--- In ". m u r m e r ." <> wrote:
> yes, it only happens with my own self-built contact mics, so i'm sure
> it's a problem with them rather than the recorder. i was just wondering
> if there might be something i could do to the mics to resolve the problem.
Try disconnecting the 0 volt wire from your mics and see if the noise still
happens. (That's assuming your mics can work without the 0 volt connection.)
LEDs produce 'dirty' current when operating, and that should not be allowed
into the audio 0 volt line because it manifests as clicks and similar sonic
detritus. Good design practice powers the LEDs from across the + and - voltage
rails (rather than 0 volts) or provides a completely separate power supply for
them.
It is possible that the Marantz's LED is feeding dirty current into the power
supply, and this is what you are hearing - the dirty LED current making its way
down the shield, into your microphones and then back into the mic preamplifier
where it is amplified as part of the signal. The effect would vary depending on
the internal circuitry of the microphone, so it is possible it would manifest
on some mics and not on others.
It might be interesting to check out the internal wiring of microphones that
don't suffer this problem and compare it with those that do. The solution could
be something very simple...
Just a suggestion...
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