Good, but expensive, news about optical volume control

Posted: 2/22/2010 7:22:56 PM

From: Escondido, CA

Joined: 2/6/2008

With all the RoHS crap, it was starting to seem like you would never be able to get analog optocouplers anymore. Fortunately, they are alive and well at Newark Electronics ... but they aren't cheap!

Perkin-Elmer VTL5C4 parts are $8.49 each! But they work great. Without any current into the LED side, the resistor side is 400kOhms.

The datasheet provides a 3 point response chart:
1mA => 1.2KOhms
10mA => 125 Ohms
40mA => 75 Ohms

The latency (or response time) is about 6ms ... way faster than you would perceive.

Posted: 2/23/2010 8:12:20 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

Interesting - Thanks Don..

Alas, 6ms is a bit slow.. Total delay / latency of 10ms starts to become percievable .. but actually, with volume control on a Theremin, probably not too important. Use as a VCA for percussive envelope shaping is where one might notice the latency.

At the price being charged, I think the better bet might be one of the "THATS" VCA IC's.. Thise IC's are superb - Ultra low noise and distortion, and some have log law (linear voltage control. log increase in volume).. The only problem is getting the damn things to work - they are quite fussy about the impedence of the control signal (current) - But when one gets this right, they are wonderful.
Posted: 2/25/2010 6:56:49 PM

From: Escondido, CA

Joined: 2/6/2008

I originally set out to use a SSM2018T part. Those work very well, but cost about the same as the VACTROL part.

I bought a few from a surplus house, but when I went to see about getting more, they were already sold out. But at least I know I could still get them if I need them.

Posted: 2/26/2010 8:05:49 PM

From: Richmond Hill, Georgia

Joined: 9/18/2005

ROHS "cr**" is correct. There was a least one NICE radio being manufactured in Germany for the HAMS that was canceled because they never could get the soldered board connections to be good a reasonable percentage of the time.

Posted: 3/1/2010 1:05:53 PM

From: Escondido, CA

Joined: 2/6/2008

"cat whisker detectors" ok, tin whiskers NOT!!

I know they meant well, trying to rid landfills of all sorts of toxic stuff, but the RoHS camp has wreaked havoc throughout the electronics world.

But, never to miss a chance for extra profit, the parts vendors jumped on this right away. They have changed part numbers in obscure ways, obsoleted parts that we have been buying for years, and provided "job security" for all the component engineers to figure out if they can use the "green" part or not.

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