Keep in mind that in a unbalanced input, the high side of audio typically
goes to the non-inverting input of the input device while the low side of
audio (not shield) goes to the inverting input. In this fashion any common
mode signal developed between the + input and the - input of the input stage
is therefore cancelled. Connecting the - to ground negates the ability to
cancel differential voltages.
Bob, K4TAX
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "Ten Tec List" <tentec@contesting.com>
Sent: Thursday, June 24, 2004 4:35 PM
Subject: [TenTec] Re: Heil ProSet adapter with Orion -- hum
> Based on the correct info from those who have the schematic for the radio,
it seems
> clear that the Orion has an UNbalanced input. In other words, I was
mistaken about
> that. If you want to use a balanced mic with any ham gear, you need to
tie the "audio
> -" line to "mic ground" at the radio. The shield is still only a shield,
and should go to the
> chassis.
>
> There's another potential issue with many rigs -- they may not have enough
gain to
> work with a pro mic, which is 150 ohms impedance. When I want to use a pro
mic with
> my ham gear (I sometimes do), I use a step-up transformer between the mic
and the
> radio. The turns ratio is not critical -- something between 1:2 and 1:4
will work, but it
> needs to be a decent audio transformer. The original Omni has enough gain
that it
> doesn't need the transformer. I do need the transformer with my Omni V
and Elecraft
> K2.
>
> Jim
>
> On Thu, 24 Jun 2004 15:08:45 GMT, Ron Martin wrote:
>
> >Jim,
> >
> >Thanks for the information.
> >
> >I believe that I will rewire the Heil (and the one I built) transition
cable
> >to do what you suggest. I do have some 'old time' balance mikes that I
> >would like to try on the Orion.
> >
> >
> >Thanks
> >
> >
> >Ron
> >
> >Jim Brown 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
> >>
> >>
> >> _______________________________________________
> >> TenTec mailing list
> >> TenTec@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/tentec
> >
>
>
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|