Audiophile Amplifier Cooling

I love our Hafler XL-280 amplifier. Rated at 145 watts RMS per channel, it produces enough energy to play loud on speakers with low efficiency levels. And its high-current abilities make it a great companion for even the most demanding speaker designs. Its fabled MOS-FET transistors create a musical and pleasing sound that is thought to be similar to tube amps, while maintaining the accuracy of solid-state amplifier designs. On the downside, the Hafler’s relatively high class-A output is anything but energy efficient and produces lots of heat as a result. Hafler did provide large external heat sinks, one on each side of the amp, to provide passive cooling, but on warm summer days, the transistors on our 1988 unit go into self-protect mode and begin limiting current, a measure that is audible through a flat and compressed sound and a helpless flapping noise instead of solid bass. When I first heard it, I mistakenly took our CD player to be at fault and had it serviced. Little did I know that what I was hearing was caused by an overheated amp.

As I learnt, there were many factors that may have caused our old amp to overheat. For one thing, the transistors are usually coupled to the heat sinks with the aid of a heat-conducting paste. When this paste becomes brittle with age, its capacity to transport the temperature away from the transistors lessens. Secondly, the perfect place for a large power amp would be close to the floor, where transformer vibration can be best absorbed, and where the temperature is usually the lowest. In our setup, however, the amp was placed at about 40cm height right under a slanted roof. This brings me to a third factor: The temperature in attic rooms — and such is our Listening Room II — are usually higher than in the rest of the house. Due to all this, there was just not enough cool air passing the transistors and heat sinks to maintain normal operating temperatures for our amp, causing it to eventually limit the current travelling though the transistors.

Hence, I needed to find a cooling solution that would solve my heat problem without interfering with the integrity of the music. And — as is usual when there is a problem — there was the immediate excitement that presented itself from a new possibility for exploration. I started browsing the web and found some existing PA solutions, involving cooling fans built into 19-inch rack cabinets, as well as a range of individual fan motors with separate heat sensors for rack installation. However, none of these offers were particularly silent, good looking, or even practical for a HiFi setup. It was not until I came across AC Infinity's "AIRCOM S9" that I began to think audiophile amp cooling was within reach, even for amps that did not have super silent air movers built in from the beginning. And yet, from the product description alone, I could already guess that some additional work would be needed.

AC Infinity builds air movers in various formats that extract heat in different ways: e.g., to the front, to the back, etc. The company has its roots in audio engineering, and I saw that the S9 conveniently had the exact width of the Hafler amp. It extracts the air from any device placed underneath and propelled it straight upward by means of three ultra-silent movers. I anticipated this design to be most beneficial for my application, although I had not yet decided whether to place the AIRCOM S9 underneath or above our amp. Since the S9 was built with modern multi-channel amplifiers in mind, rather than 2-channel vintage equipment, it was about 20cm deeper than our Hafler, which entailed that I would need to design an additional support for its rear feet to incorporate it in our setup. I chose the S9 over its more expensive sibling, the T9 (which would have had more features and digital technology on board), because I felt that fewer digital gimmicks would mean less interference on the audio stream. Sadly, both units came equipped with rather unpleasant and un-audiophile switching power supplies, a fact that was already apparent from their descriptions online. In my eyes, a contradiction to the company philosophy.

I saw that AC Infinity were selling their S9 at very affordable prices in the USA. The price for the same product from a German importer was approximately double. I weighed my options and decided to buy from the German importer, thinking that I would support a local firm, have improved support options and also receive a power supply made for the German market. It turned out that the latter was not the case, and that I had simply paid a 100% markup for the same product with US power supply that would not even fit into a German AC outlet. I was quite disappointed, made a mental note never to buy from that German supplier again and exchanged the cheap and non-compatible switching supply for a conventional regulated one with obvious audiophile advantages, as it would not cause as much as a ripple on the power grid. — While my caution regarding switching supplies is often humoured by non-audiophiles, I later read that not few of AC Infinity's customers had complaints about electronic noise radiating into their audio systems; a phenomenon that I have not experienced using a linear supply.

When switched to temperature triggered operation, the S9’s internal heat sensors will start the fan motors automatically when the amp becomes too hot. There are two modes: a simple on-off switching at a given level setting when the temperature limits are reached, and a smoother heat-dependent operation in which the AIRCOM sensors determine the level setting independently. Both settings only work when the unit is based above the amp, as heat rises upward. I consequently designed a simple stand that would position the cooler above the amp without hindering much of the original air-flow. The design has proven itself to work very well. In simple on-off switching mode, the AIRCOM S9 turns on for the first time after the Hafler XL-280 has been running for about 1-1.5 hours. It then remains on at the preset speed (level 1 of 4) for approximately 40 seconds, before switching off again for about 5-10 min. In heat-dependent mode, the S9 runs more often for shorter intervals. Obviously, the cooler the room, the less cooling is needed.

Since the AIRCOM S9's lowest level of operation should be sufficient for most household applications, the S9 is quiet enough to be classified as an audiophile cooler. While I can detect the aeolian tones associated with soft wind in a silent room, this sound is almost completely absorbed once music is playing, even when it is playing at very low volume. My observations were made sitting 2.5m away from the device diagonally. In combination with our Hafler, this audiophile fan cooling system is doing a wonderful job.

Specifications:

• Manufacturer: AC Infinity Inc
• Product: AIRCOM S9
• Type: audiophile fan cooling system
• Air movers: 3x dual-ball bearing fans
• Motors: PWM-controlled
• Manual controls: 4-step
• Thermal controls: 2 trigger modes
• Extraction: vertically upwards
• Airflow: 210 CFM
• Noise emission: 1 dBA
• Dimensions: (W) 43,2cm x (D) 34,3cm x (H) 3,8cm
• Year: 2021

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