[sdiy] SID chips

[Batz Goodfortune]

Y-ellow Ignatz 'n' all
         Just in case this is of use as an avenue of approach. A few years 
back Digikey were selling brand nu 6581s (Actualy the latter 6582s I 
think.) but they wanted US$18.00 each for them. (Ouch!)

So you might wanna weigh up the cost of getting ol' C64s shipped against 
the cost of new ones.

They are still being made and there are more than a few commercial products 
out there using them. 2 actual ready built MIDI synths and a hand full of 
kits last time I looked. But it was a while back.

Whilst I've always been threatening to do a SID synth myself, I haven't 
actually plucked up the courage to date. One of the reasons is that they 
are REALLY designed to slip onto a 65xx/moto-bus only. They are 
synchronized with the one meg clock. It's relatively easy to write to them 
but a bugger to read back from them if there's no hard bus sync. I have 
little to no experience with the 65xx processors and I don't feel the need 
to jump on yet another learning curve.

This may seem like a no contest. Just write data to the sucker and get 
sound out. But there's a catch. There is no actual routing from the LFO to 
the filter. The way you do that is in software. Read back the instantaneous 
status of the LFO and then throw it back at the filter control. But if you 
can't read back from the chip then you can't do that. So the tough 
decisions come when you figure you need to ignore your LFO and do that in 
software. More complexity.

It's almost worth just taking the entire C64, re-boxing it and trying to 
throw the software into an EPROM or something. It won't be polyphonic but 
it might be a good trade off for you.

You might even be able to butcher a couple into one box and skudge some 
MIDI routing between them or something.

For me though, my main interest was in using pairs of SIDs for stereo. Also 
using the audio inputs to process signals from an OPL3 FM synth chip. 
Imagine that in a box with 8 voices? I'm just way to ambitious for my own good.

Anyway, Hope this is of some use to you.

Be absolutely Icebox.

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