Power Supply - Watt Did You Say?
Now then, power consumption. The GeForce 7900 GTX requires a very stable 12-volt power source for best performance, reliability and most of all that gaming experience of yours.
For a GeForce 7900 GTX graphics card, NVIDIA recommends a 350-400 watt power supply with 22-26 ampere on the 12 volts rails. So NVIDIA is recommending nothing too dramatic in terms of Wattage for the power supply unit yet be aware as that's a lot of Amperage on the 12 volts rail.
And noooo! That does not mean the graphics card is pushing 22 amps ! Math people. The G71 GPU requires 100 Watts:
120 Watts : 12 Volts = 10A (x2) So if you have a PSU with dual 12 volts rails a dedicated 10-12 AMPS in that rail would be sufficient. But a TOTAL 12 volt rail ampage of 22 AMPS is recommended as other components feed of that 12 volt rail too.
What we always do with new graphics cards is we measure the wattage peak with the help of a wattage meter. Slight side note, you are looking at the overall usage of the entire PC. The meter is placed between the power connector and the PSU. So please understand that using a Wattage meter is not the most reliable way of measuring power consumption. You basically look at how much power the PSU is pulling from the wall socket in your house. So you need to look at the results as being an indication and not an exact science.
The methodology: we simply look at the peak Wattage during a 3DMark05 session to verify power consumption. The graphics card consumes roughly 120 Watts at peak during 3D gaming, this is also the reason why we see a 6-pin power connector on the card as that much power being drawn over the motherboard is simply not possible.
In 3DMark the PC shows a maximum peak of ~255 Watts. This is similar to the previous 7800 GTX reference model, but is also due to the fact the card comes overclocked.
The GeForce 7900 GTX 512 MB (XXX) with the rest of the components in the PC used up to 255 Watts.
So indeed you need 350W at the least as you want some spare wattage - 420W or better is definitely recommended. When you buy a new PSU then look at the packaging and check the Ampere rating on the 12 volt rail, it should be 22 AMPS minimum. There are some good SLI certified PSU's out there, these have dual 12 volts rails dedicated for the graphics card. We highly recommend them! In fact we have been testing quite a few of them (see here).
What would happen if your PSU can't cope with the load ?:
- bad 3D performance
- crashing games
- spontaneous resetting PC
- freezes during gameplay
- PSU overload can cause it to shut down or even break down
So many things can happen.
Temperature of the graphics card
I stated it in the 7800 GTX review already, I just love that heat-pipe design cooler. It's just so efficient and silent !! This card uses exactly the same heatpipe cooler as the reference model 7800 GTX 512MB we recently tested.
At idle, normal operation (i.e. your desktop), expect roughly 40-45 Degrees C. At 100% graphics core utilization we measured a maximum 69 Degrees C peak temperature, which is actually becoming the norm. The cooling fan at 100% utilisation does not make a lot of noise at all, in fact the HD is producing way more noise than the cooler on this card and that's very nice to observe.
Noise Levels coming from the graphics card
When graphics cards produce a lot of heat that heat needs to be transported away from the hot core as fast as possible. Often you'll see massive active fan solutions that can indeed get rid of the heat, yet all the fans these days make the PC a noisy son of a gun. I'm doing a little try out today with noise monitoring, so basically the test we do is extremely subjective. We bought a certified dBA meter and will start measuring how many dBA originate from the PC. Why is this subjective you ask? Well, there is always noise in the background, from the streets, from the HD, PSU fan etc etc, so this is by a mile or two not a precise measurement. You could only achieve objective measurement in a sound test chamber.
The human hearing system has different sensitivities at different frequencies. This means that the perception of noise is not at all equal at every frequency. Noise with significant measured levels (in dB) at high or low frequencies will not be as annoying as it would be when its energy is concentrated in the middle frequencies. In other words, the measured noise levels in dB will not reflect the actual human perception of the loudness of the noise. That's why we measure the dBa level. A specific circuit is added to the sound level meter to correct its reading in regard to this concept. This reading is the noise level in dBA. The letter A is added to indicate the correction that was made in the measurement.
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TYPICAL SOUND LEVELS |
|
Jet takeoff (200 feet) |
120 dBA |
|
|
Construction Site |
110 dBA |
Intolerable |
|
Shout (5 feet) |
100 dBA |
|
|
Heavy truck (50 feet) |
90 dBA |
Very noisy |
|
Urban street |
80 dBA |
|
|
Automobile interior |
70 dBA |
Noisy |
|
Normal conversation (3 feet) |
60 dBA |
|
|
Office, classroom |
50 dBA |
Moderate |
|
Living room |
40 dBA |
XFX GeForce 7900 GTX XXX |
|
Bedroom at night |
30 dBA |
Quiet |
|
Broadcast studio |
20 dBA |
|
|
Rustling leaves |
10 dBA |
Barely audible |
We startup a benchmark, we take the dBA meter, move away 75 CM and then aim the device at the active fan on the graphics card. We measure roughly 41-44 dBa which is to be considered a quiet to moderate noise level coming from the PC. Again, this is a very subjective test.
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