[Ham-Mac] Re: Still trying to go digital (with SignaLink, iBook G4, Cocoamodem, iMic)

[Dick Kriss, AA5VU]

On 9/26/05 11:51 PM, "Richard Cincotta" <ki4fw at hotmail.com> wrote:

> Dick,
> 
>    I communicated with you awhile back, and was unable to get my
> Cocoamodem/iBook G4 setup to work (and I was too busy traveling to worry
> about it).  Well, I'm back.
> 
>    Here's my problem.  I need to use an iMic for my input soundcard, which
> is placed in between the SignaLink A/D converter, and my iBook G4 USB port.
> But, the audio cord hookup -- going from the SignaLink to the iMic -- does
> not seem to work.  If I jiggle the plug that's stuck into the iMic input
> jack (showing the microphone) I only momentarily see the gain indicator,
> oscilloscopic ovals or PSK waterfall on Cocoamodem's screen display.   I
> can't sustain that input, however -- no matter how I hold the plug that's
> stuck in the input side of the iMic it only goes on for a fraction of a
> second.
> 

Richard KI4FW,

I am the wrong person to ask about receiving via an iMic.  I never could get
it to pass a useful signal from my Kenwood TS-570.  The only way I managed
to get a useful Rx audio signal from the Kenwood to the Mac was to run a
standard stereo cable from the output of the SL-1+ to the Line-in
(Microphone Port) on the back of the G4.  Every time I tried to use the USB
port the iMic acted like an attenuator and the signal level was too weak at
the Mac.  I gave up on the iMic but others have had success.  Maybe they can
help. FYI, Steve WB6RSE, contacted Griffin and found the iMic specifications
to be

> Input is 6630 ohms
> Output is 18 ohms

I suspect the 6630 ohms may be incompatible with my Kenwood TS-570 output as
modified by the SL-1+.

Please note my comments are regarding the receive audio only.  I transmit
from the Mac's USB Port to the iMic and in turn to the SL-1+ to the Kenwood.
The iMic works FB on the transmit side.  The ONLY reason I use the iMic for
transmit is to maintain the system beep sounds in the Mac.  If you use the
output port on the back of the Mac, it mutes the internal speaker.  By using
the USB port I can maintain the internal sounds. Yes, I tried a Y-connector
with one side going to powered external speakers but that was something I
did not like.


>    I know there's the issue of SignaLink only using the tip of the stereo
> audio plug & ground to communicate. If that's the problem, what do I need to
> do?  I guess another possibility is that my iMic is malfunctioning.
> 

I recall a very good comment from Chen that may explain the jiggle problem
you mentioned.  

".... Be aware that the SL1 uses a mono phono jack and the iMic uses a
stereo jack.  You CANNOT just plug one into the other without
shorting out the right stereo channel (or worse) -- so it is best to
buy a mono plug for the SL1 end and a stereo plug for the iMic end
and wire between them appropriately.

The "usual" stereo-mono wiring is to wire the tip of the stereo plug
to the tip of the mono plug.  Likewise, wire the sleeves (ground) of
the plugs together, and leaving the "ring" of the stereo plug unwired.

For best noise/hum immunity, use shielded twisted pair between the
plugs, the two wires of the twisted pair runs from tip to tip and
sleeve to sleeve as described above.  The shield of the twisted pair
is then bonded only to one end of the connection -- usually the
"input" end, which is the iMic microphone end for the A/D cable and
the SL1 SPKR end for the D/A cable"

Richard, have you tried the recommended Mono/Stereo cable?

> Any help from you or your knowledgeable comrades would be appreciated,
> 
> Rich, KI4FW
> 

Please let me know if you break the code on how to receive via an iMic.  As
noted I gave up. Some things are just too hard and my setup works fine
without he iMic in the receive path.

Dick AA5VU