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

[karl dalen]

--- Tom Wiltshire <tom at electricdruid.net> skrev:

> 
> 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.

Hmm, it could be that U17 Pa381 are used as a volume VCA for noise?
According to 08 manual and CEM33xx, mix between DCO happens inside
but noise are injected to filter from outside.But noise would be 
cheaper to generate inside DSPIC and feed straight into filter
trough a DAC ch. Perhaps its a expo converter for some parameters?
Which would be strange unless DAC are less then 12bits which in turn
would also be strange!

> >> 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.

It has been debated here in the past and its quite likely sound are affected
due to parameters of the ceramics,last time someone said someting about new
technology regarding ceramic cap's i cant remember who it was! Some one
should do a sonic A-B test!
 
> >> 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...

Hehe, im sure you would. :-)

Reg.
KD



      ___________________________________________________
Sök efter kärleken!
Hitta din tvillingsjäl på Yahoo! Dejting: http://ad.doubleclick.net/clk;185753627;24584539;x?http://se.meetic.yahoo.net/index.php?mtcmk=148783