Steve Pelikan wrote:
>Sometimes my older MD recorder (Sony N707) and binaural microphone pair
>works as an all-too-good radio receiver. So I spend a lot of time
>wondering about what I can do to prevent the problem. This is a bit of
>challenge because I'm best described as "electrically illiterate". Hence
>some simple-minded questions for which I'd appreciate answers and/or
>references from which I could start to learn some answers:
>
>1) I think the microphone cable is "unbalanced" because, although it
>seems to leave the microphones as a balanced line (with 2 conductors and
>a ground/shield) one of the conductors in each line is attached to the
>ground at the MD end of the cable --- where everything is reduced to a
>single TSR connector. (This sort of connection is described, of example,
>in the instructions for running WL183 microphones with PIP that I found
>at Rob Danielson's fantastically useful web site,
>http://www.uwm.edu/~type/audio-reports/Shure-WL183s/index.htm) Am I
>right that this essentially makes the whole connection unbalanced and
>therefore more susceptible to things like noise from radio broadcasts?
Yes, all PIP mics are unbalanced--even when they're wired with three
conductors.
>2) Is there any potential advantage to keeping the microphone cable
>connection balanced and performing some sort of conversion to unbalanced
>just before plugging it into the recorder? Would this be accomplished
>with a transformer that would somehow find the difference of the signals
>in the two connectors? Is it something a normal mortal could build?
I think it's best to do the grounding at the recorder input, as you
are doing. Transformers won't work because a transformer won't pass
the DC power.
>2.5) Is there also some advantage to be gained (more signal, less
>amplification needed?) for combining the information in the cable's two
>conductors rather than just grounding one of them?
No. Different types of mic will require different wiring schemes.
>3) The WL183's (for example) call for 5 V and it has been suggested that
>their performance with some MD recorders is degraded by lack of proper
>powering. Could one supply the 5v with 4 NiMH cells, and if so, where
>can I learn how to build/connect the battery to the cable/microphone?
PIP supplied by recorders is usually sufficient for nature recording.
Higher supply voltages give the mics more high-SPL capability before
mic clipping. This is important for concert tapers who work in 120 dB
situations...Nature sounds, even thunder, are usually much lower. Not
that a complete kit shouldn't include an external supply just in case
you want to stick a mic in a roaring lion's mouth or something like
that...
Regarding the RF pickup, Radio Shack has clamp-on ferrite beads
(giant beads) that you could try on the cable just before the
recorder.
-Dan Dugan
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