[kana813]

DW- "I feel this is a technology showing tremendous potentials and promise."

The recent rave review of the Tact M2150 on  http://www.stereotimes.com/, seems to indicated that the positive potential of digital amplification is here now.

Aloha,

Kana

[Curt]

Curt, This is one of those times, that if it sounds good, it is good. Not investigating and listening to this new technology because of objections to what amounts to theoretical drawbacks due to noise issues is probably
going to have you inquiring in the not so distant future about the the number of the truck that hit you.

Hi Scotty,

I'm not missing the boat, I'm discussing... passing thoughts around.

I have been playing with digital amps of several types, including tripath, for a couple of years now. I have a full digital processor/ switcher amp with no D/A from the cdp in my lab for more than a year. Some of these solutions work well for my other business and they are getting better all the time.

It's the direction things are going in. Still, that don't mean it's ready for high-end audio today.

I'll have to give these new amps a listen, but until I can this thread is full of interesting information.

[_scotty_]

Agreed on the maturity of argument, Jerry, right on! A forum will by default have different views, and that's as it should be, provided we can keep it civil.

Regarding digital amplification, in my mind there's no doubt whatsoever that this is the technology of the future. It makes sense, since our sources are rapidly turning digital, to keep the signal in the same form for as long as we can, preferably all the way. I never liked converters of any kind in between, anywhere, not if I could help it.

As o ...

I suspect this future may arrive in under 2years.
 The Acoustic Reality amps that I have heard  are very good. My own DIY
Tripath based amp is very similar. The remaining problem of deadband time which causes a distortion which looks like classic crossover notch
distortion and reduces the high frequency waveform accuracy and the perceived liquidity of the amplifier has been solved.  At least 3 companies that I know of and maybe more have zero crossover distortion. The pace of technological change has accelerated dramatically over the last decade,
this fact and the performance of the best of the current digital products
are the basis for my revision of your time table. I don't think analogue amplifier manufacturers have a 10 year window to improve on the performance of their products before digital makes roadkill out of them.

[_scotty_]

Hi Scotty,

I'm not missing the boat, I'm discussing... passing thoughts around.

I have been playing with digital amps of several types, including tripath, for a couple of years now. I have a full digital processor/ switcher amp with no D/A from the cdp in my lab for more than a year. Some of these solutions work well for my other business and they are getting better all the time.

It's the direction things are going in. Still, that don't mean it's ready for high-end audio today.

I'll have to give ...

Hi Curt, So far the only real problem with the digital amp I own is a very minor lack of liquidity. This only manifests itself when the amp is compared  VERY good analogue amps. And of course my amp is obsolete
compared to the newer designs which have no crossover notch distortion.
Its performance with this short coming is still good enough that I would take it over most analogue designs I heard regardless of their cost.

[audiojerry]

_scotty_

Your enthusiasm for digital amplification has now been made quite evident, but I don't think too many of us who have reached a very high level of performance with our analog setups are going to become digital converts without thorough aural convincing. I had the Sony C70ES, and I was impressed, but it was still not up to the calibre of my analog amp.

[Rob Babcock]

Of course, to be fair, Jerry, at the price I doubt the Sony is the best of the breed.  It was tempting to think that the new digital technology meant that assembling great audio gear could be like designing a new toaster or PC, but apparently that isn't the case.  Given all the corners that a mass market product like the Sony had to cut, it sounds like the performance is remarkable.

Shortly I will be buying the Carver to see for myself how far along digital technology is.  And from what I've read, it sounds like the Carver itself is obsolete, or rather based on Tripath technology that's already a bit dated.  I'm very anxious to see how the technology evolves over the next couple years.

[kana813]

From: "Bruno Putzeys"
Newsgroups: rec.audio.high-end
Subject: Re: Future of High-End Digital Amplifiers?
Date: 6 Oct 2003 15:16:56 GMT

Hi,

First I'd like to point out that "digital amps" is a misnomer. There
are two categories:
1. Analog-controlled class D. Switching amplifiers with an analog
input signal and an analog control system. Normally some degree of
feedback is present.
2. Digitally controlled class D. Amplifiers with a digitally generated
control that switches a power stage. No error control is present.
Those that do have an error control can be topologically shown to be
equivalent to an analog-controlled class D with a DAC in front.

The latter category initially delivered a success in the form of the
Tact Millennium. However, by their mere existence this device (and
another one of my own making, the "PPDSD" which performs marginally
better) prove that obtaining good performance from such a contraption
is largely an analog design exercise - a very complicated and
expensive one at that. After all, the distortion phenomena that stand
in the way between a perfectly formed digital control signal and a
perfect analog replica are inherently analog. Similarly, cheaper
digital class D's (such as Sony S-Master and TI's) go on to show that
at practical price and complexity levels, performance is quite
abysmal (better than 0.1% THD is unusual and be sure it ain't only
third harmonic!)

One should ask the question: would any D/A converter designer in his
right mind make it using power components? Probably not. Then how
about the old argument that digital-to-the-end is best? Well, I
think the D/A barrier should be precisely there where it allows the
signal chain to perform at its best and why should we believe that
this is necessarily right at the end? Quite obviously the concept of
a digital class D amplifier was dreamt up by DSP guys who presumed
that the signal should be kept out of the big bad analog world and at
the same time that the power stage, power supply and filter (all
analog in nature) would perform flawlessly.

The former category is a different ball game. Although most
commercially available implementations are well short of this ideal,
*analog* class D amplifiers can be made with performance figures
giving the digital variety a run for their money, at a price well
below even the cheapest digital class D's. They can have vanishingly
low output impedance right across and beyond the audio range (which
the digital ones can't!) and frequency-independent distortion (for
that "zero-feedback sound") is actually easier to achieve than with
digital ones.

So how about sound? The highish HF output impedance (caused by the
output filter) of amplifiers without post-filter-feedback (all
digital ones and many analog ones too) is responsible for their oft-
quoted tube-like warmth and air. At low frequencies the filter
impedance is low, resulting in a commanding, dynamic bass. Because
they previously had a reputation for sounding harsh (due to people
who hadn't heard them but presumed that switching couldn't mean
anything else), about every modern entry in the field was heralded as
the "first audiophile class D". Read a review about the Bel Canto Evo
or the Sharp 1-bit (which is analog btw) to see what I mean. Keep in
mind that if a device sounds radically different from what you've
held in high esteem previously, there's usually something fishy going
on.

Unfortunately, while warm and airy is nice, it isn't all you need for
real audiophile sound. I like to think audio components should sound
neutral and transparent too. A frequency response that wanders 10dB
off the line at 20kHz isn't conducive to neutrality. High THD isn't
good for transparency, especially when it goes up with frequency.
Ergo a Tact (which has flat and low THD but a nonflat frequency
response) sounds transparent but not neutral, and your average
transistor amp (which has a low output impedance but sharply
increasing THD) sounds neutral but not transparent.

Now, the technology (if you can call a circuit with 16 transistors
that) to deliver low output impedance with frequency-independent low
distortion in class D exists. Built with audiophile-grade parts it'll
frighten the pants off any high-end amp (while I'm the designer of
that circuit and thus some care reading this statement is warranted,
I do have a lot of serious folk to back up my claims). Of course,
having these characteristics it sounds more like other high-end amps
than that it sounds different, in the same vein as that the best tube
gear and the best solid state gear don't differ by miles in sound.

The upshot is:
1) digitally controlled class D: dead end street.
2) analog controlled class D: definitely the future, although you
shouldn't expect it to flatten competition from traditional solid-
state and tube amps by a tremendous margin. In the very high end
segment the three are bound to coexist for a very long time. In
mainstream gear, class D is certain to take over the scene completely,
although one serious problem remains: building a good class D amp is
an order of magnitude tougher than a linear amp, and the knowledge
required is much more diverse. It may take long before each large
company has at least one knowledgeable designer. It won't stop them
from putting class D based products on the market, but until then and
unless they buy completed amplifier modules from specialist vendors
(which eastern companies rarely do, they'd rather commit harakiri
than having to swallow their pride), they will be putting out
seriously substandard products for years to come.

Regards,

Bruno Putzeys
(Chief engineer class D audio at Philips DSL)

[_scotty_]

_scotty_

Your enthusiasm for digital amplification has now been made quite evident, but I don't think too many of us who have reached a very high level of performance with our analog setups are going to become digital converts without thorough aural convincing. I had the Sony C70ES, and I was impressed, but it was still not up to the calibre of my analog amp.

I can't say I'm surprised, the only real deficiency in the XR25S seems to come from its dynamic limitations. It does space and sound staging with the best of them but shows dynamic limitations which I suspect are a reflection of it's power supply design. I would still recomend it for the financially challenged as a worthwhile investment and a real taste of the high end on a beer budget. I would like to see any of this new digital
technology with a large conventional  power supply designed from an RF
impedence standpoint. My amp is a basic Tripath EVAL board with a power supply optimised for a 100watt 1.5mHz RF transmitter which is sort of what the thing is in some respects. Without the Jensen caps in the power supply and the Blackgate decoupling caps on the board and a revised grounding scheme it wouldn't sound all that remarkable. I think much of the current crop of commercial digital amps need to have their power supply engineered from an RF standpoint. These are not analogue amps
and an a conventional approach to power supply design that  fails to address the basic RF nature of the amp will not show off the potential of the digital technology to its best advantage.

[warnerwh]

Is it possible the laws of physics we worship are flawed?   I believe VMPS installs an input filter at 44khz on their speakers because it helps the sound.  This after the heavy filtering "beyond the audible range" from our digital sources. Maybe we can't consciously hear over about 20khz but is it possible more is going on inside out little heads that we don't know about?  I read an interview with someone from Bryston who said when they changed to metal film resistors that they'd received alot of calls asking what they'd done to their amps. It seems like the distortion,harmonic I believe, went from .005 to .003, or 2 thousandths of 1%.  Well below what most anybody would believe is perceptible.  Or is it the fact that a metal film resistor sounds different than a carbon resistor of the same exact value and if so, why?  Then there's grain, how do we measure  for it and what causes it? I asked this question in another thread and Frank Van Alstine had the best theory but it appears to me that the engineering community doesn't have a handle on it. My main question is: does it appear that our physics laws are flawed, at least when dealing with electricity?

[_scotty_]

Is it possible the laws of physics we worship are flawed?   I believe VMPS installs an input filter at 44khz on their speakers because it helps the sound.  This after the heavy filtering "beyond the audible range" from our digital sources. Maybe we can't consciously hear over about 20khz but is it possible more is going on inside out little heads that we don't know about?  I read an interview with someone from Bryston who said when they changed to metal film resistors that they'd received alot of calls aski ...

I don't think the laws are flawed but it is a certainty that we don't know all of them.  Our measurment capability does not fully describe reality either.
The VMPS filter may be present to suppress ringing in the conjugate circuit
containing the poweramp, speakercables, and speakers. I have a RC network in a banana plug that I put into my speaker binding posts per Stans recommendation and darned if the system didn't sound a little better.

[warnerwh]

" don't think the laws are flawed but it is a certainty that we don't know all of them. "

Scotty: If it's a certainty we don't know all of them then how could we know the ones we have are correct?  Couldn't it be that the ones we don't know interact with the ones we do and in effect change them? Also has anybody every watched the flow of electrons? I always wondered about the latter.

[_scotty_]

" don't think the laws are flawed but it is a certainty that we don't know all of them. "

Scotty: If it's a certainty we don't know all of them then how could we know the ones we have are correct?  Couldn't it be that the ones we don't know interact with the ones we do and in effect change them? Also has anybody every watched the flow of electrons? I always wondered about the latter.

Application of the scientific method has procured the laws we have. From the Funk& Wagnalls Standard Dictionary,"scientific method  The method used in the sciences for obtaining knowledge,in which hypotheses are tested by experimentation and observation".  My own addition . Theories which predict the future outcome of an action or experiment are the result of the
previous process. These theories are frequently called Laws. They are probably right most of the time. The "law" of gravity seems to work most of the time, at least on earth. This seems to indicate that within  this frame of reference that we can depend on theory enough to base our actions on it. With electricity we can predict what it will do under most circumstances and we can successfully utilize it most of the time. Fortunately complete understanding of electricity is not required to exploit its properties for our benefit.

[Rob Babcock]

Undoubtedly we're right about the basics, since we can reliably make it serve us.  But certainly there's a lot more to it than we fully understand.  The same applies to sound; there's a lot we know, but more that we don't.

To be diplomatic, that could be one reason measurements often don't correspond to listening results.  It's not that the measurements are wrong, or even that they don't matter, but more that we don't really know what to measure.  I'm confident (arrogant?) that over time we'll learn to measure & quantify the things that we now catagorize as "intangible."

[warnerwh]

"Fortunately complete understanding of electricity is not required to exploit its properties for our benefit."

This may be true but it appears our exploitation isn't resulting in what we'd expect sometimes. Otherwise companies wouldn't voice their electronics. They could just design them on paper and out the door they'd go.  As a matter of fact there are alot of people who feel this is the case.  Seems to me that complete understanding of electricity may help and is most likely the reason for some of the anomolies we run into with audio equipment.  I try to remember that we were still riding horses just a hundred years ago. I don't think we're so advanced as most people would like to think. My opinion is we are just coming out of the dark ages.

[DVV]

From: "Bruno Putzeys"
Newsgroups: rec.audio.high-end
Subject: Re: Future of High-End Digital Amplifiers?
Date: 6 Oct 2003 15:16:56 GMT

Hi,

First I'd like to point out that "digital amps" is a misnomer. There
are two categories:
1. Analog-controlled class D. Switching amplifiers with an analog
input signal and an analog control system. Normally some degree of
feedback is present.
2. Digitally controlled class D. Amplifiers with a digitally generated
control ...

I agree completely with Bruno. I can't help being reminded here of the struggle to marry tube voltage gain stages with silicon current gain stages - in theory, we should get something near to a perfect amp, since each technology is doing what it does best, yet the hard everyday practice showed that this was a collossal task to perform well.

If our digital amplification is analog controlled, then we are back to square two, if not square one. We end up with tremendously efficient  output stages, saving us from massive heat sinks and fans, but still greatly dependent on what the designer thought and used. In other words, we'll be seeing plenty of comments on components used in the years to come (why did he use op amp A and not op amp B, etc).

Another thought - digital amplification may do more for power MOSFETs than anything else has ever done before. I have never been thrilled by MOSFET sonics, always feeling they were a little too cold and detached (save for a few notable examples, e.g. Perreaux of New Zealand), but to the best of my knowledge, nothing makes for a good switcher as MOSFETs do (except perhaps the latest IGBT devices). Use digital output sections with UHC (Ultra High Current) MOSFETs and things start to look up. With the advent of digital amplification, I also expect to see something of a boom in the high power MOSFET market as well.

But as I said, I also expect to see analog, both tube and SS, live alongside digital for many years to come. No transition is ever that fast, and Scotty's comment on two years is, in my view, too optimistic. To be sure, we'll be seeing more and more class D amps, since they will in the end turn out to be a great solution for the cost-conscious audio industry at large, and certainly more compact, but that has no direct relation to the absolute quality.

Also, please note that digital amplification assumes some very traditional skills which refuse to go away, such as power supply design, still a critical issue. And it introduces some new problems all of its own, such as possibly high levels of power line kickback, i.e. additional and far from insignificant line pollution.

Cheers,
DVV

[Curt]

Hi Curt, So far the only real problem with the digital amp I own is a very minor lack of liquidity. This only manifests itself when the amp is compared  VERY good analogue amps. And of course my amp is obsolete
compared to the newer designs which have no crossover notch distortion.
Its performance with this short coming is still good enough that I would take it over most analogue designs I heard regardless of their cost.

Scotty,

Interesting about the XO type distortion. Tripath likes to use a differential amplifier (removes common mode switching signals/ noise) and then a 6th order LP fc=20kHz before their test instruments when measuring distortion. I wonder if the distortion is still there after all that clean-up?

I'm toying with the TK2350, it looks like it has some potential. Not bad specs to 200W. This and the TK2150 are the only two Tripath solutions I currently like. They look good enough for my other (not IRD) company's products.

I think I'll build one up, it's a new generation and time for another listen.

[_scotty_]

Scotty,

Interesting about the XO type distortion. Tripath likes to use a differential amplifier (removes common mode switching signals/ noise) and then a 6th order LP fc=20kHz before their test instruments when measuring distortion. I wonder if the distortion is still there after all that clean-up?

I'm toying with the TK2350, it looks like it has some potential. Not bad specs to 200W. This and the TK2150 are the only two Tripath solutions I currently like. They look good enough for my other (not IRD)  ...

 I don't know why the problem would be eliminated by the clean up. The distortion is a by-product of the time in nanoseconds that exists between one pair of output devices turning off and the other pair turning off. As the deadband time or BBM is reduced the liquidity improves, this is audible. My understanding of the effects of the filtering on what you measure is limited.

The TA3020 is the replacement for the TA0103A that my amp is based on.
The lower powered amps have have a little faster switching speed capability in the output MOSFETS and having a rail voltage 63volts or lower allows the utilization of Jensen 4 pole caps in the main power supply.The Jensen's were bypassed with 8mfd Hovland caps.
Attention to the power supply impedences at up to the 1.5mHz upper limit
of the module pays big benefits in the quality of the audio reproduction.
Replacing the 100mfd 100volt local decoupling caps on the board  with the same size Blackgates is also a good move. Returning the speaker ground to the star also makes the eval board based amp sound better.
      Good with your luck project.  Scotty

[JCC]

When flying next to a PHD Geneticist a few years ago, his statements that the ongoing mapping of the human genome was a waist of time impressed me. It was obvious to me that he was out of step with the reality of what was occurring. He thought that he was wiser than the world, and saw no advantage to current efforts, or maybe he stood to profit from his position or lose from the ongoing research.

It is common for an engineer to make improvements in products that cannot be measured, because we don’t know how to measure the change. This is often noticed by the audio engineer, when improvements heard by the human ear cannot be measured or even understood with all of out scientific technique. The physician marvels at somewhat miraculous events and laments a horrible event, because as humans we are limited in abilities and knowledge.

Like the recent review published in this forum, admittedly out of step with reality, but initially thought to be factual analysis. The reality of the Carver ZR’s outstanding performance is now partially accepted because of comparative listening. The laws of physics are not flawed, but the human level of understanding is not complete. While some do not admit our current limitations, others after accepting the reality of results measured with our ears eventually admit that the analysis must be erroneous. Then we work towards a greater level of understanding of the laws of physics.

The next steps are evolutionary and somewhat obvious:
·   More comparative listening, even to the Set Amplifier
·   More amazement at the performance level of the ZR, that does not have audiophile quality components
·   Analysis, tweaking, and sometimes improvement
·   And finally understanding and development of new tests and standards

[Brian Cheney]

I have received 28 pages of technical info on the ZR 1600 from Carver Pro and will quote some of the more important points.

1. Fig 3 of the manufacturer's notes illustrates the exact same oscillation near full power (200W into 4 Ohms) output that John Curl and I observed.  Carver says: "This output characteristic...is not an instability or parasitic oscillation, nor does it degrade the performance of the amplifier in any audible way.  The design of the Digital Power Processor is such to reset the overflow at frequencies well above the audible bandwidth."

2. "A sharp cutoff lowpass filter must be inserted between the amplifier's outputs and the test equipments inputs prior to making any distortion measurements."  The recommended filter is 20kHz at 60 dB/oct.  We did not use such a filter as we wanted to see the amp's performance as it would be listened to, which is perfectly legitimate and yielded the results I reported.  As for power, the manufacturer instructs that the overflow-reset portion of the waveform be disregarded.  John Curl and I stopped our test at the point where the waveform oscillated, and the oscillation waveform flattened.  BTW any amplifier will tested much better with a 20 kHz noise filter in line with the analyzer.

3. The manufacturer also states that many design decisions in the ZR series amplifiers were made in order to increase or maintain efficiency, not audio quality.

In other words, the measurements John Curl and I have real-world validity.  Power output will measure higher if the tester ignores the "overflow reset" RF oscillation.  The brickwall filter does permit measurements to appear better than what we observed, however it must be noted that such a filter would never be employed by a user and he must live with any audible consequences of the design decision embodied in the stock ZR 1600.

[neilr11]

Brian,
Thanks for the explenations on those points.  

What was your observations on the sound quality of the amp fully broken in vs. the others your were pitting the ZR1600 against?

Sounds like this amp has a way to go before being an audiophile quality product.