SID weirdness.

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Prime
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SID weirdness.

Post by Prime » Sun Nov 20, 2011 10:47 pm

Hi all,

I've been playing with my BeebSID along with some SIDs scaved off C64 motherboards (bought a job lot of 6 C64 boards, got two complete working boards and 5 out of 6 SIDs working, the 6th may work, but is still soldered to it's board !).

Anyway I have noticed something odd, the original SID I was using was a 6581 manufactured by CSG, with an 1989 date code. The ones off the C64 boards are all MOS maufactured with 1983/84 datecodes.

The odd thing is that with BeebSID disk 5 (the film themes), the 1989/CSG manufactured chip does something weird playing "The great escape", the first 3 notes are loud and then the rest of the tune is much quieter. The other tracks on the disk also seem quiet. Using any of the MOS SIDs or for that matter the 8580(?) SID from my C64C, the tracks all play louder, and don't have the variation in volume.

Also as a matter of interest the C64 boards just use standard disk caps rather than polystyrene ones.

Now wonder if I could make a 1MHz bus interface for my Atom, or even the Dragon as the 6809 bus is close enough to the 6502 :)

Cheers.

Phill.

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MartinB
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Re: SID weirdness.

Post by MartinB » Sun Nov 20, 2011 11:06 pm

Phill wrote:Also as a matter of interest the C64 boards just use standard disk caps rather than polystyrene ones.
Not using polystyrene caps in audio circuits is always just a cop out usually justified on cost and availability grounds. These caps have everything going for them in terms of their key performance parameters and their preferred use in audio applications is well documented. Whether or not yer average ear can tell the difference in a simple application such as BeebSID is debatable but in high-end audio kit, including the major SID-based synthesisers, I doubt you'd find anything other than polystyrene in the relevant parts of the system.

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danielj
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Re: SID weirdness.

Post by danielj » Mon Nov 21, 2011 9:43 am

Prime wrote: The odd thing is that with BeebSID disk 5 (the film themes), the 1989/CSG manufactured chip does something weird playing "The great escape", the first 3 notes are loud and then the rest of the tune is much quieter. The other tracks on the disk also seem quiet. Using any of the MOS SIDs or for that matter the 8580(?) SID from my C64C, the tracks all play louder, and don't have the variation in volume.
One of the filters is screwed? Have you tried out the sid-test program I popped up over on retrosoftware? I'd be interested to know if that highlights a marked difference?

d.

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flynnjs
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Re: SID weirdness.

Post by flynnjs » Mon Nov 21, 2011 10:46 pm

One of the filters is screwed?
Veering off-topic-ish, but if this is the case and it
joins the SID graveyard, does anyone know why so
many SIDs are dead?
Are we approaching a reliability cliff where a large
proportion of '80s silicon is going to pack up?
I know Furber made some comment in '09 that
he was amazed that so many Beebs still had
silicon that worked at all.

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retroclinic
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Re: SID weirdness.

Post by retroclinic » Mon Nov 21, 2011 11:04 pm

It depends heavily on the manufacturing process. A very good example of this is Fujitsu LS logic (and SGS brand made at the same plant) in the late 80s and early 90s, used very heavily on Sega arcade PCBs.

If the PCBs have spent their life in poor storage conditions, not excessively damp, but not in proper anti-static dry storage, then when these boards are powered up, I've found that most if not all of those brand of LS logic have died, or die in a cascade within a few hours of being on, whereas other brands will still be functioning. It's not always 100% the case, but when I look at boards of that era, I go straight to any Fujitsu/SGS ICs and check the output pins to see if they're up the spout first.

I suppose a lot of it is all about how the chips have been stored and used, but then again, some sillicon can just be inherantly unreliable, depending on how much care was taken during it's manufacture. The reliability of beeb boards really is amazing, I find very little problems on boards that I pull out to refurbish, and those with faults are usually something simple, and only ever one or two chips that have failed. Sockets are more problematic than anything else. Conversely, I've had Sega boards where I have to replace 75% of the LS logic ICs, and on some boards that 50+ chips.

Mark.
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