Re: Apple speaker

[Rubywand <rubywand@swbell.net>]

Michael Mahon writes ...
> 
> Rubywand wrote:
> >
> > TomMage writes ...
> > >
> > > Hello, I tried it, bought a cable with an RCA plug ....
> >  ....
> >
> >      Yes. The speaker is in the Collector circuit of the output
> > transistor--
 ....
> >
> >      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 
 ....
 
>>

 AOK, right up to here...  A non-polarized capacitor is not required
 in this circuit, precisely _because_ the transistor side of the
 capacitor never goes below ground.  A 4.7 uF capacitor, with the
 (+) side toward the transistor collector and the (-) side toward
 the amplifier will do the job nicely.

<<



     Probably, for the vast majority of setups, this is so and will save
some bother. The NP cap does take care of situations where the amplifier
input is at DC a potential notably above Ground or even higher than the
Apple Speaker output-- i.e. it is + vis-a-vis the Apple Speaker +.

     By the way, Tom lucked out big time and got a Mockingboard C,
which, it turns out, has a plug and cable specifically for connecting in
sound from the Speaker! (Most likely, the MB A has a similar
connection.)

     Evidently, all older MB's (like our Sound II) do not include the
built-in Speaker connection; so, your observation will still save a
bunch of users some bother. Thanks!


   

Rubywand