[TenTec] Re: Heil ProSet adapter with Orion -- hum

[Ron Martin]

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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