NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/rec/audio/12344

Internet Message Format | 1992-09-10 | 5.5 KB

Path: sparky!uunet!zephyr.ens.tek.com!gvgpsa!gold.gvg.tek.com!chrisc
From: [e-mail] (Chris Christensen)
Newsgroups: rec.audio
Subject: Re: Home-made audio rack - looking for suggestions
Message-ID: <[e-mail]>
Date: 10 Sep 92 23:19:55 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
Organization: Grass Valley Group, Grass Valley, CA
Lines: 114

In article <[e-mail]> [e-mail]
(Bill Vermillion) writes:
>In article <[e-mail]> [e-mail]
(Chris Christensen) writes:

OK now folks watch this!  Bill has disagreeded with me and I'm not mad
at him and I am going to disagress (sort of) with him and I'll bet
that he won't get angry with me!

>Chris - I am going counter from your recommendation on this
>one.

And that is why more than one person reads this stuff so we can share
our experiences!

>In the studio ALL of our equipment, from power amps, to speaker
>EQ, to periphral gears was mounted in wooden racks.
>The power amps were mounted in a door that would open to give
>access to the back of the amps - very compact and it works.
>The compressors, EQ, digital effects, everything, were mounted
>in custom made wooden racks.  We actually had the front of the
>cabinets curved to match the pivot of an engineers arm so that
>everyything was at the same distance from the engineer, but
>that is perhaps overkill - but it surely was nice.  All
>engineers from out of town who used it loved it.

Nice egrnomic touch, the curved bit!  I may try that when I build a
new console for my production studio.

>All the mouting rails were hardwood.  Doesn't take much to go a
>long way and therefore was not that expensive.
>This ensured that nothing touched.  We also physically grounded
>all units with a single point ground from the chassis and
>removed the grounding connector on the 3-prong plug.

Did you actually space the equipment apart so the chassis's didn't touch?

Then, if I read this correcty, you connected all of the equipment
chassis together and ran that to a single ground?

>Again this was studio work and no re-inforcement so we were
>going for the quietest environment possible.

My SR system only nets about 85 dB signal to noise in it's current
implementation.

>Our philosophy was to avoid any potential ground loops before
>we started.   Our designer/consultant was Bob Todrank of Valley
>Audio.  His installations were really some of the finest you
>would want to see .It was actually TMI when we started and we were the
>first under the Valley Audio name.  We sort of put them in
>business.

The methods that I have seen in other studios has varied widely.  I
have seen systems that used metal rack rails and wodden shelves, etc.
any time a ground loop was encountered a ground lifter was installed
on the cable.

What I have done is to use a bulk to a single point grounding scheme.
I have done this in my SR system as well as my production studio.  The
production studio is much smaller than a tracking studio.  I only have
about 20 total bits of gear to power.i

The bulk ground scheme is routinely practiced in the television industry in
very large systems that breed ground loops.   The usual method here is
to install solid copper bus bars in the racks and connect each chassis
to this bar with a large heavy coper braid.  The inter-rack bars are
connected together with even larger bus bars or a couple of bars
connected together.  This final bus bar then runs to the rooms tech
power panel.

All of the equipment is plugged into a power strip that is grounded to
the rack.

Granted the TV industry is happy if the hum is down do a couple of millivolts.. but there is audio in the facility and the egngineers *do* care about
the noise levels......These days.

I choose to use the pin 1 lift to solve my ground loop situations.  It
has worked repeatibly to solve dimmer noise in mr SR system and
intentional ground loops!  See next paragraph.

I use two amp racks in my SR system.  I have a 2500 watt rack behind
each speaker stack.  That stack is fed two 20 amp circuits from a
power snake that goes back to the power distribution panel.

I then feed the stereo audio signal to each of the racks from a
distribution amplifier in the effects rack.   When I make the
connections to the racks with the audio feed I close a great big loop.
How did I solve that quietly?  I lifted pin 1 of the cables feeding
the racks.  The differential input of the electronic crossovers now
carry the audio and there is no AC ground loop.

All AC grounds are solidly in tact with the mix position power fed
from a plug strip in one of the amp racks.

My system noise went from a subtle hum you could hear if you put your
ear to the speaker, to the noise floor of the amplifiers (yea that's
more than 85 dB but I didn't wanna say my SR system was at the 100dB
S+N level  :-)  NO BODY would believe me!

There is no doubt in my mind that my way will work for SR, Studio and
the home situation.  I also believe that your way will work in all
(?).....:-)  above systems!  Oh and all of my racks are wood with
metal rails.

So there you have it folks.  I recomend one way and Bill recommends
another way.  Take your pick,  don't intermix the methods,  keep
saftey grounds connected (in one way or another)  and don't drink
while you drive.  Stay at home, crank it up a bit and pour one for me!

--
Chris Christensen                  The opinions I express are my own,
[e-mail]            and sometimes they are wrong!
916-478-3419 FAX [phone]      After all, I *AM* only human.