Posted By
TLC
on 2022-08-26
17:18:59
|  Re: Solder's SIDcard Replica
@SukkoPera - back in the "old days" I shared a couple of mails with Solder, and he explicitly said that he used the standard CMOS i.e. the CD4520, not bipolar, not some highs speed CMOS family, because this was slow "enough" so that the thing would just work. (Definitely a hack, but it did work. The whole thing i.e. feeding the SID with data from a 2MHz bus / especially expecting the SID to supply data to a 2MHz bus is sort of a dirty hack anyway.)
When I'm at it, I should note that the original card has a slightly bad audio output buffer. That one i.e. things around the "second" NPN transistor should probably be revised. (--> Expect distortion at standard volume levels.) The "first" NPN transistor is AFAIR wired similarly to that of standard 250469 (late C64) boards, so, that one should be fine. Oh, and one more hint - the pull-down resistor connected to the SID's audio in pin is merely added to provide "digi" capability to the 8580 SID - but it also adds distortion, because it pulls the internal mixer in the SID "off" from it's intended operating point. Maybe it's wise to disconnect this resistor for the time of arranging distortion checks.
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