[SML] XLR mic cables: Pin 1 to case/ground... yes? no?

[Andy Lang]

On Tue, Mar 10, 2015 at 8:51 PM, Dale Farmer via Stagecraft
<stagecraft at theatrical.net> wrote:
> The answer is, sometimes.    And it is a matter of tradeoffs. Generally, the
> higher end the system and users of the gear are, you will connect those
> shells. Mostly this is in recording studios. Expert audio folks will
> recognize the ground loop when it shows up and have the skills and tools to
> quickly solve the problem. Inexperienced folks will waste piles of time
> chasing the ground loops and often doing more damage and dangerous things
> such as breaking off the ground pins on power cords to 'solve' the problem.

I'm going to have to respectfully beg to differ with Dale here. For
the longer version, see the Rane Note that Steve Payne linked to, it
does a great job of explaining things. For a slightly shorter
version...

As far as cables go as a general rule, NEVER tie pin 1 to the shell
for a general purpose cable. The ONLY time it should be done is to
solve a specific problem, and in many of those cases, the shield
should then ONLY connect to the shell, and not to pin 1 at all. And,
in either case, it should be very, very clearly and permanently
labeled as such. And, ideally, you should use one of those fancy
Neutrik connectors with the capacitor and choke in it to make the bond
so that it only happens at RF frequencies, and not audio frequencies.

For detailed explanations, see that Rane Note, or search Google for
writeups on the "Pin 1 Problem" by the late great Neil Muncy or Bill
Whitlock, but for the capsule version, a properly designed piece of
audio gear should have pin 1 connected to the chassis of the gear AT
THE INPUT. The idea is that the shield of the cable and the chassis of
the enclosure connect together to form the RF shield and prevent noise
from getting into the device.

Many pieces of gear are instead designed so that pin 1 goes to the PCB
ground, and then, via the long and winding path therein, to the
chassis. This is bad, and is called the Pin 1 Problem. It means that
any noise injected into the shell gets into the circuit board, and
then into the audio path. In these devices, it can sometimes be fixed
by connecting the cable shield to the shell instead of pin 1, but not
always.

But connecting pin 1 and the shell as a matter of course provides all
sorts of opportunity for induced noise to get into the circuit, and is
generally a bad thing on any circuit. On unbalanced circuits (say, if
your cable gets used with a  ClearCom pack), it's a near guarantee
that you'll get buzz in the the com, and spend far too many hours
trying to track down the responsible cable. When on tour, we once had
to put an entire local audio crew plus our touring crew on a delayed
dinner break on load-in trying to troubleshoot a buzz in the spot com
line that made it unusable, only to eventually track it down to a
single Y cable with the shell and pin 1 tied together. One. Damned.
Adapter.

-Andy