[sdiy] Interesting blog with Roland Alpha Juno details

[rburnett at richieburnett.co.uk]

The DCO is entirely digital.  There are no integrator capacitors around 
the chip, and you can see the stepping in the sawtooth output on a 
spectrum analyser when generating really low pitch notes.  You can also 
see aliasing in the spectrum when you generate really high notes, but 
it's quite a long way down in amplitude due to the multi-MHz sample rate 
at play.

-Richie,



On 2024-11-01 16:35, John via Synth-diy wrote:
> Oh, very neat. I've long wondered about the stranger waveforms on the
> Alpha Juno; I'd suspected they might be an indication that the "DCO"
> was actually pure digital and the sawtooth constructed from weighted
> binary outputs (as on the Poly-800,) with the weird stuff created by
> selectively ANDing some of the bits, but looking at his scope outputs
> there's a definite smooth slope to the sawtooth even on the chopped-up
> versions, so it appears that's not the case. Interesting!
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