[sdiy] DCOs

[John Ames]

On 10/11/16, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> Interestingly, I think the "DCO chip" in the Roland Alpha Juno series synths
> (and MKS-50) is actually an entirely digital chip that uses NCO
> (phase-accumulator) techniques.
>
> I've had discussions with Tom Wiltshire about this, and although the Roland
> documentation calls it a DCO, there are no integrator capacitors anywhere
> around the "DCO" chip on the PCB, or any other signs of analogue integrators
> operating under digital control.  There are, however, a few other things
> that point towards an entirely digital solution...
I just picked up an HS-80 (home version of the Alpha Juno 2) and I've
been wondering about this myself, because the oscillator (especially
the sawtooth) sounds absolutely nothing like any conventional DCO I've
ever heard. The only thing comparable that I can think of is the Casio
HT-6000 (and, I presume, their other "Spectrum Dynamic" synthesizers.)
That was nominally a DCO as well, but sounded closer to some kind of
odd digital construction, much like the Alpha Juno does, and it also
had a variety of very unusual waveshapes.