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From: galen@picea.CFNR.ColoState.EDU (Galen Watts)
Subject: Re: Suggestions  on Audio relays ???
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Message-ID: <Apr21.141607.55058@yuma.ACNS.ColoState.EDU>
Date: Wed, 21 Apr 1993 14:16:07 GMT
References: <C5qsBF.IEK@ms.uky.edu> <C5r60r.4ID@megatest.com> <1993Apr20.102756.1709@mala.bc.ca>
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In article <1993Apr20.102756.1709@mala.bc.ca> wagner@mala.bc.ca (TOM WAGNER, Wizzard of old Audio/Visual Equipment........Nanaimo Campus) writes:
>In article <C5r60r.4ID@megatest.com>, alung@megatest.com (Aaron Lung) writes:
>> In article <C5qsBF.IEK@ms.uky.edu> billq@ms.uky.edu (Billy Quinn) writes:
>>>I built a little project using the radio shack 5vdc relays to switch
>>>audio.  I got pretty bad 'clicks' when the thing switched.  I was doing
>>>My question is:
>>>	Is there a good relay/relay circuit that I can use for switching
>>>audio, so that there will be *NO* noise of any kind on the audio lines.
>> 
>> Are you switching high level signals or low level signals like pre-amp
>A novel circuit I used to build was a primitive "optical isolator".. It consists
>of a resistive photocell and a lamp, all packaged in a tube.  When the lamp is
>off the cell is high resistance.  Turn the lamp on and the resistance lowers

I use an H11F1   FET optoisolater to switch microphone level signals.
There is no click, since I put a .1uF cap across the LED.  Distortion
measurement are very low with mic level, and they went up to 0.03% at a
+ 14 dB line level.  All I did was put the FET in series with one leg
of the balanced line.  No hums, pops, just audio jumping out of silence.
The FET runs about 100 million ohms with the LED dark and drops to 150-200
ohms with it on.

Hey, it works, and works well.
Galen Watts, KF0YJ

