[sdiy] (Ab)use DAC as mixer?

[Rutger Vlek]

I'm also highly interested in MDACs for synth circuits (ever since I read how they're used in modern mixers). I feel it could be a nice and compact way to integrate digital control with an otherwise analog circuit. However, I really miss a good logarithmic MDAC. Does anyone know if they exist?

Regards,

Rutger
 

On 2 jun 2018, at 10:59, Tim Ressel wrote:

> Check out the datasheet for the AD7225 quad 8 bit MDAC. It has some cool examples.
> 
> --timmers
> 
> 
> On 6/2/2018 12:40 AM, sleepy_dog at gmx.de wrote:
>> Hey list,
>> 
>> this has been floating around in my mind for some years and I just remembered it again, so maybe some of you know something about this:
>> 
>> Would it be feasible to "abuse" a quad DAC with 4 independant Vref inputs as a 4 channel, digitally controlled  mixer?
>> 
>> I.e., you feed in 4 analogue voltages into the 4 Vref inputs, and control the volumes by writing digital output values.
>> The DAC I had in mind (TLV5620, price OK) only has 8-bit resolution and can stomach only 1/2 Vcc (1.65V I believe),
>> and it's positive-voltage-only, but that would do away with so much effort, in comparison to other solutions I'm aware of...
>> So If I have up to 4 audio sources which are already positive-only, *some* of which might come out of a DAC and not yet put through a reconstruction filter,
>> I could mix them all that way, and put only one reconstruction filter for the mix?
>> 
>> Yeah, it's for something like waveform mixing. Not planning on a high update rate for the digital volume levels (so far), just manual knob adjustment. Although I could imagine it might be cool to modulate that somewhat, if that doesn't get too noisy.
>> 
>> But the layman I am, I probably don't know about some horrible side effects that may have :-D
>> 
>> What can you say about the feasibility of those two aspects (and then others I may have overlooked):
>> 1) using a DAC this way in general
>> 2) my desire to skimp on the number of reconstruction filters, filtering the mix (I'm not sure I'd be using > 1 DAC output for audio, but keep it in mind as an option, when DAC resolution is moderate)
>> 
>> - Steve
>> 
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> 
> -- 
> --Tim Ressel
> Circuit Abbey
> timr at circuitabbey.com
> 
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