Dummy load

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   Previously we've always had a single channel 8R/4R switchable load made from a boiler heater coil (huge open wire wound resistor) where the 4R is tapped from the middle, encased in silversand. It still works fine, but it only had a single speakon and a single mains socket outlet for plugging in 4mm banana jacks (this fits perfectly!). 
So last summer i decided to make a new version. It should be capable of testing 4 channel amplifiers in 8R, or dual channel amplifiers in 4R.
It's based around 4*2kW (@120V) heater elements, each element measures around 7.5R. The cavity around the elements is fully stuffed with fine grain silver sand to absorb the heat from the elements.
The volume of the box was designed such that the silver sand inside wouldn't get above 60C after 2 minutes of sustained 4x1kW loads. Looking back this is probably a bit overkill as the box got quite heavy.

Box is made from scrap wood, 15mm HPL laminated birch from an old kitchen and some fenol coated birch.

Drying the silver sand out in the sun, to then be poured into the case before the side was glued in place.

The connector panel is made with 1x Speakon per heating element and 2 switches that set channel 1 and 3 to a 4R load by wiring channels 2 and 4 in parallel to them. I've also 2 sets of 4mm safety jacks to easily connect a high voltage probe for the scope or a multimeter. The switches took a while to get in as apparently DPDT switches aren't very common in the netherlands for general purpose electrics usage. Nominally rated for 16A, i guess they will be fine for the relatively short usage they will see higher sustained currents than that.

The PCBs are some custom ones i've drawn in Kicad, basically just a simple breakout so you can solder a wire into a hole instead of to the terminal.

And the final product. 

Edited by Teunos - 07 December 2024 at 9:41am