>>>>> "Levente" == Levente Harsfalvi <firstname.lastname@example.org> writes: MV> chain SIDs by connecting the AUDIO OUT straight to EXT IN MV> (strangely enough the C128 PRG doesn't mention this...) but that MV> didn't work for me... >> This is from memory, and may be completely wrong, but don't you >> have to set a bit in some register to enable EXT IN? Levente> No. Only, if you wanna filter the signal in EXT IN. Else, SID Levente> passes it completely to Audio out. Unfortunately the master volume does affect the output of the second SID. :/ Levente> But else, I see there are at least some DC couplers in the Levente> C64, placed to the EXT IN and to the output lines. I won't Levente> beg, but the problem should have been some kind of dc offset Levente> problem. To quote the PRG: EXT IN: "...The input impedance of this pin is on the order of 100 kohms. Any signal applied directly to the pin should ride at a DC level of 6 volts and should not exceed 3 volts p-p. In order to prevent any interference caused by DC level differences, external signal should be AC-coupled to EXT IN by an elctrolytic capacitor in the 1-10 uF range. As the direct audio path (FILTEX=0) has unity gain, EXT IN can be used to mix outputs of many SID chips by daisy-chaining. The number of chips that can be chained in this manner is determined by the amount of noise and distortion allowable at the final output." AUDIO OUT: "...The output level is set by the output volume control and reaches a maximum 2 volts p-p at a DC level of 6 volts. A source resistor from AUDIO OUT to ground is required for proper operation. The recommended resistance is 1 kohm for a standard output impedance." After cranking up the volume a bit on my monitor i noticed that the SIDs were indeed producing sound, but with an audible 50-Hz-ish hum. As I haven't put a suitable capacitor on EXT IN this isn't all too strange... What does AC-coupling mean? Sticking a capacitor between EXT IN and Vdd? Levente> (If you, guys are sure that SID's can be connected by AUDIO Levente> OUT and EXT IN without any extra parts then I guess I was Levente> wrong. Well, the C64 Programmers Reference Guide does mention that this is indeed possible, though it doesn't provide very many details. -- ___ . + . . . Per Olofsson ._|___|_, . . . . . + . . o o-o + . + MagerValp@Goth.Org . . + + + . - . . . o + . . . " + + . http://www.cling.gu.se/~cl3polof/
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