AW: To earth, or not to earth...

[media at mail1.nai.net]

At 6:25 PM +0100 12/01/97, Haible Juergen wrote:
>	>The trouble with using banana (EVEN Serge) is that you are
>relying on a ground loop (Bad!) for >your
>	>audio signals. This will allow 50/60Hz hum to enter the system.
>I thougt just the opposite was true. With bananas, you *avoid* ground
>loops, and hum, but you *might* get crosstalk as all your signals share a part
>of the GND connection.

This is true.  You are trading off sheilding for a simpler ground path.  My
understanding of banana patching systems is that they use voltages and
input impedances that are high enough that RF isn't much of a problem.
This is what Serge told me about their system.  Crosstalk of audio signals
seems a possible problem with a shared signal ground.

Perhaps a good compromise would be to have unsheilded stackable banana
plugs for control voltages and sheilded  1/4" or 1/8" cables for audio
signals.  Due to typical impedances, for audio it is OK to mult outputs but
not inputs.  Then again, people often like to use audio outputs as
modulation sources with their modulars.

>If I would do it again, I'd use 1/4" *symmetrical* connections, and
>nothing else.

Really??  That strikes me as a radical choice -- especially if you are
trying to avoid ground loops.  By symmetrical I assume you are speaking
European and mean TRS balanced connections  :)   Firstly, It would seem
like pure overkill for control voltages.  Secondly, you would have to
balance the outputs of each of your modules requiring either transformers
(!!!) or active balancing with additional op-amps.  Thirdly, how long a
cable run would you have in patching a modular -- is CMRR that much of an
issue??  Fourthly, even if you did decide you needed to have balanced patch
points, wouldn't TT take up much less space (although it might cost more)??

PEACE OUT :)
MARK



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