I'm posting this topic in the class D segment of diyaudio for reseons that will become apparent shortly.
The holy grail of audio amplification is the class A linear amplification because EVERYTHING is amplified and there is no crossover distortion or delay in the time base. It does not matter if it is Single Ended or Push-Pull. Linear class A is therefore our reference.
Class D is a switch-mode amplifier, similar to push-pull, it uses two MOSFET's arranged in a Cascode topology (half bridge) with a high- and low side. One for the positive voltage swing (high) and the other for the negative voltage swing (low) which produce a variable duty cycle pulse width modulated signal which in turn is recovered as an analog signal via (typically) 2nd order LC-filter which is used to drive your loudspeaker just as class A/AB. The main difference between class A/AB and D is that class D produce a binary/discrete copy of the analog signal vs class A/AB which is a direct amplification of the analog signal. Class D is very much an analog amplification method spite some claiming it as digital, which could stem from the description of the MOSFET function as being digital due to either being on or off aka 1 or 0.
The title of the thread is - Quantifying class A quality, so lets tackle that right away.
We are looking at two different approaches of how to amplify a sine-wave. One is class A which we can view as direct and the other is class D which we can view as discrete copy. Under an ideal situation, both will deliver exactly the same signal quality at the output.
Before I approach the core of the topic, allow me to quote Mytek:
We can see that Mytek is trying to challenge class A by stating that "well executed Class D circuits can challenge the best Class A and sound amazing" - Where is the evidence ?
Lets start with comparing Mytek Brooklyn amp against Accuphase A-75 which is a class A amplifier.
Mytek Brooklyn:
S/N ratio: 121 dB < good
THD: <0.01% < good
DF: 400 < good
Accuphase A-75
S/N ratio: 122 dB < good
THD: 0.03-0.07 % < good
DF: 1000 < outstanding
- Bonus, lets also look at NAD M22 which is based on the Hypex nCore NC400 module in the case of a readers protest should emerge.
S/N ratio: >120 dB <good
THD: <0.003% < outstanding
DF: 800 <outstanding
The THD range is typically accepted as:
2% - Most people can detect this.
1% Some people can detect this but is a minority group.
0.1% Typically too low to be detected and is this level is therefore considered good.
0.01% This is the audiophile level, no one can detect this.
0.001% is well bellow what we can consider problems, you are doing well if your amp has this THD. Even lower than this has no real implication and is reserved for does who have the need to brag.
Did we solve it, can we say that Mytek (Pascal) and NAD (Hypex) are in the class A range of quality factors ? - well, no. Going back to class A being direct and class D being a discrete copy and also being a switch-mode amplifier, there is something els we need to look at. We need to look at the time base of things. I don't know what components Pascal is using but I do know what NAD / Hypex is using and I want to look at the MOSFET which is the switching component here.
I've been dealing with understanding how to quantify class A performance through class D, when we actually can say that class D is on par with class A and for this, I have turned to consideration of what real time is. A friend of mine is working as a programmer and is dealing with time based functions on a daily basis and he had this to say: "In hyper-physics, real time, as in happening right now, 1ns (nanosecond) is used as the reference."
Before we look at the Fairchild MOSFET we will look at a specific area of class D, the PWM side of things. We have the ideal PWM and we have the real PWM signal. The ideal PWM is a perfect square-wave with 90 degree angles. Going from an ideal PWM to a real PWM, we have to look at how the MOSFET behave and for that we have time based reactions called: Turn-on and Turn-off delay, as well as Rise and Fall time. Finally we have under and overshoot which is the cause for something called dead time. All of these are hardware based issues which class D has to deal with.
- The Turn-on and Turn-off is a time based reaction, from the demand to react (signal turns on) to the mosfet actually reacting and vice versa for when it turns off.
- Rise and Fall time is dealing with how much time passes from signal turn on to saturation or the linear region of the MOSFET.
This comes from the Fairchild FDP52N20 data sheet:
The combination of turn-on delay and rise time amounts to (typically) 228 ns or 0.228 microseconds. That is just for the MOSFET to fully turn on.
Then there is the matter of deadtime to prevent a short between the high and low side. When the MOSFETS turn on and off, they produce a transient spike. This is especially critical since both MOSFETS can't be on at the same time due to the dead short situation which will fry them in an instant. The deadtime is therefor inserted and this can be anything between 10-100 ns. You should read this as a period where no information can be captured and is the majority of the Jitter issue in class D and digital audio as well.
228 ns is far from the ideal PWM and the concept of real time in hyper-physics. So here is my question to the community:
What do you consider to be acceptable real-time in relationship to class A's continuous amplification ? Can we accept the 100's of ns time error considering the S/N ratio and THD figures we get via Hypex and Pascal.
Note that there are far better MOSFETS such as the Infineon BSZ097N04 and I can't speculate on the MOSFET Pascla use.
- Oneminde
The holy grail of audio amplification is the class A linear amplification because EVERYTHING is amplified and there is no crossover distortion or delay in the time base. It does not matter if it is Single Ended or Push-Pull. Linear class A is therefore our reference.
Class D is a switch-mode amplifier, similar to push-pull, it uses two MOSFET's arranged in a Cascode topology (half bridge) with a high- and low side. One for the positive voltage swing (high) and the other for the negative voltage swing (low) which produce a variable duty cycle pulse width modulated signal which in turn is recovered as an analog signal via (typically) 2nd order LC-filter which is used to drive your loudspeaker just as class A/AB. The main difference between class A/AB and D is that class D produce a binary/discrete copy of the analog signal vs class A/AB which is a direct amplification of the analog signal. Class D is very much an analog amplification method spite some claiming it as digital, which could stem from the description of the MOSFET function as being digital due to either being on or off aka 1 or 0.
The title of the thread is - Quantifying class A quality, so lets tackle that right away.
We are looking at two different approaches of how to amplify a sine-wave. One is class A which we can view as direct and the other is class D which we can view as discrete copy. Under an ideal situation, both will deliver exactly the same signal quality at the output.
Before I approach the core of the topic, allow me to quote Mytek:
Mytek is using 2x Pascal U-Pro1 class D modules.
We can see that Mytek is trying to challenge class A by stating that "well executed Class D circuits can challenge the best Class A and sound amazing" - Where is the evidence ?
Lets start with comparing Mytek Brooklyn amp against Accuphase A-75 which is a class A amplifier.
Mytek Brooklyn:
S/N ratio: 121 dB < good
THD: <0.01% < good
DF: 400 < good
Accuphase A-75
S/N ratio: 122 dB < good
THD: 0.03-0.07 % < good
DF: 1000 < outstanding
- Bonus, lets also look at NAD M22 which is based on the Hypex nCore NC400 module in the case of a readers protest should emerge.
S/N ratio: >120 dB <good
THD: <0.003% < outstanding
DF: 800 <outstanding
The THD range is typically accepted as:
2% - Most people can detect this.
1% Some people can detect this but is a minority group.
0.1% Typically too low to be detected and is this level is therefore considered good.
0.01% This is the audiophile level, no one can detect this.
0.001% is well bellow what we can consider problems, you are doing well if your amp has this THD. Even lower than this has no real implication and is reserved for does who have the need to brag.
Did we solve it, can we say that Mytek (Pascal) and NAD (Hypex) are in the class A range of quality factors ? - well, no. Going back to class A being direct and class D being a discrete copy and also being a switch-mode amplifier, there is something els we need to look at. We need to look at the time base of things. I don't know what components Pascal is using but I do know what NAD / Hypex is using and I want to look at the MOSFET which is the switching component here.
I've been dealing with understanding how to quantify class A performance through class D, when we actually can say that class D is on par with class A and for this, I have turned to consideration of what real time is. A friend of mine is working as a programmer and is dealing with time based functions on a daily basis and he had this to say: "In hyper-physics, real time, as in happening right now, 1ns (nanosecond) is used as the reference."
NAD M22: The output MOSFET used is the Fairchild FDP52N20 (N-Channel).
Before we look at the Fairchild MOSFET we will look at a specific area of class D, the PWM side of things. We have the ideal PWM and we have the real PWM signal. The ideal PWM is a perfect square-wave with 90 degree angles. Going from an ideal PWM to a real PWM, we have to look at how the MOSFET behave and for that we have time based reactions called: Turn-on and Turn-off delay, as well as Rise and Fall time. Finally we have under and overshoot which is the cause for something called dead time. All of these are hardware based issues which class D has to deal with.
- The Turn-on and Turn-off is a time based reaction, from the demand to react (signal turns on) to the mosfet actually reacting and vice versa for when it turns off.
- Rise and Fall time is dealing with how much time passes from signal turn on to saturation or the linear region of the MOSFET.
This comes from the Fairchild FDP52N20 data sheet:
The combination of turn-on delay and rise time amounts to (typically) 228 ns or 0.228 microseconds. That is just for the MOSFET to fully turn on.
Then there is the matter of deadtime to prevent a short between the high and low side. When the MOSFETS turn on and off, they produce a transient spike. This is especially critical since both MOSFETS can't be on at the same time due to the dead short situation which will fry them in an instant. The deadtime is therefor inserted and this can be anything between 10-100 ns. You should read this as a period where no information can be captured and is the majority of the Jitter issue in class D and digital audio as well.
228 ns is far from the ideal PWM and the concept of real time in hyper-physics. So here is my question to the community:
What do you consider to be acceptable real-time in relationship to class A's continuous amplification ? Can we accept the 100's of ns time error considering the S/N ratio and THD figures we get via Hypex and Pascal.
Note that there are far better MOSFETS such as the Infineon BSZ097N04 and I can't speculate on the MOSFET Pascla use.
- Oneminde
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One small observation regarding those switching times - you'll note the datasheet specifies the conditions in which those times were measured, among which is a 25 ohm gate resistor and a voltage of 100v across the MOSFET.
Does the Hypex module in that NAD M22 use the same value, and/or the same supply voltage (+/-50v resulting in 100v net across each FET)?
Does the Hypex module in that NAD M22 use the same value, and/or the same supply voltage (+/-50v resulting in 100v net across each FET)?
With due respect, this is buzzword bingo. If you have a look at the acoustical section of hyper-physics site there is no mention of realtime or 1nsec at all. Realtime has never been defined by a general fixed time step but system dependent reaction time.
And 1ns reaction time correlates with 300MHz bandwidth - audio ends at 20kHz.
voltwide, distortion detectable level varies widely. Last week I played around an ugly tpa3251 post-fb mode pre-clipping behavior, it produces very noticeable distortions at levels .1-.5% of THD@1kHz(at low frequencies even worse). The same time I need a few % to surely hear single 2nd or 3rd harmonic. Pre-clipping behavior a big deal and usually underrated, and never specified.
Poor class-D. Trying to mimic class-A while class-A is not the holy grail of anything.
Guy's. 1ns is no more than a reference point. I am sure it can be argued against and already has, which is fine. My question and the whole reason for starting this thread was to get more than my own "opinion" about when or for that matter how class D can be said to have class A sound quality.
If you don't like class D, then that is fine too, all you have to do is walk away... lol, no one is forcing anyone to like or buy a class D amp.
If you don't like class D, then that is fine too, all you have to do is walk away... lol, no one is forcing anyone to like or buy a class D amp.
Interesting. So you are saying that the benchmark is not the benchmark at all ? might it be then that class AB is because of its better efficiency ?
What makes class A superior? Lowest THD I suppose. But there is more about what makes an amp superior. Efficiency for instance, weigth, price just to name a few. These debates always run in circles...
For sure, these debates run in circle and everyone has an opinion. But it looks like quantifying class A like I am trying to do to ensure that there are proper ways to say "this class D amplifier can compete with the best class A" which so far is more difficult than it once thought to be. We have quality's such as THD, S/N ratio and Damping Factor. How linear the amp is within its operational frequency band, efficiency and so forth. Weight and price are subjective just like visual appeal is subjective and even watt's or strength of the amplifier can be considered to be subjective. What I am looking for are definitions that are objective and something that most people can agree upon, and perhaps the only two are THD / THD+N and S/N ratio - low distortion and pitch black at quite passages.
Since my quantifying class A quality opens up a whole new jar of interpretations, maybe the answer is not a specific time frame but rather point towards using MOSFETS and other crucial components that allow for fastest turn-on / turn-off, rise amd fall time, slowest delays possible and the least amount of dead time in order to achieve the best PWM signal possible. There is no "close enough" or "this will do". If it can be improved and is practical, then that should be the goal. But for now, 1ns is my reference and no one els has to use that, but at least I can in a way quantify things.
1 GHz = 1 ns
25kHz = 0.04ms or 40 000 ns
35kHz = 0.028571ms or 28 571ns
44.1khz = 0.002267ms or 2267.573ns
192kHz = 0.0052083ms or 5 208.3ns
384kHz = 0.0026041ms or 2604.1 ns
1.5MHz = 0.000666ms or 666.66 ns
- EDIT -
And by the way, if we are talking about lowest THD, the NAD M22 win over Accuphase class A - NAD is an order of magnitude better.
Hi
my 2 cents
i had 28 years a Accuphase C200V and a P300V and its not Class A ...but
at the preamp I changed all caps and lucklythe amp played fine...very fine..nevertheless i sold it because my DAC (gustard A20H) sound better directly at the power amp
...the sound is always very nice but after doing DIY the relation between price and durability ....hmmm.. -----> you pay a lot for shiny, massive, commercial....blablabla.......
i accept a better craftsman ship and the durability
chris
my 2 cents
i had 28 years a Accuphase C200V and a P300V and its not Class A ...but
at the preamp I changed all caps and lucklythe amp played fine...very fine..nevertheless i sold it because my DAC (gustard A20H) sound better directly at the power amp
...the sound is always very nice but after doing DIY the relation between price and durability ....hmmm.. -----> you pay a lot for shiny, massive, commercial....blablabla.......
i accept a better craftsman ship and the durability
chris
Buyers of audio equipment comes in different classes, have low or high interest, thin or thick wallet, have almost no to expert level knowledge, have no skill or a long list of skills he or she can pour into the project. People value different things. Some are hardcore old school (tubes) while other are always looking for the latest thing. Some are pure technical and couldn't care less about refinement and design. In the end, the one using cheap equipment might be as happy with his or here choices as the one spending $2.4 million dollars.
The Honeybadger class AB available through the diyaudio store can compete against the best class AB commercial units available and until a true superior class D amp appear, Hypex and Pascal is the way to go.
- Oneminde
The Honeybadger class AB available through the diyaudio store can compete against the best class AB commercial units available and until a true superior class D amp appear, Hypex and Pascal is the way to go.
- Oneminde
THD, IMD, S/N and damping factor are numbers you can certainly compare. Needless to say that beyond certain numbers achievements might be measurable but not audible. The actual reference of class-d seems to be Bruno Putzeys latest baby, the DD-amp. Based on the technical data I suppose it outperforms any class A on this planet.
I agree and IMD aren't specked typically which it should. Chn separation is utterly important as well. I have my ideas about superior class D but will certainly take a look at the amp you mentioned, there can be no harm in inspecting what others do. In the end, all I am after is "as good as possible"
I get a hint of a TON of feedback, digital correction etc. Not a fan of that. Sure, the THD+N is looks okay, besides massive spikes at 10kHz and 14-15kHz. On top of things, its more or less a digital amplifier. They might impress with good numbers, but remember, greater than 0.01% in THD (which is already an audiophile grade) has no real benefit since no one can detect it and is therefore only used for bragging, same with S/N in the range of -110-120 dB is absolutely acceptable - sure, the lower it is the better. But digital amplification these day ... mhe, I see no need for that. Pure analog class D with a minimum amount of closed loop or open loop feedback, heck yes. The rule is: Feedback is bad. Same thing with capacitor based DC servo on the output line.. If you know what you are doing, you can achieve outstanding performance without corrupting the signal via intermediate digital modulation.
Often it is not about you as an engineer and with that I mean your knowledge about electronics, but rather development of components and their ability to work closer to a theoretical ideal. The less ideal a component is the more the engineer must compensate and compensation is in reality not a merit of excellence. So, take two engineers: Both achieve the same performance, the difference is amount of components, topology, placement, EMI, IMD figures, efficiency etc - the one who reach stable function with least amount of parts and without compromises is perhaps the better engineer. On the other hand, a complex and heavy amplifier impress more.
Take the Vitus Audio SM-103 monoblock: 150w Class-AB w 1st 100w Class-A. S/N 110 dB and THD+N 0.01% - its not using toroidal core or R-Core or latest SMPS tech, nope, its using an EI laminated core transformer which is probably the worst thing you can use in an audio amplifier and all for the low price of $40 000/pcs ... Jebus.
Well, they gotta squeeze out a profit SOMEwhere...
Those are made to be listened to, and optionally admired from the outside, not opened up and inspected, anyway
Oh, marketing...
PS: If you're referring to the first graph on the DD amp thread, you'll note that's an IMD graph, not a THD+N
Those are made to be listened to, and optionally admired from the outside, not opened up and inspected, anyway
Oh, marketing...
PS: If you're referring to the first graph on the DD amp thread, you'll note that's an IMD graph, not a THD+N
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Sure, I get that. I don't mind when engineers poured their heart and soul into a project, splashed it with some art and refinement, spent months selecting components to up the performance and stability and had a blast doing so and its relative expensive to build. I totally accept that sometimes you have to pay for quality and a bit of luxury, but when you peak inside the Vitus amp, I am not impressed. What the heck am I paying for ... The Honeybadger with superb components and choices beat Vitus any day of the week even of it is specked and built like if Lexus decided to built a tank .... LOL - but at a fraction of the cost.Well, they gotta squeeze out a profit SOMEwhere...
Those are made to be listened to, and optionally admired from the outside, not opened up and inspected, anyway
Oh, marketing...
IMD, got it
If you're refering to this plot:
This is IMD, so nothing is wrong about that. If not, what plot are you refering to?
The turn on time turn off time and dead time distortion can be corrected by feedback. Problem is you need high loop gain. And high loop gain comes with high frequency. And at high frequency, the relative error introduced by these times becomes worse....
BTW I don' think that the easy explanation of THD and how much can be decteted says it all. There is also IMD (that sounds MUCH worse than pure THD!). Plus: IMD is related to THD and there are many ways to measure it so you can produce the number you want to see
BTW I don' think that the easy explanation of THD and how much can be decteted says it all. There is also IMD (that sounds MUCH worse than pure THD!). Plus: IMD is related to THD and there are many ways to measure it so you can produce the number you want to see
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