I'm so fascinated by led/ldr combo effects...

[Devius]

I don't know what it is... the vibes, envelope filters, man thats some great stuff.
I want to build a compressor and I've come across schematics for an optical one, right up my alley. The question is... Is an optical compressor the right way to go?
I'm not super knowledgable about compressors but I do have a basic understanding of what they do. Can anyone suggest a good schematic?

[armdnrdy]

I haven't built an optical flanger yet (I have a Philosopher's tone minus the grit project lined up) but I can attest to the difference in a phaser.

I've built well matched JFET phasers and a Mutron Phasor II clone and the difference is like night and day!

The Phasor II sounds so much more liquid compared to the mechanical sound of a JFET phaser.

[PRR]

You can't watch the light in an opto comp except in dead-dark. (Room light will compress your sound to zero.)

[Ronan]

Do a google search on "really cheap compressor" I've built that one and like it.

[bonaventura]

built the RCC and love it. had a problem when i decided to shield the plastic box with aluminum foil. wasnt aware how significant the the foil changed the overall lighting inside.

i dont mean to discourage you but LDR and LED characteristics vary quite a bit so a setup fm a successful built might not work in yr particular case.

so be ready for some hardcore tweaking.

but then again, thats where half the fun is,isnt it?

[Seljer]

You can't watch the light in an opto comp except in dead-dark. (Room light will compress your sound to zero.)

Or put an external indicator led in series with the optocoupler (if the circuitry driving the led is adaptable enough to cope with the voltage drop of two LEDs)

[Kesh]

i've built the dod 280a

it's fine, but took some tweaking

the mother of all stomp box optical comps is perhaps the silonex versatile compressor.



btw, does anyone know an equivalent for the BSN10 MOSFET? I've never seen one available anywhere.

[garcho]

There's the Flatline compressor; with LDR/LED action. The Orange Squeezer is the 'classic' DIY compressor. Look for Mark Hammer mods. Ross/Dyna, and Merlin's Engineer's Thumb are two other common builds around here. The main question might be, 'squishy', or 'transparent'. Do you want to hear the compression a la electronic music or do you just want to add a little sustain to yer pluckin'?
Buy some heat-shrink and a breadboard!

[thelonious]

+1 on the Really Cheap Compressor. But as others have already said, it depends on whether you're looking for a subtle, studio-comp sound or a more obvious Ross/Dyna sound. The RCC is more subtle, but it can still squish pretty well. I've found that mine adds some fatness and grit of its own; other than that, it's fairly transparent (esp with humbuckers). I added a JFET buffer in front of mine because it seemed to load my G&L ASAT's single coils a bit... but I have a friend who uses strat with high output single coils -> RCC -> Fender Deluxe and he absolutely loves the RCC in that setup.

Also don't forget to check out Circuit Salad's Optical Orange Squeezer (http://www.diystompboxes.com/smfforum/index.php?topic=99516.0).

[midwayfair]

This is all in my humble opinion, of course, but I've boxed up a dozen different pedal compressors at this point and breadboarded several others.

The Flatline is superior to the Really Cheap Compressor. The RCC distorted even with my single coils. I think this is because in the Flatline you vary the threshold independently of the gain, and the gain of the first stage is extremely high in the RCC. So when there's little to no attenuation, you overdrive the op amp. Op amp distortion is not exactly pleasant. Worse, you'll get a tiny bit of distortion sometimes when the compressor is "turning on," i.e. the first note just before it actually attenuates.

The Flatline conversely will pretty much never distort, because the threshold is set and the sustain knob controls the gain of the dry path. I also think the decay characteristics are better in the Flatline. The Flatline has a few more parts, but you can use 4 cent 1n60P diodes from Tayda and you're talking maybe 10c worth of difference in total costs. So the Flatline counts as a "really cheap compressor" as well.

Anyway, Madbean makes a PCB for the Flatline (Afterlife) and there are tons and tons of perf and vero layouts for it.

As far as whether an optical is "the way to go" -- Optical compressors tend to be much more subtle and transparent. Some of them have, as several helpful people on this forum have pointed out before, a kind of sluggishness that makes the attack more natural. They're very good. I prefer FET compressors overall (Orange Squeezer and my own deisgn, the Bearhug), which usually have short decays, high thresholds, and super fast attacks. Finally, the Engineer's Thumb is the best OTA guitar compressor I'm aware of -- the absolute best for not subtle sustainer madness. It's sort of like a Dynacomp without any noise.

[samhay]

I have a RCC too. Initially I had trouble with distortion, but with the right LED/LDR combo and placement you can keep it clean across the entire sustain pot and still get a heap of squish out of it. I now like it a lot, but it took a lot of tweaking to get there.
While I was debugging it, I added an external indicator LED so that you can see it working without having to sit in the dark.

[thelonious]

The Flatline is superior to the Really Cheap Compressor. The RCC distorted even with my single coils. I think this is because in the Flatline you vary the threshold independently of the gain, and the gain of the first stage is extremely high in the RCC. So when there's little to no attenuation, you overdrive the op amp. Op amp distortion is not exactly pleasant. Worse, you'll get a tiny bit of distortion sometimes when the compressor is "turning on," i.e. the first note just before it actually attenuates.

Now you're making me want to build a Flatline so I can A/B!

[PRR]

> Or put an external indicator led in series with the opto...

Of course; but you can do that with "any" gain-block.

My dBx used the snazzy log-log VCA chips to smoosh the audio but a couple blinky lights to entertain the user.

OTOH, the LA-2 has two optos in a sealed can, one of them throttling current to a needle-meter for operator amusement, no blinky-light.


> wasnt aware how significant the the foil changed the overall lighting inside.

When I used to design/debug limiters, I had a dark room with tight dim lighting on my sig-gen and meter. Even putting my hand on the sig-gen knob might bounce enough light to change the output. In final trim I had a cap for the opto which could be lifted for tinkering and set down for measurement. The final build had cardboard with heavy flat-black paint over the opto, the whole thing inside a metal box flat-black inside. The few times I used it outside I draped my hat over the box; sunlight is hard to kill.

[samhay]

>> Or put an external indicator led in series with the opto...
>Of course; but you can do that with "any" gain-block.
Indeed, but in the case of LED/LDR circuits, it does mean that you can do some of the debuging/tweaking without having to sit in the dark (as long as you keep the rest of the circuit dark - I was using a Trilby the other day to try and keep the light of the LDR).
Also, for compressors that can be a bit subtle, I find it makes me feel a little better if I can see something happening with I twist the sustain/compression knob.

I came across the silonex schematic a little while ago and have been toying with the idea of putting one together. Has anyone built/used one for guitar?