Questions for the masters.

1) I have my preamp mounted in a rack case. The xlr female inputs are
very inaccessible deep in the back. Especially in the dark. I had the
idea to mount a 1RU strip at the back of the case with female
chassi-mounted xlrs. A (very) short snake of sorts, but... these are
supposed to be mounted in a metal box forming a faraday cage, not out in
the free air so there will be about 1-1,5 cm exposed signal path without
shield. The solder cups on the back of the xlr. Does this matter for mic
level signals?

2) (unrelated to (1)) Should signal ground be connected to the case in a
snake/stagebox? I believe signal ground should be connected to the xlr
connector exterior in a mic cable, thus connecting signal ground to the
box. A stagebox might also carry line level things that might introduce
hum like i.e. keyboard direct remotely powered from another mains
socket. Perhaps groundlifting should be taken care of before the stage
box rather than after?

best regards
Lars


--
lars farm // http://www.farm.se
lars is also a mail-account on the server farm.se
aim:

Lars Farm wrote:
Questions for the masters.

1) I have my preamp mounted in a rack case. The xlr female inputs are
very inaccessible deep in the back. Especially in the dark. I had the
idea to mount a 1RU strip at the back of the case with female
chassi-mounted xlrs. A (very) short snake of sorts, but... these are
supposed to be mounted in a metal box forming a faraday cage, not out in
the free air so there will be about 1-1,5 cm exposed signal path without
shield. The solder cups on the back of the xlr. Does this matter for mic
level signals?

Probably OK in a metal rack case as long as there's no source of
interference close to it inside the case. But there's only one way to
really find out.

2) (unrelated to (1)) Should signal ground be connected to the case in a
snake/stagebox?

Read this:

http://www.rane.com/note151.html

I don't think you'll find any "signal ground" in a stage box. Plenty of
chassis ground, and they should all be connected together, including the
casing.

Anahata

Anahata wrote:

Probably OK in a metal rack case as long as there's no source of
interference close to it inside the case.

It's one of them black SKB plastic cases open on both front and back so
I suppose one could consider it out in the open.

But there's only one way to really find out.

At the seventh location recording from now when the sky is lit by
northern lights and someone's mobile receives an SMS... Ah, well back to
the drawing board...

thanks
Lars


--
lars farm // http://www.farm.se
lars is also a mail-account on the server farm.se
aim:

On 10/10/05 11:13 AM, in article
1h487je.1cndsv81c869csN%see.bottom.of.page.for.lar , "Lars Farm"
wrote:

Questions for the masters.

1) I have my preamp mounted in a rack case. The xlr female inputs are
very inaccessible deep in the back. Especially in the dark. I had the
idea to mount a 1RU strip at the back of the case with female
chassi-mounted xlrs. A (very) short snake of sorts, but... these are
supposed to be mounted in a metal box forming a faraday cage, not out in
the free air so there will be about 1-1,5 cm exposed signal path without
shield. The solder cups on the back of the xlr. Does this matter for mic
level signals?

Not usually. (or else a number of major broadcast networks and installs I've
worked for wouldn't have functioned!). I'd go ahead and make the extension
and panel the way you describe. Use a good shielded cable and keep your
shield as far up to the solder connections as possible.



2) (unrelated to (1)) Should signal ground be connected to the case in a
snake/stagebox? I believe signal ground should be connected to the xlr
connector exterior in a mic cable, thus connecting signal ground to the
box. A stagebox might also carry line level things that might introduce
hum like i.e. keyboard direct remotely powered from another mains
socket. Perhaps groundlifting should be taken care of before the stage
box rather than after?

This is situation-dependant (Unless it's a studio installation as opposed to
a location recording thing). The BEST way would be to have each line on the
snake with a switch to lift the shield-to-case connection for that line.

I have had this fail BOTH ways and in two instances have NEVER figured out
what the heck was the problem. I still have a 50' 6-ch mic snake that's just
about unusable due to its uncanny ability to invent hum and buzz at low
levels in different lines with seemingly magical causes. Nothing tests
miswired on the snake, it just has different problems on different lines and
is a huge RFI-attractor. Substituting single cables or a different snake
solves the problem.

Lars Farm wrote:
Questions for the masters.

1) I have my preamp mounted in a rack case. The xlr female inputs are
very inaccessible deep in the back. Especially in the dark. I had the
idea to mount a 1RU strip at the back of the case with female
chassi-mounted xlrs. A (very) short snake of sorts, but... these are
supposed to be mounted in a metal box forming a faraday cage, not out in
the free air so there will be about 1-1,5 cm exposed signal path without
shield. The solder cups on the back of the xlr. Does this matter for mic
level signals?

Yes. Buy a sheet metal chassis for $10 or that you can screw into the
back of the panel for some shielding.

2) (unrelated to (1)) Should signal ground be connected to the case in a
snake/stagebox? I believe signal ground should be connected to the xlr
connector exterior in a mic cable, thus connecting signal ground to the
box. A stagebox might also carry line level things that might introduce
hum like i.e. keyboard direct remotely powered from another mains
socket. Perhaps groundlifting should be taken care of before the stage
box rather than after?

The overall shield on the snake goes to the case. It is not connected
to the individual "pin 1" signal grounds on each channel, except maybe
at ONE point somewhere in the system. Having the ability to lift this
can be handy, though, since sometimes racks get additional ground paths
between them due to power system issues in the field.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."