[geeks] Of video cards and power supplies...

[nate at portents.com]

Since I know some of you have expressed interest in quiet systems, I
thought I would share the following experiences...

Summary:
Due to a poor power design in reference NVIDIA cards such as the GTX 280,
audible squealing and other noises can be emitted from some perfectly good
power supplies during certain types of GPU load.  ATI cards that use
digital VRMs such as the HD4850 and HD4870 do not cause any noise to be
emitted.  I have found that changing the power supply to a design that
derives the 5V and 3.3V from the 12V in a highly efficient DC to DC
conversion process, and probably provides greater 12V rail isolation,
eliminates the noise that a GTX 280 would normally cause.

Details:
Originally I had a Corsair HX620W power supply, which is a good power
supply, as detailed in these reviews here:

http://www.hardwaresecrets.com/article/371
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=21

It's based on a Seasonic S12 design, and the biggest design flaws are that
when the there's a high (39A) load on the 12V rail 12V2 and 12V3 have a
total swing of 100mV, which is a bit high, and the power supply doesn't
have true separation of three 12V rails, which means that noise from one
12V rail can affect the others (basically they are virtual rails at best).

Initially I used this power supply with a pair of ATI HD4850 cards, and
later a pair of HD4870 cards, both of which use Volterra digital VRMs in
their power design, and there were no unusual sounds coming from my system
during any GPU workload.  Then I got a single GTX 280, and during certain
workloads (most often the main menus and load screens of many games and 3D
benchmarks), very audible sounds were emitted from the power supply.

Some sites have documented this as a problem that can be solved by
phsyically securing the analog power components to the GTX 280, such as
this site:

http://theovalich.wordpress.com/2008/11/24/nvidias-deadly-flaw-and-how-to-fix-it-no-more-gtx280-squealing/

However in my experience the sounds were coming from the power supply, as
described here:

http://www.bit-tech.net/news/hardware/2009/05/29/msi-solves-the-nvidia-gtx-squealing-problem/1

If I had an O-scope, I would certainly like to corroborate Bit-Tech's
claim about interference going from the graphics card to the power supply:

"After reporting the problem to Nvidia, we were greeted with denial - it
was unable to replicate the problem - until we sent readouts from an
oscilloscope, displaying the interference shooting back up the PCIe power
connectors into the PSU."

Anyway, I theorized that I could eliminate the sounds by getting a
different power supply, rather than replacing my graphics card or voiding
its warranty trying to 'fix' it.  After some research, I settled on a DC
to DC design by Delta that's packaged by Antec as the Signature 650,
reviewed here:

http://www.hardwaresecrets.com/article/658
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=113

With test results that showed ripple and noise below 16mV on all rails in
jonnyguru's tests, I had hope that this extremely clean and capable design
would solve the problem.  I doubted that Corsair or BFG - the company that
branded the NVIDIA reference design GTX 280 - would do anything about a
design flaw that NVIDIA is at fault for, after all.

In my experience thus far, the Antec Signature 650 has not demonstrated
any squealing with the GTX 280, and I wouldn't be surprised if other high
quality DC-DC designs such as the Enermax Revolution and Seasonic M12D
also cope well with badly-designed cards such as the NVIDIA GTX 280.

Alternatively, you could also avoid the problem by using a recent ATI
card, using a non-reference designed NVIDIA graphics card, or wait until
NVIDIA will (most likely) adopt a digital VRM solution like Volterra in
their future reference designs.

- Nate