[sdiy] Evolver DCO construction (was: Pro one clone)

[Tom Wiltshire]

On 9 Dec 2008, at 16:20, Tom Arnold wrote:

> On Tue, Dec 09, 2008 at 01:11:36PM -0000, Julian wrote:
>> The DSI website states that the DCOs on the evolver are 2 analogue  
>> and 2 digital per voice, however, the person whom i was speaking
>> with was somewhat dubious of this statement, as they had opened up  
>> an evolver, and said that they could see no suggestion of
>> anything other than DSP chips coupled to DACs.
>
> I got to see one of the Evolver prototype boards at an AES meeting  
> a while
> back.  It had a Marion chip on it.  Basically a CEM with I think  
> two VCOs
> and two Filters.  If I remember it actually had two, but one the  
> VCOs were
> not used on.

There's been discussion of this topic here before. The suspicion at  
that time was that the analogue oscillators are DCOs. I don't think  
I've ever seen a claim that they are VCOs, only that they are  
analogue, which DCOs are (No DAC, and continuous time output - that's  
analogue). The dsPIC processors used for each pair of voices have 32- 
bit digital counters to provide highly accurate reset pulses to the  
basic ramp core DCO. So much so that a "oscillator slop" parameter  
got added.

The archive is here:

http://search.retrosynth.com/synth-diy/

A search for "Roland DCOs" will turn up the most recent discussion,  
but "DCO" alone turns up a lot more.

Regards,
Tom