Optical Isolator differences

[icecycle66]

I'm trying to find suitable optoisolators, Vactrols, for less than $7 a pop.

I have the VTL5C1, 5C2 datasheet here.
http://www.aikenamps.com/VTL5C1.pdf

and about 500 other optoisolators here.
http://www.digikey.com/product-search/en?pv16=12219&pv16=2901&pv16=10721&pv16=10722&FV=fff40039%2Cfff8033f%2C1140050&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=500



What is it on the datasheet of the VTL5C1, and similar, that I am looking for to find suitable elements for stuff like the Cardinal Trem or the Nautilus?

[gtr2]

At Allied vtl5c1's are under $5.

[RobA]

At Allied vtl5c1's are under $5.

As are the C2's and C3's. Allied generally has the best prices on vactrols that I can find.
http://www.alliedelec.com
Just search for vactrol and they'll all come up.

The actual Vactrols are the cleanest of the optocouplers that I've found. The phototransistor and photodiode optoisolators are not really very good for audio when I've tried them.

[culturejam]

The phototransistor and photodiode optoisolators are not really very good for audio when I've tried them.

Agreed. They usually suck for audio, because they clip. And by audio, I mean directly in the signal path of the effect. They work fine for non-audio purposes.

[icecycle66]

Thanks for the allied link.

What parameter is indicative of the clipping and other problems found in the cheaper sensors?

[midwayfair]

In general what you're looking for is the on and off resistances. For instance, the 5C1 is 50M off resistance and <1K on resistance at the current/voltage levels we're usually dealing with. The other characteristic that could be relevant is the turn on and turn off times.

Smallbear has clones of the Vactrols for a reasonable price ($7) and they're engineered to be near or exact clones of the Perkins-Elmer pieces. For $4, he has the silonex R3, which is almost identical to the 5C3.

The bad news is that knowing whether a substitute is appropriate in a circuit is not easy, and it depends on what it's doing in the circuit. For instance, in the Cardinal you need really low light resistance to ground out Q3 and really high dark resistance to block Q2, and a big swing between on and off to get plenty of range on both. There are other optocouplers that COULD work (and not necessarily the same part count in each), but the 5C1 was the most reliable. The turn on/turn off time can be relevant, too, because it can artificially limit the range if you have a particularly sluggish vactrol. But you can also use a more limited vactrol in some oscillator designs to get a less extreme swing. A delay would be a good example of that.

In some compressors, the vactrol's characteristics determine the compression ratio or the total amount of attenuation. The 5C6 has a particularly good characteristics for some compressors, but the 5C1 and 5C3 are both extremely good in many designs, too.

In the Nautilus, the turn on time can become relevant, so you want a fast, but not too fast, vactrol ideally.

Ray Ring's Opto-Squeezer is about the only audio circuit I've found that can make good use of something like the H11F1 in the audio path. Doesn't clip there at all but it does load the pickups. You have to keep the signal under 150uA -- going over that leads to distortion.

EDIT: here's the full datasheet on all the Perkin Elmers:
http://pdf1.alldatasheet.com/datasheet-pdf/view/84387/PERKINELMER/VTL5C1.html