At 01:16 PM 6/18/2010, Josh Koffman wrote:
>Sorry to reincarnate this thread, but I finally had some time to do a
>bit of searching on using a FET to mute audio. I found this page with
>a bit of searching:
>http://www.pic101.com/audiosw/index.html
>
>The FET circuit seems simple enough to implement, but I've seen some
>chatter on a forum that this circuit won't attenuate enough with a low
>impedance. My source is low impedance, but it's also balanced.
>
>So...I'm a little confused if I could make this work. Would I have to
>use two of these circuits (one on each of the mic lines)? Would it
>make sense to power my circuit off an isolate DC/DC converter to avoid
>ground hum issues? I think it's safe to assume that my circuit will be
>off a different power source (and possibly different ground) from the
>one that the mic is connected to.

Ouch.  Using series FET switches on a balanced line means that you 
need to ensure that the switches track identically.  But: its not the 
end of the world.

Best way is to try it.  Build 2 of the first circuit shown but for 
now, eliminate the Q2 transistor.  Use a SPDT switch wired up to a 9V 
battery, with the battery (-) going to gnd and the switch armature 
going to both FET gates.

Operate the switch and see what it sounds like.  Armature at gnd = 
audio ON; armature at +9V = audio off.

Then we can go on from there.

dwayne

-- 
Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
www.trinity-electronics.com
Custom Electronics Design and Manufacturing

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