[sdiy] Chris Synths polysynth

[Mike Bryant]

If you really want cheaper DACs consider using PWM followed by RC smoothing.  And not an FPGA but something like the new Pi 2040 MCU which has lots of I/O programmability.  I suspect you could get about 20 to 24 8 bit resolution voltages for about a $1.  And when if you need more resolution combine two PWM outputs with different summing Rs.  12 or 13 bits linearity is easily attainable this way, maybe a little more.

I use such an arrangement for creating low-jitter audio PLLs.

Best to keep the MCU and smoothing RCs on a different PCB and shield it from everything else, and use a separate voltage regulator as well to keep crap off the supply.


-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of cheater cheater via Synth-diy
Sent: 20 October 2021 11:17
To: Roman Sowa
Cc: synth-diy
Subject: Re: [sdiy] Chris Synths polysynth

This is the situation I find myself in - trying to squeeze in as many cheap DACs and ADCs into an inexpensive FPGA as possible...
unfortunately I have to do all the learning from ground up :D

On Tue, Oct 19, 2021 at 11:15 AM Roman Sowa <modular at go2.pl> wrote:
>
> This is pretty amazing. And inspiring. Makes me wonder about the 
> meaning of life.
> I would love to see the inside video, showing all the boards and wiring.
> It might be easier then to guess who that is.
> This person is probably on this list giggling now quietly.
>
> As for DACs, this is always designer's choice and I will not argue 
> about that whatever was used. My personal view is that is comes much 
> cheaper in the long run to use good speced part with true linearity 
> than using various tricks to make $1 DAC with 64 LSB INL work in semi decent way.
>
> Do all CVs need good linearity? Sure they don't but since you have 
> already good DAC and S&H MUX to make pitch CVs, then why not use it 
> also for all other stuff, including LCD backlight dimmer?
>
> Roman
>
> W dniu 2021-10-19 o 09:56, cheater cheater via Synth-diy pisze:
> > https://sonicstate.com/news/2021/10/17/impressive-diy-poly-synth-in-
> > progress/
> >
> > This looks particularly cool, and the fact that Chris diy'ed it all 
> > really speaks to me. Some great sounds in the demos.
> >
> > What do you think of his choice of CV DACs? Do all synth CVs really 
> > need something as good as DAC7554 or even AD5676?
> >
> > I love the fact that the front panel is just a piece of white paper 
> > from a laser printer...
> >
> > That bare metal "aircraft panel" style construction really looks 
> > good to be honest.
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