Testing high power power amps

[bobschwenkler]

I have a 1200 watt amp I've just finished fixing up and want to sell. How are amps like this normally tested before, say, going out to stores as new? What are some methods used to test devices like this at high power outputs?

 

[JohnRoberts]

1200W is not big by modern standards but will melt your small power resistors.

The common load for serious power testing is water heater coils or something similar, If you size them right they are a fair load for an audio amp, 4 ohms or so,  Some put them in buckets filled with oil to dissipate the heat, of course don't over heat oil.

The heater coils will not be resistive enough for low distortion measurements at power. I recall having some special non-inductive load resistors for bench testing the big dogs.

JR

 

[bobschwenkler]

I suppose it's not that big by general standards. Big in regards to my experience at least...

I'm not as concerned with accurate distortion measurements etc, as just making sure the thing will hold up after I've sent it out.

Thanks, I'll look further into your information. What would you recommend for ensuring I'm not overheating, say, a heater coil such as mentioned? Oil seems excessive to me for the few instances I'll be using it, but perhaps not?

 

[JohnRoberts]

In theory pure water is not a conductor but I think most people use oil, but the heater elements are intended to sit in a water tank. 

If you are not doing long term power testing you might get away with air cooling and a fan, a 120v- 4 ohm element is more than 1200W.

heres one of several examples on WWW

http://www.synaudcon.com/site/blog/the-mother-load-a-dummy-load-for-testing-large-amplifiers/

Have fun and don't burn down your house...

JR

 

[PRR]

> you might get away with air cooling and a fan

Those water-heater elements look like only 4 square inches of surface area. I think in air even 300 Watts would put them at several or many thousands of degrees. Hot enough to change value, also melt and splatter.

They are scaled for water.

For an hour, I'd just set in a metal bucket with water over the element but not much on the seal.

If he were making a habit of this.... a 1500-2000W 120V water heater complete is $200-$250, could be plumbed to the shower for ample bathing. Little more to set up, but more fun than hauling a pot of boiling water up from the lab.

Actually, the only test for a power amp is to loan it to the loud kids down the block. If it comes back working, it's OK.

 

[bobschwenkler]

Actually, the only test for a power amp is to loan it to the loud kids down the block. If it comes back working, it's OK.

For some reason we don't have any of them in my neighborhood. I'm not missing out on anything, am I?

Thanks for the advice, I'll be looking into this before long, I'll report back in for those interested in my implementation.

Also, I've not done much testing of this type before, and none at all with dummy loads (on power amps). Are there any specific testing methods I ought to know about, or particular spots in the circuitry I should be watching in any certain ways? My intuition and knowledge would otherwise just tell me to hook it up ahead of an amp meter and give it signal.