dumbledore said:
I've posted this before; http://www.primare.net/assets/_managed/cms/files/PrimareUFPD2.pdf
regards
I've posted this before; http://www.primare.net/assets/_managed/cms/files/PrimareUFPD2.pdf
regards
Must say have not seen this before but reading it confirms to me my original suspition that class D is a no go for HIFI.
The article claims some improvements using their technology but they don't go into detail. However, from what it implies is that they have a technique to apply higher from of feedback. I expect the techique is some analogue scheme not digital. The problem is that is known fact from class A/B designs that over application of overall feedback to minimise THD and output resistance results in poor sounding amplifiers. And unfortunatelly on class D amplifiers a lot of distorsion is generated by the technique that will require considerable feedback loop gains to remove it.
The article claims some improvements using their technology but they don't go into detail. However, from what it implies is that they have a technique to apply higher from of feedback. I expect the techique is some analogue scheme not digital. The problem is that is known fact from class A/B designs that over application of overall feedback to minimise THD and output resistance results in poor sounding amplifiers. And unfortunatelly on class D amplifiers a lot of distorsion is generated by the technique that will require considerable feedback loop gains to remove it.
I believe the high-end US audio firm Jeff Rowland Design Group is to stop offering Class D amps and Instead return to using class AB.
As I mentioned in an earlier post, my one experience with class D, the Jeff Rowland Continuum 500 integrated, was not favorable.
As I mentioned in an earlier post, my one experience with class D, the Jeff Rowland Continuum 500 integrated, was not favorable.
dumbledore said:
Dumbledore,
It is quite possible to have feedback to compensate for power supply fluctuations, non linearities in the output filter and strange frequency dependent goings on in the speaker impedance. Have a look at the zetex/diodes chipset I linked to earlier in the thread. NAD have used exactly this approach in their 'direct digital' M2 amplifier, which has received very positive reviews, and not just from night club owners.
While NAD seem to be charging a small fortune for their amp, the electronics to do all this cost peanuts.
CnoEvil said:
Class D is generally used to cover amps that use a switching technique (output drivers are either full-on or full-off) rather than amps which vary the conductance of the output drivers in some linear way to achieve the required output.
'Full digital' class D take a digital input signal (usually some form of PCM) apply some DSP magic and use this to generate on / off signals to drive the output stages. Other class D topologies use the same output approach, but generate the on / off signals by comparing an input analogue signal with a high frequency reference waveform (usually triangular).
Both are class D, both have the same switching output, but the way of generating the output driver control signals is different.
Andyjm,
Had a look at the DDFA spec and must say at least somebody tried to do digital feedback which is a good way to go.
Is this technology perfected. I don't think so. There are two problems I can see.
One I already said, you will need a lot of negative feedback to remove distorsion inherent in non feedback class D output levels to acceptable levels. Is known fact that high degrees of overall negative feedback is not favourable for audiophile amplifiers.
Second the negative feedback circuitry used in DDFA is in fact quite an analog process. It requires a very precise ADC (analog to digital converter) to operate and do the digital feedback (they call it Analogue feedback preocessor). DDFA spec is not saying the ADC specification but compare that with the class A/B designs that use a bit more open loop gain and two feedback resistors then I would expect DDFA technology will require some perfecting (just remeber how much pefecting went into fixing the DAC technology which is still ongoing).
With these limitations in mind related to class D amplifiers the final listening tests will be critical. If a class D can sound near as good as reference class A/B amps then they will win eventually. But in view of above limitation class D may be acceptible for HIFI use in active speaker designs used primirily for the bass and midrange units. Driving single units with no crosovers will allow the amplifier designer to tune the output stage and initial PWM drive parameters so that smaller negative feedback will be required to achieve set THD which will address limitation one above.
Had a look at the DDFA spec and must say at least somebody tried to do digital feedback which is a good way to go.
Is this technology perfected. I don't think so. There are two problems I can see.
One I already said, you will need a lot of negative feedback to remove distorsion inherent in non feedback class D output levels to acceptable levels. Is known fact that high degrees of overall negative feedback is not favourable for audiophile amplifiers.
Second the negative feedback circuitry used in DDFA is in fact quite an analog process. It requires a very precise ADC (analog to digital converter) to operate and do the digital feedback (they call it Analogue feedback preocessor). DDFA spec is not saying the ADC specification but compare that with the class A/B designs that use a bit more open loop gain and two feedback resistors then I would expect DDFA technology will require some perfecting (just remeber how much pefecting went into fixing the DAC technology which is still ongoing).
With these limitations in mind related to class D amplifiers the final listening tests will be critical. If a class D can sound near as good as reference class A/B amps then they will win eventually. But in view of above limitation class D may be acceptible for HIFI use in active speaker designs used primirily for the bass and midrange units. Driving single units with no crosovers will allow the amplifier designer to tune the output stage and initial PWM drive parameters so that smaller negative feedback will be required to achieve set THD which will address limitation one above.
andyjm said:
how come? both, "digital" and analog, class D amps use PWM signal followed by a low pass filter to modulate the driver output. the only difference lies in that a "digital" amp extracts a PWM straight from PCM whereas "analog" amp creates PWM by modulating the analog wave with a triangular signal wave.
anyway, I'm too in the camp that too much negative loop feedback is too much. a class D will not measure fine without it. for instance in that Primare blurp they claim they use 26dB of NFB! just imagine how this thing measure in it's open loop version. unfortunately, such is the nature of transistors - switching them on and off constantly will always cause them to work in nonlinear manner.
I think class D has it's specific sound. I heard the new Primare integrated and also Devialet, those driving WA Sashas, and was underwhelmed, to say the least. Those amps sounded in a way very impressive - lots of detail in HF, but not natural at all and detached as opposed to sounding coherent and liquid, to what I'm used to.
I think class D is only good to drive subwoofer drivers, where high power and low bandwidth is needed.
busb
Well-known member
drummerman said:
I've read that pdf on & off for over a year - apart from saying that Primare use their own design using high bandwidth switching FETs, they actually say very little about the inner workings such as how this 26dB of NF is applied.
What amuses me are statements from some that its open loop characteristcs are poor is like say the frequency stability of a phase lock loop is poor without the feedback - of course it will be - it designed to use feedback!
As an owner of a Primare class D power amp, all I can add is he proof is in the pudding - especially now I've dispensed with bi-wiring & those cheap & nasty bridging plates on the back of my Totems.
As for those folk who feel uncomfortable with what PWM does to analogue - just what do they think that analogue to digital conversion does to SQ? Unless they listen to entirely analogue, perhaps it's time to stop worrying about their analogue signals being "pulled apart then reassembled."
I got QLS QA100: QA100--Full Digital Stereo Amplifier with QA660 and Energy RC70. As for comparison, I got another set of DDDAC1794+KT88 PP. After the side by side listening, my conclusion is QA660+QA100 is better.
Rethep
Well-known member
To me it seems there must be more different brands making class D amps, before i am even convinced to listen to one.
In the mean time i enjoy my rather new valve-amp and upcoming new speakers which are build for me on order, at the moment.
In the mean time i enjoy my rather new valve-amp and upcoming new speakers which are build for me on order, at the moment.
Any of you has updates on class D now that NAD and TEAC joined the club and that the D3020 made first page? Just wondering if this technology has come of age...
xlider said:
Bel Canto has been making good Class D amps for some time, but there are certainly some more interesting products lining up atm. With green issues coming to the fore, I expect to see more and more appearing over the horizon.
busb
Well-known member
It's a year now I've had my Primare power amp - no problems. Sealed box that runs cool. I could leave on but it gets switched on then off as required via a remote RF switch as is my DAC.
From what I've learned, Class D falls into two camps.
The modules by Hypex are in actual fact high speed switching analogue amps. Very powerful and very good for their size as long as you don't screw it up by using a switch mode power supply. The switching frequency is very high. Something in the region of 49KHz.
The modules I have are made by a company in Leicester. Single rail power supply. The analogue input is converted to digital using an ADC which supplies the driver and power sections and is only converted back to analogue at the output stage to drive the loudspeakers. I actually partnered these with a valve preamp and played them off against Krell. The sound was amazing.
Reading what some people have said in this thread I would conclude that the source/preamp are hyper critical to getting the right sound without that veil ( ????) over the music. None of that there with my combo. That said, the Bel Canto stuff with right partnered kit is an awesome sound too.
The modules by Hypex are in actual fact high speed switching analogue amps. Very powerful and very good for their size as long as you don't screw it up by using a switch mode power supply. The switching frequency is very high. Something in the region of 49KHz.
The modules I have are made by a company in Leicester. Single rail power supply. The analogue input is converted to digital using an ADC which supplies the driver and power sections and is only converted back to analogue at the output stage to drive the loudspeakers. I actually partnered these with a valve preamp and played them off against Krell. The sound was amazing.
Reading what some people have said in this thread I would conclude that the source/preamp are hyper critical to getting the right sound without that veil ( ????) over the music. None of that there with my combo. That said, the Bel Canto stuff with right partnered kit is an awesome sound too.
Richard Allen said:
So you're not a fan of the NAD D3020 ?
Hi-fi Choice did a review of the D3020 and it wasn't that positive..........they said that analogue budget amps were far more 'expressive' sounding.
Cypher said:
Can't comment coz I haven't heard the amp I'm afraid. Generally, I think you need to look at all of the various components in an amp. You can't just change an AB power stage for D stage, analogue or digital. You really need a clean sheet of paper. The combo that I built used a valve pre-amp and, just to be daft, I used EL84 output tubes as cathode followers on the output stage with huge capacitors.
That aside tho, D class has its uses, especially in active speakers where you need power from a small unit. I'm thinking in the bass region only. From there you can quite easily go to AB amps for mid/treble. Makes for a smaller combo in the back of a loudspeaker cabinet. Biggest thing will be the mains tranny.
It would be great to see that Pioneer, Rotel, Denon, Arcam, Marantz etc. made a product like the NAD D3020.............more choice is always welcome.
Richard Allen said:
David, I believe class D describes a switching style of amplifier, where the output drivers do not operate in their linear region, but are either fully on, or fully off. An analogue output is generated by modulating the on / off state of the drivers in such a way that after the output is filtered, the desired analogue output is achieved. There are many ways to generate the on / off signal to control the output drivers, from a fully digital approach, to an approach that relies upon an analogue input as a driver. All are class D.
What are the two class D camps you refer to?
chebby
Well-known member
Cypher said:
The Denon CEOL range and the Marantz M-CR603 / 610 / 510 are all class D. They just have a bit more 'stuff' built-in (apart from an amp and a DAC).
andyjm said:
Richard can answer for himself, but from my limited knowledge, there are Switching Amps (Class D); and Digital Amps, which are a somewhat related topology, and are sometimes (mistakenly?) called Class D.
Here is a description (more for my benefit than yours): http://www.theabsolutesound.com/articles/a-survey-of-amplifier-types-tas-217-1/
Feel free to tell me I have the wrong end of the stick.
I have heard the Devialet Premier and Wadi Intuition and was positive impress by boht, specilay the Devialet.
I am still looking at a Class D amp as a secon AMP when it need a bit more power and I think the Nuforce IA 18 can be a good option at USD 3.500. it was compared wiht the Devialet side by side and preformed very good!!
I am still looking at a Class D amp as a secon AMP when it need a bit more power and I think the Nuforce IA 18 can be a good option at USD 3.500. it was compared wiht the Devialet side by side and preformed very good!!
busb
Well-known member
CnoEvil said:andyjm said:
Richard can answer for himself, but from my limited knowledge, there are Switching Amps (Class D); and Digital Amps, which are a somewhat related topology, and are sometimes (mistakenly?) called Class D.
Here is a description (more for my benefit than yours): http://www.theabsolutesound.com/articles/a-survey-of-amplifier-types-tas-217-1/
Feel free to tell me I have the wrong end of the stick.
Nope - you have the right end of this particular stick! Happy New Year to you as well!
busb said:CnoEvil said:andyjm said:
Richard can answer for himself, but from my limited knowledge, there are Switching Amps (Class D); and Digital Amps, which are a somewhat related topology, and are sometimes (mistakenly?) called Class D.
Here is a description (more for my benefit than yours): http://www.theabsolutesound.com/articles/a-survey-of-amplifier-types-tas-217-1/
Feel free to tell me I have the wrong end of the stick.
Nope - you have the right end of this particular stick! Happy New Year to you as well!
:beer: :beer: :beer:
@CNO - (why does posting now trip the spam filter if one includes quotes?)
Good Article/explanation and thanks for the link (removed for spam filter obsessivness)
I have an ES Sony TA-DA9000ES 'Class D' 'digital' amp - i.e. it uses incoming PCM digital signals which get converted to the form of PWM digital signals alluded to in the article - DSD- as used in SACD.
Analogue signals/sources are converted directly to PWM/DSD digital signals to drive the amps output stages. In effect, it is a Tact Millenium, with Sony's proprietary take on the technology.
With the matching Sony 9000 ES series CD/SACD player which I also have, the signal path is effectively DSD from disk to the amplifiers output stages - perhaps one of the reasons I would prefer it on sonic grounds over the likes of so called 'super amps' that I've heard, such as Conrad Johnson, McIntosh, Krell, and even an Naim NAC552/NAP500 pre/power combo - I find the Sony's sense of resolution and transparency unmatched in the context of an separates system with passive speakers, perhaps not suprising if one views it as a powered DAC rather than an amplifier per se.
My Beolab 9's use B&O's ICE power modules for the 10" bass drivers - that is, Class D again, but this time using an analogue input signal to form the pulse wave to swtich the output transistors - again as the article explains.
There would appear to be pros and cons to both methods. In the case of the 'digital' Class D Sony, the signal is corrected in DSP in the 'preamp' side of things for clock and jitter errors etc, but there is no global feedback at all.
Hence, the combination of the impedance of the particular speaker being connected, and that out of the output filters in the amp to remove switching noise etc, will alter the frequency respone at the extremes to a minor degree, and controlling distortion is difficult.
Conversely, the analogue Class D aproach as used in B&O's ICE power, and also with Hypex modules amongst others, allows global feedback schemes and measured results re distortion on par with the best Class AB amps going.
However, from a theoretical POV, it's maybe a less 'pure' signal path than the 'digital' Class D option as optimised in the Sony design
In the real world however, and listening to both systems at matched volume levels, and most likely because they are active as well, the Beolab 9's comfortably see off the 'digital' Sony/Naim SBL combo in terms of resolution/detail, which is where one would expect the all digital amplifier approach to have an advantage.
Of course, that's not really a fair comparison, as the speakers (Naim SBL/B&O Beolab 9) are so different in cabinets and drivers etc, but I tend to feel that any sonic differences between either 'analogue' or 'digital' Class D, are likely to be very minor, and probably at the limit of audibility if one were to do a blind matched level AB test, and certainly more to do with the theory than actual real world practice, at least from my limited ownership experience of the two different design approaches to Class D technology.
Such is the nature of the audiophile to obsess over such nuances though....
Happy New Year to All..
JMac..
Good Article/explanation and thanks for the link (removed for spam filter obsessivness)
I have an ES Sony TA-DA9000ES 'Class D' 'digital' amp - i.e. it uses incoming PCM digital signals which get converted to the form of PWM digital signals alluded to in the article - DSD- as used in SACD.
Analogue signals/sources are converted directly to PWM/DSD digital signals to drive the amps output stages. In effect, it is a Tact Millenium, with Sony's proprietary take on the technology.
With the matching Sony 9000 ES series CD/SACD player which I also have, the signal path is effectively DSD from disk to the amplifiers output stages - perhaps one of the reasons I would prefer it on sonic grounds over the likes of so called 'super amps' that I've heard, such as Conrad Johnson, McIntosh, Krell, and even an Naim NAC552/NAP500 pre/power combo - I find the Sony's sense of resolution and transparency unmatched in the context of an separates system with passive speakers, perhaps not suprising if one views it as a powered DAC rather than an amplifier per se.
My Beolab 9's use B&O's ICE power modules for the 10" bass drivers - that is, Class D again, but this time using an analogue input signal to form the pulse wave to swtich the output transistors - again as the article explains.
There would appear to be pros and cons to both methods. In the case of the 'digital' Class D Sony, the signal is corrected in DSP in the 'preamp' side of things for clock and jitter errors etc, but there is no global feedback at all.
Hence, the combination of the impedance of the particular speaker being connected, and that out of the output filters in the amp to remove switching noise etc, will alter the frequency respone at the extremes to a minor degree, and controlling distortion is difficult.
Conversely, the analogue Class D aproach as used in B&O's ICE power, and also with Hypex modules amongst others, allows global feedback schemes and measured results re distortion on par with the best Class AB amps going.
However, from a theoretical POV, it's maybe a less 'pure' signal path than the 'digital' Class D option as optimised in the Sony design
In the real world however, and listening to both systems at matched volume levels, and most likely because they are active as well, the Beolab 9's comfortably see off the 'digital' Sony/Naim SBL combo in terms of resolution/detail, which is where one would expect the all digital amplifier approach to have an advantage.
Of course, that's not really a fair comparison, as the speakers (Naim SBL/B&O Beolab 9) are so different in cabinets and drivers etc, but I tend to feel that any sonic differences between either 'analogue' or 'digital' Class D, are likely to be very minor, and probably at the limit of audibility if one were to do a blind matched level AB test, and certainly more to do with the theory than actual real world practice, at least from my limited ownership experience of the two different design approaches to Class D technology.
Such is the nature of the audiophile to obsess over such nuances though....
Happy New Year to All..
JMac..
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