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How to add a mute system to an OpAmp


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Dear windoze killa
Thank you very much, Strange Abbreviation  :)

Dear Audioguru

I Had the same oponion to mute the signal in the same manner as you said, Of course with a BJT. I thought if the signal has a DC (i.e. 3V) then it works but when there is no DC I didn't have any oponion for Negative Cycles of Signal. Because in this condition, the Base-Collector Junction would go in Forward bias.
what would happen with a FET?

2- what I tested yesterday, In the Non-Inverting PAiA ciruit I attached, I put a NPN Transistor Between the 100k Resistor (R11) on the Noninverting pin of IC1:B and GND. When the Transistor was ON everything would work fine, when it goes Off, The Output would saturates gradually, but I didn't test it with a Sound Signal to see if It affect quality in Normal Condition.
What do you think?

ThanX
Shahriar

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Hi Shahriar,
The ordinary transistor has very reduced current gain when the signal ihas reversed polarity so the muting will be a little rectified.
Use a jFET like I said. It is a voltage-variable resistor and with the low level from the mic it will have low distortion even if you ramp the muting.
Wien bridge oscillators frequently use a jFET for amplitude control.

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Dear Audioguru

Thank you very much...

But do you have any oponion about The Transistor in the noninverting Pin.
Have I explained it clear?

Like I said, an ordinary transistor would probably rectify the signal when it is turned on which would make low-level distortion. JFETs have been used for muting frequently.
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