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Class D vs Class A or A/B

Thank’s a lot for your very detailed answers.

I think there is some misunderstanding due to my weak English.
It’s not an easy job at all writing tech things in a foreign language.
So if some of my words are misleading, I’m sorry.

But all in all we share one view I think.

You are right calculating the dynamic of a signal from peak to peak.
Thus is resulting in a lower amount of dynamic then 10dB.

But I tried to explain something different.
Every signal can be expressed by it’s RMS. Regardless of the signals crest, the RMS is what we can hear as loudness.
If I want to know how loud a signal is audible I need the RMS.
The audible RMS includes everything, from the very first beginning to the steady swinging, until the next initial finger picking attack starts the next attack again, and so on …

If I want to know how loud (how much audible power) is produced I need the average of the signal to be defined. Average can be expressed by RMS.

If I want to know how strong my amplifiers power capacity (or the cabs cone excursion) is forced I need the Peak value to be defined.

Theoretical it should be possible to estimate even for the first initial signal period of attack a RMS value.
I don’t know if anybody ever did this, but I strongly doubt such a RMS value would be very meaningful.

IMHO it it’s even not meaningful to calculate with a sine and try to hook up twice the power for clipped attack transients!

The crest of a steady swinging note is something in the magnitude of 2..3.
Sine =1.41, square =1 (as we all know).


You point out an amps capacity can be twice the rated power.
You are considering a sine wave that’s clipped until the power is twice.
That’s absolutely correct but, I’d do the consideration to a clipped bass signal a little bit different.

I don’t want to complicate this here too much. So I do a simplification, and consider only the steady swinging of string.
Let’s say the crest of the steady signal is 2.5.

I take three different signals and let them clip on a 300 Watt amp:
Nr.1 square, Nr.2 sine, and Nr.3 a steady swinging bass signal with crest 2.5

Nr.1 square:
The square starts at 600 Watt cause the square is at it is. That is 600 Watt and can therefore not be clipped to higher power value as it already is. Cause the crest of the square is 1
Nr.2 sine:
The sine starts at 300 Watt, and above with enough clipping content it ends up at 600 Watt

Nr. 3 steady swinging signal crest 2.5
The signal starts at 100 Watt (theoretical amplifier) or something approximate 150 Watt on a real amplifier.

Why only 100..150 Watt ? The amp is 300 Watt.
It’s cause of the crest 2.5

Never the less I let the signal clip until the power is 600 Watt.

But to reach the 600 Watt with the real signal’s crest of 2.5 a very lot of gain is necessary to achieve the 600 Watt.


Human’s ears are very sensitive whenever steady signals are clipped, even only a little bit.
Maybe it sounds to somebody like square waves whenever only the edge of a steady signal clips.
This behaviour leads sometimes to very misleading interpretations.
There is not a square but it often sounds like there is one.



I’d claim that the RMS of a very well audible clipped steady swinging bass sound is not significant more then 1/2 the rated amps power.

The situation can be translated 1:1 into whenever the attack transients are clipping non audible.
It’s theoretical possible to make a draw for the clipped transients, assuming the power is then twice the rated amp power. But it isn’t.

It is not twice until the gain (or overdrive) is strong enough. It needs a horrible portion of overdrive to make the signal peaks equal to be squares.


Back to Topic:
You did an estimate for the peak that can be twice the rated power and calculated down to 75 Watt rms. I did the calculation in different way, starting at very low, raised up the signal and the result was 100 Watt rms.

I’d say the result is just the same. Some watt more or less it is not a big deal and would therefore never be enough to debate on principles.

Thank you for all your statements to the many questions that I did.
Most of all your statements I agree. Some I don’t. But even that points I disagree is nothing to debate too much on principles. The whole complex of themes we discuss is nothing that can be explained in three or twenty words. Not as easy like Ohm’s low!

The themes are very complicated anyway and give therefore place to hold different interpretations and opinions without being wrong or right I think.


Some words to my own gear and what I prefer, and what I dislike, and why I dislike some modern features.

At first to point out, I dislike limiters. I hate them.
I hate them as I am a bass player but by the other hand, I like them very well in a professional amplifier driving PA loudspeaker systems..

I prefer the smooth rough sounding of conventional amps when played hard at the limit.
I dislike compressors as well. The feel is like touching a cold fish that is dead. That's my opinion, nobody needs to share.

On the other side, I like the endless power and endless dynamik feel of heavily overdriven cab systems. That means twice the rated cab power cabability as a minimum.

That is in general nothing you can buy off the rack. But it makes a very lot of fun. Class D amps can provide this by a very less weight.
That is a feature with modern class D amps I like very well. The question is only:
How much dynamic power?
 
The dynamic power can be anything the designer desires. It all depends on the tonal goals and the feel that the particular company is going for, and it is often different for different models by the same company. It's like cooking, there are many different recipes for making the same dish... each one has it's strengths and will appeal to different tastes. This is why I always recommend playing a variety of amps to see which ones you personally prefer. Or, know the tastes of somebody you trust and use their judgement.
 
If I understand you right there is firm cohesion among dynamic potential and burst time duration?
For an example: drawing a xy-chart for a given power module with burst time vers. power among the chart axis?

That would be easy to understand. It would then the designer’s goal (or choice?) how to balance burst-time vers. power?

By the way that was the main reason why I asked for the power capacity design of the switching power supply for a given amp.

ok, until I don't know the facts how the balance between burst and power is designed it is not possibly to predict anything.

But it would be interesting to know HOW it is balanced and therefore how much "average" or rms is needed to yield a certain rated value at the output.

It’s not my intention weeding out in-house secrets of design.
I don’t intend to build my own class D circuit and therefore don’t intend to spare time or money while others did a lot of investigation and research to it.
By the other hand, to put one’s cards on the table might lead to endless and meaningless discussions because the nature of audio signals is too often poorly understood.
The “TC electronics” discussion on talk bass showed clearly what might happen if it is done.
It is clear that the “TC electronic” theme was a different one.
By the other hand the TC discussion forced the discussion of the nature of audio- and bass signals. The real nature (or physic) is far different then keep only locking on sine waves with 1% or 0.1% THD.


Ok, you tell it’s all well designed/adressed and all of the design works fine. There isn’t any doubt about it. IMO it lacks the information that is needed to discuss the obviously different feel to class AB amps.

To treat a little bit more to the topic theme class AB vers. class D.

The conventional class AB with 50/60Hz net transformers is rather simple to explain.
Regardless to the specs that are given by the manufacture.
The net transformer specs say often more then the manufactures specs.
Explained with different words, if you want know the truth without doing any measurement to the amp, it is possible to calculate with the net transformer specs proportional translated into the output power. And it is easily possible to estimate if the transformer belongs to 4 Ohm amp or 2 Ohm, or significant below 4 Ohm what is as well possible sometimes. Considering the filter caps which should be dimensioned appropriate, neither too big or small.
To bring it to the point, the net transformers selection or estimation of electrical specs that is done by the designer is the basic design for the amp.

Keeping a look into my powersoft 5.000 watt amplifier shows a totally different situation.
There is a huge battery of caps. All I know is that the caps job can't be only intended for filtering.
And it's therefore an easy way to point out that the switching power supply's capacity is probably far below the rated output power. The huge battery of caps is certainly not in the casing to fill out a big gap!
I never measured the burst of my amp. But all the practical experience shows it's far enough to work fine with any audio program material.
It is possible to hide this amp up to the limit without significant audible lack in sound reinforcement.
The benefit providing a lot of "headroom" to a system however I'd consider different.
Let me here speak with the manufactures own words.

The DIGAM series amplifiers are among the most powerful professional amplifiers available and are
capable of producing much more power than many loudspeakers can handle. It is the user’s
responsibility to use

and

Powersoft recommends that you use amplifiers of this power range for more headroom (cleaner
sound) rather than for increased volume.
 
...
Ok, you tell it’s all well designed/adressed and all of the design works fine. There isn’t any doubt about it. IMO it lacks the information that is needed to discuss the obviously different feel to class AB amps.
...

I totally disagree. Myself, there is no "feel" difference. And all other data I find, blind tests, specs, etc. show that to human hearing they sound the same and play the same. Of course not "all" manufacturers designs are equal. That's true for any class. Maybe you had a bad class-d. Try more.

On power supplies, if I buy a 800w amp, I don't expect the power supply to tricked bigger into having more capacity to deliver more watts in a burst.

It could be a manufacturer maximizes the power supply, and amp to deliver 1600w burst for 500ms. I don't want that. Then you have to worry about recovery time. I want 800w continuous, if I need 1600w I'd get it.
Difference between 800w and 1600w is 3db, which is on the low end of audibility. Hardly seems worth it to worry about it.

I pay for "RMS", better FTC, EIA when I can get it.
 
I totally disagree.
no problem.

Myself, there is no "feel" difference. And all other data I find, blind tests, specs, etc. show that to human hearing they sound the same

Class D sounds more detailed with more clearness.
Manufactures Data and specs are not suitable to reflect this, rather they sometimes just look the same for two different sounding amps.

Try to listen to a prof. audio 5k Watt amp you have to charge 3.000 bucks for ore even more.
You will here the difference and the big advantage in a very clear audible sound reinforcement that class d can provide.
That was our first impression when we switched from QSC to Powersoft.

and play the same.

no, the feeling is very different even when playing only moderate loudness.
May be that I have got not enough experience with low budget class d amps, so my expressed experince may be different to other folks.

Playing hard to the amps limit is a different scenario.
But as bass player I prefer for class D more headroom then others would consider as enough. That's then a totally different story and therfore a little bit "running out of order to any rules".

Of course not "all" manufacturers designs are equal.
They would sound all the same .....

That's true for any class. Maybe you had a bad class-d.
Until now I was allways thinking I own a good one.

Try more.
Hoellstern ?
Do you ever looked what their charge is?
Some folks argue the Hoellstern performs better in bass reinforcment. Maybe it is so but, I'm very happy with the Digam amplifier.

On power supplies, if I buy a 800w amp, I don't expect the power supply to tricked bigger into having more capacity to deliver more watts in a burst.

There is no trick to make it bigger as it is.
But there are tricks to make the supply very efficient.
And there are tricks not to waist power potential.
The trick is understanding the nature of audio signals.
And I hate it to call a "trick". It's rather efficient design then a trick!

It could be a manufacturer maximizes the power supply, and amp to deliver 1600w burst for 500ms.
It could be done by maximization of the supply. But it would also mean waisting a lot of rms power potential.
Cause most the time it would then remain unused.
Do you want to pay for additional potential that you are never can use, except you would play a steady singular sine wave?
I don't want that.

Think about it!
Then you have to worry about recovery time. I want 800w continuous, if I need 1600w I'd get it.
Difference between 800w and 1600w is 3db, which is on the low end of audibility. Hardly seems worth it to worry about it.

A lot of amps on the market are able to do as you demand.

Karlheinz Stockhausen composed in the 60's an arrangement for sine wave generators.
If the arrangement would demand 80 Hz with 500 Watt RMS for a time duration of 30 seconds I would provide an amplifier that is able to perform. I would not take a 500 Watt class D but a 500 Watt class AB should be fine enough to the work for karlheinz Stockhausen composition.

I pay for "RMS", better FTC, EIA when I can get it.
[/QUOTE]

Beyond the power measurement recommendations I pay for a superb sound as well.
 
...
Karlheinz Stockhausen composed in the 60's an arrangement for sine wave generators.
If the arrangement would demand 80 Hz with 500 Watt RMS for a time duration of 30 seconds I would provide an amplifier that is able to perform. I would not take a 500 Watt class D but a 500 Watt class AB should be fine enough to the work for karlheinz Stockhausen composition.



Beyond the power measurement recommendations I pay for a superb sound as well.

The first point is where I disagree. Many people just haven't done proper gain matching between amplifiers and think they hear a difference where there isn't. It could be that simple, or it could be the measurement specs are not accurate from the manufacturer you bought from.

A good quality class-d amplifier is not fudging on the specs. And the reason why FOH is trusting of the specs. Screw FOH over and and amp maker will be black listed on riders. Again, just like any class of amplifier.

And of course class-d sounds superb. As does a modern class-ab as they are both capable of reaching beyond human hearing.
 
The first point is where I disagree. Many people just haven't done proper gain matching between amplifiers and think they hear a difference where there isn't.

In Germany we tell this:
"gegen Blödheit ist kein Kraut gewachsen"

It could be that simple, or it could be the measurement specs are not accurate from the manufacturer you bought from.

I can only tell storys from conventional AB amps.
And these were all in the limit of specs.
Don't know if any user ever mismatched the gain ...

A good quality class-d amplifier is not fudging on the specs.

By the way what is good in your opinion ?
The digam amps are known that they are not able to hold steady synth bass with low crest at their power limit for seconds.
The Hoellstern performs better I know ....

ok, I know now I have a fudging class D amp,
but I don't bother about it.

And the reason why FOH is trusting of the specs.

Oh yeah, Even I myself do it so.
Screw FOH over and and amp maker will be black listed on riders. Again, just like any class of amplifier.

Put Powersoft onto the black list ...

And of course class-d sounds superb. As does a modern class-ab as they are both capable of reaching beyond human hearing.

What by the hell is a modern class AB?
The class AB schematic design is basicly from 60's.
With some improvements in the 70's.

Don't remeber there is dramatically news with AB since the 80's. Except the power supplies and the class H (which is class AB)
 
Woo audio makes a ten thousand dollar class A monoblock amplifier that puts out something like 8 watts.

wa234-nyc.jpg
 
If I remember correctly the earliest Class A/B circuit I have seen is from a 1942 RCA tube manual?

That is approx. 10 years earlier before the class D invention.
Don't know exactly but it was somewhat in the 50's.

Would be interesting to see the schematic of the RCA amp.
But it's a valve amp, similar to some old Fender or Gibson stuff I think.
 
It is entirely possible to design a SMPS and a linear power supply to have almost identical characteristics... both static as well as dynamic. I did exactly this when developing the NeoPak and I couldn't tell the difference between the two power supplies. This was on a class AB power amp.
 
Put Powersoft onto the black list ...

I have an amp with Powersoft internals. It is great. Still you have to use gain matching to compare amps.

What by the hell is a modern class AB?
The class AB schematic design is basicly from 60's.
With some improvements in the 70's.

Don't remeber there is dramatically news with AB since the 80's. Except the power supplies and the class H (which is class AB)

I was subtly excluding MI tube amps. It's fair to say things like the passband behavior as they approach clipping can easily be duplicated with signal processing, small tube amps, or fancy feedback. It throws off thread to even mention it.