Re: small signal NPN transitor for muting microphone

"Si Ballenger" <shb*NO*SPAM*@comporium.net> wrote in message
news:43d457c6.131507868@xxxxxxxxxxxxxxxxxxxxx
> On Sun, 22 Jan 2006 16:29:36 -0800, "Walter Harley"
> <walterh@xxxxxxxxxxxxxxxxxxxx> wrote:
>
>>"RR" <RR@xxxxxx> wrote in message
>>news:dr0pr4$g5t$1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>>I have posted a circuit at this address, please have a look.
>>> http://www.psv.co.uk/MicMute.JPG
>>>[...]
> So what is the "negative-going part of the wave"? Looks like only
> a positive voltage is being modulated.

The schematic would be more clear if it read from left to right, instead of
right to left as it presently does. If I understand what the OP is trying
to do, the microphone is the signal source; normally, the microphone drives
the preamp, and the OP is attempting to mute it by shorting its output to
ground via the transistor.

If the microphone is indeed a dynamic (coil) type, as indicated on the
schematic, then its output is AC with very little DC component, with
magnitude on the order of 10mV.

You're right that I'm wrong, though. It would mute the negative-going part
of the wave, if the signal were strong enough. Indeed, it would mute it
regardless of the base voltage, because of the collector-base diode being
forward-biased. It's horribly distorted, though.


.

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