Re: Varied IIgs Q's

[Rubywand <rubywand@swbell.net>]

Edhel Iaur, Esq. writes ...
> 
> .... 
> The 4-pin sound connector near the front inside the IIgs: can I just
> grab some of these pins, and connect 'em to a stereo audio out?
> Microphone/Audio in?
>

     As far as I can recall (without unstacking our GS and popping the 
lid), there are two on-motherboard Sound connectors. One, named "J-17" 
normally has a plug attached which goes to the internal speaker; the 
other is a seven-pin connector named "J-25" located near the memory 
Expansion Slot.

     Some GS's have a small sub-board attached near the front. A GS 
without the sub-board might have pins showing-- I don't know--;but, this 
would not be an especially good place to attach stereo cables or a 
microphone.

     In fact, at least on a ROM-01 GS, there is no good place to connect 
a mike to the motherboard because there is no built-in input 
buffer/amplifier. You will need to add a sound input board, such as the 
one Roger Wagner supplied with HyperStudio. A Slot card named "Sound Ace" 
is another option; or, you can build your own. The output of the board 
would go to J-25.

     Similarly, at least on a ROM-01 GS, there is no built-in "stereo" or 
two-channel Sound output. You can plug a stereo plug into the Sound 
output on the back and run two cables to a stereo amplifier; but, this 
just sends the same signal to each amp channel.

     To obtain true two-channel (or more) output, you need a fairly 
simple circuit which de-multiplexes the GS Analog Sound output available 
at connector J-25. J-25 also includes the signals needed to do the 
de-multiplexing.

     A typical GS "Stereo Board" plugged into any Slot will connect to 
J-25 and deliver two-channel output to a stereo amp.


> .... 
> Would it be harmful to the IIgs's sound circuitry if I plug an
> unamplified speaker (according to its back, it's 8 ohm, 3W max) into
> the earphone jack of the IIgs?
>

     You can do this without harming your GS; just be sure to use a 
_stereo_ plug. A mono plug will short the output to ground. One nice 
feature of the output supplied via the Sound Output jack is that it 
includes both the composite "GS Sound" signal and the 'old Apple' sound 
signal.


> My Phasor sound card seems to work fine in the IIgs, but it now has
> lotsa interference (the kind I described before--the interference
> changes sound as the IIgs thinks about different kinds of tasks).
> Would moving it to some other slot reduce the noise?  It'll work in
> basically any slot, and I don't mind if I have to go to the control
> panel and disable the mouse, serial ports, 3.5" drives, or move my
> hard drive controller to another slot.  Since the IIgs gets quite
> toasty after a while* (the Phasor itself is no fridge, either), I'm
> rather wary of covering my Phasor with aluminum foil, etc. to ditch
> the static.
>

     The GS Slot bus (i.e. power lines) is known to be fairly noisy, 
especially on the ROM-01. This is due, mainly, to skimpy motherboard 
traces supplying power to the boards in the Slots. Skimpy power supply 
wires are another noise source.

     The cure is to fatten power lines (+5V, +12V, GND) going to at least 
two Slots-- Slot #3 and Slot #7 work well-- and to fatten power supply 
leads. Moving your sound board to Slot #1 may reduce noise a bit, but, 
probably, not much.


> ....
> What the heck is up with the 640 mode? .... I zoom in on a
> blue area in the 640 mode, and I see a magenta and white dither.
> ....

     As you observe, the dithering is horizontal-- one dot next to 
another. (This is different from most hires 'old Apple2' dithering, which 
is vertical.) Since two dots are used to represent a color, dithering has 
the effect of reducing horizontal 'dot resolution' for dithered colors.


Rubywand