SV: [sdiy] Mopho modulation DAC configuration, update rate, etc

[karl dalen]

2010-02-06 skrev Dave Manley <dlmanley at sonic.net>:
 As the
> frequency increases, the amplitude of waveforms decrease,
> and they look increasingly very non-ideal, and
> "stepped".  The voltage at the VCA control input is
> very poorly smoothed.  I'll try to get some scope
> captures and post them.

Interesting find.
 
> I didn't measure the min frequency.  The waveforms of
> course look much better at the lower frequencies, where they
> find their main use.
> 
> One annoying find: there's no way to completely shut off
> both VCOs.  The VCOs have a mix pot that lets you turn
> either off, or get a mix of the two, but you can't simply
> turn them both off.  The sub-oscillators do have their
> own independent level controls, as does the noise.  You
> can set the VCOs to their pulse wave, and set their duty
> cycles to 0 or 99%, but this wasn't reliable - it only shuts
> off the outputs completely at some frequencies.

This is very normal behaviour, you will find the exact same response in
the 3396. Somewhere i read that the VCAs in the low cost CEM chips
are very simple, Dough Curtis even refers to them as CA3080 like.

What's even more annoying are that he has skipped to implement
the mix waves and the spiky triangle wave! 

KD

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