Danger, Will Robinson! (//e audio out connection)

["Joel" <joelbuckley54.nospam.@hotmail.com>]

"Simon Williams" <DONTemail@luddite.ca> wrote in message
116059.PBUDTKEI@news.telusplanet.net">news:116059.PBUDTKEI@news.telusplanet.net...
> Anyone tinkered with replacing the IIe's crappy speaker with a line out?
> I'm a little hesitant to connect the wires up to my stereo without first
> hearing from someone who's already been electrocuted =8-O
>
> SW


You do want to be careful.

I had written an article on this back in the 80's.
The 2 wires to the speaker are from a darlington and +5V.
I f you had assumed they we're the more typical signal + ground pair and
connected them to an external device (like a VCR or monitor which also
connects the two devices grounds through the video connection) you can short
out the Apple's 5 volt supply. Not good!

You need to isolate the signal with a capacitor.
This effectively becomes a high pass filter, so the capacitor value would
depend on the input impedance of the device your driving and your cutoff
frequency.
If you used 1kHz as your low cutoff and wanted to drive an 8 ohm load, you
would want a 22 microfarad capacitor.
15V electrolytic will be fine.

If you are driving a line input, the input impedance is much higher, and you
can get by with a smaller capacitor.

There are actually a couple of ways to hook it up.

1. Make a ground connection to somewhere on the motherboard. (Ground does
NOT go to the internal speaker.)
Identify the signal line to the speaker (not the 5 volt line) and put the
cap between it and your signal out line.

2. If you want to be able to just hook it up at the speaker connection (or
at the internal speaker), use two caps.
Run one cap from the 5 volt pin to external sound ground.  Run the second
cap from the signal pin to external sound signal out.

Someone else said it wouldn't work without the speaker connected, but in the
//e there is actually an LED loading the darlington in parallel with the
speaker.
Though the load is less.
According to my ancient notes, if you connected signal out ground to +5v
through a capacitor, you will get a louder external signal if you leave the
internal speaker connected.
If you connect signal out ground directly to Apple ground (which you may be
doing without knowing it if you are connecting composite video out to the
same device), you get a louder external signal with internal speaker
disconnected.

Boy, you thought it was going to be easier than all that, right?

Makes you not even want to bother.