[Ham-Mac] iMic Impedance

[Steve Lawrence]

Steve, what do you think they were talking about?  If it is the output 
from
the iMac to Mac (or audio in to the sound card) this may be the 
problem. I
have no idea what the Mac expects.

Dick, AA5VU
_________________
Dick - All I can do is describe my experience.

I initially connected the audio out directly from across the headphone 
stereo out of an FT1000D at the front panel using some RS adapters to 
parallel the connections. I did not have to make any changes to the 
volume setting for my Proset earphones and there was plenty of signal 
to the iMic and then the software on a G4.

The FT1KD audio output to the headphone jack is capacitively coupled 
from Op Amps and drives the iMic 6.6K very well.

The Mic input impedance is 500-600 ohms which the Proset mic drives 
easily. The 18 ohm output of the iMic has no problem driving the rig.

Because of hum, I subsequently inserted 600-600 ohm mini telephone 
modem transformers in each line for isolation. That is, two in the 
stereo audio out to the iMic and one in line with the input to the rig. 
(I used only the tip signal from the stereo iMic output to drive the 
rig.) A small switch box selects data from the G4 (iMic) or Mic from 
the proset. Hum problem solved with no loss of drive on any line.

Additionally, the VOX keys quite nicely from the audio tones obviating 
the need for an optocoupler in the PTT line and the expense of a USB to 
serial adapter (and the hassle of getting the right optocoupler). Wish 
I had discovered this sooner!

In short, at least in my case, I have a very simple and straight 
forward set of connections from my rig to the computer via an iMic with 
some isolation transformers for hum mitigation and a simple switch box 
to select data or a mic for SSB.

It's evident from the postings that YMMV.

GL all & 73, Steve WB6RSE