Simple Mac Audio Hookup

Bob Dixon (rdixon@stargate.acs.ohio-state.edu)
Mon, 3 Apr 1995 13:52:39 -0400 (EDT)


A while back I posted an article here describing various approaches
to attaching an external microphone or other audio source to one
of the modern Macs that uses the infamous non-standard "long" miniature
phone jack, and normally requires the special proprietary Apple
microphone.

I have now boiled these approaches down to a single one, recommended
for those who just want a simple way to make it work, using easily-
available components. All the components needed are available at
Radio Shack, and they are not difficult to assemble.

Here is the list of needed components with Radio Shack catalog
numbers and costs:

Audio Amplifier 32-2041 $ 70
Audio Patch Cord 42-2387 4
Load Resistor 271-120 2
Microphone 33-3004 50

Total 126

This cost is of course far less than the cost of your computer.
You can get a less expensive microphone, or use one you already
have, but be sure that whatever you use is UNIDIRECTIONAL. It needs
to have a standard monaural phono plug on the end of the cord, or
else you will also need to get the necessary adaptor at Radio Shack.

Here's how you connect these components:

1. Take the patch cord and cut it off about two inches from
one end. Discard the short piece. On the cut end of the long piece,
use a knife or other tool to remove about 3 inches of the
outer gray insulation. Peel off the foil shield from that
3 inches. You should have left three wires, a bare one,
a red one and a black one. Remove about half an inch of the
insulation from the red and black ones. Twist the bared ends
of the red and black wires together.

2. Take the load resistor and bend its wires so you can plug them
into the "com" and "8" terminals on the back of the amplifier.
Push in the buttons, stick the wires in and release the
buttons.

3. Take the patch cord prepared in (1) above and stick the
bare wire wire into the "com" terminal (joining one of the
wires from the load resistor that is already there).
Stick the bare ends of the twisted black and red wires into
the "16" terminal.

4. Plug the other end of the patch cord into the microphone jack
on the back of the Mac.

5. Plug the amplifier into a wall outlet. Ignore the extra power
cord that comes with the amplifier; that is used only to run
the amplifier from your car. Be sure the power switch is
turned off before doing this.

6. Plug the microphone into the front panel of the amplifier,
where it is labeled "microphone 1".

7. Set the amplifier controls as follows:
Mic1 - 1/3 of the way up from min.
Mic 2 - min
Phono/aux - min
Tone - high
Master Volume - 5

8. Turn on the amplifier. Turn on the switch on the microphone.
Start CU-SeeMe on your Mac and connect to "self".

9. In the Audio window, click on the boxes so there are
Xs in the Send, Receive and Lurkers boxes. Click on the top
box so there is NO X in the Push to Talk box.
Slide the threshold arrow to the third mark from the bottom.

9. Talk into the microphone. You should hear yourself in your
speaker, and the bar in the audio window should go up about
half way when you talk.

10. If your audio is too strong or weak as shown by the sudio bar,
turn the mic1 knob on the amplifier up or down as needed.

11. If your audio sounds distorted or scratchy or has hum
in it recheck all your connections.

12. After everything works, disconnect from "self" and connect
to wherever you wish.

You should now be on the air. This connection provides very high
quality audio. People often tell me mine is the best they have
heard on CU-SeeMe.

No doubt there are other components or approaches that could be
used, perhaps at lower cost, but this one uses parts that
anyone should be able to find.

Good Luck!

Bob Dixon
Advanced Technology Group
Ohio State University

Reflector 128.146.116.8