[BC] The XLR pinout debate

[Peter Smerdon]

Cowboy wrote:
> On Saturday 12 August 2006 06:23 pm, Peter Smerdon wrote:
> 
>> I'm recalling that before the standard, pin 2 hot was common in UK and 
>> Europe, and pin 3 hot in US and Japan.
>> Australia was importing pro audio gear in about equal measure from both 
>> camps, so it was a right royal mess down here.
> 
>  Though it should not have been so.
> 
>  The equipment doesn't really care which is + and which is - since both
>  are carrying an AC signal.
>  An amplifier will amp an AC signal regardless !
>  The only time it would matter, would be if different wiring were on the same
>  cable, or in the case of some polarity dependant device, like the mod input
>  on an AM transmitter.
>  At no other time would it make a hill of beans, until people start thinking
>  it does, and "fix" something that isn't broke !

In a perfect world, yes. Here's my real-world experience.
Station A is wired "pin 2 hot", station B is wired "pin 3 hot" - Station 
A owner buys station B, and starts sharing resources like OB gear. Now 
we have a jumble of XLR leads with the "traditional" hot wire (red, 
white, whatever) wired to different pins.
Eventually the two stations are bought under the one roof (a "pin 2 hot" 
plant naturally).
After a couple of bouts of phase "strangeness" on stereo circuits caused 
by legacy XLR cables miswired I did a stocktake - after investing in a 
cable wiremap tester.
I found a worryingly large number of pin 2<->3 transposed cables in the 
spare & OB cable stockpile.
My take on the reason - careless or clueless techs repairing the cables 
over the years since the acquisition, dealing with only one end, and 
wiring it to their idea of what's right. Some of these cables found 
their way into the combined station studio rebuild as one side of a 
stereo pair.
They would have gone largely unnoticed in a typical OB lash-up, and if 
they did cause a problem it could have been blamed on some other factor 
at the OB.
Now whenever I have to open up one of the pin-3-hot leads, and resolder 
one end, I take the time to rewire both ends to the standard.

Oh, and then was the Otari MX50 tape machine at another facility I 
worked for, which had unbalanced outputs on XLRs pin 3 only (factory 
standard issue - output balancing was optional on this model, and Otari 
had the "pin 3 hot" standard). A tech who should have known better (no, 
not me <g>) wasted an afternoon trying to figure out why he had no audio 
from his "pin 2 hot" adaptor cable.

I've forgotten who said it, but the quote comes to mind "The good thing 
about standards is that we have so many of them. You can choose the one 
that suits."


> 
>  I know of no manufacturer that ever sold any broadcast grade gear that
>  reversed the polarity between input and output, except the boxes
>  very deliberately designed to do so, like a symetripeak <sp>.
> 
>  Oh, sure, we all know ( or we all should know ) that positive pressure on the
>  microphone diaphragm is supposed to produce positive going voltage at the
>  output pin labled + but how do we know what the polarity was on the
>  record ( that's CD for you kids ) when it was recorded ? 
Yeah, I remember when audiophile recordings went through a phase (ouch!) 
of advising listeners to experiment with reversing the wiring polarity 
on _both_ loudspeakers to find the correct "absolute" phase. That way 
when (eg)the drum skin "blew", the speaker diaphram "blew" not "sucked".

Ya can't do that with the earbuds on an iPod(tm) he he he....
(personal comment on the dumbing down of audio)

>
Cheers!

-- 
=============================
Peter Smerdon.

Radio 3mp - Easy Listening
sen-1116  - Let's Talk Sport

Melbourne, Australia.
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