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Old 18th September 2009, 12:20 PM   #11
Did it Himself
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Here you go. Thinking about it a bit more as I was drawing it I think you don't need any extra resistors to get clean switching as the amps input will never have its input broken away from being able to source current.

Click the image to open in full size.

Use a DPDT switch, the top half shown above is the normally closed ones and the bottom/right is the normally open ones.

The only downside to this is you would either need two switches or a quad gang one to switch stereo passively. If you used relays to switch the signal then you could still use the one switch but you would obviously then need a battery or power to run the unit.
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Old 18th September 2009, 12:44 PM   #12
MondyT is offline MondyT  United Kingdom
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Cheers Richie!

Looks simple enough, I suppose the only thing to do is try it and see if it is quiet. The only downside is that I need the switch to be a foot operated device and DPDT seems quite rare in foot operated components, SPDT is the more common. My ideal would be a momentary action switch with the electronics providing the latch, but this would mean more complexity

Ray
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Old 18th September 2009, 03:56 PM   #13
AndrewT is online now AndrewT  Scotland
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use the footswitch to pull in or release a dpdt relay.
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Old 18th September 2009, 05:28 PM   #14
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Alternatively if you only need it to reduce the signal level not totally kill it, it can be done with one (SPDT) switch.
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Old 18th September 2009, 08:56 PM   #15
MondyT is offline MondyT  United Kingdom
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Hi

Thanks for your replies. I would like if possible to reduce it to point where it couldn't be heard rather than just reduce the volume. Andy's idea of a small DPDT relay could be a good idea as I could aslo add an LED to indicate the swtiches state easily. I am just uncertain if the resistor switching can be relied on not to click or pop during switch in and out. I will need to try a few experiments to see.

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Ray
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Old 18th September 2009, 09:04 PM   #16
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Quote:
Originally Posted by MondyT View Post
Geek, do you have any circuits for using a Bi-Polar transistor for the mute as I *never* seem to have much luck with FET circuits with signals as high as 2.5v pk and using 9v batteries
The one used by Yamaha for a decade was just a 4.7-10K resistor in series with the output, collector to that on the output side, emitter to ground, base to the controller chip through a little R-C circuit for shaping. There was no Vcc on the collector.

Tried it on a breadboard with a 2N5088 and worked well for line level mute

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Old 19th September 2009, 07:46 AM   #17
MondyT is offline MondyT  United Kingdom
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Thanks Geek

I tried this circuit attached based on a transistor I have knocking about and it seems to work quite well and I get at least -50dB reduction in volume. Is this what you mean?

The 2.2K series resistor is about as high as I want to go as I want to feed a 20K amplifier line input. Not sure if I have suitable values for the R-C components in the transistor base, or indeed if I have the R-C bit configured correctly. Can you experts give me any pointers here?

Cheers
Ray
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Old 19th September 2009, 10:41 AM   #18
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Originally Posted by MondyT View Post
I am just uncertain if the resistor switching can be relied on not to click or pop during switch in and out. I will need to try a few experiments to see.

Cheers
Ray
The resistor is not switched in or out, the signal path is never broken, so there will be no pop or click.
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Old 19th September 2009, 11:11 AM   #19
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Hi Ray,

Quote:
Originally Posted by MondyT View Post
Thanks Geek
I tried this circuit attached based on a transistor I have knocking about and it seems to work quite well and I get at least -50dB reduction in volume. Is this what you mean?
You're welcome!

That's pretty much the circuit, yes.


Quote:
...Not sure if I have suitable values for the R-C components in the transistor base, or indeed if I have the R-C bit configured correctly. ..
Now that I see your base time constant circuit, that rings a big bell for values.


Quote:
The 2.2K series resistor is about as high as I want to go as I want to feed a 20K amplifier line input.
I recall a tuner w/muting using this circuit and was followed by an emitter follower so they could get away with higher levels of resistance in series. But it did have a little "thump" as it switched.

Maybe an opamp follower/linedriver (balanced for DC, hence no thump) if you want to get fancy?

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Old 7th March 2013, 07:04 PM   #20
Baldin is offline Baldin  Denmark
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Default jFet as shunt switch

Old thread, but looking at the same subject


I'm working on a turn on / turn off circuit for Op-Amp's, working with a fet as a shunt switch on the op-amp's output

I want it to work on the regulated supply lines directly and not sensing on AC lines.

The output shut be shunted until the supply line has reached say 80%
At turn off is should react as fast as possible

Found a good inspiration here Class-A power amplifier project - Current-Drive - The Natural Way of Loudspeaker Operation ... and worked a bit further on it.

Not sure whether I need to do more with the gate circuit .... any ideas?
Guess j108 would be an ok choise for this application.

V2 simulates the negative supply line and V4 is the signal coming out of the op-amp

Any thoughts on this circuit??
Thanks in advance, Baldin
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