could be your prob, especially with an indicator led. the indicator led leakage will totally make the compressor wack. this is a fairly easy circuit to nail, so that would be my first thought.

if you DIDN't make it lite proof, you should. stick the led in one side of a piece of drinking straw or whatever, and the ldr in the other, then seal it with electrical tape.

before ya do that tho, i would play with the distance between led and ldr. in my experience there seems to be sweet spots where it will react best. once ya find the sweet spot distance, seal it off from the light and you should be ok. if that doesn't work, replace it with a proper spec'd vactrol. but most of the time, homemade ones work fine.

jmo..ymmv, and probably should

[patrick398]

Thanks for the reply man, it's reassuring to hear that it's an easy one to nail. So the circuit isn't too fussy about the LED/LDR specs?
It is heatshrinked...heatshrunk? together yeah and i've also got some tape over the indicator LED to avoid leakage. With the compression pot (mines a trimmer) up fully it actually sounds great, it's just that when you give it the beans you can REALLY hear it being slammed and hear it recovering.
Perhaps the super-bright blue is too much

[pinkjimiphoton]

try un heatshrinking it, and in a dim room, move the led and ldr further apart, you may find it works better a little distance between them, or even with the led's side pointing at it. this circuit DOES have a lot of squish, so sounds to me like its working fine.
wondering if maybe hacking a small trimmer in there to control the led's brightness may help? i'd have to look at the schematic, to be sure or to really advise,
but so far i've found distance can be crucial... even angle sometimes.

good luck... you'll get it!

[patrick398]

Just took a quick glance at the datasheets for the suspected LDRs and since the GL5539 has a bright resistance of 30-90k and dark resistance of 5M i think it's probably that. Seems like a huge swing for something like this no? I'm no expert but that sounds like what i'm hearing.
I'll try and tinker with the distances tonight when it gets dark
Thanks for the tips Jim

[pinkjimiphoton]

hope it helps, patrick.
if it doesn't, let me know, i think i may have a couple of the proper vactrols lieing around.

[patrick398]

I ended up having to bend the LDR so it basically just faced the veroboard, with the compression control above about half it was still compressing too much when i hit a chord. I've got it to where i can live with it now, though it's made me want to build another properly to really see what it can do. What vactrols are best?
Thanks

[pinkjimiphoton]

sorry, i couldn't get in for a few days due to overactive security software...
i gotta look up the vactrol on my other computer, cuz i have a memory like a sieve since a stroke a couple years back.
but try something like an nsl-32, i know that will work in this circuit cuz i just built one maybe a month or two ago.
you got dis pat... keep at it, and defeat the bug!!