Not 15A: 150A transistor req'd for 75-150W class AB amplifires with low THD+n over 12W? OP+some of post 9 req'd reading to understand subject first

[mike7877]

@mike7877 You need to sit the next couple of plays out. Cheers big fella.

Thanks for your contribution

 

[solderdude]

Can you expand on your theory that a single '150A' transistor would be enough to create a low distortion amp.
What design do you have in mind.
You seem to know a LOT about circuit design.
It makes me wonder why such an amp does not exist yet. Perhaps you could design such an amp and simulate it in Spice showing great performance.
Afterall ... in spice you could just 'design' devices that have those properties.

Let me know when you have come up with the revolutionary design that will increase performance of AB amps.

 

[mike7877]

Can you expand on your theory that a single '150A' transistor would be enough to create a low distortion amp.
What design do you have in mind.
You seem to know a LOT about circuit design.
It makes me wonder why such an amp does not exist yet. Perhaps you could design such an amp and simulate it in Spice showing great performance.
Afterall ... in spice you could just 'design' devices that have those properties.

Let me know when you have come up with the revolutionary design that will increase performance of AB amps.

I made this thread asking if the reason distortion (THD+n) increases at 12 watts with 15A transistors (at the 8-10% max spec'd current on amplifiers that have effectively unlimited power supplies) is that the transistors start operating in their nonlinear range at that point (12w)

Nobody answered me - my original postulation remains the only theory. As far as I can tell there is no other plausible reason.


I'm not good at designing circuits start to finish. I've done it before, I could do it again. But I more enjoy looking at circuits and sometimes fixing them.
The design of my amplifier's would be basic - common. Not unlike the simpler amps reviewed on this site. Most of the (potential) benefit would be from the transistor itself, so my focus wouldn't be there.

In the mean time, still waiting on verification of the reason for the observed THD+n increase. Once someone with the appropriate skillset lurks this thread and confirms or denies, there's still design and so many other things before etc etc. (and that's only if something similar enough doesn't already exist). Double caveat: and that's only if the 12 watt increase isn't the result of a gremlin

If, if, if, if.

Close to transistor availability (if it goes that way - or the discovery and availability of an existing alternative), I'd start working on my amplifier's design. It would be heavily influenced by my favourite amplifier and the person helping me. I guess it's obvious I don't know a tonne about circuit design lol. I'm not an engineer so I don't feel too bad about it. I do like looking at circuits though, and fixing them sometimes (but only if the bits aren't too small and there aren't too many of them. Bad dreams without an electron microscope, the layers - they're all empty.

 

[jrosser]

I made this thread asking if the reason distortion (THD+n) increases at 12 watts with 15A transistors (at the 8-10% max spec'd current) on amplifiers that have effectively unlimited power supplies is that the transistors start operating in their nonlinear range at that point (12w)

Nobody answered me - my original postulation remains the only theory. As far as I can tell there is no other plausible reason.

I don't think that a single simplistic parameter such as the datasheet maximum current rating would identify a "good" output device, nor would that necessarily be a dominant factor in the overall performance of the whole design.

There is extensive discussion about the parameters that do matter, and the various sources of distortion by the legendary Doug Self here http://www.douglas-self.com/ampins/dipa/dipa.htm

The section on Large Signal Nonlinearity might be relevant to your original question.

 

[solderdude]

I made this thread asking if the reason distortion (THD+n) increases at 12 watts with 15A transistors (at the 8-10% max spec'd current on amplifiers that have effectively unlimited power supplies) is that the transistors start operating in their nonlinear range at that point (12w)

The answer is no.
It is not the current rating or amount of OP devices but the design around those components.
The component choice, overall circuit, gain, PCB layout, (overall and/or local) feedback and the load determines this point.
Part of it is the OP devices (be them FET, MOSFET, or transistors.

When you have spice or Multisim you can tinker with component properties and circuits and see how that works out.
To include PCB layout issues is another thing entirely and can also be simulated.

 

[mike7877]

The answer is no.

It is not the current rating or amount of OP devices but the design around those components.
The component choice, overall circuit, gain, PCB layout, (overall and/or local) feedback and the load determines this point.
Part of it is the OP devices (be them FET, MOSFET, or transistors.

When you have spice or Multisim you can tinker with component properties and circuits and see how that works out.
To include PCB layout issues is another thing entirely and can also be simulated.

I'm sure there's a lot to it, but how is it then, that the 3700, 4700, 6700, and 8500 all have falling THD+n until 12W...What are the odds? The 3700 and 4700 do have similar layouts, but the 6700 and 8500 are completely different from them and each other...

I'll tell you the odds: Less than a billion to one. Not in the history of the universe.

But they're all 12 watts. And the only commonality is the 15A rating of the transistor.

And the group who tuned each circuit.

But the thing is... why would they tune the 105W amp to 12W and the 150W amp to 12W


These aren't rhetorical questions - I do want you to answer.

And I'd like you to answer why you didn't put what you wrote in post 25 in any of your earlier replies

 

[solderdude]

It simply is reaching its maximum S/THD-N ratio at those levels. It is determined by the design.

There is no 'tuning' of an amp to 12W. No conspiracy, no deliberate 'holding back' of performance, no deliberate choice of 'inferior' OP devices, just sufficient engineering for the intended purpose which is not SOTA but good enough for the money.

I already answered all of this in post #2 but you did not seem to get the gist of what I wrote.

 

[mike7877]

It simply is reaching its maximum S/THD-N ratio at those levels. It is determined by the design.

There is no 'tuning' of an amp to 12W. No conspiracy, no deliberate 'holding back' of performance, no deliberate choice of 'inferior' OP devices, just sufficient engineering for the intended purpose which is not SOTA but good enough for the money.

I already answered all of this in post #2 but you did not seem to get the gist of what I wrote.

So harmonic distortion is rising above the noise floor and continuing to gain ground until clipping.

It always seems to rise... what's the cause?

Why isn't it controlled for?

It's terrible! If you can see it, you can hear it. How does it sound? Like a lack of detail and listening fatigue. How does a lack of detail sound? Like rolled off highs

"But frequency response is flat"

Maybe it is, but that's not how hearing works.


So we know why it should be gone

So why aren't designers fixing their faulty designs?

I can't help but think that a transistor with a more linear output would at least reduce second harmonic distortion (asymmetical)


Edit: and third harmonic distortion from rounded peaks "higher supply voltage, higher current transistor"
-more heat, lower performance

balancing act.


But so many of these designs are so bad they're unlistenable. Turn them to move a 6 inch woofer 1/16th inch and you can't hear the person beside you.

6 inch woofer playing same song moving 1/4 inch? Easy to hear them



The reason someone who says they can hear the difference between amplifiers can't A/B them on the spot double blind is they don't get time to get familiar and with their own music. The distortion profile of one can be so different from another that you can tell which amp is playing just by how one synth sounds. Double blind that person after practice with that song they know, and they'll pick right 100% of the time.

Harmonic distortion is why this hobby isn't 10x bigger.


There are people with $10K amps and speakers who still haven't heard high fidelity music

 

[wwenze]

But they're all 12 watts. And the only commonality is the 15A rating of the transistor.
And the group who tuned each circuit.
But the thing is... why would they tune the 105W amp to 12W and the 150W amp to 12W

This is a real observation but unfortunately one that the answer might be too far for the common person to answer.

Anyway first to counterprove the claim that power is the issue I just need to find a class AB that does better than 90dB @ 15W without the kink at 15W. And I found it, so let's continue.

The issue is that, like as mentioned a few posts up, it is hard to determine what is the cause of that 15W THD within the entire feedback loop. Yes, it could be the 15A transistor, if that was the commonality you discovered. But is it all 15A transistors or just that particular model? Furthermore, all transistors being 15A begs another question - How same or how different are the circuits that support those output transistors? Wouldn't the similar overall design have a greater say to the behavior than a single factor? Hence why I went to find another amp with a different behavior.

Of course, a person with the capacity would easily be able to swap out the transistor for a higher-current one or just parallel some and see how it changes for better or for worse (since the rest of the circuit isn't changed). Or you can double the rest of the circuit i.e. parallel amp and shift the 15W to 30W into a half-impedance load, although that doesn't really tell us anything new since the amps are doing the same job. Of course, changing the load impedance and observing how the problematic point changes can tell us whether that is due to voltage or current, but then again are voltage and current really separable in a full-circuit analysis...

Also, re:faulty design, an amp where THD+N stays constant vs increase output voltage isn't a faulty design. It just means distortion overtook noise. And that is bound to happen at higher voltage levels.
Yea in fact the more I read this thread the less I understand what is the issue...
Heck, if the THD stays constant vs output voltage it would suggest that the problem isn't the transfer curve linearity at the macro scale isn't it?

 

[dorakeg]

Like the Denon rate about 100watt for 9 Channel. That 900watt combine power max. But your Denon will just consume 600-700 watt from power supply. How can you output be higher than input. And I have not talking about power doubling at lower ohm speaker.

I want to point out that the 100watt x 9 channel is not all channels driven. If you use just 1-2 channels, you will get 100watt max. However of you drive all 9 channels continuously, you won't get anywhere close to 100w. I would say it's more like 50-60w.

AVR power per channel vs overall power is a little more complex. This is because users are highly unlikely to be driving every channel at max power simultaneously. Hence, even though your max power may be 500-600w, each channel can still get max of 100w.

Another thing is that amps power can momentarily exceed their rating because of power caps (some call it dynamic or transient power). The caps is like a reservoir of stored energy. Hence, when energy need is more than what the transformer could supply, these caps provide the energy.

AFAIK, manufacturers do not necessary specify continuous power esp. for AVR. So, if they just say 100w, they can also mean dynamic power instead of continuous. Some will specify continuous but not all. Some will also specify the 100w is on but only when specific number of channels are driven.

Its entirely possible for an AVR to have 100w per channel, all channels driven continuously. However, it will get expensive...

 

[SIY]

So harmonic distortion is rising above the noise floor and continuing to gain ground until clipping.

It always seems to rise... what's the cause?

Why isn't it controlled for?

It's terrible! If you can see it, you can hear it. How does it sound? Like a lack of detail and listening fatigue. How does a lack of detail sound? Like rolled off highs

"But frequency response is flat"

Maybe it is, but that's not how hearing works.


So we know why it should be gone

So why aren't designers fixing their faulty designs?

I can't help but think that a transistor with a more linear output would at least reduce second harmonic distortion (asymmetical)


Edit: and third harmonic distortion from rounded peaks "higher supply voltage, higher current transistor"
-more heat, lower performance

balancing act.


But so many of these designs are so bad they're unlistenable. Turn them to move a 6 inch woofer 1/16th inch and you can't hear the person beside you.

6 inch woofer playing same song moving 1/4 inch? Easy to hear them



The reason someone who says they can hear the difference between amplifiers can't A/B them on the spot double blind is they don't get time to get familiar and with their own music. The distortion profile of one can be so different from another that you can tell which amp is playing just by how one synth sounds. Double blind that person after practice with that song they know, and they'll pick right 100% of the time.

Harmonic distortion is why this hobby isn't 10x bigger.


There are people with $10K amps and speakers who still haven't heard high fidelity music

So much nonsense packed into a single post. I do congratulate you for the efficiency.

If you want to actually understand what you're talking about instead of randomly scribbling, spend some time with basic texts from Douglas Self and Bob Cordell.

 

[solderdude]

So harmonic distortion is rising above the noise floor and continuing to gain ground until clipping.

It always seems to rise... what's the cause?

Circuit design, PCB design, component choice, load.

Why isn't it controlled for?

It is controlled by the feedback path.
There are practical limits in a design such as open-loop gain, amount of NFB, PCB layout, component choice.

It's terrible! If you can see it, you can hear it.

That part that is not true.
Whether you can hear it depends on the recording, listening SPL, harmonic spread, speaker itself and the listener.

How does it sound? Like a lack of detail and listening fatigue.

How distortion sounds depends on the level of distortion, harmonic spread, the recording (masking).
0.01% is inaudible with music... well maybe with some specific recordings, listening levels and knowing what to listen for (training) and depending on the harmonic spectrum it could be detectable.

Maybe it is, but that's not how hearing works.

Hearing is designed to give a person an edge for early warning of danger. Fortunately you can also enjoy music or the voice of a loved one with the hearing as well.
It is a very poor 'absolute' measurement device.

So we know why it should be gone

We know when it isn't relevant. It does not have to be gone or below measurable levels.
It only has to be below audible levels. Fortunately we can measure, far, far, far below/beyond audible levels.

So why aren't designers fixing their faulty designs?

Because they don't need to above a certain point when the design goals are met.
The design goals determine what is deemed 'good enough'.
Some designers like to push circuits to the design limits determined by available parts and physical limits.
AVR amp sections nor ADC/DAC do not fall into this category.

I can't help but think that a transistor with a more linear output would at least reduce second harmonic distortion (asymmetical)

That is correct.

But so many of these designs are so bad they're unlistenable.

That's not my opinion. Unlistenable speakers and headphones.... sure. Problematic rooms... sure. Electronics... never unless they are broken or really poor in design.

There are people with $10K amps and speakers who still haven't heard high fidelity music

Depends on your definition of high-fidelity.

 

[BDWoody]

I think we can safely close this thread.