I built a dummy load box using a pair of Caddock 100 Watt 4 Ohm non-inductive metal film resistors. The resistors, along with a 55C thermostat are mounted to the bottom of a heatsink extrusion.
Two 40mm fans on the rear panel pull air through the front (the panel with all the holes) and exhaust out the back once the heatsink reaches 55C. The power for the fans is 5 Volt USB.
I used a simple heavy-duty SPDT switch to select 4 Ohm or 8 Ohm load. The input terminals are regular speaker binding posts and the output is a Neutrik XLR/TRS combo jack. The output is floating to feed a balanced signal to downstream stuff. The wiring is 14-gauge silicone insulated.
At about 120 Watts for 1 hour (8 Ohms) the fans hold the heatsink steady at 68C and shut off (when the input is removed) at around 33C. I am sure I could improve the cooling efficiency by baffling around the heatsink, but for the time being, I am happy with the setup.
Like my other instrumentation efforts, the panels were designed in KiCad and ordered in aluminum from JLCPCB.
Two 40mm fans on the rear panel pull air through the front (the panel with all the holes) and exhaust out the back once the heatsink reaches 55C. The power for the fans is 5 Volt USB.
I used a simple heavy-duty SPDT switch to select 4 Ohm or 8 Ohm load. The input terminals are regular speaker binding posts and the output is a Neutrik XLR/TRS combo jack. The output is floating to feed a balanced signal to downstream stuff. The wiring is 14-gauge silicone insulated.
At about 120 Watts for 1 hour (8 Ohms) the fans hold the heatsink steady at 68C and shut off (when the input is removed) at around 33C. I am sure I could improve the cooling efficiency by baffling around the heatsink, but for the time being, I am happy with the setup.
Like my other instrumentation efforts, the panels were designed in KiCad and ordered in aluminum from JLCPCB.
Attachments
Dummy load using BOSE SA2 amplifier
I repurposed a BOSE SA2 standalone amplifier (Please don't use a BOSE SA3 since they can be used standalone.....)
Discusssed here.... Non inductive resistors... Fine for testing my amplifiers since they peak around 50W/channel....
Audio dummy load
I repurposed a BOSE SA2 standalone amplifier (Please don't use a BOSE SA3 since they can be used standalone.....)
Discusssed here.... Non inductive resistors... Fine for testing my amplifiers since they peak around 50W/channel....
Audio dummy load
Attachments
I use four large waterheater elements, only in my application they're convection cooled. They're about 10 ohms each, and I have it configured such that I can get either two 5 ohm loads, one 10 ohm load, or a 2.5 ohm load. Seems to serve well enough, and I've put about 2 kW continuous into it for over an hour without killing it.
Ideal? Probably not, but it was cheap and seems to work acceptably. Not sure how inductive it is, but I can still measure about 0.002% THD from a power amp with it. That's the limit of my analyzer at the moment.
Next step is to build a 10:1 divider for it. Might see if I can get away with an uncompensated divider for this one. Should be possible if I keep the impedances low enough.
Ideal? Probably not, but it was cheap and seems to work acceptably. Not sure how inductive it is, but I can still measure about 0.002% THD from a power amp with it. That's the limit of my analyzer at the moment.
Next step is to build a 10:1 divider for it. Might see if I can get away with an uncompensated divider for this one. Should be possible if I keep the impedances low enough.
My dumb project.
Here’s a dummy load I built for running in new amplifiers before I trust them on speakers.
Two Ohmite 7.5 ohm 100W non-inductive resistors (Digikey AP1017R5J-ND) mounted to a big heatsink. They actually measure 7.8 ohms, but I bought the 7.5 ohm resistors because they were cheaper than 8 ohm, and in stock.
Here’s a dummy load I built for running in new amplifiers before I trust them on speakers.
Two Ohmite 7.5 ohm 100W non-inductive resistors (Digikey AP1017R5J-ND) mounted to a big heatsink. They actually measure 7.8 ohms, but I bought the 7.5 ohm resistors because they were cheaper than 8 ohm, and in stock.
