Saturday, February 23, 2008

Er teknologi alltid et framskritt?

Saturday, February 16, 2008

The sound of silence

Can you build a completely quiet HTPC box? Can it run on off as little as 300W?

Finally! My MythTV PVR box is no longer the loudest in the living room. The two to three laptops that live there easily out-hums the larger box since I moved the machine into its new "HTPC Classic" cabinet made by mCubed. It is a good looking black aluminum fronted case with a mirror (plexi)glass "visor" across the front and symmetrically placed "on" and "eject" buttons. The DVD players front plastic has been pulled off and the mirror glass on the left side of the visor is taped on in it's place. Looks good and sounds good :-)

I wrote about the machine components earlier. Suffice it to say that it's a simple Athlon motherboard with a dual core Athlon64 X2 65W CPU. It was an ideal choice with regards to price, power and power consumption. I'll concentrate on the case and how it works this time.

The central idea with this cabinet are the huge heat sinks on the (out)sides, and mounting heat pipes on the hot things inside to channel the heat to the heat sinks. No moving parts cooling. Adding to that "vertical silence" aluminum disk casings with heat sinks and an all embracing rubber mat that goes around the disk inside the case. And mounting holes on rubber piles you also get pretty durn quiet disks. I can still hear the occasional seek sound, but there isn't much cause to seek the disk unless it's used. The disks are, according to their S.M.A.R.T. based temperature Munin graphs running at exactly the same temperature as before, except that I stacked them other way so the other one is now the hottest one. Graph shown below. To the left of the gap is before, to the right is now.

There are two interesting questions in this conversion:

  • Will I get by with a 300W PSU?
  • Will things stay cool enough?

Power and cooling

Reading forums and such one easily arrives at the conclusion that any PSU smaller than 500W is just too small for current CPUs and graphics cards and disks and whatever. I had chosen a low W CPU for this, a low featured mother board, and not the coolest graphics card either. The graphics card manages on the power it gets from the PCI-E bus, unlike some others (which need the new PCI-E power connectors or other extra power sources). The Munin graphs for voltages stayed exactly the same, even when playing back video and recording at the same time.

When it comes to temperatures things now are definitely hotter in some places. The GPU used to have a angry small fan. The scary bit here is that the new cabinet is positively perforated, and has 3 large vents in the back at the top, so I can hold my hand over the vents and gauge the temperature for myself. The GPU gets HOT. The NVIDIA measuring tool says it gets to 70-80C now, with heat pipes. It used to be 50C, with the angry fan. I hear from friends that their graphics cards run all the way up to 125C. 80C should be OK then. But I'll still check the couplings some times to see if I can get better heat transfer.

The PVR350 TV input card does realtime MPEG2 encoding in hardware. It has always been sitting in a poorly ventilated corner of the machine, with only its heat sink to defend itself with. Which it has done for many years now, and I've had no idea with how hot it gets. But with the vents I've realized it gets plenty hot. Fortunately, even without a fan in the case it now gets more air circulation than ever, due to the case perforations. It, and the GPU now serves the living room as a low intensity heat source (as it did before, come to think of it). By the time the air leaves the vent it's less than 30C).

Very difficult to build though

The other thing apparent from this graph is that I used almost 4 days (well, evenings, after the kid was asleep) from turning the machine off in the old cabinet and turning it on on the new one. It was bloody hard to mount everything in the cabinet. This was my hardest PC building project yet.

I have mounted my own kitchen, all manner of IKEA things, and a couple of PCs before. Building a mCubed box should not be attempted by anyone that is easily frustrated by such construction projects. Each and every one of the illustrated instruction sheets or pamphlets carry a disclaimer that a un-experienced PC builder should not try this at home. They are not kidding. There are instructions with everything that went into the case. But no where as detailed as IKEA instructions. You're required to figure out a good number of things while you work. The first thing that puzzled me was the CPU bracket spacer pieces. There were two sets, slightly differing, but both the same length. Of course I mounted the wrong ones first. It was obviously the wrong ones once I tried to complete the CPU bracket mounting as the nuts would never engage the screws properly. But I suspect that a number of people tried force before arriving at this conclusion.

Most of the troubles stem from the small inside. On the outside the cabinet is a standard width ATX desktop cabinet, and it's 5cm deeper. BUT, the afore mentioned huge heat sinks take up quite a lot of the width of the cabinet. On the inside there is enough space for a standard ATX mother board, the drive cage and the fan less 300W PSU. After that there is hardly any space for routing power cables, or anything else. In theory I should be able to fit 3 hard drives and the DVD drive into the cabinet, but I'll never get in a third drive, that drive bay is occupied by power cables so they don't have to lie messily around across the mother board. Not that I'm very happy with the degree of neatness I achieved. While mounting I dreamed that Lian Li would buy mCubed (Lian Li make the most easily buildt/mounted PC cabinets I know, they're also quite expensive).

Removing the cables to make room, I set about fitting the heat pipes. The ones for the CPU were easy and the heat pipes were very easy to bend as needed. That was one the least crowded side of the cabinet. The north bridge and the GPU heat pipes were to be terminated on the other side. This side already dominated completely by the PSU. I needed 5 very time consuming tries (over two evenings) to get the heat pipes in place.

In retrospect I notice that there are no pictures of the GPU and north bridge heatpipes mounted at the same time anywhere in the mounting instructions. If it wasn't for the fact that I've seen reviews of complete machines in this case I would have suspected that no-one had attempted mounting both at once before.

It's very crowded in the corner where the north bridge and GPU heat pipes have to go: Power lead to the PSU, TV-input card, mother board power, IDE cable, SATA cable, and a myriad of HDD-led, power-on and such mother board "heads" that have to be connected to get the thing working. And the iMON LED panel USB cable. In addition to all the power cables that are just hanging in that corner.

Another thing is the DVD-tray opening switch. In the baggie with stuff for the cabinet there is a small thing with some clear rubber lens shaped bits. They don't stack well at all. I had to find something else to pad the distance for the DVD-tray opening switch.

Pretty though

On the other hand. Everything is quite nice looking, if crowded. Plexi glass and chrome all over the inside. Black aluminum on the outside. The heat pipes are a bit unevenly finished, but not ugly, and the heat pipe clamps I received had quite coarse rounded milling patterns on them. Somewhere in the history of those metal squares there has been a large milling machine with a uneven cutting tool. No matter, the ample cooling paste that came with everything easily filled in the unevenness where it counted. And the outside is fault-less.

What I don't have to do with this setup is change cooling water every 6-12 months. And no cooling tower in the corner of the room either.

And they provide the screw drivers needed for putting it all together. An especially long stemmed screw driver is needed for fastening the drive and power cages. I would have had to go shopping for tools unless they had provided those I needed. And they also provide enough cooling paste, in every package that needs some. Nice touch.

Recommendations for mCubed

Please, if anyone from mCubed ever reads this, I have some suggestions for the box:
  • Deliver the PSU with a power lead that has a shorter connecting block, or even a 90 degree knee in the block. This will take less space from the heat pipes and stuff
  • On the PSU side of the cabinet make more holes spaced 1/3rd longer apart so that the heat pipes may enter the clamp blocks between the clams. As it is now the clamps are so closely placed that in effect there is only one clamp block
  • The north bridge of most computers hides behind the graphics cards. It is likely that a random user needs 3 90 degree angles to be able to connect the equipment to the clamp block. And it's bloody hard to mount both north bridge and GPU on that side together - see also the previous point.
  • If somehow the PSU could be rotated 180 degrees along the long axis so that the lead connection comes close to the wall of the cabinet this would save space and heat pipe logistics. Drop the knee on the lead then.
  • A FAQ please? What happens if I unbend a 90 degree knee on a heat pipe (I guess it breaks open)? Can I cut a heat pipe or are they based on a fluid heat transport (I guess it's based on fluids due to the way the pipes are sealed in the ends. But does the two lower heat pipes from the CPU work really well then, their up goes towards the CPU, not away as with the two higher ones do)?