Re: [ARSCLIST] Audio equipment cable shielding

[phillip holmes <insuranceman@xxxxxxxxxx>]

Sorry to interject at a late date, but I somewhat disagree.  If you have a 
transformer in the preamp (I have 3 that have the transformers on a 3' 
umbilical), then sitting them right next to the table could induce hum.  If 
you have a 3' tonearm cable (pretty typical I believe), use all 3' and get 
the transformer away from the cartridge.  Move that table away from anything 
with AC transformers.  If you insist on having a preamp next to your table, 
then get a DC preamp and make shorter cables for the possible sonic benefit 
(just remember that MM cartridges are designed with a certain amount of 
capacitance in mind).  I had a horrible problem with a Grado that I THOUGHT 
was a ground problem.  No, it was a flyback transformer (I suspect). 
Anyway, I got the TV monitor further away and the hum vanished.  On another 
table, the Grado picked up hum from the transformer in the table (it had DC 
motor drive instead of AC synchronous).  Also, I've had a moving magnet pick 
up hum from 2' away from the transformer in a CD player.  One thing I've 
noticed with modern electronics is that the transformer is never completely 
off (or they'd be impossible to turn back on with a remote control).  With 
moving coil cartridges, less popular with archivists for obvious reasons, 
you can paradoxically escape some of these problems.  They have a low output 
impedance so they can drive longer cable without high frequency rolloff. 
Also, the seem to be less susceptible to induced hum.  I have one Denon 
cartridge with an insanely low output of .13 mv.  Driving about 3' of cable 
into a step-up transformer which then drives a further 2-3' of handmade 
cable, there is no hum.  The transformers are shielded, and they are in a 
shielded case (the shields can't take much more captain, or she's gonna 
blow).  Also, there were multiple options for wiring up the grounds and 
shields (proper phono cabling will have a shield and a ground wire which can 
be connected different ways).  One option was noisy.  Another way that 
seemed to be counterintuitive, worked marvelously.  Sometimes you can get 
rid of hum by experimentation and luck.  It doesn't always follow textbook 
rules.  One observation I made was that Grado cartridges invent hum. 
They'll find hum and amplify it from the next town over.  If none exists, 
it'll send out a work order and gremlins will move a huge transformer where 
you can't see it and cause mental illness, indigestion and high blood 
pressure.  I'd ditch them if you have noise problems and go to Stanton. 
Stanton seems to be much better shielded.  I don't like the sound as much as 
Shure and Grado, but the hum can cause suicidal thoughts (I'm not 
exaggerating that much--you should hear me rant and cuss and turn red when I 
can't get rid of a hum).
Phillip
----- Original Message ----- 
From: "Robert Hodge" <rjhodge@xxxxxxx>
To: <ARSCLIST@xxxxxxxxxxxx>
Sent: Wednesday, April 19, 2006 8:29 AM
Subject: Re: [ARSCLIST] Audio equipment cable shielding


> You MUST keep the turntable close to the preamp ! No more than a foot or 
> two away. And with SHORT cables- coiling them up is NOT good! This applies 
> to the Archeophone too ! ( I know you have one, which is why I mentioned 
> this)
>
> Anything else will be fatal to the signal .
>
> It doesn't matter what you use - the low level of signal that a cartridge
> generates requires a high level of preamplification which requires a 
> preamp of very high gain. This gain makes hum a very easy thing to pick 
> up.
>
> Bob Hodge
>
> Robert Hodge,
> Senior Engineer
> Belfer Audio Archive
> Syracuse University
> 222 Waverly Ave .
> Syracuse N.Y. 13244-2010
>
> 315-443- 7971
> FAX-315-443-4866
.