I've been trying to track down some strange hums in a friend's studio.
I've traced it to the Calrec Mini-Mixer that drives the monitors (
Active nearfields, i forget the make )


Here is the strange part. The Mixer will create a hum when the gain is
at "-8" but when set to unity gain, with all inputs down, it will be
quiet. When you increase the gain past "0" the noise increases again.

We were trying to track this down to the point where we had just the
calrec plugged directly into the active monitors, with a balanced
cable, shield lifted on the monitor input.

Does anyone have any experiance servicing these boards? It does sound
like a grounding issue, but the strange way that we can get rid of the
noise with the master faders at "Unity Gain" make me think something
has gone foul in the master section.

Any ideas would be apreciated.

On 9 Apr 2005 23:52:37 -0700, in rec.audio.pro "nmm"
wrote:

I've been trying to track down some strange hums in a friend's studio.
I've traced it to the Calrec Mini-Mixer that drives the monitors (
Active nearfields, i forget the make )


Here is the strange part. The Mixer will create a hum when the gain is
at "-8" but when set to unity gain, with all inputs down, it will be
quiet. When you increase the gain past "0" the noise increases again.

We were trying to track this down to the point where we had just the
calrec plugged directly into the active monitors, with a balanced
cable, shield lifted on the monitor input.

Does anyone have any experiance servicing these boards? It does sound
like a grounding issue, but the strange way that we can get rid of the
noise with the master faders at "Unity Gain" make me think something
has gone foul in the master section.

Any ideas would be apreciated.
Does sound like a ground problem, but it there might be something
oscillating at RF, and this is suckng the supply rails down.
Stick a scope on it if you have one (hum finding by internet is tricky
at the best of times)

martin

"Wales is a big welsh-shaped rain collection device"

nmm...
My idea....
There may be an ultrasonic oscillation occurring only at certain gain
settings, which the ears are not able to appreciate, only noticing a funny
left-over hum.
I suggest you look at the connected - but no-signal - mini-mixer busses or
monitor o/ps on a scope.

Shield lifted: do you mean *screen*? I assume XLR mating pairs. If so, the
monitor amp i/p screens per channel should be made at the signal receiving
end, yet lifted at the Calrec Mini-mixer Mon Send bal'd o/ps.
[If you meant XLR shell, I would say the shell (4th pole) does not need a
connection to screen at short-run line levels.]
Jim

"nmm" wrote in message
ups.com...
I've been trying to track down some strange hums in a friend's studio.
I've traced it to the Calrec Mini-Mixer that drives the monitors (
Active nearfields, i forget the make )

nmm wrote:

Here is the strange part. The Mixer will create a hum when the gain is
at "-8" but when set to unity gain, with all inputs down, it will be
quiet. When you increase the gain past "0" the noise increases again.

I agree that this sounds like a grounding problem internally somewhere,
probably on the buss. I suggest you call Masque Sound, because one of
the techs there owns a Minimixer personally and has spent a lot of time
hacking on the thing. I can't remember the guy's name, but I talked with
him at the last AES show and he really seemed to know the ins and outs of
the box very well.

Does anyone have any experiance servicing these boards? It does sound
like a grounding issue, but the strange way that we can get rid of the
noise with the master faders at "Unity Gain" make me think something
has gone foul in the master section.

Maybe, or it's possible that when you change the loading on the mix buss
things start going wrong.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey wrote:
nmm wrote:

Here is the strange part. The Mixer will create a hum when the gain is
at "-8" but when set to unity gain, with all inputs down, it will be
quiet. When you increase the gain past "0" the noise increases again.


I agree that this sounds like a grounding problem internally somewhere,
probably on the buss. I suggest you call Masque Sound, because one of
the techs there owns a Minimixer personally and has spent a lot of time
hacking on the thing. I can't remember the guy's name, but I talked with
him at the last AES show and he really seemed to know the ins and outs of
the box very well.

Does anyone have any experiance servicing these boards? It does sound
like a grounding issue, but the strange way that we can get rid of the
noise with the master faders at "Unity Gain" make me think something
has gone foul in the master section.


Maybe, or it's possible that when you change the loading on the mix buss
things start going wrong.
--scott
I seem to recall hearing this about the calrec mini mixer before..