--- Olin Lathrop <olin_piclist@EMBEDINC.COM> wrote: > Debbie Hynes wrote:
> > Attached (4k gif) is a schematic of a hydrophone amp I made yonks back.
> > It used a mylar spkr but didn't work too well under water coz it
> > couldn't hack any pressure. But it should function ok as a microphone?
>
> This seems to be the same basic concept with a better DC bias arrangement
> and transformer coupled output.  That makes sense, but I don't see what
> advantage you are getting from R5 unless this circuit had to work with a
> particular transformer you happen to have already.

It did - the o/p transformer was a mini AF PCB type. R5 was supposed to improve
the LF response somewhat. It was a real junkbox project. :)
I thought a long run of cable underwater would pick up 50Hz hum pretty bad but
it didn't so the diff o/p wasn't really necessary.
Debbie

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