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Dummy Load Build- Input Welcome

Hikmat said:
amazing work! any chance you would be interested in Dummy load build for noobs? i know you make your own case and heatsink but maybe there’s a way to source them online?
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Thanks, I don't make videos, but will try to post a parts list here and could answer whatever questions you have. The heatsink came from ebay and I don't know where to get another, and it was modified anyway. I think you could probably mount the resistors on the bottom of the case (maybe on another thicker aluminum plate) and just let the fans blow directly on them. I still want to re-make the case with spelling corrected, and could probably be talked out of the current one if you give me some time.

I have used it few times including with my Spec 2 at full power, and it worked fine. I didn't leave it on long enough to see how long it would take for the overtemp to trip, but will do that when I get to the full restoration. I haven't even made the cover for it yet..

For now, here are corrections to the scope and 12V circuits.

Dummy_Load_1[1].jpeg
 
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Reviving an old thread I know but I landed here because of the OP's thread on his SPEC 2.
This is an awesome build and I may steal a few ideas to build my own. Kudos to @kevin b
I have always heard that amplifier dummy loads need to be non-inductive (https://www.parts-express.com/8-Ohm-200W-Non-Inductive-Dummy-Load-Resistor-019-030?quantity=1) and the OP used wire wound resistors (RX24 200W 8R High Power Resistor, Aluminum Housing Power Resistor, 8 Ohm 200 Watt Wirewound Resistor with Mounting Holes for Power Supply Audio Elevator Industrial : Amazon.ca: Industrial & Scientific) which makes them inductive. How much does this really matter? Thoughts?
 
xlbee said:
Thoughts?
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Not much. Dunno what the inductance actually is but can't be all that high. Could do some tests to power resistors I have available. With a sine wave of 1 kHz it prolly won't matter at all but power tests with a square wave could lead to surprises. The 50 watters on my dummyload are non-inductive so I will have to look for regulars to compare.

Edit: my Dale NH-50s test 195 nH and 7.97 ohm, the RH-50s I have do 1.60 µH and 12.1 ohm (part from a three resistor 4R dummyload). At 20 kHz the reactance of 1.6 µH is 0.2 ohm so that's not a whole lot.
 
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PE9ZZ said:
At 20 kHz the reactance of 1.6 µH is 0.2 ohm so that's not a whole lot.
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Interesting. So if one were simply doing a power limiter adjustment at 1 kHz or testing for maximum output before clipping/distortion at 1kHz then it probably doesn't matter much at all. If however you are testing frequency response and THD under load all the way up to 20 kHz (or maybe even 40 kHz just for fun) then it might make a bit of difference.
Given that speakers are not pure resistive loads, I realize that a non inductive load does not accurately represent a speaker load but is used so that the industry can have a standard way of doing amplifier measurements without being impacted by the differences of an infinite number of speaker designs. I guess it just depends how precise you want to be.
 
You can never cater for a plethora of speaker configs. A power amp has to dictate to the speaker how to behave. It's called damping factor. If it does that well your amp sounds good. It is a special measurement. Almost nobody does that as it already has been done during development of the amp. Or should have.

The purpose of a dummy load it to provide a known load and prevent you going deaf. Whether it has a tiny bit of inductive reactance in it doesn't really matter.
 
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