[Ham-Mac] Use of iMac

[Dick Kriss, AA5VU]

On 3/3/05 12:15 PM, "Jack Brindle" <jackbrindle at earthlink.net> wrote:

> The problem is a bit different than I had understood initially.

QSL my typo error on the 4.7 vs 4.7k ohms

Some additional information without re-quoting Jack and others. When I first
ran into the problem I suspected a defective iMic that was purchase new from
a local store. I talked to Griffin and they exchanged the iMic.  The
replacement did exactly the same thing even though it had the older 8/16/20
chipset. For this reason I do not suspect the iMic.

For grins I just tried it again and there is electrical connectivity but the
received signal thru the iMic/USB port is much lower than via the Built-in
Audio port. I know attenuation is not the correct term but the iMic acts
like a major attenuator.   Little or no decoding thru the iMic and what I
consider a normal easy to print signal direct.  I was using the same jumper
cable. Yes, I tried the iMic slide switch in both positions. God only know
which one is what as they are not marked. One seemed to reduce the already
weak signal

To compund the academic exercise Griffin's response to my early inquiry said

> An impedance mismatch with the line amplifier
> (inside the iMic) might cause the signal coming out of the iMic to be lower
> than normal but we rarely see this problem anywhere.  The iMics signal level
> is enough to drive more headphones which are typically of around 30ohm
> impedance. 
>
>The output impedance of the iMic is AC coupled 18ohms at 150uF.

This was really confusing because they talk about driving headphones and
could not comprehend the ham radio application with the output is via the
USB connection, not the speaker plug on the iMic. I have no idea what the
Mac needs to see from the USB output of the iMic; however, it seems to be a
weak sister compared to the direct connection via the Built-in audio port.

If you are just getting started the sound card terminology is very
confusing. In my setup the audio output from the rig is the input to the
SL-1+ interface and it's output is the input to the Mac (or iMic) and this
becomes input to the software program. For the transmit path the output from
the software program and Mac is the input to the SL-1 and it's output is the
audio input to the rig.  Each device has different labels and it does get
confusing. The PC sound card community at least uses color codes. HiHi

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

I gave up looking for iMic magic and use the G4's built-in audio because it
works.

End of Shaggy-Dog story

73 de Dick, AA5VU