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

[Steve Payne]

The jensen transformer site has a lot of good reading material on it
including the ones mentioned by Andy Lang. Click on resources

http://www.jensen-transformers.com/

http://web.mit.edu/~jhawk/tmp/p/EST016_Ground_Loops_handout.pdf

On Mon, Mar 16, 2015 at 7:34 PM, e-mail frank.wood95 via Stagecraft <
stagecraft at theatrical.net> wrote:

> I agree with Andy.
>
> The important principle is that there are two different grounds. There
> is the safety ground, which dictates that all exposed metalworl must
> be connected to it. Certified double-insulated gear is exempt from
> this provision.
>
> And then there is the audio signal ground. The two must, ultimately,
> meet, but only under strictly controlled conditions. The Rane Note is
> a very clear explanation of this, and worth your study.
>
> Unfortunately, some XLR connectors automaticallyl connect pin 1 to the
> shell. This is unequivocally bad news, and few, if any, cable testers
> will show this up. Only measurements or visual inspection will reveal
> this fault. You probably can't do this witha visiting company's gear,
> but it is the first place that you should look at for hum problems.
>
> It has been said many times, but will bear saying again. NEVRR, NEVER,
> NEVER, LIFT THE SAFETY GROUND CONNECTION. It may provide you with a
> temporary solution.  It may also provide you with a dead performer.
>
> On 14 March 2015 at 17:01, Andy Lang via Stagecraft
> <stagecraft at theatrical.net> wrote:
> > 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
> >
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>
>
> --
> Frank Wood
>
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