[sdiy] using a dac as a digitally controlled amplifier

[Tom Wiltshire]

I've done similar things using unipolar multiplying DACs (MDAC) to fake a genuine bipolar MDAC. I was generating a digital LFO signal, and then using the DAC to control the LFO Depth. Clearly, changing the depth changes the LFO offset, but if you feed half the LFO Depth CV to a differential amp along with the DAC output, it will correct the shifting offset.

 Much simpler for audio is to get a proper bipolar MDAC. They do exist. Multiplying DACs don't *only* deal with unsigned values, just "often".

> On 4 Aug 2024, at 19:49, chris <chris at chrismusic.de> wrote:
> 
> The problem with that may be that (AFAIK) multiplying DACs only multiply
> unsigned values.
> 
> I once did a crude attempt with an MCP4922 (two multiplying 12 bit DACs).
> I level shifted the input so that ground level was at 2.5V. Varying the
> DAC value also shifts 2.5 input ground level. 
> IIRC, I usedone channel for variable level shifting. 
> Messy
> 
> Could be possible with a DC offset and AC coupling after the DAC
> 
> Chris
> 
> 
> 
> On Sun, 4 Aug 2024 13:13:42 -0400 Benjamin Tremblay via Synth-diy
> <synth-diy at synth-diy.org> wrote:
> 
>> Is there any practical application for synthesizers to pass an analog signal in as a reference voltage to a DAC?
>> 12 bit DACs are pretty cheap these days, but VCAs aren’t expensive either. 
>> Aside from cost, why would I want to use a DAC as a “DCA”? 
>> 
>> I can imagine making a state variable filter using a dual DAC as the ‘gain' stages.  
>> It’s the kind of thing I would try just to see how well it worked… 
>> 
>> I suppose you inject one or more DACs into an oscillator to directly control pitch and waveform, some kind of DCO where stability and simplicity are cost-effective. 
> 
> ________________________________________________________
> This is the Synth-diy mailing list
> Submit email to: Synth-diy at synth-diy.org
> View archive at: https://synth-diy.org/pipermail/synth-diy/
> Check your settings at: https://synth-diy.org/mailman/listinfo/synth-diy
> Selling or trading? Use marketplace at synth-diy.org