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opto device in compressor?

12/28/1999 1:43 AM
opto device in compressor?
Hi everybody!  
I was wondering how i could desing the opto part of a compressor,with a photoresistor and a lamp.The problem is i don't know which lamp and photoresistor to choose,i bet the lamp should be about 30 v one,and the res,should be about 1 meg.  
I think i'll use a triopde and heptode valve;the triode for primary amplification,and dephasing;then run the oposite phase in the photoresistor;and the normal signal through the lamp.And mix the two signals in the heptode.  
Best regards.  
12/28/1999 6:17 PM
Scott Swartz

I see you are still interested in a tube based compressor. I am continuing to work on the optical design I mentioned a few weeks ago, and plan to make it available on the net in some manner, perhaps with a PC board from RG for the side chain circuitry. I will contact RG about this after the design is proven. He may or may not be interested in this.  
I can't tell how your idea in the post is supposed to work. What is the side chain? A normal compressor has a level detector that outputs a DC control voltage which is controlling the gain. This is where the ratio and threshold are set.  
On your photoresistor question, the response time of the photoresistor is probably the most critical parameter, but resistance range also is important. Check out this link for some good info:  
This is the company that makes "Vactrols" - used to be EG & G, now its someone called Perkin Elmer Optoelectronics.  
If you want to start your own design, I would recommend that you purchase the book "The Stompbox Cookbook" by Nicholas Boscorelli, as it has a lot of good compressor ideas that can be modified to incorporate tube gain stages.  
This book is available here:  
PS Thanks to Aron and his board for telling me about this book and a source for it. This book was also recently added at Antique Electronic Supply
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