If the Orion uses balanced input, then why do they label pins 1 and 2 as
Mic (1) and gnd (2)? And the PTT switch uses PTT (3) and gnd (2). It
appears to be an unbalanced input, and handling of the "gnd" connection
is what we've been discussing. I'm saying all of this without having
looked at the schematics, just the pinout of the mic connector in the
manual and the accompanying diagrams.
73, Duane
On Thu, 24 Jun 2004 08:17:20 -0500 "Jim Brown"
<jim@audiosystemsgroup.com> writes:
> 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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>
>
Duane Calvin, AC5AA
Austin, Texas
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