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<li style="font-size: 11pt; list-style-type: "➢ ";"><span style="font-size: 11pt;" class="elementToProof">OTOH I would love to see someone doing 100-outs MUX with single DAC
</span><span style="font-size: 11pt;" class="elementToProof">spitting 16-bit precision at 1Msps
</span><span style="font-size: 11pt;" class="elementToProof">Roman</span></li></ul>
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I think the uneven capacitance alone to each of the S/Hs would make this impossible. And the noise from all the control signals to the gates are almost bound to cross critical tracks.<br>
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<div id="divRplyFwdMsg" dir="ltr"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Synth-diy <synth-diy-bounces@synth-diy.org> on behalf of Roman Sowa <modular@go2.pl><br>
<b>Sent:</b> 08 December 2023 14:07<br>
<b>To:</b> Danjel van Tijn / intellijel <danjel@intellijel.com>; SDIY <synth-diy@synth-diy.org><br>
<b>Subject:</b> Re: [sdiy] Generating a large number of CV outputs</span>
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<div><span style="font-size: 11pt;">I'm triggered, because that's something I was recently evaluating (but<br>
don't feel like doing for various reasons).<br>
The DACs can be as cheap as they wish, but will never be S&H-MUX cheap.<br>
Surely there are cheap excellent 12-bit DACs now with price per channel<br>
below $1 but that's still a lot of money. You could also consider<br>
96-channel DAC and just don't bother designing huge circuitry around it,<br>
but not only it cost $80 in singles but also is huge BGA monster.<br>
<br>
I reckon you're not doing it for space or military, so IMHO the mux way<br>
is the only way still.<br>
<br>
With 100 outs at "few" kHz update rate you're struggling with 1us analog<br>
MUX settling time, and when you say 16-bit, that makes me shiver.<br>
What you can do is split it to couple of separate muxes with their own<br>
DACs, and feed them sequentially. Huge analog circuitry with lots of<br>
muxes, opamps, caps and countless meters of traces will be happier<br>
getting an update every 10us rather than 1us. Interlace DAC update<br>
moments with MUX address changes to make sure new output is well settled<br>
before MUX opens.<br>
Also, with multiple DACs and MUXes you can spread the circuitry on the<br>
board so DAC's opamp will not have to drive too much, but only a couple<br>
of MUXes gathered around it.<br>
<br>
OTOH I would love to see someone doing 100-outs MUX with single DAC<br>
spitting 16-bit precision at 1Msps<br>
<br>
Roman<br>
<br>
<br>
W dniu 2023-12-08 o 01:35, Danjel van Tijn / intellijel pisze:<br>
> What is the current ideal way to generate a large number of CV outputs<br>
> from a single CPU?<br>
><br>
> Let's say I wanted to generate 100 outputs with an update rate of a few<br>
> kHz and an equivalent bit depth of 12 or 16 bits.<br>
><br>
> I know that back in the day when DACs were extremely expensive, the<br>
> designs would use a single DAC and then demux to a bunch of S&Hs.<br>
><br>
> Now that DACs are cheaper, is it better to chain a bunch of 8- or<br>
> 16-channel DACs?<br>
><br>
> Or would it make more sense to use an FPGA and create a giant<br>
> multi-channel 1-Bit DAC?<br>
><br>
> Looking at some Elektron hardware teardowns it appears that they are<br>
> using the latter approach.<br>
><br>
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