I haven't looked at Class D for a few years and wondered about the current state of the art.
Not which amp has the best performance (seems to be the Purifi 1et400 at the moment) but the circuitry and techniques used.
There is a lot of interest in the SMPS world in Zero Volt Switched and similar circuits - of which there is a remarkable number of different variations.
But not all of the SMPS concepts work well as Class D amps.
Is the audio world still stuck on what is essentially a bipolar version of a buck converter?
I notice that at least one tech company has a ~6 MHz
ZVS Class D amplifier for industrial use EPC9065 High Frequency ZVS Class-D Power Amplifier but their audio amp looks quite ordinary.
The specs of the Purifi 1et400 are pretty impressive, does anyone have any information about the circuit?
The switch speed is 500 kHz which is not exceptional, so is the amp essentially similar to the earlier nCore Hypex amps that achieved low distortion from careful feedback loop optimisation?
If so then there's a reasonable case not to bother with expensive SOTA semiconductors or ZVS complications, just stick with silicon MOSFETs.
David
Not which amp has the best performance (seems to be the Purifi 1et400 at the moment) but the circuitry and techniques used.
There is a lot of interest in the SMPS world in Zero Volt Switched and similar circuits - of which there is a remarkable number of different variations.
But not all of the SMPS concepts work well as Class D amps.
Is the audio world still stuck on what is essentially a bipolar version of a buck converter?
I notice that at least one tech company has a ~6 MHz
ZVS Class D amplifier for industrial use EPC9065 High Frequency ZVS Class-D Power Amplifier but their audio amp looks quite ordinary.The specs of the Purifi 1et400 are pretty impressive, does anyone have any information about the circuit?
The switch speed is 500 kHz which is not exceptional, so is the amp essentially similar to the earlier nCore Hypex amps that achieved low distortion from careful feedback loop optimisation?
If so then there's a reasonable case not to bother with expensive SOTA semiconductors or ZVS complications, just stick with silicon MOSFETs.
David
I am currently using an SMSL DA-8s power amplifier which I discovered through Z reviews. In his review he states that it is the best class D amplifier he ever heard and he has heard a lot of them. After listening to mine for several months I cannot disagree. It drives my Alpair 11ms speakers really well. It dynamically slams them to the point that no one would ever guess that they were full range drivers. For an amplifier this amazing, its surprisingly very affordable.
The current state of the art class D amplifiers are these days all self oscillating types, which was originatet by Carsten Nielsen of ICEPower some 25 years ago.
CN develloped a dual feedback loop system with an inner and an outer loop.
The outer one embrasing both the output filter and the inputsection (not buffer circuits).
The inner one only from modulator to PWM output.
The inner one is very fast and stable, the filtered one contains bare anything else than audio signals.
The answer to that came from Pytzeys (Hypex) nCore products, which bettered all others on THD+N. There is a good reason for at least some of it though. Hypex nCore only has a gain of arround 13 dB, which is not enough for normal use in HI-FI.
Professionals might find it usefull though, because output from i.e. mixing consoles can be pretty hot.
Aneways if you want to bring the gain to usefull hights in home HI-FI gear, you´ll have to ad a gainstage, which then will apply the missing noise compared to others.
Indeed this is academic, because there is no noise, when your noise level is only 28 µV.
But suddenly other class D amps looks more compettitive.
Still there is only very few vendors of high end class D, in this moment I know of only four namely: ICEPower, Pascal, Hypex and Purifi. The latter two ones are both Putzeys creations, and thus might share much of the same technology. I.e. is both Purifi ET400 and Hypex nCore modules low gain types with arround 13-15 dB gain without bufferstage.
The interesting part in Hypex modules is the very high loop gain, which Putzeys have achieved, which leads to the impressive performance in the lab.
This is surely a result of very thorough analysys of distortion sources in class D amplifiers such as Hypex ucD amps. ucD is a higher gain type with about 27 dB.
So as you can see trees don´t grow into heaven. Low gain is a choice for some, but not for others.
The development of new and better components for class D is going pretty well.
IRF has done a lot to better their output FETs and gatedrivers. ICEPower has develloped their own ICEEdge chipset with modulators and gatedrivers. These chips has until now only been used in one of ICE´s models, namely the full bridge 1200 AS and 1200 AS2, the latter is two channel.
Both are with on board SMPS, and it seems as this is what ICE will stick with in their modules. On the side of this ICE delivers technology to a lot of makers of HI-FI, TV´s, mobile phones etc. where the ICE technology is used in chips or so.
Basicly they are sticking to the original patented technology in refined versions.
As a spinoff of ICE Pascal went on air for the pro-segment.
They have a lot of high power modules with hanger supplies, monitoring and so on.
Their technology is pretty much undisclosed, but might seem less interesting to HI-FI makers because of less impressive performance. But they really are compettitive in regard to watts pr USD. And that is paramount in the pro segment.
They found their way into HI-FI anyway, i.e. Brooklyn, Gato, and also Aavik, which was tested in stereophile, with misserable measuring results, not related to the calss D section though.
To my best knowledge you should consider the ICE 1200 AS or AS2 as the cream of class D. It is pretty expensive, but the power is sufficient for most purposes.
CN develloped a dual feedback loop system with an inner and an outer loop.
The outer one embrasing both the output filter and the inputsection (not buffer circuits).
The inner one only from modulator to PWM output.
The inner one is very fast and stable, the filtered one contains bare anything else than audio signals.
The answer to that came from Pytzeys (Hypex) nCore products, which bettered all others on THD+N. There is a good reason for at least some of it though. Hypex nCore only has a gain of arround 13 dB, which is not enough for normal use in HI-FI.
Professionals might find it usefull though, because output from i.e. mixing consoles can be pretty hot.
Aneways if you want to bring the gain to usefull hights in home HI-FI gear, you´ll have to ad a gainstage, which then will apply the missing noise compared to others.
Indeed this is academic, because there is no noise, when your noise level is only 28 µV.
But suddenly other class D amps looks more compettitive.
Still there is only very few vendors of high end class D, in this moment I know of only four namely: ICEPower, Pascal, Hypex and Purifi. The latter two ones are both Putzeys creations, and thus might share much of the same technology. I.e. is both Purifi ET400 and Hypex nCore modules low gain types with arround 13-15 dB gain without bufferstage.
The interesting part in Hypex modules is the very high loop gain, which Putzeys have achieved, which leads to the impressive performance in the lab.
This is surely a result of very thorough analysys of distortion sources in class D amplifiers such as Hypex ucD amps. ucD is a higher gain type with about 27 dB.
So as you can see trees don´t grow into heaven. Low gain is a choice for some, but not for others.
The development of new and better components for class D is going pretty well.
IRF has done a lot to better their output FETs and gatedrivers. ICEPower has develloped their own ICEEdge chipset with modulators and gatedrivers. These chips has until now only been used in one of ICE´s models, namely the full bridge 1200 AS and 1200 AS2, the latter is two channel.
Both are with on board SMPS, and it seems as this is what ICE will stick with in their modules. On the side of this ICE delivers technology to a lot of makers of HI-FI, TV´s, mobile phones etc. where the ICE technology is used in chips or so.
Basicly they are sticking to the original patented technology in refined versions.
As a spinoff of ICE Pascal went on air for the pro-segment.
They have a lot of high power modules with hanger supplies, monitoring and so on.
Their technology is pretty much undisclosed, but might seem less interesting to HI-FI makers because of less impressive performance. But they really are compettitive in regard to watts pr USD. And that is paramount in the pro segment.
They found their way into HI-FI anyway, i.e. Brooklyn, Gato, and also Aavik, which was tested in stereophile, with misserable measuring results, not related to the calss D section though.
To my best knowledge you should consider the ICE 1200 AS or AS2 as the cream of class D. It is pretty expensive, but the power is sufficient for most purposes.
An awful lot of preamps have far too much gain for the power amp. Personally I like the idea of going hotter out the preamp into a low gain power amp, but I don't have to be compatible with anyone but myself
Although I am a big fan of TPA325x - they do not play in the league described above considering bandwidth, frequency response and THD. The improvements since Nielsen are impressive, but beyond audibility and thus not relevant for my designs. More important these chips include a bunch of protection features that make them nearly undestructable on my work bench - the workhorse for DIY-audio.
just my 2c
Btw, Nielsen deserves a place in the hall of fame not only in audio- but in the smps world as well. He invented a genius control scheme to control LLC smps. I think fairchild make use of this idea.
just my 2c
Btw, Nielsen deserves a place in the hall of fame not only in audio- but in the smps world as well. He invented a genius control scheme to control LLC smps. I think fairchild make use of this idea.
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Well I don´t think I forgot Pascal.
The TPA chip amps are not really in the same league as the others.
It is 4-8 USD chips, suited for multichannel audio and TV´s.
Lars Risbo, former employee of Texas now of Purifi, did design some of them.
He was actually the designer og the TACT digital amplifier with equibit technology in the late 90´s.
An awful lot of preamps have far too much gain for the power amp. Personally I like the idea of going hotter out the preamp into a low gain power amp, but I don't have to be compatible with anyone but myself
That´s a choice.
But you can increase gain with less noise in the class D modulator than in the frequency domain, if you know how to.
Why equate the cost of the chip to the overall performance? The silicon used in the Purifi amps won't cost much different to 4-8 dollars either.
At low power levels and with post filter feedback the TPA amps are as good as the others. Better than some and worse than others but certainly within the same league.
Thank you for the information.
No real surprises, which is what I wanted to check, but a fine summary.
Why do consider the ICE as the cream rather than the Purifi, only the power?
...hotter out the preamp...but I don't have to be compatible with anyone but myself
I was initially surprised by the numbers for the NCore and Purifi amps.
But I noticed the Benchmark AHB2 class H amp is less than 10 dB Gain in Low mode and takes ~10 V from the preamp.
Sure helps the S/N ratio, probably the way of the future.
I do have biamped horns > 110 dB so it does matter to me.
Best wishes
David
I consider the ICE 1200 AS as better than the competition because of the sound quality.
I´m not a fan of thin and airy sound as i.e. the nCore 500, also the ucD amps do have clean sound, but without the human touch.
The ICE 1200 AS is in this regard very different, and I really don´t think, that it is a matter of power.
But that said, I´ve experinced pretty different things with ICE. Their modules do not sound alike all together, the peak IMHO is the one mentioned.
Anyways it is interesting, that almost all the very best class D amps in some way relate to DTU in Copenhagen Denmark.
That was caused by a professor at DTU ( Denmarks Technical University). He pushed his students to solve the basics on switching amps, thus CN did his Phd on exactly that, leading to the first selfoscillating class D amps.
Pascal is danish as well, and now Putzeys is a partner in Purifi company, witch is also danish, and both managed and co owned by Peter Lyngdorf. Lars Risbo who was earlier at TI, is now also a part of Purifi.
Pretty cool I think
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And you have done statistically valid tests?
What test protocol, sample size, P level?
Best wishes
David
I was thinking of trying this myself. Have you already done it? And what were the performance gains?
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