[TenTec] Heil ProSet adapter with Orion -- hum

[Robert & Linda McGraw K4TAX]

It is clear that folks here do not know the difference between balanced to
ground and unbalanced above ground.

Bob, K4TAX


----- Original Message ----- 
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: "tenteccontestingcom" <tentec at contesting.com>
Sent: Thursday, June 24, 2004 8:17 AM
Subject: RE: [TenTec] Heil ProSet adapter with Orion -- hum


> On Wed, 23 Jun 2004 23:33:10 -0500, George Skoubis wrote:
>
> >I shouldn't bring this up again for someone will blame it on the "Pin 1
> >problem".  The fact is there's typically 4 connections for microphone
> >audio.
> >There is the Audio Hi or +,  Audio Lo or -, Audio Ground, and Audio
> >Shield.
>
> I suspect that the problems here may be related to the difference between
balanced and
> unbalanced audio wiring.
>
> Virtually all ham gear uses UN-balanced audio -- as I understand it (I'm
not flush enough to
> own one), the Orion uses a balanced mic input, which is a nice step up,
but it can lead to
> problems when you interface an unbalanced mic. A balanced mic uses only +
and - for
> audio -- the shield is ONLY a shield.
>
> An unbalanced mic uses the shield both as a shield AND as "audio -", so if
you want to
> use an unbalanced mic with a balanced input, you must connect the shield
to both chassis
> and "audio -".  The chassis connection terminates the shield, and the
"audio -" connection
> completes the audio circuit.
>
> There's another big advantage to having a balanced audio input -- you can
plug a pro mic
> directly into it!
>
> The Standard wiring (AES and IEC) for a cable-mounted XLR connector is
>
> 1  - Shield
> 2 - Audio high
> 3 - Audio low
> Shell - no connection (there are VERY good reasons why this is the
Standard, and they
> involve the prevention of ground loops in installed systems).
>
> The correct wiring for a chassis-mounted XLR connector carrying balanced
audio is
>
> 1 - Chassis
> 2 - Audio high
> 3 - Audio low
>
> The correct wiring for balanced audio is:
>
> Shield to chassis
> Audio High to Audio High
> Audio Low to Audio Low
>
> Much equipment, including all of the pre-Orion Ten Tec gear I have seen,
is built
> improperly, in that it takes the shield to the circuit board and not to
the chassis. There are
> two fixes.
>
> 1)  Rewire the equipment connector to disconnect the shield (pin 1) from
the circuit board
> and connect it to the chassis. (Best)  Unfortunately, lots of equipment
use connectors that
> are mounted to the circuit board, and it is difficult or impossible to
rewire them correctly.
>
> 2)  Rewire the cable-mounted connector to connect the shield to the shell.
(Second best,
> but it fixes all but the most severe problems).
>
> Hope this helps.
>
> Jim Brown  K9YC
>
>
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