Scythe Kotetsu CPU Cooler: A Compact King

Weighing just over a pound and having only a single 120 mm fan, the Scythe Kotetsu still manages to compete and beat much of the larger competition.

April 30, 2014 by Lawrence Lee

Product	Scythe Kotetsu CPU Cooler
Manufacturer	Scythe
MSRP	US$35

Scythe took a big step last year with the Mugen 4. It wasn’t a particularly revolutionary or even evolutionary design and in fact it was almost identical to its predecessor. However, it was one of the best CPU coolers we’ve tested, thanks in no small part to an upgraded modern mounting system which we’ve been suggesting they switch to for years. Its modest composition also made it relatively light and more affordable than much of the high-end competition, and of course Scythe fans are renowned for their pleasant acoustics.

The Kotetsu.

While Noctua, Prolimatech, and Thermalright have gone on to produce some massive dual fan heatsinks during a cooling arms race, Scythe has refrained from participating, preferring to focus on more pragmatic fare. The Kotetsu is one such cooler, essentially a more compact and affordable version of the Ashura, which is a wide tower cooler with a 140 mm fan and six heatpipes. The Kotetsu is smaller in every dimension except height, and is equipped with only a 120 mm fan and just four heatpipes. Its dimensions and shape are similar to dozens of others, which is rare for a Scythe product.

We were somewhat disappointed by the performance of the Scythe Ashura. It wasn’t a bad cooling solution by any stretch of the imagination but it was a letdown as a follow-up to the Mugen 4. We suspect its oddly shaped base prevented it from realizing its full potential, and while the Kotetsu base has a similar surface, it appears to have been refined.

The box.

Contents.

The Kotetsu ships in a modestly sized boxed adorned with color pictures of the product and a few badges touting its various features. Its contents include the heatsink itself, a 120 mm fan, mounting hardware, thermal compound, one set of fan clips, and a brief assembly guide. As per usual, it’s compatible with every modern desktop socket and older ones going back 8 years.

Scythe Kotetsu: General Specifications (from the product web page)
Model Name	Kotetsu CPU Cooler
Model Number	SCKTT-1000
Compatibility	160
Socket compatibility	Intel®: Socket LGA775 Socket LGA1150 Socket LGA1155 Socket LGA1156 Socket LGA1366 Socket LGA2011 (Square ILM)AMD®: Socket AM2 Socket AM2+ Socket AM3 Socket AM3+ Socket FM1 Socket FM2 Socket FM2+ Please note that for mounting on motherboards with the AMD-Socket, the original back plate of the motherboard will be necessary. Please confirm if it is on hand prior to your purchase.
Dimensions	130 x 58 x 160 mm / 5.12 x 2.28 x 6.3 in (WxDxH)
Weight	480 g / 16.93 oz (Heatsink only)
Accessory	Mounting plate x2 (Intel), mounting plate x2 (AMD), mounting bar x1, screws for clips x4, mainboard screws x8, mounting screws x2, back plate spacer (Socket 775) x1, washers x4, wrench x1, fan clips x2, thermal grease, backplate, installation manual
Baseplate Material	Nickel-plated Copper
Fan Specifications
Model Name	GlideStream 120 PWM
Model No.	SY1225HB12M-P
Fan Size:	120 x 120 x 25 mm / 4.72 x 4.72 x 0.98 inches
Noise Level	5.3 ~ 28.0 dBA
Air Flow	20.7 ~ 79 CFM
Fan Speed	400 rpm (±200) ~ 1400 rpm (±10%)
Voltage / Current	DC 12V / 0,09A
Static Pressure	1,18 ~ 15.3 Pa / 0,12 ~ 1.56 mmH²O
Bearing Type	Sleeve Bearing

PHYSICAL DETAILS

The Kotetsu has a traditional composition for a budget tower cooler. Its 56 aluminum fins are friction-fit to 4 x 6 mm thick copper heatpipes, which in-turn, are soldered to a nickel-plated copper base. According to our measurements, the heatsink’s dimensions are 130 x 58 x 161 mm (L x
W x H) and its weight is 490 grams (tack on another 120 grams for the included 120 mm stock fan).

In typical Scythe fashion, the Kotetsu’s heatpipes are arranged in straight rows. Interestingly, the fin-stack is not uniform, with a third as many fins at the center than on either side.

According to our instruments, the fins are 0.35 mm thick and spaced 1.66 mm apart, on average. This arrangement is denser than most modern heatsinks, which typically impedes low airflow performance.

With raised sides, the face of the heatsink is sculpted for a 120 mm fans only. Trenches have been cut into the side for two sets of fan clips even though only one pair is provided.

The base is similar to the Ashura. It has a convex surface with an apex at the center, the peak of a very shallow hill. However, some of the nickel has been stripped away in the middle, revealing a more coppery color compared to the silvery edges.

The Ashura’s base is uniform by comparison.

The Kotetsu shares the same stock fan as the Mugen 4, a GlideStream 120 PWM model with a nominal speed of 1400 RPM.

INSTALLATION

The most critical aspect of installation is that the heatsink
be securely mounted; A firm mounting results in good contact between the cooler’s
base and the CPU heatspreader and more efficient heat conduction. Ideally it
should also be a simple procedure with the user having to handle as few pieces
of hardware as possible. The Kotetsu uses the same mounting assembly as the Ashura, which satisfies everything on our checklist.

Mounting system assembled sans heatsink.

Mounting clips installed and thermal compounded applied.

The crossbar is fitted to the slots above the base.

Fully assembled on our LGA1366 test platform.

The Kotetsu cleared all the surrounding board components with plenty of room to spare. The distance between the bottom fin and the board PCB was 53 mm.

The thermal compound footprint wasn’t exactly even but the very faint residue at the center indicates excellent contact where it counts the most.

Imprint left by the Ashura. The amount of residual compound in the middle is sizable by comparison.

TESTING

Before thermal testing, we took some basic physical measurements.

Approximate Physical Measurements
Weight	490 g (+120 g with stock fan)
Height	161 mm
Fin count	56
Fin thickness	0.35 mm
Fin spacing	1.66 mm
Vertical Clearance*	56 mm
* measured from motherboard PCB to bottom fin of heatsink

 

Large Heatsink Comparison: Average Fin Thickness & Spacing
Heatsink	Fin Thickness	Fin Spacing
SilverStone Heligon HE02	0.52 mm	3.30 mm
Thermalright HR-01 Plus	0.45 mm	3.15 mm
Thermalright HR-02 Macho	0.34 mm	3.12 mm
Thermalright HR-22	0.53 mm	2.74 mm
Scythe Ninja 3	0.39 mm	2.64 mm
Noctua NH-U12P	0.44 mm	2.63 mm
Noctua NH-C12P	0.47 mm	2.54 mm
Noctua NH-D14	0.43 mm	2.33 mm
Thermalright Archon SB-E	0.49 mm	2.33 mm
GELID Tranquillo Rev.2	0.40 mm	2.30 mm
Phanteks PH-TC12DX	0.39 mm	2.30 mm
GELID GX-7 Rev.2	0.31 mm	2.25 mm
Phanteks PH-TC14PE	0.40 mm	2.21 mm
be quiet! Dark Rock 2	0.38 mm	2.22 mm
Prolimatech Armageddon	0.51 mm	2.08 mm
Prolimatech Megahalems	0.50 mm	2.00 mm
Zalman CNPS10X Quiet	0.40 mm	2.00 mm
Scythe Ashura	0.43 mm	1.97 mm
Scythe Kabuto & Zipang 2	0.34 mm	1.94 mm
NZXT Havik 140	0.41 mm	1.91 mm
Scythe Mugen-2	0.31 mm	1.89 mm
SilverStone Tundra TD03 (radiator)	0.43 mm	1.86 mm
Swiftech Polaris 120	0.43 mm	1.85 mm
SilverStone Argon AR01	0.30 mm	1.85 mm
Thermalright Venomous X	0.53 mm	1.84 mm
Scythe Mugen 4	0.30 mm	1.82 mm
Noctua NH-C14	0.38 mm	1.79 mm
Enermax ETS-T40	0.40 mm	1.79 mm
Scythe Yasya	0.32 mm	1.78 mm
be quiet! Shadow Rock Slim	0.42 mm	1.73 mm
SilverStone Argon AR03	0.42 mm	1.72 mm
Noctua NH-U14S	0.42 mm	1.72 mm
Cogage TRUE Spirit 1366	0.40 mm	1.70 mm
Arctic Cooling Freezer Xtreme Rev.2	0.30 mm	1.70 mm
Scythe Kotetsu	0.35 mm	1.66 mm
Scythe Grand Kama Cross	0.38 mm	1.66 mm
Reeven Kelveros	0.47 mm	1.61 mm
Zalman CNPS9900 MAX	0.16 mm	1.59 mm
Thermalright Silver Arrow	0.32 mm	1.57 mm
Cooler Master Hyper 212 Plus	0.43 mm	1.54 mm
Thermalright Ultra-120 eXtreme Rev.C	0.56 mm	1.52 mm
Zalman CNPS10X Extreme	0.42 mm	1.50 mm

Testing on larger heatsinks like this one is done on our
LGA1366 heatsink testing platform, while smaller coolers are tested
on our LGA1155
heatsink testing platform. A summary of the test system and procedure
follows.

Key Components in LGA1366 Heatsink Test Platform:

• Intel Core i7-965 Extreme
  Nehalem core, LGA1366, 3.2GHz, 45nm, 130W TDP.
• Asus
  P6X58D Premium ATX motherboard. X58 chipset.
• Asus
  EAH3450 Silent graphics card.
• Intel
  X25-M 80GB 2.5″ solid-state drive. Chosen for silence.
• 3GB QiMonda
  DDR3 memory. 3 x 1GB DDR3-1066 in triple channel.
• Seasonic X-650 SS-650KM
  650W ATX power supply. This PSU is semi-passively cooled. At the power levels
  of our test platform, its fan does not spin.
• Arctic Silver
  Lumière: Special fast-curing thermal interface material, designed
  specifically for test labs.
• Noctua 140 mm fan (used when possible with heatsinks that fit 140x25mm
  fans)
• Nexus 120 mm fan (used when possible with heatsinks that fit 120x25mm
  fans)
• Nexus 92 mm fan (used when possible with heatsinks that fit 92x25mm
  fans)

Key Components in LGA1155 Heatsink Test Platform:

• Intel Core i5-2400 Sandy Bridge core, LGA1155, 3.1 GHz, 45nm, 95W TDP, overclocked/volted to 3.6 GHz and 1.300V.
• Intel DP67BG ATX motherboard.
  P67 chipset.
• Asus
  EAH3450 Silent graphics card.
• Kingston
  SSDNow V 30GB 2.5″ solid-state drive. Chosen for silence.
• OCZ Platinum Extreme Low Voltage DDR3 memory. 2 x 2 GB, DDR3-1333 in dual channel.
• Seasonic X-400 SS-400FL
  400W ATX power supply. Passively cooled
• Arctic Silver
  Lumière: Special fast-curing thermal interface material, designed
  specifically for test labs.

The systems are silent under the test conditions, except for the CPU cooling
fan(s).

Normally, our reference fans are used whenever possible, the measured details
of which are shown below.

Reference Noctua 140mm fan Anechoic chamber measurements
Voltage	Speed	SPL@1m
12V	1250 RPM	28~29 dBA
9V	990 RPM	21 dBA
8V	880 RPM	18 dBA
7V	770 RPM	15~16 dBA
6V	660 RPM	13 dBA

 

Reference Nexus 120 mm fan Anechoic chamber measurements
Voltage	Speed	SPL@1m
12V	1080 RPM	16 dBA
9V	880 RPM	13 dBA
7V	720 RPM	12 dBA

 

Reference Nexus 92 mm fan Anechoic chamber measurements
Voltage	Speed	SPL@1m
12V	1470 RPM	17 dBA
9V	1280 RPM	14 dBA
7V	1010 RPM	12 dBA

Measurement and Analysis Tools

• Extech 380803 AC power analyzer / data logger for measuring AC system
  power.
• Custom-built, four-channel variable DC power supply, used to regulate
  the fan speed during the test.
• PC-based spectrum analyzer:
  SpectraPlus with ACO Pacific mic and M-Audio digital
  audio interfaces.
• Anechoic chamber
  with ambient level of 11 dBA or lower
• Various other tools for testing fans, as documented in our
  standard fan testing methodology.
• SpeedFan,
  used to monitor the on-chip thermal sensors. The sensors are not calibrated,
  so results are not universally applicable. The hottest core reading is used.
• Prime95,
  used to stress the CPU heavily, generating more heat than most real applications.
  All instances are used to ensure full stress.
• CPU-Z,used to monitor the CPU speed to determine when overheating occurs.
• Thermometers to measure the air temperature around the test platform
  and near the intake of the heatsink fan.

Noise measurements are made with the fans powered from the lab’s variable DC
power supply while the rest of the system is off to ensure that system noise
do not skew the measurements.

Load testing was accomplished using Prime95 to stress the processor, and the
graph function in SpeedFan was used to ensure that the load temperature is stable
for at least ten minutes. The temperature recorded is the highest single core
reading. The stock fans were tested at various voltages to represent a good
cross-section of airflow and noise performance.

The ambient conditions during testing were 10~11 dBA and 21~23°C.

STOCK FAN MEASUREMENTS

Specifications: Scythe Kotetsu Stock Fan
Manufacturer	Scythe	Power Rating	2.16 W
Model Number	SY1225HB12SM-P	Airflow Rating	20.7 ~ 79 CFM
Bearing Type	Sleeve	Speed Rating	400 (±200 rpm) ~ 1,400 rpm (±10%) (PWM-controlled)
Frame Size	120 x 120 x 25 mm	Noise Rating	5.3 ~ 28 dBA
Hub Size	36 mm	Header Type	4-pin PWM
Blade Diameter	113 mm	Starting Voltage	3.5 ~ 4.0 V
Cable Length	30 cm	Weight	120 g
Corner Type	Open	Retail Availability	No
Additional notes:

The Kotetsu’s stock fan is identical to that of the Mugen 4. This Glide Stream 1400 RPM PWM model is not sold to the public though there is a 1300 RPM variant available for sale. The fan’s structure is similar to that of the Slip Stream series, with a small hub and struts curved in the opposite direction of the blades.

Stock Fan Measurements
Voltage	Speed	SPL@1m
12V	1410 RPM	29 dBA
9V	1130 RPM	22~23 dBA
7V	900 RPM	16 dBA
6V	790 RPM	14 dBA
5V	670 RPM	12 dBA
Measuring mic positioned 1m at diagonal angle from the center of the heatsink. Ambient noise level: 10~11 dBA.

1400 RPM is well-suited for a CPU cooler, allowing for a versatile range in terms of noise. The fan was fairly loud at full speed (29 dBA@1m) but it quieted down dramatically as the speed was reduced, becoming quiet somewhere around 1000 RPM. Furthermore, at 800 RPM, it was almost inaudible, and at <700 RPM, it was practically silent. The SPL measurements were very close to the Mugen 4 sample with a variance of at most, 1 dB.

According to ASUS’ Fan Xpert 2 utility, the included fan is controllable down to ~400 RPM and ~560 RPM via voltage and PWM control respectively.

As we’ve remarked in previous articles, the Glide Stream 120 has a pleasant sound. Its acoustic profile was mostly bereft of tonality, sounding smooth and innocuous. It whined somewhat at higher speeds, but this is typical of almost all sleeve bearing fans. Faint clicking was also observed at lower speeds but this was only audible at close distance.

TEST RESULTS

Test Results: Scythe Kotetsu (stock fan)
Fan Voltage	Fan Speed	SPL@1m	Thermal Rise
12V	1410 RPM	29 dBA	34°C
9V	1130 RPM	22~23 dBA	35°C
7V	900 RPM	16 dBA	38°C
6V	790 RPM	14 dBA	41°C
5V	670 RPM	12 dBA	42°C
Reference Nexus 120 mm Fan
12V	1080 RPM	17 dBA	37°C
9V	890 RPM	14 dBA	38°C
7V	720 RPM	11~12 dBA	41°C
Measuring mic positioned 1m at diagonal angle from the center of the heatsink. Ambient noise level: 10~11 dBA.

The Kotetsu proved to be an excellent cooler, generating a thermal rise above ambient of 34°C at 12V — this is a tremendous result at any noise level, even 29 dBA@1m. At the lowest tested fan voltage/speed, the result was only 8°C higher. The stock fan’s performance was pretty good as well, though our reference Nexus fan had a 3°C advantage at 14 dBA.

HEATSINK COMPARISON TABLES

°C Rise Comparison: CPU Coolers with Single Stock Fan (Any Size)
SPL (dBA@1m)	20	19	18	17	16	15	14	13	12	11
Scythe Kotetsu					38		41		42
Thermalright Archon SB-E	39						40			43
Thermalright HR-02 Macho		39				40	41		43
Scythe Mugen 4					40			42		45
Noctua NH-U14S		38			40			43
be quiet! Shadow Rock Slim		40			41		42
Scythe Yasya			40					43
Cogage TRUE Spirit 1366				41		43			46
Zalman CNPS10X Quiet	40						42		47
Scythe Ashura		42				44
Cooler Master Hyper 212 Plus			41					44	54
Silverstone Argon AR03			43							48
Scythe Ninja 3			44					46
SilverStone Argon AR01			44							50

Despite it’s modest size, the Kotetsu’s performance was top-notch out-of-the-box even against the much larger Thermalright Archon and HR-02 Macho. Compared to other coolers that ship with a single stock fan, the Kotetsu bested them all, though the margin of victory was quite slim.

°C Rise Comparison: CPU Coolers with Single 120 mm Reference Fan
Heatsink	Fan voltage / SPL @1m*
	12V (~17 dBA)	9V (~14 dBA)	7V (~12 dBA)
Scythe Kotetsu	37	38	41
Scythe Mugen 4	37	39	41
Thermalright Ultra-120 eXtreme Rev.C	38	40	43
Thermalright Venomous X	38	41	43
Prolimatech Megahalems	38	41	44
SilverStone Argon AR03	38	41	45
Noctua NH-U12P	39	42	44
Scythe Mugen-2	39	42	45
Phanteks PH-TC12DX	40	42	45
Cogage TRUE Spirit 1366	40	42	45
Zalman CNPS10X Quiet	40	43	46
SilverStone Argon AR01	41	43	46
Scythe Yasya	41	43	47
Thermalright Ultra-120 eXtreme	40	43	48
Cooler Master Hyper 212 Plus	41	44	48
*Note: there are minor differences in measured SPL due to the variety of fan orientations and mounting methods offered by the compared coolers.

When we equal things out by using our reference Nexus 120 mm fan, the Kotetsu retains its lead, essentially on par with the Mugen 4, and a step ahead of the Thermalright U120E and Venomous X.

MP3 SOUND 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.

These recordings are intended to give you an idea of how the product sounds
in actual use — one meter is a reasonable typical distance between a computer
or computer component and your ear. The recording contains stretches of ambient
noise that you can use to judge the relative loudness of the subject. Be aware
that very quiet subjects may not be audible — if we couldn’t hear it from
one meter, chances are we couldn’t record it either!

The recording starts with 5 second segments of room ambiance, then the fan
at various levels. 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.

• Scythe Kotetsu/Mugen 4 with stock fan at 1m
  — 5V (11 dBA@1m)
  — 6V (13 dBA@1m)
  — 7V (16 dBA@1m)
  — 9V (23 dBA@1m)
  — 12V (29 dBA@1m)

FINAL THOUGHTS

The Scythe Kotetsu is an amazing heatsink, delivering elite level cooling despite its relatively modest size and lightweight construction. It seems to have managed this by improving on the base design of the Ashura while retaining its superb mounting system. The Ashura’s base appears almost perfectly conical with its apex refracting light like a prism. The surface of the Kotetsu’s base isn’t as severely shaped, with the area around the center forming a sort of plateau indicated by the surrounding discoloration. So while the two coolers have similar compositions, the larger Ashura doesn’t make as much contact with the CPU heatspreader, and ends up losing out to its smaller cousin. This reinforces the argument that base shape may be the most important aspect of heatsink construction.

The Kotetsu is a complete package, excelling in every area. The stock fan, typical of Scythe heatsinks, not only performs well but has an excellent sound that rivals any current out-of-the-box cooling solution. The mounting system is easy to put together and very secure; the only thing that could make it better is thumbscrews. It’s also a tremendous value as the MSRP is a very low US$35.

Unfortunately, the Kotetsu is currently available only at a handful of retailers in Europe and Asia though we did find it listed at one North American site (out of stock and priced at US$10,000 to dissuade ordering). Given Scythe’s recent distribution issues, it’s unclear when we’ll see it in the wild on this side of the world, but we anxiously await its arrival.

Our thanks to Scythe
for the Kotetsu CPU cooler sample.

Scythe Kotetsu
receives the SPCR Editor’s Choice Award

* * *

SPCR Articles of Related Interest:

Thermalright HR-22 CPU Heatsink
Noctua NH-U14S Slim 140mm Tower Cooler
Scythe Ashura CPU Cooler
SilverStone Tundra TD03 Liquid CPU Cooler
Scythe Mugen 4 CPU Cooler: Scythe Strikes Back
NoFan CR-95C Copper Fanless CPU Cooler

* * *

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