Power amplifier tests with respect to FTC: 16 CFR Part 432 (July 5, 2024) requirements on output power claims

[amirm]

The same test, 5 minutes 150W:

That's a toy amplifier. Come back with results of amp producing 1500 watts in stereo or bridged.

 

[peng]

That's a toy amplifier. Come back with results of amp producing 1500 watts in stereo or bridged.

Also, 8 ohm isn’t that bad but we already know 4 ohm tests are more appropriate for real world applications.

 

[amirm]

Maybe the real dummy is me ; cause i make subs and buy (used prosound) amps that operate in the several kW territory....and i need huge dummy loads to test the amps.

Here's my under $100 ... >14kW dummy load into 8/4/2 Ohms.

I have eight 16 Ohm 3500W 230V AC water heater elements. Regularly under $20 a piece.
I went to 3-4 nearby Lowes with my Fluke, and cherry picked their inventory to find ones that were as close to 16 Ohms as possible. Tolerance ending up being a fat +/- 0.1 Ohms

Do the series/parallel wiring for 8 /4 / 2 Ohms, and put them in a bucket of water for cooling. they heat up FAST !!!!
Best thing besides low price and enormous load capability, is their resistance change is negligible after heating up...at least within the time frames of testing I did...a few minutes or less.

View attachment 417225

I can't use stuff like that. My tests need to be repeatable. And fixture usable indoor with no risk of fire in the case of overload or amplifier shorting.

 

[mhardy6647]

Heatsink?
Heathkit Cantenna.
If it's good enough for RF, it's fine for AF!
50 ohms, though.

source: https://www.worldradiohistory.com/Archive-Catalogs/Heathkit-Catalogs/Heathkit-1970-800-03.pdf (cat. pg. 56)

 

[mcdn]

Maybe I missed it there, but did you measure the resistance before and after applying full power for several minutes? I saw the theoretical calculation.

Including the power leads, it's 2.022 ohms at 20C and 2.042 ohms at 60C which is where it reaches steady state at 800W. That's 95ppm/C for the 4R7 resistors, which is bang on spec! (LCSC part page).

 

[rdenney]

Heatsink?
Heathkit Cantenna.
If it's good enough for RF, it's fine for AF!
50 ohms, though.

View attachment 417281
source: https://www.worldradiohistory.com/Archive-Catalogs/Heathkit-Catalogs/Heathkit-1970-800-03.pdf (cat. pg. 56)

I actually have a Cantenna. Note that 1000 watts at 50 ohms is only 4.something amps, while at 4 ohms would be 16 amps. That makes a difference! I use mine for tuning up a 600-watt RF amp, which uses three 811A vacuum tubes and has a big, honking fan to keep them from melting.

[edit note: sigh.]

Rick “need to fire that puppy up, so to speak” Denney

 

[mcdn]

I can't use stuff like that. My tests need to be repeatable. And fixture usable indoor with no risk of fire in the case of overload or amplifier shorting.

It's not a proper product but my SMD dummy load won't catch fire, is instrumented for temperature, has reliable supply chain and accuracy through JLC build and 1% parts from LCSC, and only requires a couple of 140mm fans and a small 3D printed enclosure and some cheap heatsinks. If you want an over temp shutoff then it would be easy enough to add a big relay to the input.

 

[Old_School_Brad]

I can't use stuff like that. My tests need to be repeatable. And fixture usable indoor with no risk of fire in the case of overload or amplifier shorting.

It's very easy to make repeatable. A circulating water pump and a temperature reading and there you go.

@mcdn also made this genius load, add a safety thermostat to break power to the testing equipment and it's good to go whilst you're making coffee.:

Silly surface mount dummy load module

That is a huge difference. Are you sure the thermal coupling with the heat sink is good and/or your IR measurements from the heat sink are accurate? I would be cautious to double the power before checking all is ok. Yeah, that’s why I’ll put a thermometer on each heatsink. The airflow is...

www.audiosciencereview.com

 

[amirm]

It's very easy to make repeatable. A circulating water pump and a temperature reading and there you go.

What are you talking about? How would someone in China replicate my test if I claim the amp is shutting down with my own homemade load like that? I also can't have liquid that can spill. Or high voltages that can be dangerous in such a fixture. At 1000 watts and 4 ohm, we have 62 volts running through the fixture.

My current dummy resistors have very high peak current but only for very short amount of time. The problem is long term testing.

 

[amirm]

It's not a proper product but my SMD dummy load won't catch fire

I assume you mean temperature rise over time. A short that dumps 1,500 watts into it won't be detected by any thermistor.

 

[Old_School_Brad]

What are you talking about? How would someone in China replicate my test if I claim the amp is shutting down with my own homemade load like that? I also can't have liquid that can spill. Or high voltages that can be dangerous in such a fixture. At 1000 watts and 4 ohm, we have 62 volts running through the fixture.

My current dummy resistors have very high peak current but only for very short amount of time. The problem is long term testing.

1. The load is easily accessible for purchase.
2. The ambient temperature is recorded.

This applies to both devices.
That’s all you need to replicate it.

You don’t need an open barrel in your living room -a fish tank would work just fine. You can add a Pink Panther as decoration.

I assume you mean temperature rise over time. A short that dumps 1,500 watts into it won't be detected by any thermistor.

If it impacts the output air temperature, a safety thermostat will detect this situation as well.
Also; smoke detector.

 

[pma]

That's a toy amplifier. Come back with results of amp producing 1500 watts in stereo or bridged.

Most of your tests are with amps that cannot make 150W/8ohm for 5 minutes. You called that toy amplifiers , so now you have no excuse why not to test them for rated power according to FTC. I can do such tests up to 300 - 400 W rated power. BTW, the post was about the resistors to be used in the dummy load.

 

[amirm]

If it impacts the output air temperature, a safety thermostat will detect this situation as well.
Also; smoke detector.

I don't know why I am bothering to answer....

A smoke detector is there to save lives. It is not there to stop the fire. Or even detect its onset.

A short in an amplifier can vaporize and set load resistors on fire in a blink of an eye.

 

[mcdn]

I assume you mean temperature rise over time. A short that dumps 1,500 watts into it won't be detected by any thermistor.

1500 watts isn’t a problem for a few seconds. I’ve already got a microprocessor monitoring board temps. It would be easy to add other checks. The hard part is knowing what to check for and what to do about it. Maybe temperature is enough to cover most bases if the time constant is say 2 seconds?

 

[amirm]

Most of your tests are with amps that cannot make 150W/8ohm for 5 minutes. You called that toy amplifiers , so now you have no excuse why not to test them for rated power according to FTC. I can do such tests up to 300 - 400 W rated power.

An amp that can only produce 150 watts into 8 ohm for second or 10 hours is a toy amplifier in this day and age. I wouldn't dream of using such a puny amp to drive my speakers.

A serious amp produces this much power:

If folks want me to run such tests continuously, then the load needs to be able to easily handle 1200 watts or even more:

This is what a $100 kit amp can do:

So yeh, 150 watts is nothing.

 

[pma]

1500 watts isn’t a problem for a few seconds

Correct. The problem is with long term tests. BTW, it is funny enough that AP in their app notes show 50W resistors as a test load. Maybe Amir uses the same ones?

 

[amirm]

1500 watts isn’t a problem for a few seconds. I’ve already got a microprocessor monitoring board temps. It would be easy to add other checks. The hard part is knowing what to check for and what to do about it. Maybe temperature is enough to cover most bases if the time constant is say 2 seconds?

An amplifier could easily short out during any kind of testing like this. Having the amp fail is fine. But the load must be safe under all conditions. No risk of damage due to worst case conditions of a powerful amplifier driving it.

 

[Old_School_Brad]

I don't know why I am bothering to answer....

A smoke detector is there to save lives. It is not there to stop the fire. Or even detect its onset.

A short in an amplifier can vaporize and set load resistors on fire in a blink of an eye.

So what? If it shorts enough to affect the air temperature, it gets disconnected.

I don’t see what’s causing your hesitation.

And if you’re trying to catch a fire that starts in the blink of an eye, I’ll tell you no such device exists. You handle precautions after the fact.

 

[pma]

Unfortunately, it is impossible to have technically oriented debate with Amir, based on facts and evidence, in case you disagree with him. He automatically takes it as a personal attack and turns the debate to absurd reasoning.

 

[mcdn]

An amplifier could easily short out during any kind of testing like this. Having the amp fail is fine. But the load must be safe under all conditions. No risk of damage due to worst case conditions of a powerful amplifier driving it.

If the amp shorts internally there’s nothing the load can do about it, and the load will see zero volts, or have I misunderstood your point? If the amp under test goes open rail at e.g. 60V and the load starts heating up, that can be detected and a relay opened by the microcontroller, but it would need to be a big relay. Anyway seems a bit academic when the load can sink 1kW. For big amps use one load per channel.