Stress Test Amplifiers

Jeff Duns

Member
Joined
May 12, 2014
Morning All,

My current employer has been developing an in-house avmangament team.
The growing pains for them are harsh. Currently one of the problems is the testing, disposal, repair and re-issuing of old gear.

I need some help in building a test bench to load stress amplifiers. I currently have an inventory of 50+ amplifiers that I need to go through to see what their issues (if any) may be.

A previous employer had a workbench to stress test amplifers, where a we connect the amps to a dummy and let the amps run to see what the issue might be. The issue I have currently is the amplifers are a mix or 4/8ohm and 70v

Can anyone give me some guidance on where to start and what not to do. I have basic electronic repair and diagnosic knowledge.

Thanksk for oyur help,

Cheers
 

TJCornish

Well-Known Member
Joined
Mar 27, 2012
Location
St. Paul, MN
Get heavy electric heating elements from someplace like Grainger. Choose so you have the impedance you want to test at - 4 ohms is probably the right choice for those amps, and enough current capacity. Mount these elements in a large plastic garbage can filled with water. Here's a picture of a similar setup: https://soundforums.net/threads/3723-Powersoft-K3-K20-M50Q-(Part-II)?p=26177&viewfull=1#post26177

MAKE SURE YOU FILL THE CAN WITH WATER!! The elements are dissipating the output from the amplifier, and this makes heat (duh).

Depending on what you're trying to test, putting a signal in and watching what comes out with a DMM might be enough. Going deeper requires some kind of waveform display. Note that if you're trying to hook an oscilloscope up to your amplifier outputs, you really need an isolated differential input probe to prevent blowing up your scope.

While running, wiggle, thump, etc. You can compare operation of similar models to see if one of them runs particularly hot, etc.

The procedure for 70v is similar, and if the amp is large enough, you can probably use your 4ohm load to test these too, or you may be able to rewire your heating elements to a higher impedance. Modern 70v amps are often exactly the same as 4ohm/8ohm amps with a high pass filter. Older ones and/or small ones may have a real transformer output which may be a little harder to test unless you run a higher load impedance.
 

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