DDDumy Load, a versatile power dummy load tool - diyAudio
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Old 8th January 2014, 09:11 PM   #1
dddac is offline dddac  Germany
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Default DDDummy Load, a versatile power dummy load tool

The name is just aligned on all my DDDAC stuff, so a bit a joke.

The Dummy load however is not! You know this: Testing an amplifier or power supply, fumbling together some resistors which are in the hobby box. Never get to the right value and when you don't watch for a moment, smoke gets in your eyes

So I finally found the time to make something "for the rest of my life" and just wanted to share this as an idea how you could make your own test equipment.

I selected, very arbitrarily, 2x9 Values of 100Watt resistors. Idea is that with a patch panel and patch cable, most useful combinations can be done, by creating series and parallel values. (1E 2E2 3E3 6E8 10E 22E)
Three values might look out of line (100E, 1K and 3k3) but these coming in handy with tube amplifiers
Decided to make it double (useful with stereo )

And it should look good as well , so I spent some money on a nice Front from Schaeffer... (as I do for all my projects )

Bought a "Pesante" Chassis in Italy with a mounting rack, which also works as extra heatsink and mounted the whole bunch. All worked out fine and beyond my expectations; all resistor values are within 1% (checked this with a precise current source and high quality DC voltage meter)

No rocket science as you see, so let the images speak for itself
Attached Images
File Type: jpg DDDummy Load 1.jpg (404.6 KB, 275 views)
File Type: jpg DDDummy Load 2.jpg (300.4 KB, 270 views)
File Type: jpg DDDummy Load 3.jpg (391.7 KB, 268 views)
File Type: jpg DDDummy Load 4.jpg (475.8 KB, 267 views)
File Type: jpg DDDummyload 01.jpg (390.5 KB, 259 views)
Attached Files
File Type: pdf DDDummy Load Front.pdf (32.4 KB, 19 views)
File Type: pdf DDDummy Load v1.pdf (177.8 KB, 30 views)
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Last edited by dddac; 12th January 2014 at 10:21 AM. Reason: typos...
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Old 9th January 2014, 05:21 PM   #2
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Quote:
Originally Posted by dddac View Post
I selected, very arbitrarily, 2x9 Values of 100Watt resistors. Idea is that with a patch panel and patch cable, most useful combinations can be done, by creating series and parallel values. (1E 2E2 3E3 6E8 10E 22E)
...... ...... all resistor values are within 1% (checked this with a precise current source and high quality DC voltage meter)
No rocket science as you see, so let the images speak for itself
Are these resistors non-inductive type ?. How about force cooling them with a fan ?.
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Old 9th January 2014, 05:54 PM   #3
dddac is offline dddac  Germany
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I am not sure if they are official non inductice, but measured with my Audio Precision 2322, I could go up to 200kHz without significant impedance Change

Fan cooling is not necesarry Unless you use them all at the same time at 100 Watt
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Old 13th January 2014, 01:38 PM   #4
tvrgeek is offline tvrgeek  United States
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But loads on amplifiers are not restive, they are complex. Power supply load testing, fine. Amps can get quite upset with complex loads which is why the old Power Cube was invented. I would love to see a DIY version. Inductive loads, not that bad. High C ( as some speakers or worse, audiophile cables) can be.
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Old 13th January 2014, 07:42 PM   #5
dddac is offline dddac  Germany
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Originally Posted by tvrgeek View Post
But loads on amplifiers are not restive, they are complex. Power supply load testing, fine. Amps can get quite upset with complex loads which is why the old Power Cube was invented. I would love to see a DIY version. Inductive loads, not that bad. High C ( as some speakers or worse, audiophile cables) can be.
good point, you can easily put those in parallel with the resistive load. Would have been nice in ine chassis, but as you can see it is full already !

maybe time for the DDReactive Load
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Old 13th January 2014, 07:58 PM   #6
tvrgeek is offline tvrgeek  United States
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Ah, toss in a few 2u's. There's room.

There have been several SPICE models for speakers presented. Might find one and build it real. Of course, when you think you have got it solid, some clown will put a crossover notch in the midband that drops to zero.

I have been exploring amplifier protection with my "Reasonable" amplifier model. Learned a lot. So much more to learn. One thing that comes out is no matter how clever you are, you still need some basic stupid fail-safes, like a snap switch on the heat sink and some fuses. I have been simulating this with a 2 Ohm, 4 uF load at clipping. Ugly things come out in the Bode plots forcing me to drastically limit the IPS bandwidth.
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Old 14th January 2014, 12:36 AM   #7
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I have had a home made bare chassis one of those for years.
The biggest amp I have ever tested on it was 500W per channel and the owner claimed that it once belonged to Pink Floyd.
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