[sdiy] Chris Synths polysynth

[cheater cheater]

That's a good consideration, Mike. While 100*10 cents per module is
fine, 100*1 euro per module is not.

On Sat, Oct 23, 2021 at 12:46 PM Mike Bryant <mbryant at futurehorizons.com> wrote:
>
> Whilst the EDN circuit is obviously higher performing, the OP was after 100s of DACs so adding extra MCU ports and a S/H probably isn't going to meet his cost target, whereas a simple alteration to the PWM encoder may give higher performance for free.
>
> That said, I agree Arturia not doing something like the EDN channel for a single channel output on one of the most important functions of the keyboard is over cost-cutting.
>
>
> -----Original Message-----
> From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Roman Sowa
> Sent: 23 October 2021 08:06
> To: synth-diy at synth-diy.org
> Subject: Re: [sdiy] Chris Synths polysynth
>
> Or why not simply make sigma-delta modulator like in any audio DAC today?
> Shouldn't take much of FPGA resources.
>
> This morning I came up with an idea of PWM decoder giving solid output after single PWM cycle using 2 opamps and 4053, but it looked so obvious that I thought it had to be done before, so did some googling and found this, which is basicaly the same concept, but overly complex:
> https://www.edn.com/pwm-dac-settles-in-one-period-of-the-pulse-train/
>
> Roman
>
> W dniu 2021-10-22 o 15:36, Mike Bryant via Synth-diy pisze:
> > Good links.  They also led to this one where the writer suggests bit-reversing the counter to give a simple form of PDM replacing PWM.  Definitely an idea I'll bear in mind.
> >
> > https://www.edn.com/three-paths-to-a-free-dac/
> >
> >
> >
> > -----Original Message-----
> > From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of
> > Steve via Synth-diy
> > Sent: 22 October 2021 14:24
> > To: synth-diy at synth-diy.org
> > Subject: Re: [sdiy] Chris Synths polysynth
> >
> >
> > I found these articles interesting, but have not tried in practise
> >
> > https://www.edn.com/cancel-pwm-dac-ripple-with-analog-subtraction/
> >
> > https://www.edn.com/fast-pwm-dac-has-no-ripple/
> >
> >
> >
> >
> > Am 22.10.2021 um 12:15 schrieb Vladimir Pantelic via Synth-diy:
> >> Arturia uses a dual PWM scheme in all of the their Keystep and
> >> Beatstep products, basically following the circuit laid out here:
> >>
> >> http://www.openmusiclabs.com/learning/digital/pwm-dac/dual-pwm-circui
> >> t
> >> s/index.html
> >>
> >>
> >> it works nicely, BUT also introduces a >4ms slew on all CV outputs,
> >> no biggie if driving an analog synth and it gets hidden in the
> >> attack, but a real nuisance if it gets sampled by a digital module...
> >>
> >>
> >> On 10/21/21 11:34 AM, Tom Wiltshire wrote:
> >>> Here’s the correction:
> >>>
> >>> Imagine you have a DAC with 4-bit resolution. If we use one with a
> >>> step-between-values of 1V, and then add the output of another with a
> >>> step-between-values of 1/16th of a volt, we can make an 8-bit DAC.
> >>> That’s basically what you do with the PWM. The process is helped by
> >>> the very good linearity of digital-counter-based PWM as a method of
> >>> producing a voltage.
> >>>
> >>> I’ve used a 3-bit PWM scaled to produce 1V per step and a 4-bit PWM
> >>> scaled to produce 83mV per step to produce Pitch CVs. It worked very
> >>> well and produced good CVs across the 8 octaves. The reduced bit
> >>> depth of each PWM DAC means that the output frequency can be higher
> >>> without the PWM clock frequency having to be super-high, and this
> >>> improves the effect of filtering and the responsiveness of the CV to
> >>> changes.
> >>>
> >>>> On 21 Oct 2021, at 09:54, cheater cheater via Synth-diy
> >>>> <synth-diy at synth-diy.org> wrote:
> >>>>
> >>>> Correct me if I'm wrong, but I think summing two PWMs will just add
> >>>> 1 bit of depth.
> >>>
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