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
>>
>>
>> _______________________________________________
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>
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