AX760 really annoying harmonics

[Arksun]

Hi, recently put together a new PC Build, thought I'd splash out on high quality PSU so went with the AX760.

 

I had hoped it would be ultra quiet, and I'm using very quiet case fans so didn't want any whine, but there's a problem.

 

We're not even talking super high frequency here either, its a few harmonics but the one that really sticks out to my ears is a 1khz tone. Once my brains latched onto it it drives me a bit crazy, and that sine wave just seems to travel through everything.

 

Here's a couple recordings I made using a field recorder, placed right up against the PSU grill. One is the AX760, the other is a much older NesteQ PSU I have in my other PC, no mid-range harmonic issues whatsoever:

 

http://musicprogressive.com/psunoise/AX760%20noise.mp3

http://musicprogressive.com/psunoise/NesteQ%20Noise.mp3

 

Here's the frequency plot for both (with 4db/oct slope):

 

http://musicprogressive.com/psunoise/AX760%20psu%20noise.jpg

http://musicprogressive.com/psunoise/Nesteq%20E2CS%20X-Strike%20750W.jpg

 

Is this considered normal for an AX760? Is that the price for high efficiency, if so should I get a gold or bronze certified one instead? Is it even likely this noise will reduce over time or get worse?

 

I'm concerned if I RMA it i'll just get another one with whiney noises.

 

I should also state that I dont think this is a bios issue as it makes this noise even when the PC is off, just mains supplying power to the PSU, with the little red power symbal lit on the motherboard (but not actually running).

 

Windows running or not, the harmonics are still there same level and I dont really want to run my case fans super loud to try and drown the sound it, kinda defeats the point of building a quiet PC :/

[jonnyguru]

I'm afraid this is something we see more and more as power supplies are engineered for better efficiency. Most of the Corsair product lines have had this address since last year (see: http://www.corsair.com/en/blog/2013/september/coil-whine), but since the AX is made in a different factory than all of the other current Corsair product lines, it didn't get the same "tweaks".

[Arksun]

Yeah. The thing that confuses me though is that the frequency is relatively low. Usually any kind of coil whine might go down into the audible range as low as 15khz but no lower. Here I'm hearing a harmonic concentration between 0.7 to 1khz with the 1khz being the dominant tone.

 

Should such a relatively low whine be something of concern in terms of stability? or still considered normal for an ultra efficient design.

[jonnyguru]

Sure it's not coming from the fan? Maybe bearing noise?

[Arksun]

Positive. Fan isn't spinning, PC is drawing at most 240W with Prime95 running,so well below the threshold the AX760 kicks the fan in. Double checked the little switch on the back which can be enabled to have fan running all time.

 

Interestingly the noise doesn't bother me as much anymore now, maybe it got a bit quieter. I've got some absorbtion material i can place to the side of the back of the case which also helps (overheating shouldn't be an issue given the max power draw and psu's efficiency). Just as long as 700hz-1khz tones aren't some indication of a problem I might just keep it, its voltages are very stable.

[Arksun]

Latest Update. The noise level has reduced further, maybe the particular component causing it just needed some burn in/settling in time or something. So I think I'll keep it for now.

[jonnyguru]

Maybe settling? I mean... we are talking about copper wire wound around a core a number of times. It's not unheard of for something like that to settle into place.