Mute circuit with LED indicator

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NewYorkDave

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Joined
Jun 4, 2004
Messages
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Location
New York (Hudson Valley)
Saw this in one of my trade magazines and thought it'd be of interest to the folks here...

http://www.reed-electronics.com/ednmag/index.asp?layout=articlePrint&articleID=CA468422
 
Thanks for the schematic Dave.

Now, I have a question. What would be the advantage of using a circuit like this over say just wiring the output to go through a switch/relay, and "lifting" it to mute? I'm thinking up ideas for a simple monitor controller and was planning on doing the latter using 2 DPDT relays and having an LED be powered along with the relay coil (in the lift/mute position).

Thanks.
 
I dont know if it will apply to this particular example, but one benefit of fet muting is that in the examples I have seen, it usually doesnt click. The signal seems to ramp down, so it's much harder to hear the mute. On a latched relay, its much more common to hear the mute clicking in. Even if the mute itself doesnt introduce a click to the audio path, the instant drop of program can often be heard as a click... Much easier to mute program with fet mutes and have it "work" in a mix. The relay mutes in my console now click and it drives me nuts, I wish there was a way to fix that...

dave
 
Thanks for that Dave, I used to get EDN on line before my laptop crashed last Christmas. I must re-register. Did you see Harry Bissell's Envelope Follower a while back? He incorporated this into a guitar processor and I am reliably informed that it is one of the best low ripple followers designed.
Stephen
 
[quote author="Ethan"]What would be the advantage of using a circuit like this over say just wiring the output to go through a switch/relay, and "lifting" it to mute?[/quote]

I'd be asking what benefit would a relay mute serve? Much more expensive, bulkier, large current demands and possibly signal degredation due dodgy relay contacts - plus anything mechanical will wear.

Go for the fets 100% in my opinion, and i'd be using a toggle flip-flop with a nice soft switch

Yeah never seen that fet symbol either

my 2 cents :wink:
 
Shouldn't C1 be reversed? I never remember exactly those symbols but the curved plate should be the negative side, am I wrong?

Frank
 
Hi Adam,
(and someone please correct me if I am wrong.)  Audio doesn't enter the 555.  They place this switch, in their sugg implementation, on the wiper of a volume control. so audio enters one end of pot, leaves at center wiper with this dangling off like a flashy 80s earring, and the last lug grounds.
or in lieu of a volume pot just attach the collector to your signal.
looks like a quick and easy breadboard experiment :)

andy
 
80hinhiding said:
The link that was posted by NewYorkDave doesn't seem to work anymore.  I'm looking at adding a latching mute switch with an led indicator to my project and wondered if the following circuit is one that would prevent clicks that you sometimes get with muting.
http://www.electroschematics.com/6226/touch-control-mute-switch/

Audio input would go to pin 6 on the IC?

And what affect, if any, would this circuit have on distortion/noise levels?

Adam
Using a bipolar transistor for a mute is an old cheap way to perform a mute. There are probably lots of better mutes to copy around the WWW.  This thread is 12 YO which may explain why the link doesn't work.

JR
 
JohnRoberts said:
........ There are probably lots of better mutes to copy around the WWW.  This thread is 12 YO which may explain why the link doesn't work.

JR

any working link  ?
thanks
 
80hinhiding said:
Can you recommend a simple circuit for me to try out?  I have lots of BC548 and BC547 transistors on hand.
I don't recognize those part numbers (and I'm too lazy to look them up) but if they are general purpose bipolar transistors they are pretty much what I suggested avoiding.

The last and only time I used bipolar transistors as mutes was in a 4 track cassette deck design that I inherited back in the 1980s  already mostly finished (I  had to redesign a bunch of it, but didn't change the mutes). Bipolar transistor mutes were popular in old school designs because the could be turned on/off easily from a single rail. There were undesirable for a number of reasons, 1) base current flowing through the emitter to turn on the device, corrupts ground quality, 2) intrinsic junctions can be turned on by larger signals  and add distortion, 3) you need to spec in specialized bipolar part numbers that are optimized for the application (if they still make them).

Do a search for JFET mutes that do not have those problems, there have been many discussed in this forum over the years  so I see little reason to reinvent that wheel.


ps. I revived the 12 year old thread because it was directly related to what I am looking to achieve, and as far as I know New York Dave was a trusted source on the world wide web, this GroupDIY site being included in that web. :)  I thought someone might have that circuit or know of a way to do this in a similar fashion without having to dig through the web, wondering about the credibility of the source.

Hope you're well John.

A
There are many here who could design a JFET based mute and have. You could join that club with a little more research.

I am doing OK considering... thanks for asking.

JR
 

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