Upgrading the SFX Sound Expander

From: Richard Atkinson (rga24_at_cam.ac.uk)
Date: 1999-04-01 22:45:10

I got the old desoldering pump out today and installed a 24 pin IC socket
in my Sound Expander. Now I can choose between the original YM3526 'OPL'
chip, or the enhanced PC-style YM3812 'OPL2' chip I took out of an old PC
sound card. This provides extra waveforms in addition to the usual FM
synthesis sines. I'll be checking them with an oscilloscope later to see
how they compare with the ones in the PC documentation.

The procedure is very simple; just take out the old chip and put the new
one in; pinouts are exactly the same and the new one is entirely software
compatible with the old - well, in the sense that it only implements extra
registers, which by default are disabled - any software for the old chip
stupid enough to go around poking at unimplemented addresses may of course
be broken, but since there's hardly any software for the Sound Expander
anyway, I think that's hardly a problem! ;)

It works fine with the supplied software at least; next I'll try to write
a little program in a combination of BASIC and machine code to give you
access to the registers and play with it like a cheap FM synth.

Any other Sound Expander owners wishing to try out this mod should find an
old Adlib or SoundBlaster card (or early versions of SoundBlaster Pro) and
look for a YM3812 chip; the card I used was in fact an Aztech Sound Galaxy
(original SB compatible) which is now rendered utterly useless by the
whole operation.

But then again, it always was... :)


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