[sdiy] CV/Gate delay project..

Brian Willoughby brianw at audiobanshee.com
Sat Jan 30 23:32:51 CET 2021

$1.44 Microchip MCP3221A 12-bit SAR
$2.02 Microchip MCP3465R 16-bit delta-sigma (not recommended)
$3.76 Cirrus Logic WM8196SCDS/V 16-bit 12Msps AFE
$3.98 Texas Instruments ADS7054 14-bit 1Msps SAR

The last one is part of a family of pin-compatible chips that range from 8-bit to 14-bit, 1 Msps to 2.5 Msps, and some are differential (which you won't need for CV). Chips are available in a couple of packages, but they're not through-hole.

I'm getting the impression that through-hole is in low demand, and thus is high cost. Personally, I just pay an assembly shop to handle the surface mount, and I don't worry about it.

You can use a quality analog multiplexer in front to share one high-speed ADC across multiple CV inputs. Some ADC have this mux built in.

The key is to have the analog signals separated from the digital signals, so that the ADC does pick up the noise from the microprocessor.

Brian Willoughby

On Jan 29, 2021, at 13:04, Jean-Pierre Desrochers wrote:
> You are right Tom..
> I'm looking now for at least 14bits ADC.. 16 bits will probably be.
> 12 bits DAC's should be fine.
> Maxim MX7705EPE+ 16 bits ADC could do (I think).
> As a note here:
> I saw that synthesizers.com has a quantizer module Q171
> that uses ADC/DAC process on incoming CV’s.
> Here are the specs:
> Specifications:
> Panel Size: Single width 2.125"w x 8.75"h.
> Quantization Method: Processor controlled ADC/DAC.
> ADC Inputs: 10-bit with precision buffer/scaler.
> DAC Outputs: 12-bit with precision buffer/scaler.
> Gate Inputs: 0-5V minimum, rising edge.
> Gate Outputs: 0-5V, 5ms on, 2ms minimum off.
> Power: +15V at 30ma, -15V at 30ma, +5V at 50ma.
> https://www.synthesizers.com/products/q171/q171data.pdf
> The CV inputs are fed to precision opamps OPA4277
> then routed to a micro MEGA644P’s  internal 10 bits ADC.
> The CV outputs are from 12bits DAC’s LTC1448.
> So… I’ve not tried this module but assumes it works correctly
> using a micro’s internal 10bits ADC and an external 12bits DAC.. ??
> Hmmm.

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