Re: Apple speaker

[Rubywand <rubywand@swbell.net>]

TomMage writes ...
> 
> Hello, I tried it, bought a cable with an RCA plug at one end and two > bare wires on the other end. Tried hooking it up by splicing into the > speaker wires and also disconnecting the speaker wires at the post and > hooking up directly to the posts. Neither method seems to work, do you > have any idea why??

 ....


     Yes. The speaker is in the Collector circuit of the output
transistor-- one end of the spkr goes to a resistor and capacitor
connected to the output transistor Collector and the other goes to +5V
(not ground).  To get an audio output signal, the spkr must be in place;
or, you can substitute a 1 watt resistor-- something in the 22-39 Ohm
range.

     The output should come from the side of the spkr (or 1 watt
resistor) going to the resistor & capacitor connected to the
transistor-- i.e. the side which is _not_ the +5V side. The output goes
through a coupling capacitor to the center lead of your RCA plug. The
Ground side of the RCA plug goes to ground.

    "Ground" is DC ground = any motherboard trace area which is
connected to the ground side of the power supply. For example, the
outside "shell" of the composite video output is soldered to ground. 


     Here is a rough picture ...


     +5V side
        |
        |
        []< Speaker or 27 Ohm resistor
        |
        |---------------------|(--)|------------------------ Output
        |                   10uF  10uF                    to Amplifier
        |       2 caps connected as bi-polar capacitor  
        |
      Transistor                           _________________ Ground
       side                                |
                                        DC Ground

     You can get a bi-polar coupling capacitor at Radio Shack (2uF-5uF
is fine) or make one by connecting two 10uF caps neg end to neg end.
(The value is not critical, two 5uF caps connected back to back is
fine.)                              


Rubywand