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QUIET FAN SWAP FOR HP MICROSERVER
It was inevitable that SPCR modify the MicroServer for lower noise. What are
the usual methods to reduce noise in an existing computer?
- Reduce the transfer of vibration from the hard drives to the chassis.
This is not really possible here, given the plug-in design of the HDD
bays.
- Lower fan noise by reducing RPM or replacing fans with slower, smoother
ones. This is not a practical option with the PSU fan, which made very
little acoustic contribution anyway. The 1100 RPM minimum 120mm fan is a perfect
target for this approach.
We mentioned that this primary cooling fan is a 4-pin PWM type with a pin-pattern
that is non-standard. This means you cannot plug any old PWM fan into the CPU
fan header on the MicroServer meotherboard and expect it to work. Our first
step was to examine the connector. A close comparison revealed that it is not
quite the same as the 4-pin connector on other PWM fans used in PCs. The latter
is designed to fit either 3-pin or 4-pin fan headers; the HP connector can only
fit on a 4-pin header.
We also examined the information that SPCR forum members unearthed. Much thanks
to vlrnmz and camlin for the
information they shared. Here is the 4-pin configuration information for
the HP MicroServer from camlin:
HP MicroServer
4-pin CPU fan header |
| Pin |
Name |
Color |
| 1 |
Control |
green |
| 2 |
GND |
black |
| 3 |
+12V |
red |
| 4 |
Sense |
yellow |
What you need to know now is the normal pinout for 4-pin PWM
fans. From AllPinouts:
|
|
| Pin |
Name |
Color |
| 1 |
GND |
black |
| 2 |
+12VDC |
yellow |
| 3 |
Sense |
green |
| 4 |
Control |
blue |
|
| Pin |
Name |
Color |
| 1 |
GND |
black |
| 2 |
+12VDC |
red |
| 3 |
Sense |
yellow |
| 4 |
Control |
blue |
|
|
Header on mobo
|
Pinout
|
For some AMD CPU fans
|
So armed with this information, a couple of possible Scythe PWM fan candidates
were identified, the connectors compared, and modifed. This requires a very
small screwdriver to unlock the conductor pins from the connector and swap them
around to the desired slots. The center guide on the plastic connector also
needs to be removed, as it will stop it from fitting on the HP fan header. This
was accomplished with a sharp utility knife.
The labels on the photo are self explanatory. The Scythe fan color
code is different from either of the ones described by AllPinouts.
|
Rather than installing the fan, it was tried first, by plugging it into the
fan header with the chassis door open, then powering up the system with the
fan on the outside. The first fan to be tried was a Scythe SY1225SL12LM-P. This
is a PWM version of the popular SlipStream series, with a rated maximum speed
of 1300 RPM. After the initial full speed burst at turnon, the fan slowed to
an extremely slow speed, which caused a fan error message to display and the
system to power down immediately. The system wants to see a faster fan. Since
the >3000 RPM stock fan ends up spinning at 1100 RPM, the PWM fan controller
applies a duty-cyle of about 35%. That meant the Scythe must have been spinning
at under 500 RPM.
The next fan to be tried was a Scythe SY1225SL12HPVC. This is a PWM fan rated
for 1900 RPM, equipped with a manual speed control. With the control set to
full speed, it would surely run fast enugh (~700 RPM?) for the system to boot.
And indeed, it worked.
The Scythe Slip Stream120mm PWM Adjustable fan on the left worked as
a replacement fan in the HP MicroServer. The 1300 RPM Scythe PWM fan did
not run fast enough. |
Then came the task of removing the stock fan. After the four Torx screws are
removed from the back panel, follow the course of the cable to the motherboard
header and carefully snip several plastic wire ties. The Scythe fan has a much
a shorter cable, so it had to be run a bit differently. This required the removal
of the motherboard. Finally, the dongle with the PCI slot cover plate and rheostat
had to be put somewhere. The control could be removed from the plate and mounted
somewhere on the back panel, but for testing, it was left resting behind the
optical drive. Be careful that the fan wires don't catch on the fan blades.
The fan experiments could now begin.
The Scythe fan controller was temporarily tucked behind the optical
drive. Do not leave it this way. |
Many drive combinations and loads were tried with various fan speeds, with
all temperature and noise data recorded. All that is not presented here,
to reduce information overload.
First, the manual fan control was used to determine the minimum fan RPM allowed
before auto-shutdown. The BIOS fan monitoring screen was left on while the fan
knob was rotated. It turned out to be somewhere around 500 RPM; the exact value
was difficult to pinpoint. It is probably safe to consider 550 RPM as the minimum
speed.
With the Scythe fan at 550 RPM, the baselline noise was just 16 dBA. However,
a tonal peak at ~2.7 kHz which had been masked by the stock fan before was now
apparent. This comes, evidently, from the power supply or its fan. It is not
clear which is the culprit without examining the PSU by itself. In any case,
since hard drives would always add to the overall noise, there is no point in
keeping the fan speed so low. It was raised to 700 RPM, bring the SPL up to
17 dBA@1m, and this became the default for SPCR's Scythe-fan-modded MicroServer.
The Scythe fan @ 700 RPM brought the baseline noise down 6 dB from
the stock fan baseline. |
Other smooth sounding fans could be used, of course, with or without manual
control. To achieve 700 RPM speed on the motherboard's built-in fan controller,
if we assume 35% estimated fan duty cycle, you'd need a PWM fan with rated speed
of no more than 2000 RPM. Note, however, that our 1900 RPM Scythe spun at 1080
RPM with its manual control set to maximum, which implies about 50% duty cycle.
This means that the PWM controller in the board interacts differently with different
fans.
Here is the essential cooling and noise data for the 700 RPM Scythe mod.
|
HP MicroServer w/ Scythe PWM fan @ 700 RPM
Windows 7 w/ 4 WD Green AV drives
|
|
State
|
HDD*
|
CPU
|
AC
|
Fan RPM
|
SPL
|
|
idle
|
28~31°C
|
30°C
|
37W
|
700
|
20 dBA
|
|
Prime95
|
33~36°C
|
59°C
|
54W
|
700
|
20 dBA
|
|
* The temperatures of the hottest and the coolest
drives.
|
HDD temperatures are not affected by the drop in fan speed, although the CPU
ran 6°C hotter, to a still modest 59°C. This kind of extended 100% CPU
load will never happen in a NAS or home server. The overall noise signature
is much nicer than the 4 dBA reduction would suggest. You still might not want
this system on your desktop, as HDD seek noise is clearly audible, but you'll
probably be fine with it in the same room.
The Scythe fan @ 700 RPM brought the noise down 4 dB compared to the
stock fan. |
Finally, some audio recordings of the MicroServer.
AUDIO RECORDINGS
These recordings were made with a high resolution, lab quality, digital recording
system inside SPCR's own 11 dBA ambient anechoic chamber, then converted to
LAME 128kbps encoded MP3s. We've listened long and hard to ensure there is no
audible degradation from the original WAV files to these MP3s. They represent
a quick snapshot of what we heard during the review.
Each recording starts with ambient noise, then 10 second segments of product
at various states. For the most realistic results,
set the volume so that the starting ambient level is just barely audible, then
don't change the volume setting again while comparing all the sound files.
* * *
Discuss
this article in the SPCR forums.
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