Lowest ripple PSU for low power HTPC?

[necris]

Hello,

I am building an ultra-low power fanless audiophile system, dedicated just for stereo listening, with 600MHz Via C3, mini-ITX motherboard, single RME PCI sound card, integrated graphics and no mechanical drives. It is known that EMI/RFI noise affect the sound quality to considerable extent. Now I'm choosing the right PSU for this thing and I have several questions:
1. In PSU ripple graphic characteristics, which category is most important in my case? (3v, 5v, 12v)?
2. Which particular PSU would you recommend in my case? I bet my system wouldn't draw more than 50w max.
3. What would be a better option in terms of ripple - PicoPSU+12v wall wart adapter, or high quality 'regular' computer psu?
4. Having in mind low power usage, could I disable the PSU fan?

Many thanks in advance for your comments,

--
N

[blivit4]

The noise ridding on the PS voltage lines just isn't the thing that will generate noise in the audio, because in most cases isn't directly poewring anything (so to speak). The PS voltages will go through DC-DC converters and there will be filtering and bypass caps after the derived voltage are obtained.

Where most noise will come in is from is from the digital circuits getting into the analog audio section. Computers generate all sorts of EMI. Good design practice for handling mixed digital and analog signals is to employ separate ground planes, shielding and differential inputs for high common mode rejection for the analog circuits. How the MB is designed, components used and assembled will affect how much EMI is generated. A well designed audio card is the thing you need. A switching PS can certainly generate all sorts of EMI, and I would assume that good ones generate less.

A PicoPSU located outside of the computer case could certainly help introducing more noise inside the computer.

[necris]

Originally Posted by blivit4

Where most noise will come in is from is from the digital circuits getting into the analog audio section. Computers generate all sorts of EMI. Good design practice for handling mixed digital and analog signals is to employ separate ground planes, shielding and differential inputs for high common mode rejection for the analog circuits. How the MB is designed, components used and assembled will affect how much EMI is generated. A well designed audio card is the thing you need. A switching PS can certainly generate all sorts of EMI, and I would assume that good ones generate less.

A PicoPSU located outside of the computer case could certainly help introducing more noise inside the computer.

Thanks for reply. I guess if I choose a regular SM PSU, it would make sense to keep it outside the htpc box in order to reduce EMI?
My audio card is among the best available (RME), but I believe there is always room for improvement.

[blivit4]

If it's a good audio card and it's neater to mount the supply in the case than try that first.

[Zap]

How about using a digital audio output (SPDIF) and doing the D/A conversion externally? Translation: Hook up the PC to a receiver/preamp using a Toslink cable. Wouldn't that effectively avoid tainting the analog portion of the audio?

[necris]

I also have external DACs but that's not the issue. I like my RME pci soundcard analog out the most, so I'm trying to make environment for her as good as possible