[sdiy] Innovative Oscillator Design (or not ?)

Roman Sowa modular at go2.pl
Tue Apr 9 13:20:44 CEST 2024


Typical DCO does not modulate charging current for integrator but 
provides constant one. So the idea is not to apply varying voltge or 
current, but switch it in time between one value and zero.
Obviously the switch to be used here is the biggest challenge to make it 
work good, but that's not the point.

Roman

W dniu 2024-04-09 o 11:52, cheater cheater pisze:
> I'm having trouble understanding how it is different from a juno alpha
> style DCO. i get that it's different, i just don't know how.
> 
> On Tue, Apr 9, 2024 at 10:45 AM Roman Sowa via Synth-diy
> <synth-diy at synth-diy.org> wrote:
>>
>> This is not doable with simple PWM. You talk about closed loop control,
>> but then it will have to make huge corrections from cycle to cycle,
>> leading to blurry, modulated waveform. Assuming 10kHz range, the low end
>> using 8-bit PWM is like 40Hz, and next step is one octave higher. To
>> make it work you have to constantly measure the VCO output voltage and
>> not just the cycle period and adjust PWM multiple times during single slope.
>> The slopes of the triangle will not be smooth anyway, but steppy. The
>> steps will have the slope the same as the highest frequency triangle,
>> that is when PWM is at 100%.
>> PWM frequency is independent of VCO frequency, so at some frequencies
>> you might expect intermodulation that will blend all over audio band.
>>
>> Interesting idea and I don't hink I have ever seen it, although it
>> highly resembles switched capacitor filter. Who knows, maybe there is a
>> way to use commercially available switched cap filter ICs to work as
>> VCO. But IMHO there is a lot more other simpler options to make VCO.
>>
>> How about using common $2 Sigma-Delta DAC to control the integrator
>> switch? It makes it so much easier. Wide range precise control of 24
>> bits, every note is kept stable with single write to the DAC. The MCU
>> only writes the DAC on pitch change, and possibly check tuning from time
>> to time but it will not drift at all if you use proper integrator parts.
>>
>> Roman
>>
>> W dniu 2024-04-09 o 08:52, M J Bauer via Synth-diy pisze:
>>> Attn: Synth-DIY community...
>>>
>>> A while back (2022), I had an idea for an oscillator design which could
>>> be used in modular or hybrid synth's, but I have not yet tested the
>>> concept. The oscillator may be digitally controlled or voltage
>>> controlled, or both at once. I'm not sure if this technique has already
>>> been tried and proven. I haven't seen any evidence of it, so I would be
>>> grateful if anyone with a greater knowledge of the art can tell me if
>>> this is a novel idea, or a concept that has appeared before. (See
>>> attached summary.)
>>>
>>> M.J. Bauer
>>>
>>>
>>> ________________________________________________________
>>> This is the Synth-diy mailing list
>>> Submit email to: Synth-diy at synth-diy.org
>>> View archive at: https://synth-diy.org/pipermail/synth-diy/
>>> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
>>> Selling or trading? Use marketplace at synth-diy.org
>> ________________________________________________________
>> This is the Synth-diy mailing list
>> Submit email to: Synth-diy at synth-diy.org
>> View archive at: https://synth-diy.org/pipermail/synth-diy/
>> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
>> Selling or trading? Use marketplace at synth-diy.org


More information about the Synth-diy mailing list