Vasily Ivanenko has written an article detailing his AF dummy load project:
I’ll describe a simple 8, or 4 Ω dummy load to test your home brew guitar power amplifiers.
Low cost 16 Ω / 25W wire wound, aluminum shell, chassis mount resistors seem abundant. I got mine on eBay. Wire wound resistors vary in quality, design and tolerance. Some even exhibit low inductance by winding with an Ayrton-Perry bifilar technique. Resistor tolerances range from 10% down to ± 0.5 % + 0.05 Ω. Typical manufacturer power ratings are done at 25C, however, these devices are meant to sit on a heat sink when used and that’s why the aluminum housing contains 2 relatively large mounting holes.
The current source introduced in this article is capable to handle current up to 6A with maximum input voltage of 50V. This is an operational amplifier based adjustable current source and it uses LM358 in a general voltage follower configuration. To handle large currents we use four 0.1Ω 20W resistors as “load resistor”, and those load resistors are drive through pair of 55N06 N-channel MOSFET transistors.
The power supply unit of this project is build around 9V x 2 (2A) step-down transformer and it is design to get regulated 12V DC voltage. In our design this 12V power source is used to drive LM358 Op-Amp and 12V cooling fan.
I bought a couple of IXYS linear MOSFETs (IXTK90N25L2) a while ago to test their capabilities when used as electronic load, and the result was quite impressive. So I decided to build another electronic load using both MOSFETs. As you can see in the video towards the end, this electronic load can sink more than 100 Amps of current while dissipating more than 400W continuously and can withstand more than 1kW of power dissipation in pulsed operation mode.
This is a quick post to showcase 100W 4 channel AF dummy load which we build to test the output stages of audio power amplifiers. This dummy load use 4, 8Ω 100W wire wound resistors which are available in eBay. In this unit all 4 resistors are mounted on 170mm × 40mm × 60mm high gauge aluminum heat sink.
I finally found some time to check out the UCload project. A couple of weeks ago I quickly soldered the PCB and wrote a quick’n’dirty firmware for it. The basic functionality was working, but it wouldn’t do good for the shiny display.
Today I locked myself in my mancave and shut myself off from the world. Turned the light down, pulled loud music from the speakers and started coding like hell!! Not exactly but I found some time to write some more decent firmware for this load. In a previous revision of the PCB I forget the pull up resistors and swapped the SDA and SCL signals. I corrected that and made some small other changes (still ****ed up the silkscreen) in revision 2. The hardware is quite OK and rock solid (prolly more due to the robust FET then my analogue skills :)). However I managed to use a 1n4148 diode to measure the temperature. Connect it to the heat sink and if that one gets to hot turn on a fan. It accuracy is terrible but capable of detecting over temperature :)