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DIY Speaker / Amplifier Dummy Load

 Giovanni Militano  Canadian Flag   To email Gio, type out the email address.

DIY Speaker / Amplifier Dummy Load

This is a simple DIY Speaker dummy load that was put together very quickly. After constructing an AMP6 T-Amp kit, and while testing the maximum power output using 4.7 ohm 50W ceramic power resistors the hot resistors had begun to scortch a cutting mat they were resting on and also melting the wire insulation of test leads which had fallen on one of the hot resistors. So rather than test with unsecured hot resistors, it was necessary to build a properly enclosed speaker dummy load that would not be a fire hazard.

Rather than just using a load resistor across the output of an amplifier, it is often nice to also be able to hear output during testing. The schematic below shows two dummy loads, built into one enclosure. With a speaker connected, the amplifier will see either a 4.3 or 7.4 ohm load while the attached speaker will receive less than about 1% of the output power. You can check the net load for yourself by following the basic electronics formulas. With a simple setup like this you can test at high power without risking damaging speakers, going deaf or driving other people crazy. If a speaker is not connected to the dummy load, the amplifier will see either a 4.5 or 8 ohm load.

DIY Speaker Dummy Load Schematic

Figure 1: DIY Speaker Dummy Load Schematic

The two dummy speaker loads are housed in the same type of aluminum baking pan that I used for my 50EH5 Single Ended Tube Amplifier. To help promote cooling, I mounted the 50W resistors to heat sinks that had been salvaged from dead computer power supplies. The 4.5 ohm resistor is attached to the larger heat sink. The aluminum enclosure also helps dissipate some heat from the resistors. Since the resistors are cooled somewhat, it is ok to apply more than 50W of power for a very SHORT period of time, but don't get carried away.

DIY Speaker Dummy Load

Photograph 1: Underside View of DIY Speaker Dummy Load

I used binding posts to allow for easy connection to and from the dummy load. The binding posts also make it easy to add a small capacitor or inductor if you want to try different load scenarios when testing an amplifier.

DIY Speaker Dummy Load

Photograph 2: DIY Speaker Dummy Load

 NEW  - Matt shares with us his build of a fantastic looking dummy speaker load box. The dummy speaker load box is configurable for 2-ohm, 4-ohms, 6-ohm, 8-ohm, 16-ohm and 32-ohm loads.