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Review: 4 Socket-A Heavyweight Heatsinks

October 25, 2002 by Mike Chin

We have three celebrated heavyweights and a renown low-noise specialist for our first heatsink roundup review. The contenders: Thermalright SLK800 and AX7, the venerable Swiftech MC462A, and the CNPS6000Cu from low noise specialist Zalman. All are socket-A (AMD) heatsinks noted for their excellent design, superb finish and good performance. The first three are darlings of overclockers and performance nuts who usually use noisy high airflow fans; the Zalman is designed specifically for good cooling with low noise (read: low airflow).

4 heavyweight HS contenders

They were chosen in anticipation of high performance with our quiet reference fan. The main question we're asking is:

How well does this HS perform with this low noise, low airflow fan?

If you have not already done so, you're strongly urged to read page one (at least) of our Heatsink Testing Methodology article. We do things differently; the article explains it all in detail.

Thermalright SLK800 - p.2

Thermalright AX7 - p.3

Zalman CNPS6000Cu - p.4

Swiftech MC462A - p.5

Test Results, Data Analysis and Conclusions - p.6

*

PRODUCT Thermalright SLK800
Manufacturer Thermalright Inc.
Supplier Thermalright Inc.
Manufacturer's Suggested Price (MSP) US$45 (without fan)
Reasons chosen
  • The most rave-reviewed cooler around these days.
  • All copper design with thin fins and larger than usual air gap between them suggest good low airflow performance.
  • Sturdy- and friendly-looking clip.
  • Great looking finish on all copper design.
  • Excellent fan flexibility.
  • Clever overall design.

Thermalright SLK800

Thermalright SLK800 socket-A heatsink next to one-inch tall elastomeric fan mount.

SLK800 is the current socket-A flagship of the Thermalright line. It has been highly rated by many review sites, especially when mated with high airflow fans.

Specifications

  • L87 x W56.4 x H48 (mm) - Top, without fan
  • L57.5 x W56.4 x H48 (mm) - Bottom
  • L25 x W56.4 - Base
  • Weight: 505g (heat sink only)

Thermalright SLK800 base

As you can see from the photos, the finish of the SLK800 is excellent. The finish of the base is flat and smooth enough for all but the most fastidious. The mounting clip is captive in a tunnel that runs the length of the HS and engages all three lugs on each side of an AMD motherboard socket (or two for socket 370), making it secure and tight. A blade screwdriver (of the correct size) is needed for mounting, which is quickly and easily achieved.

Thermalright SLK800 installed

An interesting aspect of the design is that the base is narrower than the width of either an AMD or socket 370 processor. The design provides a good airflow path all the way down to the top of the CPU, so some direct cooling can be expected. The base of most heatsinks completely covers the CPU, so that the airflow cools only the heatsink. When an 80mm fan is used, it hangs a bit over the sides of the SLK800 so that other motherboard components (such as the chipset) benefit from the airflow.

Four pads much like those on the corners of AMD processors are included in case you fear core chipping (by wobbling the HS on the chip during mounting). They were not used; as already mentioned above, no trouble of any kind was encountered during installation. The small size of the base and the nicely designed clip makes this HS very easy to install.

The base extends up in a pyramidal profile to about 1.5 inches (~3.5 cm) so that it forms a hefty U-shaped channel around the mounting clip. Each of the 34 fins are soldered along the entire contact path with the base so that the heat path between fin and base is quite extensive. Unlike many HS, there is no gap right through the center of the fins where the clip resides.

The fins themselves are very thin. The 505 gram mass without fan exceeds AMD's recommended maximum of 300 grams by a big margin. But with the 6-lug clip design, unless the computer is moved around a lot, there is little to worry about. Shipping with the SLK800 installed is probably unwise, however.

Thermalright SLK800 with fan

The simplicity of the fan mounting system shows some clever thinking. There are several holes into which the one-piece stiff wire clip on either side slip into. The same wire clips does the job with 60, 70, and 80 mm fans of varying thickness -- there are several sets of holes on the sides to accommodate the different sizes and the top of the fins are stepped to fit each size fan nicely.

Socket-A Heatsink Roundup Intro - p.1

Thermalright AX7 - p.3

Zalman CNPS6000Cu - p.4

Swiftech MC462A - p.5

Test Results, Data Analysis and Conclusions - p.6

*

PRODUCT Thermalright AX7
Manufacturer Thermalright Inc.
Supplier Thermalright Inc.
(MSP US$30 (without fan)
Reasons chosen
  • Raved about almost as much as the SLK800.
  • Cool factor: novel design looks like a miniature high-end power amp for home or car.
  • Copper base and larger than usual air gap between fins suggest good low airflow performance.
  • Sturdy- and friendly-looking clip.
  • Great looking finish.
  • Very nice price!

Thermalright AX7

Thermalright AX7 heatsink next to one-inch tall elastomeric fan mount. Looks like a skinny pawn (from a chess set), doesn't it? (It works well, BTW.)

Like the SLK800, the AX7 is a unique looking design with a similar captive 6-lug mounting clip. It features aluminum fins soldered to a highly polished, substantial copper base. Its general quality seems exceptional at the US$30 suggest retail price.

Specifications

  • Dimension: L77 x W77 x H80 (mm)
  • Weight: 430g without fan

Thermalright AX7 base

The finish of the AX7 is excellent, especially the base. Even though it looks very different from the SLK800, there are some design similarities:

  • No hole in center of HS, which is solid aluminum, part of the one-piece fin structure.
  • Captive 6-lug clip, very easy to use.
  • Fan airflow allowed to spill over onto proximate motherboard components.

One differences is that the fan airflow is more omnidirectional. The fan also mounts a bit differently. It is meant to be used with an 80mm fan but other sizes can probably be used. Four long screws and rubber grommets to help damp vibrations are supplied. The screws fit nicely between fins as shown below.

Thermalright AX7 fan mounting

Being much larger around the base, the AX7 is more difficult to install (and uninstall) than its more expensive sibling. On the test motherboard, the HS only just clears a bank of capacitors on the south side of the CPU socket. They do get nudged during installation.

Thermalright AX7 installed

While lighter than the SLK800 by 75 grams, it is no lightweight. A 80mm fan will increase the weight by ~140 grams on average, so while it is perfectly secure in normal use, shipping with it installed in a PC is probably not recommended.

Socket-A Heatsink Roundup Intro - p.1

Thermalright SLK800 - p.2

Zalman CNPS6000Cu - p.4

Swiftech MC462A - p.5

Test Results, Data Analysis and Conclusions - p.6

*

PRODUCT Zalman CNPS 6000cu
Manufacturer Zalman
Supplier Zalman
MSP US$40 (complete with fan, fan bracket, Fanmate controller, thermal grease, etc.)
Reasons chosen
  • Designed and marketed specifically as a good performance low noise solution.
  • Unique all-copper design inspires confidence about low airflow performance.
  • Used by many low noise PC aficionado.
  • Great set of accessories.
  • Excellent finish.
  • Priced nicely for extensive package.

Zalman CNPS600CU with Fanmate, fan & fan bracket

Zalman CNPS600CU with Fanmate 1 fan speed controller, 92mm fan and fan bracket.

The CNPS (Computer Noise Prevention System) 6000CU is a natural evolution of the original model (3000?) Zalman introduced a couple of years ago. It is still unique in design, being formed of many thin copper fins that are clamped tightly together, polished to make a very flat smooth base, and the fins spread like an Oriental fan or cards held in your hands. A primary benefit of the design is the large heat dissipation area that is achieved; this is extolled for all the Zalman heatsinks. The 6000CU is considerably larger than the original, but the basic design has hardly changed.

Specifications

  • Dimensions: 95~110(L) x 63(W) x 65(H) mm
  • Dissipation Area: 2600~2900 square cm
  • Base Material: Pure Copper
  • Weight: 462 grams

Zalman CNPS600CU base

Zalman 6000CU shown with clip mounting tool -- and now familiar 1" doo-hickey

As with the other heatsinks in this roundup, the finish is excellent, the base being polished to a mirror finish. The above photo shows the slots in the fins designed to allow high airflow circulation. Note that the 6000 CU does have a slot right through the center of the fins for the clip to fit through. This does reduce the total available fin area somewhat; perhaps by ~15% (judged by precise eyeballing). But it allows more airflow, too.

Opening up the Zalman package is as fun as a Christmas stocking: there are more doodads and goodies than you'll encounter in most HSF packages. Aside from everything shown in the above photos, there also a tube of thermal grease, screws from the fan mount, and not one but two mounting clips. (See photo below.) There is even a little well-illustrated fold-out manual in English and Korean. They're serious about user-friendliness!

Zalman CNPS600CU accessories

Fanmate 1 is a nicely packaged voltage regulator with a small control knob that provides 5-11 VDC when plugged a standard motherboard fan header. RPM sensing is not lost if you're using a fan that provides the proper third wire for it (although some motherboard hardware monitoring circuits will go whacky at rotations below ~1200 RPM). It is supplied with all Zalman HS that are fan-equipped. It is a very useful tool for noise control.

Fan bracket installed

Fan bracket installed in a system.

Fan Bracket BR123 allows any 80-92 mm fan to be suspended just over the HS, any heatsink. Vibration and turbulence noise tends to be reduced compared to direct mounting to the HS. Cooling power might be affected very slightly by the larger distance between fan blades and HS. With the Zalman "flower" heatsinks, as there is no method to attach a fan directly, the bracket is a necessity. With a little creativity, you can do lots with this clever device, as John Coyle did with his, such as mounting other fans on different points of the bracket to cool other things in the PC..

The supplied 92mm fan is surprisingly noisy considering its inclusion in the CNPS package. It's rated at 36 dBA at the full 12V speed of 2800 RPM and 20 dBA at the minimum speed possible with Fanmate 1. Even at the minimum setting, it is louder than our reference Panaflo at 12V.

There was some trouble with the clip, which is really the weakest part of the 6000CU. Because it engages only one lug on each side of the socket, a lot of pressure is needed, and it is not that secure, especially when the 462 gram mass of the HS is considered. The clip mounting tool works nicely, allowing pressure to be safely applied, but the clip also seems too easily bent.

When the 6000CU sample was first received, one of the two supplied clips was used without close examination in a tower system. It worked fine that evening, but overnight, the clip slipped off the worn top lug of the socket. Less than 10 seconds after the boot beep in the morning, I had a toasted XP1700+ on my hands.

Most of the blame can be laid ton the worn lug of the workhorse motherboard, which has seen too many heatsinks come and go. For most home users this is not an issue, socket mounting lugs are worn and damaged only by reviewers, nuts and really sloppy users. But close examination of the two supplied clips showed they were not quite identical:

clips

Can you guess which is the one that slipped off?

With the motherboard out in the open on the test bench, it is easy to secure either of the 2 clips. But when mounting the HS on a motherboard that is already in a case, with the difficulties of access and not being able to see clearly around the area, I could not mount the slightly splayed clip properly. The picture on the left below is the best that be done with the slightly off clip. As you can see, it would not take much to make the clip slip off the edge of the lug. Gravity in a tower case was enough. The right image shows the other clip in place properly.

You need a bit of lateral force as you're pushing down on the clip with the tool to get the clip to engage the lug securely. That's very difficult to get with a North-South (for want of a better term) oriented socket like this one when the motherboard is already installed in a case.

one bad, one good

Let me repeat: this is an unfortunate accident. The clip can be improved, but it is very unlikely that you will have any problem with it at home. To be on the safe side, it is worth removing the PSU so you can have a good look at both sides of the socket lugs when you attach the 6000CU -- or any other HS, for that matter!

Socket-A Heatsink Roundup Intro - p.1

Thermalright SLK800 - p.2

Thermalright AX7 - p.3

Swiftech MC462A - p.5

Test Results, Data Analysis and Conclusions - p.6

*

PRODUCT Swiftech MC462A
Manufacturer Swiftech
Supplier Swiftech
Purchase price ~US$40 (without fan) in mid-2001; now discontinued
Reasons chosen
  • Already in possession of one and still similar enough to current Swiftech models.
  • Was raved about for a long time as king of the socket-A HS by everyone..
  • It has quite good low airflow performance.
  • Great looks, finish& design.
  • Probably the most secure HS mounting system

Swiftech MC462A

Swiftech MC462A: this one shows some wear but it's still a polished heavyweight.

Everyone already knows about this big bad boy by now. Introduced in late 2000, the Swiftech MC462A is the second generation version of the 462, with cutouts in the corners of the thick and huge copper base to avoid interference with components on some motherboards. Since then the MCX version introduced Helicoid pins to increase dissipation area, and the latest MCX462+ sports a base that is half an inch thick, compared to the mere 0.375 inch thickness of the MC462A.

Suffice it to say, the MC462A is already on hand and has proven to be an excellent cooler with both high and low airflow applications. It is finished beautifully, and the base smoothness is absolutely the tops. So why not compare it to today's leaders?

Specifications

  • CNC machined, C110 copper base, 3"W x 3"L x .375"H, flatness better than 0.001", micro surface finish 8 or better.
  • 269 Pins made of High Thermal Conductivity aluminum alloy ( 230 W/m-K)
  • Overall dimensions with fan 3"x3"x3", without fan 3"x3"x1.56"
  • Weight: 20oz (560g) without fan.

These days, there are at least a handful of HS that use the mounting holes around socket-A with bolts and nuts that go right through the motherboard, but Swiftech started the trend with the 462. This system ensures safety for big heavy heatsinks that overstress the normal mounting lugs on the plastic CPU socket. The MC462A uses 4 bolts that go into aluminum standoffs that must be secured to the motherboard. (See blue arrows in the photo below). This can only be done when the motherboard is not installed in the case.

Swiftech MC462A mounting standoffs

The screws don't actually clamp the HS in place. Instead, they engage 4 springs of specific properties. The springs ensure just the right amount of pressure. Swiftech's web site shows a torture test in which a a barebones system with a 462 equipped CPU was dropped 3 times from a height of 30 feet without any damage to the CPU, motherboard or HS. That suggests a 462-installed system might even survive freight shipping. A very nice mounting system, if a bit involved.

Swiftech MC462A installed

Because of the pin configuration, the airflow is omnidirectional. That is, it flows out from the HS in all directions, to provide some cooling for components on all sides of the CPU. It is a big HS but appears to fit most socket-A motherboards. Also, the mounting system doesn't require any angling or tilting of the HS during installation, so you won't be pressing the edges against components that are close. Once the standoffs are in place, it really is a nice system to use, and it's virtually impossible to damage the CPU during installation or removal.

Socket-A Heatsink Roundup Intro - p.1

Thermalright SLK800 - p.2

Thermalright AX7 - p.3

Zalman CNPS6000cu - p.4

Test Results, Data Analysis and Conclusions - p.6

*

TEST RESULTS

Each heatsink was cleaned and installed in turn on the test system as per the manufacturers' and Arctic Silver's instructions. The system was allowed to cool between tests for ~5 minutes with a large AC domestic room cooling fan running at full speed, the airflow directed over the entire test setup. The test platform and procedure is described in detail in our HS Test Methodology article, and so will not be covered here. (Do read the piece for a fuller understanding of our approach!) The reference Panaflo fan was simply placed on top of each heatsink, blowing down.

The complete set of tests were repeated on three consecutive days to check to the consistency of the test system. The variance for the diode reading with Prime95 after 20 minutes was within 2° C. That is, the highest and lowest readings were within 2° C of each other.

Interestingly (and this is noted with some relief), the variances were quite consistent between the heatsinks in each test set. In other words, compared to the tests run on day 1, all the day 2 tests were 2° C higher, and all the day 3 temperature were 1° C higher. It is not possible to determine the precise cause of this variance, which may be cumulative. It is 5% in the worst case. The numbers shown here are the averaged results.

There was some concern about whether the use of a 80 mm fan instead of the 92 mm size supplied with the Zalman 6000Cu might hurt its performance. A 92mm Silencer fan (from PC Power & Cooling), rated for 23 dBA and 28 CFM, was substituted for the Panaflo on the 6000Cu at several test points. There was no appreciable change in CPU temperature. Due to the many slots in each fin, the airflow from the Panaflo can be felt all around the HS, despite the fan being much smaller than the top area of the fins.

The commentary below refers mostly to the diode temperatures with Prime95, as core temperature under long term 100% load is the most critical data.

Note that 20+ minutes of Prime95 by itself is far more stress than most user would subject their system to in normal circumstances.

Reference Panaflo fan

Reference Panaflo FBA08A12L1A 80mm fan: 24 CFM, 21 dBA @ 1 m, 12V

  • All temperatures in degrees Celsius.
  • Diode: reading from XP1600+ CPU internal thermal diode
  • Socket: reading from in-socket thermistor on ABIT KT7A-R motherboard, latest BIOS
  • Board: reading from DigiDoc thermistor placed ~ 4 inches over northbridge chip on motherboard
  • The room temperature during all the testing: 22° Celsius., measured with DigiDoc thermistor ~6 inches above CPU HS and fan.

Results at 12V: Much as Expected

Model
° C at Idle, 10 mins
° C with Prime95, 20+ mins
Diode
Socket
Board
Diode
Socket
Board
SLK800
33
31
24
41
35
24
AX7
38
34
24
48
40
24
6000CU
43
36
25
56
45
28
MC462A
38
33
25
48
40
26

The Panaflo is rated for 24 CFM airflow in free air at 12V. The Thermalright SLK800 comes out on top by a substantial margin, especially at 100% CPU load. Second place is shared by the AX7 and Swiftech MC462A, which post identical numbers, a surprising 7° C behind the leader. The Zalman comes in last, a whopping 15° C behind the leader and 8° C behind the second placers when under load.

Results at 7V: Tighter grouping

Model
° C at Idle, 10 mins
° C with Prime95, 20+ mins
Diode
Socket
Board
Diode
Socket
Board
SLK800
40
36
24
50
44
25
AX7
44
38
25
55
47
26
6000CU
49
43
27
63
52
29
MC462A
44
39
25
55
48
26

At 7V, the Panaflo can be expected to blow about 14 CFM (according to calculations). It is very quiet at this voltage. Rankings are little changed, but the gaps between the contestants have narrowed by a few degrees.

Results at 5V: An Upset!

Model
° C at Idle, 10 mins
° C with Prime95, 20+ mins
Diode
Socket
Board
Diode
Socket
Board
SLK800
49
42
25
70
58
27
AX7
50
45
26
63
56
27
6000CU
59
51
28
79*
64
30
MC462A
51
47
26
70
57
27

*Stopped before 20 minutes -- see text below.

At 5V, the Panaflo is pretty much inaudible but still blows about 10 CFM (according to calculations, not by measurement). Interestingly, rankings have changed dramatically. At idle, the Thermalrights and the Swiftech are tightly placed in a 2° C window. This is within the margin of error for the test system; they might be considered about equal. But with the CPU under load, the AX7 is now clearly top dog, and the SLK800 and the Swiftech share second place 7° C behind! *The Zalman probably hit thermal overload; the temperature was still creeping up when the plug was pulled on after 18 minutes to avoid CPU damage.

High Power Fan Check

Finally, a high power fan that is likely to be used by performance enthusiasts was brought in for a kind of reference check. The fan is a Sanyo-Denki 80 x 32 mm model 109P0812A201 rated at 53 CFM, 45 dBA, 4600 rpm, 0.56 amp. Quieter than the 80 CFM Delta that is sometimes marketed with high power HS, but loud enough to deafen most ordinary folks. It is the official lower noise fan that came with the Swiftech MC462A. Measured 1 cm from the frame (like the Panaflo), the noise reading is 85 dBA(!), and the vibration it produces is enough to make the whole test platform hum and buzz when simply placed on top of the HS. Here's what it does with these HS:

Sanyo-Denki fan @ 12V
Diode reading in ° C
Idle
Max
SLK800
31
37
AX7
37
44
6000CU
39
47
MC462A
36
41

The SLK800 comes out on top as expected. The Swiftech rises with the high airflow, confirming the often repeated statement that it is optimized for performance with high airflow. The AX7 falls a few degrees behind, and the Zalman brings up the rear with a perfectly respectable 47° C. Now, none of the contenders exceeds 50° C, which is remarkable considering this is the in-die core temperature. The price is a gradual decline into deafness.

DATA ANALYSIS

The test system's AMD XP1600+ (Palomino core) is rated to produce 62.8W maximum at the default 1.75V Vcore. All monitoring programs show the test motherboard's Vcore, set to default, to be 1.81~1.84V, slightly higher than normal. This puts the power up a bit; let's call it 65W. This assumes Prime95 working in Windows XP causes the XP1600+ to dissipate 65W.

HS cooling performance is best summarized by ° C/W or how many degrees the object temperature rises for each watt of heat it dissipates. A specification of 1° C/W means temperature rises by 1° C for each watt of heat -- this is very bad performance for a CPU HS, BTW.

Using 22° C (measured 6 inches above the fan intake) as the room ambient temp, the ° C/W calculated for each HS at each fan voltage (with Prime95) is shown below.

Temp rise is probably the simplest, most useful data here. If you're considering using one of these HS with a similar CPU, just add the appropriate temp rise number to your case ambient temp and you'll get a reasonable prediction of performance in your setup. Temp rise refers to the temperature rise in ° C over ambient temperature - the difference between diode temp readings and the room ambient.

Model
Panaflo 12V

Panaflo 7V

Panaflo 5V
Sanyo-D 12V
Temp rise
° C/W
Temp rise
° C/W
Temp rise
° C/W
Temp rise
° C/W
SLK800
19
0.29
26
0.40
48
0.74
15
0.23
AX7
26
0.40
33
0.49
41
0.63
22
0.34
6000CU
34
0.52
41
0.63
58
0.88
25
0.38
MC462A
26
0.40
33
0.49
48
0.74
19
0.29

Note that the high airflow (53 CFM) Sanyo-Denki has the most dramatic impact on the 6000CU: an improvement of 9° C (compared to the result with the 24 CFM Panaflo). The Sanyo-Denki fan improves the Thermalright models only by 4° C and the high-airflow optimized Swiftech by 7° C.

CONCLUSIONS

Real world conditions are tougher than those in our lab. When a system is installed in an enclosed case, the ambient temperature is sure to rise at least 5° C, sometimes 10° C or more, depending on particulars. Many quiet PC enthusiasts run systems with no case fan or just one low airflow fan. In consideration of these factors, low noise enthusiasts are urged to add 10° C to the results above when trying to guesstimate what their temperatures would be. Note too, that the results here are specific to the XP1600+ Palomino.

It is best to regard the test results not in an absolute way, but rather, as comparative guidelines. The result obtained with any of these heatsinks will vary greatly on the particulars for each system.

#1 - Thermalright SLK800: There is little question that the SLK800 is a topnotch performer with almost any level of airflow. Its overall design is ingenious and well executed, and extremely user friendly. Its small footprint makes it feasible to install even on motherboards with little room around the socket. We are in agreement with the overclocking and performance community: this is one hell of a HS.

#2 - Thermalright AX7: Beaten out from second spot by the Swiftech only in the extreme airflow contest (which we don't really care about here), the AX7 is an excellent performer and a tremendous value. Like the SLK800, its clip is user-friendly and easy to use, even though its larger size makes it difficult on tight motherboards. Its performance with the 5V Panaflo is an amazing victory -- but remember that the actual temperature reached was in excess of 60° C. If you add 10° C for an approximation of in-case temperature, use of a 5V Panaflo with this HS -- or any other in this round up -- on an XP1600+ or higher power processor is not a safe recommendation.

#3 - Swiftech MC462A: There are good reasons why this model was the kingpin for so long. It retains its edge well against newer competitors sporting more recent technologies. Sheer size and mass, combined with manufacturing excellence and a great mounting system combine for good cooling performance even with low airflow. The performance of its descendants is something I look forward to examining.

#4 - Zalman 6000Cu: Saved from humiliation with its fine high-airflow performance, the 6000Cu suffers in comparison with the other contenders. The soft 2-lug clip is the weakest part of its design, and is probably responsible for the poor showing here. An afterthought following the tests: Does this particular Zalman clip provide enough pressure between the CPU die and the HS base? Weeks of preliminary test setup experimentation meant all of the HS in this survey were mounted and removed from the motherboard many times. It is possible that the Zalman clip suffered more deformation and metal fatigue than the clips on the Thermalright models, causing a reduction in contact pressure. A follow-up on this suspect clip is promised.

This review has naturally resulted in a few small changes of the rankings in our Recommended Quiet Heatsinks, which you'll want to review before making any buying decisions.

Socket-A Heatsink Roundup Intro - p.1

Thermalright SLK800 - p.2

Thermalright AX7 - p.3

Zalman CNPS6000cu - p.4

Swiftech MC462A - p.5

* * * * *

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