Amplifier Cooling Upgrade

This article was first published in 2004.

Amplifiers live and die on the basis of heat. If they get too hot, the output power drops and the likelihood of distortion rises. Get really, really hot and they stop working forever... That’s especially the case with subwoofer amps which work longer and harder than any other amps in the car. It’s also harder to hear sub distortion so it’s easy to have the sub turned up a bit too high for long-term amplifier health. However, improving amplifier cooling is easy - and you don’t need to be an electronics expert. The cost can also be near zero – all you’ll need is a small fan, some surplus heatsinks and a few hours of time.

And as a bonus, you can also improve the amp’s appearance.

The amp that we modified was a cheap secondhand unit that while nothing fantastic, when run in bridged mode produces adequate power for a high efficiency subwoofer. It’s labelled as costing AUD$129, but we knocked this secondhand price down to a neat one hundred bucks.

Turning it over reveals a pressed sheet steel cover...

...which is easily undone by removing four screws. Nearly all amps use similar construction.

This is what the amp looks like inside. As you can see, the printed circuit board normally hangs upside down when the amp is mounted horizontally. A thick aluminium extrusion forms the main body of the amp and the electronic devices needing heatsinking are clamped against its inner surface.

Here are the power transistors clamped against the inside of the extrusion – the whole housing then acts as the heatsink.

Improving the heat transfer away from these electronic components requires some heatsinks and a fan. These heatsinks were salvaged from other equipment, as was the fan. You’ll find heatsinks in nearly any piece of electronic gear that’s thrown away. For their new role, the heatsinks were shortened with a hacksaw and then smoothed with a file.

Heatsink compound (available from electronics shops) should be applied to the top of the components before attaching the heatsinks. The compound thermally connects the heatsink and the component, providing much better heat transfer.

This tube of heatsink compound – enough for probably five amplifiers – cost AUD$3.65 from www.jaycar.com.au.

The heatsink compound was applied to each component and then....

...the new heatsinks were screwed into place. While these heatsinks look puny compared with the heatsinking abilities of the whole case, the fact that these will have airflow passing over their fins makes them much more effective than their size would suggest.

Both ends of the amp used heatsinked components so new heatsinks were added at the other end as well.

Here are the new heatsinks in place at one end...

...and at the other.

We decided to replace the original bottom cover with a new one on which the fan could be located. To improve appearance, the new cover was made from 5mm thick clear acrylic. Here the acrylic is shown with its protective paper in place – leave it there until the job is completely finished.

The hole for the 2¼ inch fan was cut with a holesaw. In this case the fan was able to be located inside the amplifier – there was just enough clearance. If there isn’t room, it can be mounted on the outside. The fan draws air from inside the amplifier. So that this air flows over the new heatsinks, intake air holes (shown by the green arrows) were positioned directly over the new heatsinks.

The new bottom panel, yet to be cleaned but with all the holes in it. The upper section of each hole was chamfered slightly with a pointy grinding stone rotated in an electric drill. The panel was attached to the amplifier using the original screw holes.

Be careful when cutting and drilling acrylic. It is quite brittle and can easily shatter when being worked. Use a blunt drill!

The new panel in place.

The wiring for the fan was brought out through a new hole drilled in one of the end plates. It was then connected across the remote and earth inputs, so that the fan operates only when the amp is turned on.

The fan that is used is actually a 24V design. But it works fine on 12V, is compact and was available for nothing (like the heatsinks, it too had been salvaged from other equipment. In fact, it came from a discarded photocopier.)

The fan was a tight fit inside the amp – the leads of this capacitor needed to be bent slightly to create room.

Here are the chamfered intake holes positioned directly above the heatsinks at one end of the amp.

A Velometer Jnr instrument was used to measure the airflow through just one of the intake holes. As the instrument shows, there is more than 200 feet per minute airflow through each hole.

No before/after testing was done of the temperature build-up in the amp but you can be certain that with the added heatsinks and the fan-forced air movement, cooling has been improved.

The amp can now be either mounted ‘bottom-up’ to show off this view, or alternatively mounted conventionally but spaced 10-15mm above the mounting surface to allow for air movement.