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Re: IIgs to arcade monitor experiment

MdntTrain wrote:


The IIgs video has these output specs:
  RGB:  1 Vpp @ 75 ohm impedance
  Sync:  4 Vpp @ 2k impedance

An arcade monitor (non VGA type) typically has these input specs:
  RGB: 4 Vpp @ 5k impedance
 Sync: 2 - 4 Vpp @ 35k impedance.

Video: these numbers don't look well matched, and I'm not sure what to
do about it yet.    If I connect the IIgs RGB directly to a higher
impedance than 75, the signal voltages are higher..


Yes, most likely about 2 Vpp at no load. Will look very washed-out,
but nothing will burn.
The ideal solution is using special hi frequency op-amps built pretty much for this purpose. Make it 8 Vpp at no load, add a series resistor of 68 ohm before the cable and a terminating resistor of 75 ohm at the monitor side. One per R G B. 
One can also use a simple 2 transistor amp.

This assumes that the polarity of the R G B and sync are the same.

However if you don't know much about electronics, you may not want to
experiment.



 not as high as

4V... but maybe enough for sufficient contrast.   However, does the
IIgs video signal get screwed up somehow if I don't load it with 75
ohms?

Sync: looks like a better situation.. as the voltages start out in the
right range.   I'm not sure but my guess here is that the 35k sync
input impedance won't be a problem for signal integrity ... as either
2k or 35k are "high impedance" inputs.

Any thoughts are greatly appreciated as always.

JS




-Alex.