Hi
Many manufacturers 'float' the DC supplies so that there is no direct
ground connection from the supply to the desk. Some have a 'chassis'
connection taken through to the desk where you then have an OPTION of
connecting it. To my mind this is the proper way to do things so that
there is flexibility in the grounding system to cope with pretty much
all eventualities. I would actually take it a small step further and
have a pair of inverse parallel connected diodes, a low value resistor
(say 22 Ohms) and a capacitor all in parallel, tying the desk 0 Volts
connection loosely to chassis (mains earth) at the supply so that in the
event of a failure it would be safety earthed but no great ground loo[p
current would flow unless it were more than about 0.7 Volts (which would
imply that you had a problem elsewhere which should be fixed).
In reply to a previous comment, yes many desk power supplies create a
large hum field so should be away from the sesk.
Matt S
FabLiquid wrote:
Hi
Its really funny but i had major problems with my previous supply. Not
hum related but causing a lot of spikes and stuff. I swapped it for a
bran new one i got from neotek a couple of months ago. All the
problems went away but theres hum now. My elite was really quiet
before. Theres probably something obvious that im missing!
Nik
Fab Liquid Recording Studios
On 1 Feb 2010, at 23:39, Matt Syson <[email protected]> wrote:
Hi
There are not many power supply designs (mechanical aspects rather
than electronic circuitry) that really like, being easy to repair
without killing either the supply or yourself when you need to
actually do some 'fault finding'.
Having a supply that puts out 'mains induced hum' onto its output
wiring smacks of total incompetence, and having to use 'hum bucking'
techniques on production gear is ridiculous.
Assuming the electronics when remote mounted away from the
transformer regulates correctly and provides a clean supply (which it
probably will) I would advocate a rebuild of the supply in a larger
box, possibly with a replacement transformer with reduced hum field.
From those that have played with these supplies, are the transformer
cores going into saturation by any chance?
Barak will be running at 50 Hz, which will encourage 'bad behaviour'
in this respect.
Matt S
Ike Zimbel wrote:
Hi Brian, Jim,
It sounds like this was essentially a "hum-bucking" coil. I have
often wondered if the power transformer is inducing hum into the
internal wiring in the PS-3. A while back I started to experiment
with both twisting various wires and shielding the transformer to
see if it dropped the noise floor, but time constraints cut that
short. I will have to look at that again one of these days.
I paid a visit to the Neotek factory ca. 1988. One of the reasons
that I went was because of the kind of thing that Brian is talking
about, although I got the feeling that folks were at least /trying/
to be helpful. This would have been during their "we have a switch
problem era" when they were having to repair or replace literally
thousands of defective Schadow switches. I remember seeing a bench
where several motherly looking ladies were, IIRC, replacing the
actuators in the Schadow switches in what must have been Elite modules.
On that visit, I met Craig, the owner/designer, and he seemed
pleasant enough until I started to push the issues that I was having
with PS-3's at the time. Then he seemed to lose interest in the
discussion fairly quickly and I was ushered out... I'm not sure when
Neotek was sold to Martinsound, but this must have been around the
time that the wheels were starting to come off, so I'm sure he had
a few things on his mind.
It's too bad that we don't have any former Neotek staff on this
list, the way we have some very prominent former Ampex people on the
Ampex list.
Best,
Ike
On 1/31/2010 10:42 PM, Brian Roth wrote:
Hey Jim,
It may have been only three or four feet of wire vs. six or
eight....it's been over 20 years ago. BUT, after months and
multiple phone calls to Chicago (with the desk's owner muttering
about legal action), we finally received that "solution" from a
tech there. It seemed this desk was not the only one with the
problem.
Indeed, the wad of wire reduced the noise floor, which was most
noticeable on the 2-mix bus, down to an OK (but not perfect)
level. I vaguely recall a -60 something noise floor before, and
maybe high 70's after.
Sidebar: Neotek's owner/designer (one and the same? I never knew)
would not take calls, and we dealt with a few less-than-friendly or
un-helpful folks along the way.
Best,
Bri
Jim wrote:
Hey Brian,
How goes buddy!
Anyway, I'm having a hard time getting my head around this
statement....................
Solution? Install six or eight feet of 18 or 16 GA wiring INSIDE
of the PS-3 (??) PSU box in series with the "ground return"
wiring, and then fuck with the positioning of that series "wads of
wire" inside of the PSU to "null" the noise.
WTF?
Regards, Jim
At 03:16 AM 1/29/2010, you wrote:
Hello Ike, et al:
I recall a new Neotek desk that was delivered here in OKC... 20+
years ago. I cannot recall if it was an Elan or Elite.
From DAY ONE it had "hum issues" on every bus. As I worked with
it, I was shocked to discover the grounding system, which was
"every ground was connected to every ground", including random
connections to the metal work on the front panels.
This was a NEW desk from Chicago.
Audio ground returns were randomly connected to the front panel
metal.
I quickly tested the desk with a battery=powered power
amp/speaker combo in order to eliminate any wiring probs, with no
I/O besides my battery-powered system, and at other times my
iso'ed scope.
It still hummed/buzzed. Many other tests done..including one
oddity...as I "unscrewed" modules from the frame, the noise changed.
Desk's owner yelled and cried at "Chicago", with no replies for
months. Desk owner SCREAMED, and finally had a reply apparently
from the "unknown mystery circuit designer"...
Solution? Install six or eight feet of 18 or 16 GA wiring INSIDE
of the PS-3 (??) PSU box in series with the "ground return"
wiring, and then fuck with the positioning of that series "wads
of wire" inside of the PSU to "null" the noise.
That came directly from "Chicago".
Egads.....
Best,
Bri
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