[TenTec] Heil ProSet adapter with Orion -- hum

[Robert & Linda McGraw K4TAX]

Yes, it can be an unbalanced input but above ground.  There is nothing that
says an unbalanced input has to have the unbalanced side connected to
ground.

Bob, K4TAX


----- Original Message ----- 
From: "Duane A Calvin" <ac5aa at juno.com>
To: <jim at audiosystemsgroup.com>; <tentec at contesting.com>
Sent: Thursday, June 24, 2004 8:36 AM
Subject: Re: [TenTec] Heil ProSet adapter with Orion -- hum


> 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 at 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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> > TenTec at contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
> >
>
>
> Duane Calvin, AC5AA
> Austin, Texas
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