Re: Reduce color saturation


"TSM" <nonsidice@xxxxxxxxxx> wrote in message
news:44bab2ad.23997666@xxxxxxxxxxxxxx
No, because they don't produce the same image. One is a Neo Geo MVS
and the other one is a Sega STV (Titan). So they are different boards.
The owner is supposed to adjust R, G & B with trimmers on the
monitor's board. But I can't open my monitor any time I want to swap
boards. So I wanted to build some circuit to alter color saturation.

OK - I think I see what your problem is now. Apologies, I was
misled by the use of the word "saturation."

What you're trying to do here really ISN'T reducing the
"saturation" in the standard color use of the word; the problem
is that the cards in question don't do a very good job of
keeping their video signals within standard levels, and they
need you to adjust the video amp gains in the monitor as a
result (or else the cards are likely to overdrive the video
amp and produce the problem you're seeing). If the sync
signals are separate, you MIGHT try simply sticking some
series resistance in the video lines to drop the level as seen
by the monitor - this will cause an impedance mismatch, but
if the signal is fairly low-frequency (and most of these old
arcade games are running at TV rates anyway, so it shouldn't
be that bad), it's not going to be that much of a problem.
Sticking a 25 to 50 ohm* variable resistance (a trimpot) in
series with each video signal, ahead of the monitor inputs
(or just before the output connections at the board) could
let you play with this and see if it helps, at least. If that doesn't
do it, you'd have to work out some way to drop the signal
levels while maintaining the right termination impedance -
which likely would require an active buffer. But try the trimpots
first - they're cheap and easy, and stand at least a fair chance
of working.

Bob M.

* - These values assume a standard 75 ohm video system.


.

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