Audio card noise


 Last year I got a new pc, which I replaced my old computer (obviously).
When I switched to the new pc I noticed a lot of noise in the audio signal.
As soon windows would start booting, that horrible noise would start.
The noise was purely interference from the pc, since it changed depending on what the pc was doing.
Also, the noise is present when recording with the sound card, so all of the recordings are ruined by the interference.  

I notice the same issue with a pc in my mothers office.
 On the other hand, my old pc had no such issues, the audio was always crystal clear with no noise, regardless what the pc was doing. 

 For now I have a semi solution to the problem. Since I built myself a homebrew usb dac wit the PCM2705 chip.
I also added a simple amplifier to it, and I also added a resistor and capacitor on the power line of the amplifier to try to isolate the noise form the usb power a bit.
 That helped a bit, but I can still hear it, especially when I plug a usb chip programmer, then I can hear a horrifying frequency, which makes me go crazy!. 

 I think that the main problem here is the power supply. Since I didn't want to spend too much money when building my pc, I got a power supply which was just fit, without too much extra power, and I think that that is the problem.
The power supply is probably giving out the necessary power, but it can't handle all of the noise made by the system. 

 So I think that the only decent solution here is to either try to get a better power supply, or to have a dac which is completely externally powered, so it doesn't get any interference from the pc.
But then again, modern 12V ac adapters are switching adapters, and if you try to power anything that is audio related, without that device having some decent filters on the power line, you will get a very messy audio!  

 So if the power supply is really the issue here, what sort of power supply is needed to avoid such issues, or how much more powerful does it need to be? Can anyone test this?

Switching adapters are actually not that bad. Many "audiophiles" swear by toroidal transformers, but that's just a myth along with a lot of other myths, although they have some benefits, but then switching transformers have just as many benefits over toroidal trannies.

I would try with a ferrite ring. Buy a ferrite "clip-on" sleeve (costs about 0.5 USD) with an inner diameter that's 4 times bigger than the outer diameter of the cable between the wall-wart and the DAC. Make two loops in that cable, then clip on the ferrite ring (about 2 inches from the DAC connector) so that the cable passed through 3 times and around it two times. It will solve a lot of the noise issues you have.

Ferrite rings can be used for a lot of noise problems, and you can't oversize, the bigger the ferrite ring and the more passes, the better the performance, but usually, the aforementioned solution suffices.

Another really important thing about power supplies is the grounding. There are two common issues that pop up with grounding in audio applications, of which the main one is the ground loop. The ground is what the word says, it's a connection to the earth, and it's universal, that means that the ground (the black wire) of your audio path connection is linked to the ground of your electrical connection. Electricity - like any energy - will always follow the easiest path, aka the path with the least resistance or impedance. The audio signal is attenuated by lowering the resistance to ground. that means that what separates the audio path from the power supply ground, is maybe a single 100kOhm resistor or a single 100kOhm potentiometer (variable resistor). That means that noise and EMI on the ground connection shared by all the devices (which also contains noise generated by those devices, in the case of digital devices, that's a lot of noise), will sneak into the audio path and feedback on itself. There is an easy fix for this, and that is decoupling the power-side ground connection from the audio circuit. That will not cause the audio circuit to lose power, because it's always connected through the audio-side ground connection to ground. A ground loop has a distinct character, it's a kind of lower pitched hum or rumble sound, not just hissing noise or the higher pitched scratchy EMI noise. So if you hear a ground loop, just cut a small piece of electrical tape, and tape off the negative side of the DC connector to your DAC, and it will go away.

Since it's 12V you need, another cheap solution is to buy a Roland 12V filtered power supply. Those are not expensive, but they just work. They have a small enclosure on the DC cable that contains a combination of magnetic filtering with a ferrite core and a rudimentary LC network that filters specific frequency ranges that have no place in the audio signal. Another solution, if you're a guitarist, is to get a pedal board power supply. Those mostly use toroidal trannies (one per output, they have multiple outputs), which makes them more expensive, but they also use a voltage regulator per output and the outputs are insulated as far as that is possible from each other, which eliminates a lot of noise. There is a limit to what can be done in terms of making a mains connected power supply noise free, it's never as clean as battery power, but in comparison to plain unfiltered wall warts, there is a huge difference. If you're not a guitarist, investing in such a power supply is just stupid.

If you want to have the cleanest possible result, you can buy 10 NiMH "baby" cells (which usually put out 1.25 to 1.3 V DC), and roll up two transparency sheets to line them up in series. All together in series, they will put out 14.4 V at maximum load and 11.8 V at minimum load, which is the voltage range commonly referred to as "12V", and a perfectly safe range to operate most 12V rated devices with. At an averag 4Ah of energy load for baby cells, that DIY battery pack will last you a very long time between recharges, and NiMH batteries will recharge rapidly, so that's a pretty good solution also. That will give you perfect noise free DC power.

The problem with DACs is that they contain both a digital part and an analogue part. Digital parts cause noise, that's just what they do, so sometimes it pays off to move around the parts on the board to find a placement that leaks less noise. It's the same with trannies, valves, etc... there is always a placement solution that leaks minimal noise.

What kind of cables are you using? Make sure they are good quality and have strong shielding. Also run any audio cables separate from everything else, is dvi, & everything else that runs from the back of the PC.

Could also be that your premises is the common ground point for the street. If that's the case interference will be impossible to eliminate unless you move. My girlfriend's parents place is like this, the interference there is nasty.

I don't think that my audio equipment is the problem, since with the old pc I didn't had any of those issues.
Even if I were to plug my headphones directly do the sound card output, or to the dac output, I would still get that interference noise.

The Roland 12V filtered power supply sounds like a neat solution for powering a dac, but I can't find one with a schuko (European) plug.

Took a quick look at, apparently the Boss PSA is only available in 9V any more. Bad luck. The Boss 12V they have is unfiltered.

You can easily make your own filter though, just a 0.5 EUR ferrite ring and 1.5 EUR worth of capacitors and miscellaneous stuff and 10 minutes of your time.

Had a similar issue when I was trying to hook a power amp to my soundcard to drive some speakers. The way I had it setup, was to have it powered off the computers PSU, and even with a high quality Corsair/EVGA PSU, it was giving off noise, however if it was fed power through a laptop charger, no noise. 

What I ended up narrowing it down to was a poor ground and lots of noise. A ground loop isolator took care of the noise for me. What PSU and soundcard are you running?

Power supply: XFX450W, and the soundcard was the one on the 990FX motherboard, now it is the pcm2704 usb dac chip (homebrew).

Just had my brother ask me last night about noise on his headset. Turns out the headset, while it plugs into the AUX for the audio signal, has an inline USB AMP that can not be bypassed.

Here is what I think is going on in both cases. Dirty power. Computer power supplies are VERY noisey, even high quality ones. What this means, is that if an amp/preamp is powered by a PC PSU without proper filters, it is going to pass on that noise and amplify it to the speakers/headphones. The solution for this is to find an outside power source to power your USB DAC, because adding filters to an audio signal is never the ideal way to do things.