Quiet DIY OC'ed Pentium D 830 System, Part Two

Do-It-Yourself Systems
Viewing page 2 of 4 pages. Previous 1 2 3 4 Next

EXTRA VRM HEATSINKS

This led to the next idea from the SPCR forum, suggested by diver and golemB: Why not add some copper to the VRM to catch the existing airflow?

I bought some Swiftech MC14 BGA RAMsinks and stuck them on the various hot spots of the VRM. These are forged copper heatsinks designed for video card DRAM chips, and seemed ideal for this application. Swiftech claims a 6°C advantage over the competitor. Since the PLL chip also ran very hot, I added a heat sink to it as well.

To install these heatsinks, I had to temporarily remove the Ninja. Here are before and after pictures. Note the discoloration of the board and torroids near the VRM (top center) after running the system for seven months with poor VRM cooling.

VRM and PLL before adding heat sinks
VRM and PLL before adding heat sinks.

VRM and PLL heat sinks installed
VRM and PLL with heat sinks installed (and Arctic Silver 5 ready for Ninja remounting).

Here is a photo looking down through the top case fan. The copper at the top left is one of the VRM heat sinks. The whitish part at the top is the base of the Ninja. The foam on the top of the Ninja duct is also visible. The airflow to this fan is constrained to the two-inch channel at the top of this photo. As described in Part One, the foam and coins in the center are to damp the ringing of the fan hub.

View of VRM heatsink and baffle foam through top fan

The combination of baffle and heat sinks dropped the VRM temperatures a lot. The main MOSFET heat sink went from “YOW!” hot to too hot to hold a finger on (subjective I know, but I think that would indicate at least a 10°C drop), and the heat sinks on the other MOSFETs and the PLL were now somewhere between warm and hot to the touch. I guess I should have measured the temperatures, but didn’t think to do so.

ADDING A VIDEO CARD DUCT

SPCR forum responses from diver and scara asked: Why not move the video card heat directly out of the box?

I thought about this for a while, and came up with a duct that would capture some of the motherboard fan air flow and direct it across the heat pipe radiators and out of the box. The duct is composed of the video card PCB as its bottom, the motherboard as its far side, and styrene panels as its top and near sides. The top of this duct would collide with the north bridge duct, so it requires a curved cut to let the two ducts mate properly. Here is a photo of the video card duct before installation. The notch at the bottom is for a capacitor on the motherboard, the notch at the top is for the heat pipes, and the deflector at the top is intended to smooth the air flow.

VGA baffle before installation, back/bottom view
Video card duct before installation, back/bottom view.

When installed, this duct sits on top of the video card PCB, and butts against the motherboard and the back of the case, as shown in this photo. The motherboard fan is just to the right of this photo. The rear panel PCI blank above the video card slot was removed to let the hot air out.

Closeup of VGA duct showing how it nestles onto the PCB
Video card duct after installation.

This duct removed 30~50W of heat from the motherboard air flow, allowing both lower temperatures and slower fan speeds.

OPENING UP THE UNUSED 5.25" BAYS FOR BETTER AIR FLOW

An SPCR forum response from PhillyB mentioned the Scythe Kama Bay. This sparked the thought: Why not have two ingress air streams, one feeding the CPU fan, and the other feeding the motherboard fan?

If these worked reasonably well, it would be possible to close up the case, and have dust filters on all air streams. The P180 already has a dust filter on the ingress path to the lower half of the upper bay, and installing a Kama Bay would provide one for the upper half. A simple baffle could keep the two streams separated. This would double the input air flow cross-section and nearly double the total upper chamber air flow. The Kama Bay (with its dust filter but without its fan) would occupy the three unused 5.25" bays at the top front of the case.

Here is a photo with all the fans, ducts and baffles installed. The Ninja, north bridge and video card ducts dovetail in the center, the VRM baffle is above the Ninja duct, and the chamber baffle is wedged between the motherboard fan and the DVD drive PATA cable. This photo also shows the last two RAMsinks, mounted on the south bridge and the TV card processor.

all four baffles and ducts installed
Two fans, three ducts, two baffles, and some copper.

The top-half air flow in this arrangement is straight through the Kama Bay dust filter, the CPU fan and Ninja duct, then out the back of the case.

The bottom-half air flow is more convoluted. It enters through the P180 dust filter, goes through the motherboard fan, and is split into three parts. The center part flows through the video card duct and out the back of the case. The top part flows through the north bridge duct, across the motherboard and VRM, into the top case fan chamber, then through the top case fan and out of the case. Finally, the bottom part swirls around the south bridge and TV card, then flows over the near side of the video card duct, then to the motherboard, where it joins the top part flowing over the motherboard and out the top of the case.

Installing the Kama Bay required fitting the steel P180 drive clips to its shell, which meant drilling some holes. These clips are made from a very hard steel. Unless waste material is clamped to both sides, drilling the holes causes even Bosch titanium bits to wander severely. The plastic holders the clips come on work well as bit guides. Remember: measure twice, drill once! Here is a photo of the Kama Bay with all the hardware installed, ready to be put into the case.

Kama Bay with mounting hardware attached
Scythe Kama Bay with P180 clips attached.

The clips need to be bent outward slightly to engage the chassis slots because the Kama Bay is a bit narrower than a standard CD/DVD drive.

Doubling the air flow in this manner let me close the case and still use slow fans. The motherboard temperature rose significantly (about 8°C) but not enough to cause errors.

NOTCHING THE SLIDING CHAMBER SEPARATOR

SPCR member BigA suggested: Cut a notch in the rectangular sliding plastic that separates the upper and lower chambers of the P180.

This allows the SATA HDD data and power cables to go from the upper to the lower chamber while still sealing off the air flow. Here's a photo:

Notch in the sliding panel for the SATA data and power cables
Notch in the upper/lower chamber sliding panel to accommodate cables.

This was probably the simplest mod so far, and worked well.

SWITCHING TO NEXUS FANS

At this point, I was running with four DustProof AcoustiFans, all at 5V, their lowest reliable operating point. The system was very quiet — the house and neighborhood had to be silent to have any chance of hearing the computer noise. It was too quiet to record with the gear I had. Interestingly, I could not detect any difference in sound level with the case open or closed.

However, although the volume of the noise was pleasingly low, the nature of it was rather annoying. The CPU fan in particular put out a thrumming sound reminiscent of a distant propeller airplane. The motherboard fan also did this, but to a lesser extent. The cause of this thrumming was obviously the close proximity of the downwind side of the fan blades to the Ninja fins and the motherboard and video card duct edges. Also, there was a distinct 245-Hz tone.

I could live with the thrumming per se, but unfortunately these two fans were so close in speed that the thrumming beat about once a second, making it very hard to ignore.

Thinking that a different brand of fan would run at a different speed and get rid of the beating, I ordered a couple of Nexus 120mm orange fans. These have long been MikeC's favorites, and MadShrimp's comparison notes that the Nexus at 7V significantly outperforms the AcoustiFan DustProof at 5V at about the same sound level. I guess the reason I had taken so long to try these fans is that I just don't like the color. Why can't they make some plain black ones like everyone else?

When these fans arrived, I did some direct A/B comparison tests. In free air, the brand-new Nexus was slightly quieter than the seven-month old DustProof at each voltage. Of course the Nexus spins slower at each voltage, so that was no surprise. What was a surprise was the difference in sound when I put a finger near the fan blades. Both were annoyingly loud with an obstruction on the upwind side (this effect is well documented on SPCR and elsewhere). However, on the downwind side, the difference was striking: the Nexus was much quieter. This difference appears to be due to the shape of the frame bevel, which is deeper on the Nexus.

When I mounted a Nexus on the Ninja, there was no audible thrumming anymore, and the 245-Hz tone was also gone. Encouraged by this success, I ordered two more Nexus fans, so I could replace all the DustProofs.



Previous 1 2 3 4 Next

Do-It-Yourself Systems - Article Index
Help support this site, buy from one of our affiliate retailers!
Search: