Power amps: continuous output power measurements

[mhardy6647]

All y'all know how the hams (amateur radio operators) do it (or, at least, how they used to do it), yes?
A noninductive load (resistor with high power handling capability) -- immersed in a can of oil.

source: https://www.worldradiohistory.com/Archive-Catalogs/Heathkit-Catalogs/Heathkit-Catalog-1977-Fall.pdf pg. 23

The question of steady-state vs. dynamic testing is a longstanding topic of discussion in audio circles. Old folks (i.e., folks even older than I!) probably remember the IHF "music power" standards* - which were (I think) meant as a good-faith attempt to establish repeatable power test criteria that would be relevant to the real world use of a hifi audio amplifier. Later, of course (1974), the US Federal Trade Commission (!) established very rigorous test criteria, with a 30 minute (if memory serves) preconditioning at 1/3 rated power that really pushed a power amplifier's capability. Those were the days of massive (linear, of course -- mostly) power supplies and heat sinks.

________________
* see, e.g., https://www.worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1969-03.pdf pg. 26 of the issue

 

[Bjorn]

That's one of the reasons I did get them for lows,anything else I checked at this time (sirca 2019) was either vague or vastly lower (time) .

Not that it matters a lot,but I did torture one of them with a cheap horrible 15" sub at 20Hz while making rounds around my house (no attached neighbors) to see if it was audible and the test was lasted a while.
It did get hot though,it's heatshink (the one specified by ice) must have been way over 50° but strangely no clipping kicked in with the sine,nor it shut down,despite the power I used (poor sub was about to explode)

The one spec'ed in the post above mine don't think is Ice,or is an old one?
Edit:It can be,the test is at combined 50Hz/1Khz,so makes sense.

I guess we have looked at different modules.

I was considering the ICEpower 2000AS HV. It's rated with 2000W in 4 Ohm. But not very impressive if one looks more at the details and huge difference with continous operation as one can see below.

 

[MaxwellsEq]

When amps are tested here at ASR as well as other places, output power is one of the things measured. I can't however find any information about the duration of such a measurement. They are also conducted at 1 kHz only, if I'm not mistaking?

Now - consider we want our amps to drive home theater subwoofers covering the 10-80 Hz range. Typical action movie soundtracks contain a lot of more of less continuous low frequency signals at very high levels. An example I like to use is the scene from Interstellar where Matthew McConaughey's character fly into the black hole. In that scene there's extremely high level in the LFE channel around 25-30 Hz (I think - will check this), and it literally lasts for minutes. The first time I saw that movie at home, I had to pause it just to check if nothing had caught fire!

The question is - can our amps deliver high power at low frequencies for an extended period of time, which will be the requirement for home theater subwoofers?

I set out to do some experiments on this topic and get some answers. In the next post I will describe a proposal on how it could be done. Comments, corrections, input of any kind is more than welcome.

I recommend this thread:

(Suggestion on) Testing power amplifiers according to IEC 60268-3 standard

(Suggestion on) Testing power amplifiers according to IEC 60268-3 standard I would like to start the debate on ASR power amplifier testing and suggest some degree of conformance with current standards. --------------------------------------------------- The part 3 of IEC 60268 applies to...

audiosciencereview.com

 

[Doodski]

I could just drive it continuously with a sine wave but that can damage the amplifier and possibly my dummy load.

I used Dale 250W4R loads mounted on a large car amp heatsink for soaking car and home audio amps. The issues I had was a burned table top from the heatsink getting so hot it browned the table top and amps would smell because they got hot. The clincher on this is that these amps had been serviced by me and I knew they where OK for a thermal tracking stability soak test. To soak unknown amps is a bit danger zone so I agree on not blowing up any gear that way.

 

[Doodski]

All y'all know how the hams (amateur radio operators) do it (or, at least, how they used to do it), yes?
A noninductive load (resistor with high power handling capability) -- immersed in a can of oil.

View attachment 379783
source: https://www.worldradiohistory.com/Archive-Catalogs/Heathkit-Catalogs/Heathkit-Catalog-1977-Fall.pdf pg. 23

The question of steady-state vs. dynamic testing is a longstanding topic of discussion in audio circles. Old folks (i.e., folks even older than I!) probably remember the IHF "music power" standards* - which were (I think) meant as a good-faith attempt to establish repeatable power test criteria that would be relevant to the real world use of a hifi audio amplifier. Later, of course (1974), the US Federal Trade Commission (!) established very rigorous test criteria, with a 30 minute (if memory serves) preconditioning at 1/3 rated power that really pushed a power amplifier's capability. Those were the days of massive (linear, of course -- mostly) power supplies and heat sinks.

________________
* see, e.g., https://www.worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1969-03.pdf pg. 26 of the issue

I soak tested every single amp @ 1 k Hz that came across my workbench. Got them good and hot and monitored the current down to milliamperes to keep a eye on thermal tracking and runaway. So if a customer came back with a blown amp I knew they had a issue in their system. They came back often... I gave them the first return with the blown amp a free repair but with solid easily understood instruction about their system is blowing their amplifier. I liked testing them so I did a really thorough job of it.

 

[Speedskater]

John Atkinson at Stereophile now uses the CEA recommendation of operating at one-eight spec power into 8 Ohms for 30 minutes before testing.
In the past, he used a 1` kHz tone at one-third power into 8 Ohms for 1 hour.

 

[NTK]

The new (revised) FTC amplifier power rating rule has been finalized and will be published in the US Federal Registry soon.

FTC Issues Final Amendments to Amplifier Rule to Make Testing Methods More Useful to Consumers

The Federal Trade Commission has issued final amendments to its Amplifier Rule to help consumers make direct comparisons of home entertainment ampli

www.ftc.gov

Here are the relevant text (IMHO) from link:

​

§ 432.2 Required disclosures.​

Whenever any direct or indirect representation is made of the power output, power band or power frequency response, or distortion characteristics of sound power amplification equipment, the manufacturer’s rated power output shall be disclosed subject to the following conditions:​

(a) The rated power output is measured in compliance with the standard test conditions in § 432.3;​

(b) The rated power output is disclosed clearly, conspicuously, and more prominently than any other representations or disclosures permitted under this part;​

(c) The disclosure of the rated power output is clearly and conspicuously labeled ‘‘FTC Power Output Rating’’;​

and(d) The disclosures or representations required under this section shall not be made by a footnote, asterisk, or similar notation.​

​

§ 432.3 Standard test conditions.​

* * * * *​

(e) Any power level from 250 mW to the rated power shall be obtainable at all frequencies within the rated power band of 20 Hz to 20 kHz without exceeding1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier’s auxiliary input, or if not provided, at the phono input. Provided, however, that for amplifiers utilized as a component in a self-powered subwoofer in a self powered subwoofer-satellite speaker system that employs two or more amplifiers dedicated to different portions of the audio frequency spectrum, any power level from 250mW to the rated power shall be obtainable at all frequencies within the subwoofer amplifier’s intended operating bandwidth without exceeding1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier’s auxiliary input, or if not provided, at the phono input.​

* * * * *​

(g) Rated power shall be minimum sine wave continuous average power output, in watts, per channel (if the equipment is designed to amplify two or more channels simultaneously), measured with all associated channels fully driven to rated per channel power.​

(h) Associated channels for multichannel amplifiers shall include, at a minimum, the left front and right front channels used for reproducing stereo programming. Provided, however, when measuring the maximum per channel output of self-powered combination speaker systems that employ two or more amplifiers dedicated to different portions of the audio frequency spectrum, such as those incorporated into combination subwoofer-satellite speaker systems, only those channels dedicated to the same audio frequency spectrum should be considered associated channels​

​

§ 432.4 Optional disclosures.​

Other operating characteristics and technical specifications not required in§ 432.2 may be disclosed. Provided, that:​

(a) Any other power output is rated by the manufacturer, expressed in minimum watts per channel, and clearly and conspicuously labeled ‘‘This rating was not tested under the FTC standard’ ’without the use of a footnote, asterisk, or similar notation to make the representation;​

(b) All disclosures or representations made under this section are less conspicuously and prominently made than any rated power output disclosure required in § 432.2. Any disclosure or representation bold faced or more than two-thirds the height of any rated power output disclosure required in § 432.2 is not less prominent;​

and(c) The rating and testing methods or standards used in determining such representations are well known and generally recognized by the industry at the time the representations or disclosures are made, are neither intended nor likely to deceive or confuse consumers, and are not otherwise likely to frustrate the purpose of this part.​

​

 

[Sokel]

I guess we have looked at different modules.

I was considering the ICEpower 2000AS HV. It's rated with 2000W in 4 Ohm. But not very impressive if one looks more at the details and huge difference with continous operation as one can see below.
View attachment 379795

2000as is just a 1200as on (brief) steroids.
1200as is the sweet spot (at this time at least,ice have promised to up the game to 5kW (peaks) at some point) .

User positive feedback (mine as well) is that they shine in mono and at lows (no matter if it's 1200as1 or 1200as2,they are both exactly the same at mono,difference maybe is that 1200as2 can do well in asymmetric impedance too)

 

[LTig]

[..] Typical action movie soundtracks contain a lot of more of less continuous low frequency signals at very high levels. An example I like to use is the scene from Interstellar where Matthew McConaughey's character fly into the black hole. In that scene there's extremely high level in the LFE channel around 25-30 Hz (I think - will check this), and it literally lasts for minutes. The first time I saw that movie at home, I had to pause it just to check if nothing had caught fire!

Do you mean this scene?

This is the spectrogram:

Or is it this one?

This is the spectrogram:

In both scenes the majority of energy is around 30 Hz. However this may be due to youtubes compression algorithm.

 

[staticV3]

However this may be due to youtubes compression algorithm.

Here's what YouTube's audio compression does to the frequency response:

 

[Sokel]

Do you mean this scene?

This is the spectrogram:
View attachment 379889

Or is it this one?

This is the spectrogram:
View attachment 379890
In both scenes the majority of energy is around 30 Hz. However this may be due to youtubes compression algorithm.

I think that it only the LFE channel demonstrated.
The stereo content which I have posted in Bass thread has strong 30's but no much below it.

 

[dualazmak]

I am afraid that my point would be out of the scope of OP's concern, but...

If you (we) would like to measure "apparent (nominal) power consumption" of our audio gear(s) while they are "working", we can easily use Clamp-On Tester/Ampere-Meter.
(ref. thread "Apparent (nominal) power consumption of whole audio system during daily audio listening sessions: how SDGs-friendly is it? (not the idle power, please.)"

 

[StigErik]

@LTig : Its the 2nd scene. I recorded the LFE channel using VLC, which can dump the audio to a WAV file. Playback source was the Blu-ray with DTS-HD MA sound. Thus my analysis of the frequency spectrum was done only on the LFE content.

 

[StigErik]

2000as is just a 1200as on (brief) steroids.
1200as is the sweet spot (at this time at least,ice have promised to up the game to 5kW (peaks) at some point) .

User positive feedback (mine as well) is that they shine in mono and at lows (no matter if it's 1200as1 or 1200as2,they are both exactly the same at mono,difference maybe is that 1200as2 can do well in asymmetric impedance too)

The ICEpower 2000AS modules are obviously based on the 1200AS, since it has "1200AS" written on its PCB. The power supply voltage is higher, but the maximum power it can deliver seems the same.

I've run one of my 2000AS modules through my test. To protect my dummy load I decided to run short bursts of just 3 seconds. The 2000AS module can deliver about 1200W in 4 ohms, one channel driven, without going into protection or "hiccup mode". It basically turns the amp off! I think it would have been better to use just a soft-clip limiter.

Here's 10 Hz at 1500W/4ohm. As you can see, the amp turn itself off after approximately 200 ms. It comes back 2,75 seconds later.

This is 10 Hz at 2000W/4ohm. It now starts to clip/compress the waveform, which makes it take a little longer time to enter protection mode - 400 ms to be exact. And as you see, the waveform is severely distorted here as well. After 400 ms it turns itself off, and recovers after 1,75 seconds.

 

[StigErik]

I also tested the 2000AS1/2 with 30 Hz signal, just like on that Interstellar soundtrack. The amp shut itself down after 3 seconds at 1000W.
I've not (yet) managed to get the 1200AS2 into protection mode, but I suspect it will with load below 4 ohms, or below 2x8 ohms for the 2-channel version.

ICEpower has obviously made some good protection systems on these amps, but in my mind they are too intrusive since they turn off the audio completely.

 

[StigErik]

I have other amps that I will test as well, but I want to build my new dummy load first. Still waiting for parts...

The amps are:
Hypex NC122MP
Hypex NC252MP
Hypex NC502MP
Hypex Nilai500DIY

 

[DonH56]

The new (revised) FTC amplifier power rating rule has been finalized and will be published in the US Federal Registry soon.

FTC Issues Final Amendments to Amplifier Rule to Make Testing Methods More Useful to Consumers

The Federal Trade Commission has issued final amendments to its Amplifier Rule to help consumers make direct comparisons of home entertainment ampli

www.ftc.gov

Here are the relevant text (IMHO) from link:

​

§ 432.2 Required disclosures.​

Whenever any direct or indirect representation is made of the power output, power band or power frequency response, or distortion characteristics of sound power amplification equipment, the manufacturer’s rated power output shall be disclosed subject to the following conditions:​

(a) The rated power output is measured in compliance with the standard test conditions in § 432.3;​

(b) The rated power output is disclosed clearly, conspicuously, and more prominently than any other representations or disclosures permitted under this part;​

(c) The disclosure of the rated power output is clearly and conspicuously labeled ‘‘FTC Power Output Rating’’;​

and(d) The disclosures or representations required under this section shall not be made by a footnote, asterisk, or similar notation.​

​

§ 432.3 Standard test conditions.​

* * * * *​

(e) Any power level from 250 mW to the rated power shall be obtainable at all frequencies within the rated power band of 20 Hz to 20 kHz without exceeding1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier’s auxiliary input, or if not provided, at the phono input. Provided, however, that for amplifiers utilized as a component in a self-powered subwoofer in a self powered subwoofer-satellite speaker system that employs two or more amplifiers dedicated to different portions of the audio frequency spectrum, any power level from 250mW to the rated power shall be obtainable at all frequencies within the subwoofer amplifier’s intended operating bandwidth without exceeding1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier’s auxiliary input, or if not provided, at the phono input.​

* * * * *​

(g) Rated power shall be minimum sine wave continuous average power output, in watts, per channel (if the equipment is designed to amplify two or more channels simultaneously), measured with all associated channels fully driven to rated per channel power.​

(h) Associated channels for multichannel amplifiers shall include, at a minimum, the left front and right front channels used for reproducing stereo programming. Provided, however, when measuring the maximum per channel output of self-powered combination speaker systems that employ two or more amplifiers dedicated to different portions of the audio frequency spectrum, such as those incorporated into combination subwoofer-satellite speaker systems, only those channels dedicated to the same audio frequency spectrum should be considered associated channels​

​

§ 432.4 Optional disclosures.​

Other operating characteristics and technical specifications not required in§ 432.2 may be disclosed. Provided, that:​

(a) Any other power output is rated by the manufacturer, expressed in minimum watts per channel, and clearly and conspicuously labeled ‘‘This rating was not tested under the FTC standard’ ’without the use of a footnote, asterisk, or similar notation to make the representation;​

(b) All disclosures or representations made under this section are less conspicuously and prominently made than any rated power output disclosure required in § 432.2. Any disclosure or representation bold faced or more than two-thirds the height of any rated power output disclosure required in § 432.2 is not less prominent;​

and(c) The rating and testing methods or standards used in determining such representations are well known and generally recognized by the industry at the time the representations or disclosures are made, are neither intended nor likely to deceive or confuse consumers, and are not otherwise likely to frustrate the purpose of this part.​

​

A quick read says they at least cleaned up the multichannel requirements, which is likely to give a lot of manufacturers severe heartburn.

 

[StigErik]

And by the way ... here's one of my 4-channel ICEpower 2000AS2 amps.

 

[Doodski]

And by the way ... here's one of my 4-channel ICEpower 2000AS2 amps.

View attachment 379931

WhOa! That's pretty serious stuff. Very serious...

 

[valerianf]

@StigErik it is a very good idea to make the power test with a real soundtrack.
Let us take the case that you have a Salon 2 tower speaker.
In this case you do not need any subwoofer but you only need to mix the LFE chanel from Interstellar with the FR channel and send it to your amplifier under test.
Let us see at what power level the protection will trigger...
Some distortion may occur before the protection is engaged.
Be careful: with a protection designed similar to the one for the Onkyo TX RZ50, it is engaged permanently without any indication to the user.
I strongly recommend to power off the amp during a few minutes before starting the test.