From: bill@bilver.uucp (Bill Vermillion)
Subject: Re: Making cables
Organization: W. J. Vermillion - Winter Park, FL
Date: Fri, 14 Aug 1992 20:39:37 GMT

In article <124350004@hpwin052.uksr.hp.com> mow@hpwin052.uksr.hp.com (Mark Payne) writes:
>hmm

>I'm not sure that earth lifting your interconnect loom is a good idea. Sounds
>like you have individual cores of 2 signal (twisted) plus drain (screen).
>I think I would wire the patch bays up with the drain and the spare connected
>together to the jack plug earth at both ends.

>I would then only earth lift signal wires on individual interconnect  links 
>from bits of kit to the patch bays.. Keep a few "special" jack/jacks for this.

>In the end I often find the only way to stop hum loops is to lift the ground
>wire on the mains on some kit... DO THIS AT YOUR OWN RISK and not at all 
>if you have and sense.

Well here is how we did it.   

All the grounds on the jack at the patch bay were kept separate and run
to one point.

All the ground pins from all the AC powered devices were cut off.   A
12 or 14 guage stranded wire was run from each of these to the same
point as the patch pay.

All the auxiliary equipment had their grounds removed and the portable
device had a banana jack that plugged into a grounding socket that went
back to the single point ground.

All the auxilliary permanent in the control room equipment (eg
compressors, Pultec EQ, Lexicon, etc) rack mount equipment was mounted
in a custom WOODEN rack with hardwood mounting rail so no equipment
chassis could touch each other.

All the power amps were mounted in a solid door that had hardwood
mounting rail.

There was NO way any equipment could touch the frame of another piece.
EVERY piece of equipment had it's own ground independant of the power
line.  

All these grounds were carried to one place and bonded together, and
then they attached to a rod that came up through the cement floor in
the center of the console that went about 15 feet into the earth. 

We took the main feed for the building and then feed that through a
Transtector (and later added a Volt-Guard).  This filtered feed was
then split two ways into two 25KVA tranformers.  And each of these
feeds fed a separate control room.

You'd have to work pretty damn hard to get a ground loop in that
instance.

We also split the feed before Transtector to feed the rest of the
building.  No lights,  office machines, etc were on the studio side of
the tranformers.

Never really had much of a hum problem.  And we grounded at ONE point
only.   Some felt we went to the extremes but it only takes one wrong
move in the wiring to defeat all your other good work.

Weird thing was we did have ONE hum problem.  We would get induced hum
in the the heads of our Stevens 24/32 track machine.   By properly
orienting the machine we could get rid of it.

Turns out the hum was being induced from a power transformer on a pole
about 100 feet away from the building.  

There is always something that reaches out to get you :-)

We had two studio and each was fed from it's own
-- 
Bill Vermillion - bill@bilver.oau.org  bill.vermillion@oau.org
                - bill@bilver.uucp 
                - ..!{peora|ge-dab|tous|tarpit}!bilver!bill

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