Commodore 64C sound question...

[dave4shmups]

I like the design of the Commodore 64C a lot better then the original Commodore 64. But is the sound as good as the original model? I think there was some kind of modification made to the SID in the Commodore 64C, but I'm not positive about that.

[Unseen]

I like the design of the Commodore 64C a lot better then the original Commodore 64. But is the sound as good as the original model? I think there was some kind of modification made to the SID in the Commodore 64C, but I'm not positive about that.

That's slightly complicated... There are two main variants of the SID, the 6581 and the 8580 (there are 6582s, but they are just 8580s internally). The first one exists in quite a few revision which all sound a bit different and due to process variation there is even a sound difference between 6581s of the same revision (mainly in the filters). The 8580 is much more consistent. The main difference between the two is how the filters influence the sound and the fact that the 8580 has much lower DC bias, which reduces the volume of some styles of sample playback. For some tunes which use "not officially documented" register combinations (more than one waveform turned on at the same time), both chips behave quite diffent. All these differences basically mean that tunes composed for one chip may not sound as good as tunes composed for the other one - but this goes both ways. As far as I know the current scene tends to mainly target the 8580, sometimes with a "fallback mode" that improves sound on the old 6581.

Unfortunately you cannot tell which SID is in the computer just by checking if it's an old-style "breadbin" C64 or a newer "flat" C64 (*). The 8580 was only used on the newest PCB revision (Assy. No 250469, sometimes called "short board") while the 6581 was used on all previous PCBs. Commodore however has fitted both styles of case with both types of PCB. It is possible to use either SID in a PCB that was meant for the other one, but it needs some modifications on the PCB because the filter capacitors are different and the SID needs an auxilary supply voltage that is different for the two chips (12V on the 6581, 9V on the 8580).

(*) You can tell the difference by looking into the user port though unless it's one of the rare-ish C64s with full metal shielding. If you can see the keyboard connector near the left edge of the board, it's an older one that should have a 6581, if the connector isn't there it's a 250469 which should have an 8580.