Re: [ARSCLIST] Audio equipment cable shielding

["Richard L. Hess" <arclists@xxxxxxxxxxxxxxx>]

At 08:53 AM 4/19/2006, you wrote:
> At 01:21 PM 4/18/2006, you wrote:
>
> > Kurt Nauck:
> >
> > > We are doing some re-arranging of our studio here at
> > > the shop.  We're encountering hum from the audio
> > > cables being in proximity of power cables and possibly
> > > from florescent lighting (!)
> >
> > Are the audio cables balanced?
>
> No, unfortunately. If I use an rca to xlr cable converter, can I 
> carry a balanced signal from my turntable to my preamp, or do I need 
> a special device?

Balance is more than the cable type.

The preamp needs to be very close to the turntable - preferably 
3-feet or less.

Let's look at your issues for a moment.

You say you're getting hum. Is it just in the turntable or in the 
entire line-level system?

Turntables are very, very fussy because the signal levels are low, 
the impedance is fairly high, and the signals are unbalanced.

All three of these work against you.

The turntable needs to be separately grounded (not via the cartrdige 
cables), the cables need to be short, and preferably grounded at the 
preamp only - let the shields connect to the cartridge, but not the arm/TT.

Then, if your preamp is unbalanced, go into something like an Aphex 
124A balancing box, then balanced to your sound card (hopefully you 
have a balanced input sound card like the CardDeluxe, most of the 
MOTU boxes, or RME boxes or better).

But, the biggest risk is in the TT->preamp area. I would not try and 
run that through a patch bay or switch or long cables. I suspect you 
might have multiple TTs and preamps and want to switch. At the 
moment, I cannot think of very many good ways to do that. Perhaps I'd 
use a small BNC patch panel, perhaps with all the grounds tied 
together--it depends--one can argue it both ways. I do not tie the 
line-level unbalanced shields at my patch bay.

Cheers,

Richard


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