[Ham-Mac] Sound Card

[Jack Brindle]

The problem is a bit different than I had understood initially. There  
is a big difference between having a drive impedance of 4.7 ohms and  
one of 4.7K. There is also the addition of the Tigertronics box, with a  
transformer with 600 ohm input and output impedance. It becomes an  
interesting academic exercise to determine just what might be going on  
with the entire circuit. Note, though, that a 4.7K output driver will  
have much less drive capability that a 4 ohm speaker output. The best  
way to realize this is to model the circuit as a voltage source with a  
series resistor that has the value of the output impedance. In the case  
of a speaker output, this is only 4 ohms. In the TS570 case, the  
resistor would be 4.7K ohms. But both should be able to work with audio  
input devices.

There is one thing that now jumps out at me. Apparently things work  
just fine when connecting the TS570 through the SL-1 to the G4's audio  
input. This being the case, things should likewise work with the iMic.  
The iMic will have about the same input impedance as the Mac's input  
port. So, if one works, the other should also.

This brings us back to the iMic and what is different about it and its  
setup. It might be worth while to try the setup again, making sure that  
all connections and settings are correct. Early iMics seem to work  
different from current ones. I have an older iMic that has also given  
me problems with its input. Like Dick, my response at the time was to  
put the iMic on the shelf. I later found an Onkyo UH33B audio processor  
and use it for my shack audio interfacing. Besides the iMic settings,  
the two things that have troubled me are the small slide switch, which  
is not labeled on mine, and the mini-phone connector on the input. The  
switch selects between low and high level inputs. Presumably this adds  
an amplification stage to the circuit in the right configuration,  
although you have to guess at the proper selection in my iMic.

The iMic does work for audio input, others have indicated that. It's  
just a matter of finding the magic.

On Mar 3, 2005, at 7:14 AM, Dick Kriss, AA5VU wrote:

> The problem I had was my Mac G4 1GHz AGP was near deaf to signals from  
> the
> ACCY2 port of the TS-570D(G) when interfaced via a Griffin iMic to the  
> G4's
> USB port.  The G4 hears very well when interfaced direct via the same  
> cable
> to the Line-in/Mic port to the Apple Built-in audio processor. My non
> technical assessment is there must be some kind of mismatch between the
> TS-570's output and what the iMic expects.  I liked W6FB's comment  
> that it
> acts like having a 200:1 SWR on an antenna.

- Jack Brindle, W6FB
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