[sdiy] D to A convertor for wavetable osc

[Eric Brombaugh]

Adam Schabtach wrote:
>> I've had great luck with the Cirrus/Crystal CS43XX series of 
>> I2S stereo DACs.
> 
> Have you tried using these to generate DC control voltages? The spec sheet
> implies that they work down to 0Hz, but I have it in my head that
> sigmal-delta DACs don't do DC.

I've used the CS4334 (5V, 8-pin SOIC) and CS4344 (3.3V 10-pin TSSOP) and 
they both work down to DC. Or close enough that I can't tell - I've used 
them for LFOs with periods ~30 seconds with no visible distortion or 
attenuation. Based on that I can't imagine that they wouldn't hold a 
voltage indefinitely.

The main problem with the CS4334 is that the voltage you get for data = 
0x0000 (Vq) is internally generated and isn't available on a pin, so if 
you want to DC couple it you need to guess at what to subtract out. It's 
not too big a deal though.

The CS4344 fixes this problem by providing Vq on a pin so you can use 
that as the 0 reference in a downstream buffer stage to get a true 
bipolar signal.

Eric