[sdiy] using a dac as a digitally controlled amplifier

[brianw]

I would expect that a DPOT would not allow its setting to be updated anywhere near audio sample rates.

A typical DAC is designed with the assumption and/or requirement that the Reference Voltage be constant. There is usually some sort of (external) filtering to remove as much noise above DC as possible. At the very least, there is usually no support for high bandwidth response between the VREF input and the main output.

An MDAC, in contrast, is designed with the assumption that the Reference Voltage will be changing. The bandwidth supported is something you would need to find in the corresponding data sheet.

In a way, a DPOT flips the two. The "Reference" Voltage input is expected to be an AC signal, and audio rates are very common. Meanwhile, the digital-controlled section probably only allows changes at rates well below audio frequencies. A number of DPOT designs actually have internal zero-crossing detection, such that every volume change is delayed until the next zero crossing. If you were attempting FM with such a chip, the results would be very distorted compared to expectations.

Brian


On Aug 5, 2024, at 11:38 AM, Mattias Rickardsson <mr at analogue.org> wrote:
> Is this MDAC "trick" more or less equivalent to using a "digital potentiometer", or are those ICs significantly different?
> 
> /mr