Cooling an overdriven amp (1 Viewer)

[xslntx]

I've got an older Kenwood amp, a KM-105. I'm using it as a subwoofer amplifier. It's rated for an 8 Ohm load only, but both subwoofer drivers are 4 ohms. I have each driver wired to it's own channel, as I can't afford the power loss of wiring them in series. I'm fairly sure if I push it the way it's running now, it won't last long, so I'm looking for an active cooling solution.


I've got a couple computer fans laying around, and I can wire them into the amplifier to be switched with the main power, I'm just not so sure as to how to go about installing them.

My plan was to completely cover the top air vents, save for one spot in the center, where I'll put the fan blowing upwards. It'll take in air from the side vents, blowing over the heatsinks on it's way to the fan. Any thoughts? I'll take some pictures to make it more clear in a few minutes.


Also, does anybody have any experience with the KM series amplifiers from Kenwood? Are they any good?

 

[Adam Gregorich]

Bryan-

Welcome to Home Theater Forum. I'm not familiar with the Kenwood KM series, but its not a good idea to overload any amp. ATM makes some of the best cooling systems: http://activethermal.com/page8.html

 

[xslntx]

Thanks Adam. I know overloading amplifiers isn't the greatest thing to do, but it was free, and it's all I have right now. I'm not looking to spend any money for the time being, hence why I'm looking to design my own cooling system, I'm just no engineer.


With regards to the amp, I should also mention, though the amp is rated at 8 ohms, it has outputs for 4 speakers. Left and right, banks A and B. Would I be correct in assuming that, if it were to drive four 8 ohm speakers, it would create a four ohm load for each channel? And if so, would that mean that it should be fine driving just two 4 ohm woofers?

 

[Robert_J]

Would I be correct in assuming that, if it were to drive four 8 ohm speakers, it would create a four ohm load for each channel?

Not always. Sometimes the A/B switch connects the speakers in series. It all depends on the receiver's design.

I've got a couple computer fans laying around, and I can wire them into the amplifier to be switched with the main power, I'm just not so sure as to how to go about installing them.

Computer fans are 12v DC. The receiver's switched output is 120v AC. You need an AC to DC converter that supplies the appropriate voltage and amperage. It can be as simple as connecting the fans to a wall-wart.

 

[xslntx]

I went ahead with the fan installation. It was straightforward, and I think, it turned out great. I did some more digging, and found that the amp is indeed stable at 4 ohms with just two speakers, outputting 200wpc RMS. I was told it wasn't necessary for it to be actively cooled, but with my usage, I figured it'd help it last longer.



I drilled a small hole through the back of the unit, installed a rubber grommet, and fished the adapter's wire through. The original plan was to disassemble the adapter and install it within the amplifier itself, but I couldn't find my soldering iron.






Next, I cut a hole in the top cover, between the capacitors and rear panel. I found this to be the best place, partly because of the ample amount of space, but it's also the one place where air doesn't have a direct path from the bottom of the unit upwards.

For the fan to be effective, I also had to seal the top air vents of the unit. Thus, air will flow through the vents in the bottom and sides, effectively cooling both heatsinks, as well as the transformer.




This is the end result. I will eventually get around to painting the top panel, but there's no hurry. After pushing it for a good three hours, the amplifier didn't break a sweat. Air coming out the fan was warm as expected, and upon removing the top cover, the heatsinks were easily cool enough to touch. Before this procedure, they'd be too hot to touch.



... The spider on that white piece of wood kept getting away from me.