Hi Richard:

I thought about a turntable-to-preamp patchbay and decided it's just too likely to have problems. If 
the grounds are all tied together, doesn't the whole of the system become a potential hash/rf 
pickup? Phono cartridges are crazy about rf fields -- I make sure to keep my cellphone far from the 
studio and there's only an old-school WECO telephone anywhere near the equipment. Those Blackberry 
things are horrible about putting out crap -- you hear it all the time on interview shows. I can't 
understand how they got FCC licensed!  Anyway, though, my end result was, since I don't switch 
turntables often, just to physically change the RCA and ground wires to the preamp. If I had a setup 
where multiple turntables were used often, I'd have multiple preamps like a radio station or DJ rig.

-- Tom Fine

----- Original Message ----- 
From: "Richard L. Hess" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, April 19, 2006 9:32 AM
Subject: Re: [ARSCLIST] Audio equipment cable shielding


> 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
>
>
> Tape Restoration Seminar:    MAY 9-12, 2006; details at Web site.
> Richard L. Hess                   email: [log in to unmask]
> Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
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