NC252MP (class D) vs. A250W4R (classAB) burst measurements into 4ohm//2.2uF load

[MaxwellsEq]

I agree, but I see quite a big issue what I described just above your post. Regardless the uW peaks in audioband, which may seem low level (but let’s not forget that power uses voltage squared so mV reflects in uW), the noise flat across 22Hz-22kHz was 22mV and 6mV A weighted, and these are very, very high levels of noise voltage in audio band.

I quite agree - that's one of the most disturbing findings from your research. What I need to understand is - a) is this typical of all Class D amplifiers, or this particular implementation; 2) what happens when you vary the load characteristics - does this slowly creep up with capacitance, or does it suddenly "switch on" at a certain value of impedance*; 3) does it get worse as you go more extreme; 4) is this reproducible in other people's labs.

* which would imply a corner case where the advice would be "don't use this amp with these speakers"

 

[JktHifi]

I think Class D was invented for car audio which use battery and cannot sustain non-stop playing for days. Meanwhile Class AB can be played non-stop for days and years because it gets the electricity from home.

Don’t reinvent the wheel. Just upgrade the class AB amplifier for the better world.

 

[boXem]

 

[MaxwellsEq]

I think Class D was invented for car audio which use battery and cannot sustain non-stop playing for days. Meanwhile Class AB can be played non-stop for days and years because it gets the electricity from home.

Just don’t reinvent the wheel. Upgrade the class AB amplifier for the better world.

I'm sorry, but I don't agree with you.

 

[JktHifi]

I'm sorry, but I don't agree with you.

That’s what I know. Could you explain why?

 

[IAtaman]

Let's focus on the circled area.
f = 110 Hz
Z = 8 ohm
phase = 50 ° cap.

Resolved vector =
6.13 Vert. // 5.14 Hor.
=> Xc = 5.14 ohm

C = (10^6/(2*3.14*110*5.14)) = 281.6 microFarad

Maybe my math is a bit rusty. It's been a while since I juggled vectors and this was in electrical grid and cabinet design so maybe some things can't directly be translated into audio and maybe I read the graph wrong.

Oh that was fun. Haven't done that in ages. I might be wrong as I am probably more rusty than you but is seems to me that you mixed the real and imaginary components of the vector. Xc should be 8.sin(-50) = -6.13 resulting in 236uF, which still does not seem right.

 

[tomtoo]

That’s what I know. Could you explain why?

Fact is that many hifi class ab are bad constructed regarding thermal isues. Thermal isues can happen with all amps if bad constructed. In fact class d has it more easy couse you have not to get ride of so much heat.

 

[JktHifi]

Fact is that many hifi class ab are bad constructed regarding thermal isues. Thermal isues can happen with all amps if bad constructed. In fact class d has it more easy couse you have not to get ride of so much heat.

I have both at home. I found the Class D is hotter when I touch the amp. Probably because smaller, putting all components in a small form size factor.

And the longer I listen to music from Class AB, the better and more enjoyable sounds. From Class D, it’s only a few hours and begin fatigue. Might be caused by the speaker, the Class D is soundbar.

 

[Deleted member 48726]

Oh that was fun. Haven't done that in ages. I might be wrong as I am probably more rusty than you but is seems to me that you mixed the real and imaginary components of the vector. Xc should be 8.sin(-50) = -6.13 resulting in 236uF, which still does not seem right.

True. 50 degrees means that the larger component of course is Xc.

 

[boXem]

Fact is that many hifi class ab are bad constructed regarding thermal isues. Thermal isues can happen with all amps if bad constructed. In fact class d has it more easy couse you have not to get ride of so much heat.

Fact is that car audio doesn't run on battery

 

[MaxwellsEq]

That’s what I know. Could you explain why?

PWM had been understood for some time before being implemented. I recall when I was taught about them that PWM's earliest use was in power supply design.

The simplest amplifiers are single gain stages, such as a single transistor amp, which needs to be always on to work and so is Class A. Class A is inefficient, Class B is more efficient, but suffers crossover distortion. Class AB is a compromise, but it's not particularly efficient. Class AB is fine, but does need heat management.

 

[tomtoo]

I have both at home. I found the Class D is hotter when I touch the amp. Probably because smaller, putting all components is small form size factor.

And the longer I listen to music from Class AB, the better and more enjoyable sounds. From Class D, it’s only a few hours and begin fatigue.

I did say it already, it depends on construction not class. Both thermal isues and sound.

 

[IAtaman]

I have both at home. I found the Class D is hotter when I touch the amp. Probably because smaller, putting all components in a small form size factor.

And the longer I listen to music from Class AB, the better and more enjoyable sounds. From Class D, it’s only a few hours and begin fatigue. Might be caused by the speaker, the Class D is soundbar.

Right, because we all know random personal experiences are the most reliable source of factual information when it comes to decision making about categories of products.

 

[JktHifi]

PWM had been understood for some time before being implemented. I recall when I was taught about them that PWM's earliest use was in power supply design.

The simplest amplifiers are single gain stages, such as a single transistor amp, which needs to be always on to work and so is Class A. Class A is inefficient, Class B is more efficient, but suffers crossover distortion. Class AB is a compromise, but it's not particularly efficient. Class AB is fine, but does need heat management.

Do you mean Class AB need larger heatsink?

 

[Matias]

Back to the topic please.

 

[Sokel]

Right, because we all know random personal experiences are the most reliable source of factual information when it comes to decision making about categories of products.

Yes,but can we get back to the subject as all this has been subjected 385967363 times in various threads?
I'm really interested in that cause one my friends does have ELS and it would be interesting to test them with both Purifi and Ice powers we have around.
I just want to know where to look,as the ABX test we did seemed way too easy and I want to see if something like this will happen there.

 

[IAtaman]

Right, back to the topic, sorry.

If I understood correctly, Amir's view is that the noise is is the result of intermodulation between oscillations caused by reactive load and the amp's pwm frequency, and since both of them would be attenuated by the speakers, they will not have a chance to interact and cause the intermodulation distortion we see. Is that correct? @pma, you were explaining to holdt you can not simply model a speaker with a simple resistance and reactance if I understood you correctly. Doesn't that support what Amir said, that a resistor and a cap is not a good representation of a speaker load?

What also confuses me a bit is that behavior of amps under different types of loads is a very basic test, most opamp datasheets would have it graphed under different load, Vcc and gain conditions. However, If I was able to follow the conversation correctly, it is said that the class D amps have never been tested with highly reactive load used in pma's tests before, and we might be seeing a behavior never seen previously, which is the source of my confusion. Is it not done before because it is an such edge case that has very little real like implications or is there another reason for it - because it sounds very obvious.

 

[fpitas]

With RF amps, power amps in particular, load pull tests are used to exercise the amp over a wide range of impedances to check for stability, IMD, etc. Load pull equipment can be a simple “trombone”, an adjustable length line stretcher (transmission line) with an open termination port that itself can be shorted, left open, or loaded with resistance. Adjusting the length causes a rotation of impedance around the Smith Chart, from capacitive to inductive and back again. More complex load pull equipment uses active circuitry to accomplish the same goal. I’m wondering why load pull techniques aren’t also applied to audio amps - or are they? If not, why not?

There's a thing called a PowerCube (I think) that does just that.

 

[Sokel]

There's a thing called a PowerCube (I think) that does just that.

Isn't that what Amir is testing lately?

 

[fpitas]

Isn't that what Amir is testing lately?

Now that you mention it, I think that is so.