3 Zalman Power Supply Units Roundup

Today we are going to introduce to you three newest power supply units from a well-know manufacturer of PSUs and cooling solutions – Zalman. Our tests showed that these three products definitely deserve your closest look especially if you are about to go for an advanced high-performance system and value low noise and excellent cooling.

by Oleg Artamonov
03/12/2004 | 02:09 AM

The Korean Zalman is a well-known manufacturer of CPU cooling systems with an original, although sometimes disputable, design. The developer has always been striving for minimizing the noise from its cooling solutions having invested a lot of time and effort into the so-called Computer Noise Prevention System as Zalman and did reach this goal just when the fast-growing frequencies and heat dissipation of central processors had provoked the arrival of efficient, but very noisy cooling systems, to users’ unanimous indignation.


Zalman’s ambition went further as the company started producing a small but carefully collected assortment of computer parts, including ATX power supply units (PSU). Zalman classifies them as CNPS systems, too.

This article is going to take a closer look at three different PSUs that sell under the Zalman trademark.

Zalman ZM300A-APF

The junior model of the PSU series from Zalman comes in a plain white box, but you receive the same accessories as the purchaser of the more advanced products: a power cable, a ZM-MC1 adapter for attaching system fans, and a comprehensive user’s manual. The manual not only contains installation instructions and the list of declared specifications, but also explains some PSU-related terms. For example, you can learn the difference between passive and active power factor correction there.

The adapter (you see it next to the PSU in the snapshot) is plugged into any of the PSU power connectors for IDE devices (PC plug). On the other end of the adapter we have four 3-pin connectors for attaching system fans. Two of them receive +12V voltage and the other two get +5V voltage; in other words, you can easily reduce the rotation speed – and the noise! – of the attached fans. It seems reasonable, however, to try to modify the adapter for outputting two +7V currents as I guess there are few users who have four system fans in their computer, while two fans that work at an intermediate voltage (and speed) are a more likely situation. You probably know that this modification is performed by supplying +12V to the fan’s “plus” and +5V to its “minus”. This operation requires just a thin screwdriver and half a minute of your precious time: detach both 5V wires from the PC plug connector and move the black +12V wire (“ground”) into the cell where the red +5V wire used to be.

The external resemblance of this PSU to products from FSP Group is confirmed as we open the PSU case: it is marked as “FSP300-60PLN”. In other words, we have a PSU from FSP Group that sells under the Zalman trademark. It is quite natural as FSP Group is more involved into OEM manufacture, while Zalman operates in the retail market.

The device is the height of accuracy inside: everything is neatly soldered up and fitted together and all potentially hazardous elements have heat-shrinkage insulation. The line filter is soldered on the main board and consists of two inductors. The filter wire also has a ferrite pipe on (you see it in the snapshot – it is wrapped into heat-shrinkage cambric and is fastened to the heatsink with a nylon brace). Such trifles indicate high quality of the PSU. If the manufacture saw to every little detail, we may expect that everything else will be up to the mark, too.

The PSU deviates somewhat from the industry-accepted standard as it uses the relatively rare single-cycle circuit. Accordingly, the high-voltage rectifier at the input has one 180uF, which corresponds to two 360uF capacitors in the ordinary two-cycle circuit. The capacitance is rather low for a 300W PSU, but this model uses active power factor correction and has demands less from the capacitance of the rectifying capacitor.

The manufacturer also took care of the heatsinks, which have exactly the necessary thickness, about 4mm. It is a fact that the thinner the heatsink is, the wider the temperature gradient along this heatsink is. That is, the insufficient heat conductivity of the thin aluminum sheet results in the temperature on top of the heatsink being much lower than that at the bottom (where the heat-producing transistors and diodes are fastened). So the top of the heatsink doesn’t play any role in cooling. Practice shows that the 4mm thickness is the most reasonable choice for a small heatsink – without spending extra material, but providing enough cooling. Larger heatsinks may require to be around 6-7mm thick, but they are not for standard computer PSUs then.

Among other pleasant trifles we may notice the diode assemblages and transistors placed into liquid paste for better heat conductivity (besides the standard heat-conductive isolators) and equipped with ferrite pipes on their pins for filtering high-frequency noise. Regrettably, such care about small things is rare nowadays…

I was most curious to see the cooling of the PSU. Zalman promotes actively its Computer Noise Prevention System brand claiming that equipment under this brand contributes to making your computer less noisy. Meanwhile, we have an ordinary 80mm fan (Protechnic Electric MGA8012HB) here, which is also installed into other PSU models from FSP. The fan is connected via an automatic rotation speed controller (you can see its sensor on top of the heatsink with the output diode assemblages). As our measurements showed, the fan speed is increasing steadily from 1370 to 1900rpm as the load grows from 50 to 280W. There is no activation threshold as in other models from Fortron/Source (for example, in FSP300-60BTV) – the speed increases smoothly. The fan produces some noise, of average loudness, not annoying. However, this PSU can’t be called perfectly noiseless.

The PSU offers you seven IDE plugs, two FDD plugs, ATX12V, AUX and 20-pin ATX connectors. Most of the cables have an 18AWG section – that’s the norm for a good 300W PSU.

As I have mentioned previously, this device features active correction of the power factor. It allows reaching a power factor of 95-98% against 70-75% in PSUs without such correction or with passive correction.

The oscillogram of the output +5V voltage looks reassuring: the wave peaks don’t exceed 20mV in average. Short peaks only appear when switching transistors change their status, but such peaks are nearly unrecognizable by the oscilloscope I use.

It’s nearly the same with the +12V power rail, only the swing is higher, but the maximum acceptable swing on this rail is also higher, according to the standard.

I can’t say this is the ideal picture as I saw PSUs with no noise at the output at all, but the noise we have here is acceptable and is not a problem at all.

The unit shows excellent voltage stability. For example, 7% instability of the +12V voltage is considered a good result, and 10% instability is downright poor, so the 6.3% shown by the ZM300A-APF is simply an excellent result.

The test graph shows that the unit produced no significant artifacts like a too-long time it takes the output voltage to stabilize after a sudden load change (if the voltage regulator is bad, the voltage needs 0.5-1s to get stable changing by 100-200 millivolts in the process). Such voltage surges here boast small amplitude and do not last long.

So the ZM300A-APF should without doubt be placed among the best PSUs we have tested so far in out labs as it shows a high quality of manufacture and excellent characteristics (well, these things usually go along together). I can’t call this unit perfectly noiseless, but it uses a good fan and a rotational speed control to make this noise as quiet as possible.

Zalman ZM400A-APF

The more advanced (400W) model from Zalman comes in a comely black box. The dimensions of the box as well as its contents are practically identical to the package of the ZM300A-APF: a PSU, a user’s manual, a power cable and a ZM-MC1 adapter for attaching system fans.

You should be aware that despite the high claimed power, only the maximum current on the +5V bus exceeds that of the above-described model (40A against 30A), while other characteristics are identical. So if your computer system has problems with the overloaded +12V bus, you can’t solve them by installing a ZM400A-APF instead of the ZM300A-APF. That’s because the ATX standard clearly defines recommended allowable currents for PSUs up to 300W (30A on the +5V power bus, 28A on the +3.3V power bus and 15A on the +12V power bus). If the PSU has a higher wattage, each manufacturer chooses his own way: some increase currents on all buses, others do this for one or two buses only. By the way, I’m talking about high-quality products now, as low-end PSUs often have “paper” characteristics, which don’t necessarily coincide with their actual capabilities.

The PSU seems to be different from the above-described model, but this impression is only due to the black color of the case. In fact, the ZM300A-APF and the ZM400A-APF have absolutely the same cases.

The PCB now carries the name of Zalman, but this label shouldn’t confuse you: the internal structure of the unit is not absolutely identical, but very close to the ZM300A-APF, which is manufactured by FSP Group. It is of course possible that Zalman is producing these units in its own facility under a license from FSP, but not very likely. The habitual letters “SPI” (SPI Electronics is a member of FSP Group) are written on the power transformer of the PSU. I don’t have exact data about how the ZM400A-APF fits into the model range of FSP Group, but it’s quite logical to suppose that it is a closest relative of the FSP400-60PFN.

This unit has a more respectable look in comparison to its lower-wattage predecessor. The filtering capacitors have increased their power (the input high-voltage rectifier now uses a 330uF capacitor – double capacitance compared to the ZM300A-APF. I couldn’t make out the capacitance values of the output rectifiers, as all components are very tightly packed in the unit, but their larger dimensions indicate certain changes). The T-shaped heatsinks also have impressive dimensions: the thickness of the vertical pole is about 4-5mm, while the horizontal line is one millimeter wider. Small and thick ribs cover both parts of the heatsinks and the whole construction provides efficient cooling of the transistors and diode assemblages.

ZM400A-APF, like the previous PSU, features active correction of the power factor: the circuit board is visible in the second snapshot of the internal structure of the device, to the left of the big capacitor of the high-voltage rectifier.

This unit comes with a more expensive fan from NMB (Minebea Co., Ltd.), the 3110GL-B4W-B30 model. The maximum speed of this fan is 2700rpm and it is pumping 31.78 cubic feet per minute producing 28dB of noise at the same time.

Our measurements showed that the rotational speed of the fan is smoothly changing from 1200 to 2250rpm depending on the temperature. The thermal diode sits on the end of the heatsink – you can see it in the first snapshot of the internal unit construction. The fan is absolutely silent under the minimal load, as its speed is very low (so don’t be afraid if it doesn’t spin up at all when you turn your system on). According to the manufacturer, after a “burning” test with a load of 375W, the fan reached the speed of 2250rpm, but was modestly loud – about 23-24dB.

The unit has seven IDE power connectors, two mini-plugs for floppy drives, ATX12V, AUX and 20-pin ATX connectors. Most cables have a 16AWG section, which is the norm for high-quality units of 300W wattage and up.

The oscillograms of the +5V voltage show no considerable fluctuations: in fact, we have only noise here.

Small fluctuations appear in the oscillogram of the +12V voltage and sometimes short voltage surges appear when the inverter transistors are switched. However, these fluctuations are much below the maximum acceptable level. Thus, the PSU shows excellent results in this aspect, too.

The stability of the voltages is somewhat poorer than we had with the previous model, but this is caused by the increased load: such behavior is usual for PSUs of different wattages, but assembled according to similar circuit schemes. However, this instability is not catastrophic – the unit still shows excellent performance. The test graph shows no serious artifacts, save for the higher +12V surges when the load changes, but this is explained by the fact that the +5V power bus has a wider load range now due to the higher wattage of this unit.

I’m sure this model deserves your attention. As its predecessor, ZM400A-APF is a high-quality product, showing excellent results in our tests. Add also such nice features as an effective thermal control and a very quiet fan – the last feature is really rare in PSUs of such high wattage as manufacturers often prefer to put a powerful fan to solve the cooling problem altogether. On the other hand, if your computer experiences problems with its current 300W PSU, ZM400A-APF won’t help you in all cases. Particular bus that cannot provide enough power to the components of your system.

Zalman ZM400B-APS

This is the newest PSU from Zalman coming in a colorful box, although different from the package of the ZM400A-APF. The contents of the box remained the same, though. We have a 400W PSU in a black case, a power cable, a user’s manual and a ZM-MC1 adapter.

The unit itself is different, however. Just look at the connectors: besides the ordinary seven PC plugs for IDE devices, the unit offers two connectors for SerialATA drives – you don’t have to use adapters anymore. Moreover, the maximum load current on the +12V power bus has increased to 12A, while other parameters remained the same.


The internal structure of the device requires no comments. As you see in the snapshots, it is analogous to that of the above-described ZM400A-APF. Moreover, the PCB marking reads “ZM400A”. In other words, the difference between the models is reduced to the availability of the SerialATA connectors and the higher output current without any significant changes in the circuitry. So we turn to the testing part right away.

The fan and the thermal regulator where this fan is actually attached don’t differ from those of the previous PSU. It is the same quiet NMB 3110GL-B4W-B30 blower that changes its speed from 1230 to 2050rpm depending on the wattage. As you see, the difference in the absolute speeds is small, while the curves showing the dependence of the speed on the load are just identical.

The oscillograms fully repeat the results of ZM400A-APF, while the voltage stability parameters are somewhat different:

The stability of the +5V voltage degenerated more than the others, by about 2%. This is mostly because of the higher maximum load current on the +12V power bus – of course, it was higher in our tests, too. The stability of the other voltages changed slightly, so this unit also gets our applause.

The first visual inspection made it clear that ZM400B-APS was just a slightly improved ZM400A-APF. It boasts the same highest quality of manufacture and a very quiet fan. Considering the small difference in price, the newer model has a higher appeal to the customer.


So we have tested three power supply units selling under the Zalman brand. According to the company’s website, the model range now includes four models: the three we have just introduced to you plus ZM300B-APS model.

All three units are manufactured for Zalman by FSP Group, a respected maker of high-quality PSUs. The quality is high in this case, too, and the attention to every minute detail is really impressive. The characteristics of the devices also match best models from other renowned companies. By the way, I think the argument about the best PSU, whether it should come from Zalman or from FSP, doesn’t make any sense, since Zalman actually sells top models from FSP.

300W ZM300A-APS can be regarded as an excellent choice for mainstream computers: 300 Watts is enough for a majority of system configurations, save for the most advanced ones. You shouldn’t be misled by the company’s claims about its noiselessness, though. This PSU uses a good, but quite ordinary 80mm fan for cooling.

400W ZM400A-APF and ZM400B-APS are an ideal choice for hi-end computer systems, including two-processor workstations that put strictest demands on the power source. If you have a choice between these two units, you’d better go for the newer model, ZM400B-APS, which surpasses 300W PSUs in all parameters, while the ZM400A-APF won’t always help you if the standard 300W PSU is insufficient for your system. Both models are equipped with very quiet fans from NMB with an effective temperature control circuit. This feature distinguishes these products from other PSUs of the same wattage.