Handling a complex load by power amplifiers

[sarumbear]

You seem confused about the point PMA is trying to make. Maybe you should make an effort in understanding the theory..

That’s it. It’s theory mixed with engineering without separating the two. Every scientist and engineer knows that they shouldn’t be mixed. His tests are meaningless. If you want to test your theory, your rig must be representative of devices that is expected to be used along with the amplifier in test.

Any EE will know that an amplifier with feedback and load dependant output impedance is prone to issues. You can analyse those issues and think of various ways to stop them happening. The engineer then decides which option fits their design brief, budget priority or SOTA. Once the amplifier is built they then test it.

Anything else is what a hobbyist will post, which is fine until he declares an amplifier to be unusable. Then others chime in to say the same to the level of declaring the engineers useless, etc.

In my view those members have done a disservice to ASR.

 

[Deleted member 48726]

Sorry, no sale. You don’t get to ask someone to elaborate when you yourself are unwilling (or perhaps unable, I don’t know) to do so. If you think I’m misunderstanding pma’s posts then you can explain what exactly you think I’m misunderstanding, at a level of detail similar to the detail I provided in response to your last request/demand. As for whether you were referring to Amir, I’ll leave it to others to assess for themselves what a plausible reading of your statement is, and I’ll reiterate that the main point was not Amir but rather the claim that “bad gear” is being “praised because it’s cheap” - a claim for which you’ve still provided no examples or evidence.

Finally, I would like it if we could find a way to wind down this particular exchange. It’s about to start going in circles (if it hasn’t already), and if @AdamG247 were to tell us to knock it off already, imho he’d be well within his rights.

He would be indeed. Phishing should not be allowed.

 

[BDWoody]

Let's move on please.

Does that make it easier?

 

[MaxwellsEq]

Okay.
That last point reg. SMPS. -Can you point me to where more info about this can be had?
Is it because of lower response time, higher switching speed?

This is an interesting thread about tonebursts and recovery. @restorer-john had previously reminded me that reviews from the last century sometimes showed recovery tests.

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

Back when I was more involved in the audio world a number of manufacturers performed very extensive internal testing and produced large characterization reports. Those almost never went "outside"; they were considered proprietary, and most consumers would not understand them. The...

audiosciencereview.com

How well an amp under load recovers from an impulse depends on its inherent stability (and hence feedback approach) and the stability of the power supply. Given a classic transformer, rectifier, capacitor model, the capacitor is topped up twice the mains cycle. If an impulse drains that capacitor, it can only be topped up again in the next cycle. A SMPS tops up its capacitor much more frequently, so if the capacitor is drained, it's topped up pretty instantaneously. In theory, then, the impulse should have less long-cycle impact on the juice to the power stage (assuming no regulator)

What I've not seen is this presented as a test to prove or disprove it, but the thread above has some interesting research!

 

[restorer-john]

The PowerCube presents a complex load to the amplifier. The phase angle is calibrated at 1 kHz but you could use it at other frequencies (guessing most testers just use 1 kHz).

The 'power cube' is the complete older system AFAIK. It also uses a PC, but the analyzer and generator are internal and the unit interfaced to a PC via a pair of PCI cards.

The 'active load box' is what @amirm is using, which interfaces with his AP using the 'active loadbox utility'. It has physical loads (2x20), so using it at frequencies other than 1kHz will present completely different phase angles to the five (-60,-30,0,+30,+60 degrees) in the software. Judging by the output, the AP utility is pretty clunky looking and not nearly as polished as the output from the older complete power cube system.

 

[DonH56]

The 'power cube' is the complete older system AFAIK. It also uses a PC, but the analyzer and generator are internal and the unit interfaced to a PC via a pair of PCI cards.

Yah, I keep using them interchangably, sorry.

The 'active load box' is what @amirm is using, which interfaces with his AP using the 'active loadbox utility'. It has physical loads (2x20), so using it at frequencies other than 1kHz will present completely different phase angles to the five (-60,-30,0,+30,+60 degrees) in the software. Judging by the output, the AP utility is pretty clunky looking and not nearly as polished as the output from the older complete power cube system.

Yes, that is the issue; you'd have to calculate or measure the phase angle (reactance) for frequencies other than 1 kHz. It's a known impedance so you'd think the AP could handle the calculations for other frequencies.

 

[theREALdotnet]

For the next round of testing, may I suggest a negative impedance load, like a tunnel diode?

 

[sarumbear]

For the next round of testing, may I suggest a negative impedance load, like a tunnel diode?

Are there any speakers that has such a load?

 

[theREALdotnet]

Are there any speakers that has such a load?

Speakers? Why do you bring speakers into this?

 

[sarumbear]

Speakers? Why do you bring speakers into this?

You are joking right? We are talking about audio power amplifiers, yes?

 

[Deleted member 48726]

You are joking right? We are talking about audio power amplifiers, yes?

Of course he's joking!

 

[theREALdotnet]

You are joking right? We are talking about audio power amplifiers, yes?

Apologies for being obscure.

 

[tmtomh]

Apologies for being obscure.

It was quite clever, actually.

 

[sarumbear]

It was quite clever, actually.

I agree and feel bad that I missed the joke.

 

[MAB]

Apologies for being obscure.

The obscurity actually helped summarize.

And it naturally led to this:

Speakers? Why do you bring speakers into this?

You are a genius. Two of the greatest posts I have ever read.

 

[MAB]

I agree and feel bad that I missed the joke.

Sorry to say, I am glad someone missed the joke. Next time, I volunteer to be that person!

 

[tmtomh]

I agree and feel bad that I missed the joke.

Online communication can be difficult to interpret sometimes - we've all been there!

 

[AdamG]

Online communication can be difficult to interpret sometimes

I wish to edit your last word..sometimes—->usually, mostly, often……

 

[TNT]

Seems like you missed his point. I have already adopted, at potentially huge expense (power cube as I have it costs $21,000), for something that may not be revealing at all. Even cheap amps are able to pass complex angles at 4 and 8 ohms.

At 1k - thats whats tested, right?

//

 

[tmuikku]

Hi all,

alright, is there any hints on amplifier datasheet to indicate it would work fine also on these complex loads?
Would it be correct to assume that if an amplifier adverts to be able to work on say 2ohm loads then it would indicate good ability to supply current for reactive loads on nominal 4 or 8ohm speakers?

Googling with power factor correction many high watt PA amplifiers seem to advert PFC on their power supplies. An advert I watched yesterday from Youtube seemed to suggest this PFC is what enables it for 2ohm loads. So, in case of these class D chip amps I'd guess its about cooling of the device and PSU that makes or breaks the performance.

Also, there is simple way to "fix" the complex load by adding parallel resistor to the amp output / speaker input. This resistor draws extra current and power, but if it sufficiently reduces heat generated inside the amplifier the net effect could be close to zero extra heat waste? Seems simple fix, so probably not true?