Commodore SID chip variation videos

If you’ve been watching my streams or VODs recently on Twitch, you’ll have seen that I’ve got back into Commodore 64 stuff.  Since I only stream real hardware like the hideous poser that I am, I got a real C64.  Then I got a backup.  Then because I wanted to try a pseudo SID setup I bought a cheap newer type to gut for parts.  Then because that one turned out to be corroded inside and not as useful for parts as I’d hoped, I bought another new type.  Then I found one of my original ones had a bad sound chip, then….

Anyway, at this point there are four working C64s in the house and before I start cannibalising one and selling the best of what’s left as the third unit I decided to compare the various sound chips.  I have two 250466 ‘old’ C64Cs and two new 250469 newer types.  These came with the 6581R4AR and 8580 SID chips respectively.  SIDs contain some analogue components, and from new (and over time) they don’t all sound exactly the same.

For testing I used a C64SD unit loading Sanxion from a SD card, because it doesn’t take long to load and has excellent music which does use the filters in places.  The videos were poorly captured with OBS and then had to be converted due to a settings error, then lined up in Sony Vegas to try to get the sound in sync as much as possible.

Here are the two newer machines with 8580s, the one on the left is from 1989, on the right is 1991.  They’re very similar which is expected from this chip, but there are still differences here and there which cause some sounds to move or be more apparent in one channel. Interesting note these have a problem with video voltage not being as high as it should be – watch the left side as it draws the title screen.

And here are the older machines with 6581R4AR, these sound much more different especially on the title tune. This was the final incarnation of the 6581 and sounds closest to the 8580 in terms of ‘punch’. These have a better quality of video output but are more prone to colour band artifacts, I’m planning to try a mod to remove the modulator and replace with a simple s-video amp soon which should clear that up. The one on the left is my ‘main’ C64 which is getting all the upgrades and mint parts. Bear in mind, despite the differences this pair of chips actually have the same batch code, they didn’t even make that many R4AR versions.

And just for fun (soon this will be implemented in hardware with a MIXSid board), here’s the better of the new ones on the left, and the main older C64 on the right. It’s hard to find parts of the audio where they sound the same on the title tune. Also note the vastly better video output of the older model.