> Isaac Marino Bavaresco wrote:
>> It would be weird an audio circuit that picks mechanic vibration
>> directly from the board.
>
> Not wierd, just nostalgic.  12AX7s were pretty good at picking up
> vibration.
> You could lightly tap them with a pencil or something and quite clearly
> hear
> it in the output.  I even saw a case one where the amplifier oscillated o=
n
> its own because it was placed too close to a PA system speaker.
>

I've also seen microphonic ceramic capacitors. One in particular was in
the playback preamp of a broadcast tape cartridge machine.

Harold


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