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Thread: Commodore 64 SID chip question (2 versions?)

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    ServBot (Level 11) k8track's Avatar
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    Default Commodore 64 SID chip question (2 versions?)

    So I was digging around on Wikipedia about the C64 and found this:

    Quote Originally Posted by Wikipedia
    There are two versions of the SID chip, the first version was the MOS Technology 6581, which is to be found in all of the original "breadbox" C64s, and early versions of the C64C and the Commodore 128. It was later replaced with the MOS Technology 8580 in 1987. The sound quailty was a little more crisp on the 6581 and many Commodore 64 fans still prefer its sound. The main difference between the 6581 and the 8580 was the voltage supply: the 6581 uses a 12 volt supply, while the 8580 required only 9 volts. A voltage modification can be made to use a 6581 in a C64C board (which uses 9V).
    Now I'm convinced that I must have a later version of the C64C. I bought one (used) back in 1988, but lost it in a lightning storm in 1993, when I promptly replaced it--I noticed that the keyboard was different (how the letters and symbols were printed on the keys, I mean). I wonder if I had one with the original chip first. I'm basing this on the fact that when I play SID tunes on SIDPlay on my Mac, the sound is really crisp and clear, and listening to the same music on my C64C, it sounds a bit blurry.

    Is the keyboard the key to distinguishing between these early C64C's with the "good" SID chip and the later ones with the "bad" one in it? I'd like to know which version I have--is there a website that shows the difference? I know I could get the original "breadbox" version to eliminate all doubt, but I really prefer the C64C keyboard (and my dust cover is specifically for that model anyway).
    "As you traitors roast in your own juices, I will be safely ensconced three miles below the earth's surface, listening to my wax-cylinder player and enjoying a delicious phosphate!"

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    Admitedly I've never seen more than one case for the C64C, though to be honest I've not handled a huge number, I always prefer the breadbin

    Having said that, there is the small possibility you got a breadbin in a new case; there was a case mod available to put your motherboard inside to make it look more like the Amiga (the basis of the C64C redesign).

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    I thought it was just me but I swear the C64 I have now sounds different (worse) than the 128 I used to have. It's hard to explain...it's like it hits sour notes or something.

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    Aside from the volume register "bug" (which is how samples were done) that was fixed in the 8580, there were other minor tweaks and changes made. The filters aren't quite the same either, and tunes that use them can sound much different when played on the opposite chip to the one they were composed on. Possibly what's happening here.

    What sort of C64 do you have now Kid Ice?

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    Quote Originally Posted by Kid Ice
    I thought it was just me but I swear the C64 I have now sounds different (worse) than the 128 I used to have. It's hard to explain...it's like it hits sour notes or something.
    Yeah, that's one of the many ways a SID can go bad. I've got one that sounds awful, way off on about a third of the notes. Couldn't stand listening to it long enough to determine if it was random or specific notes. It's a breadbox 64 so I think it's the original design.

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    The other point I was going to make has been mentioned by Wookie. Some SIDs are just plain awful, but that's just the way they've been made. First C64 I ever had was the best sound wise and I actually put the SID from it (when the machine died) into my next one. But it's a combination of things and it didn't quite sound as good. Almost but not quite. Certainly a lot better than the SID that was there before however that I took out!

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    Another possibility is the 50hz/60hz difference. I have a German breadbox that sounds noticeably different from my us systems. It's like you describe, the notes are sour or out of tune.

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    The way Commodore did things, it would be nearly impossible to tell what's under the hood based on external appearance. A 64C with the newer-style keyboard would most likely have one of the later motherboards in it (with the 8580 and other revisions), but it's entirely possible a 64C with an older-style keyboard could have the later motherboard too, because Commodore would use up whatever parts they had. I believe some early 64Cs shipped with breadbox motherboards, and I know breadbox 64s shipped with VIC-20 keyboards.

    And of course, if any particular machine ever went in the shop, all bets are off as far as what could be inside.

    I know besides the SID chip itself, the supporting circuitry could affect the sound. The capacitors that were used as filters varied over the years, and I seem to remember there was some disagreement over which ones sounded best, especially once the stereo SID mods became common.

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