[sdiy] Re: Prophet 08 (was Roland DCOs)

[Tom Wiltshire]

On 27 Feb 2008, at 15:39, karl dalen wrote:

> --- Dave Manley <dlmanley at sonic.net> skrev:
>
>> There are still a few
>> mysteries - I never got around to figuring out what that PA381  
>> dual VCA
>> is doing, or what the mystery chip is next to the DAC.
>
> Most likely a buffer for the DAC since they often are not capable
> to deliver the current to the storage caps.The PA381 may be used as
> final volume setting + velocy.

Don't forget that the photo shows TWO voices, so it's probably one  
VCA per voice.

>
>> I was also
>> surprised by the ceramic chip caps used in the filter, after hearing
>> discussion about the suitability of different cap materials for audio
>> use (makes me wonder if the Moog LP uses chip caps in their filter).
>
> Its peculiar indeed, i have studied the Andromeda and it seams to
> use ceramic caps as well.

Although it might not be a great idea, commercial synths often seem  
to use it as a way to keep costs down. I can't think of any other  
reason why you'd want to put ceramics in there.

>> There was also the unresolved issue about what exactly the  
>> "oscillator
>> slop" parameter does. Regarding the code, you could always get a hold
>> of one and plug into that RJ-45 debug port ;-)
>
> Does the DSPIC have memory protection or tampering blocking function?

Yes, it can do, and in this case probably does. You could probably  
write your own code from scratch and upload that instead, but  
altering what DS has done isn't going to be easy. More's the pity -  
I'd LOVE to...

Regards,
Tom