How do DACs prevent EMI in the line out circuit?

[LostArk]

Forgive my ignorance, but a DAC must output a signal to an analog circuit at some point. Isn't it true that analog circuits are subject to picking up EMI? That's not to say that digital circuits aren't susceptible, just that in theory interference doesn't affect output (e.g. ethernet). So, if a DAC is housed in a box with noisy components such as an SMPS power supply, wouldn't at least some of that noise be present in the analog line out signal? Is that what the SNR spec is referring to? I'm trying to figure out how paranoid I have to be about using the built-in DAC on my integrated amplifier (wrt interference from the main transformer etc), VS buying a DAC with an outboard linear PSU etc. Thanks!

 

[solderdude]

Forgive my ignorance, but a DAC must output a signal to an analog circuit at some point.

Yes, that's its main purpose. You are hereby forgiven and are granted absolution.

Isn't it true that analog circuits are subject to picking up EMI?

Yes, it can, but depends on the level and nature of the EMI as well as possibly shielding, PCB layout and off-board wiring and possible taken counter measures (shielding, HF filtering etc) and sometimes usage of ferrites.

That's not to say that digital circuits aren't susceptible

Indeed, when frequencies, amplitudes and entry points in a circuit have reached certain values these circuits too can be susceptible.

So, if a DAC is housed in a box with noisy components such as an SMPS power supply, wouldn't at least some of that noise be present in the analog line out signal?

Not necessarily but sure, when a DAC is not 'competently designed' there sure could be some of it visible both in common and differential mode.

Is that what the SNR spec is referring to?

No, it refers to the distance between the max output voltage and the total 'noise' level when no signal is present. This includes everything in the audible band so also mains hum and its harmonics, unwanted signals (where ever they originate from) as well as noise.

I'm trying to figure out how paranoid I have to be about using the built-in DAC on my integrated amplifier (wrt interference from the main transformer etc), VS buying a DAC with an outboard linear PSU etc. Thanks!

Do you hear any noises other than some faint hiss when you have the volume fully open with a digital '0' playing (there are test files for this) ?
If not stop being paranoid. When you do you need to rule out possible ground loops or have it measured or buy another device.

And finally to answer your burning question "How do DACs prevent EMI in the line out circuit?".
They do this by proper engineering (PCB layout, wiring, measures, filtering).
Some fail however, a lot of them don't.