Just ordered a Trends 10.1 Class T Digital Amp - A whopping $130

[Mallette]

"5. I am reminded of two historical transitions: 1) the 1960's changeover from SS to tube; 2) the 1980's change from LP to CD. In each case, there was a landslide movement to adopt the new thing and everyone raved about the improved sound. In a few years, everyone cried about the horrible new sound and those who cared went back to the old technology.

People who previously would not consider running solid state in their systems under any condition -- are running these amps.

Right. I get that. My point was, this "dumping" has happened in the past with the same fervor, and then it reversed itself when people had a few years of that sound under their belt. Not saying that's what WILL happen, I am just suggesting it has happened in the past. I think these amps are cool as can be. They interest me a lot, and I thinks it's a very exciting technology. But, does that mean I have to agree they are the best power amps in the world? But for those who do, enjoy man!"

One of the first things I discovered in my first year in this community was a largely unrecognized polarization into music hobbyists and equipment hobbyists. What makes it difficult is this is not a hard line but an almost indetectable crossover. The majority of the shooting wars spring up along this fault line, with slaughter occuring on both sides without a clear understanding of just what started the war in the first place.

Personally, I can think of only two things over my 40 years in this hobby where I "switched" after my initial impressions. One was SS. When the first SS amps appeared I was using a Grommes "Little Jewel" 17 watt amp with Frazier Super Monte Carlos. I brought home a 40 watt Kenwood that was about half the size of the Grommes and marveled at the silent, effortless power from this little box that produced almost no heat (a real issue in pre-air conditioning days). It was twenty years before I realized that some of the magic had gone away with my Grommes. Same thing with the CD, but it did not take but about 10 years before that lesson was learned. But, in general, I've never changed my mind about a component after first audition since I became experienced enough not to equate "new" with "better." After 2 years, my class D still sounds like it did first time out of the box...accurate but not clinical, musical without coloration. To me, the best of tubes and SS with less of the shortcomings of either. This makes me happy because it means less wear on my Dynaco ST-70i which needs to last my lifetime and be ready to pass on to my son. The class D is disposable and replaceable from pocket change.

Subject only to mishap or sudden wealth, my Klipschorns, VPI/JMW TT, Class D amp, ST80i, Super PAS4i preamp, Fraziers, and a few other things in my system are not subject to change as the only thing I hear from them is the quality of the source material.

But let's emphasize cost performance for a moment. The thread title ends "- A whopping $130" Certainly pretty good for a 2 channel amp. OTOH, I paid 127.00 for 7X100w of TI chipset Class D and neither the cost nor the "Panasonc" name nor "It's not a TriPath" has had any impact on my opinion that it delivers music >= anything I've ever auditioned. The verdict of my ears is final and not subject to change unless medical science uncovers a way to extend hearing into the ultrasonic or something. While there may be amps that look better, have better connectivity, or even a tiny bit better sound, to expend 10-100 times the money to achieve this would be a disservice to my common sense and to my family finances.

If I had 50 megabucks in the bank would I spend 500 kilobucks on my system? But of course, as I'd need to coordinate with the Italian marble accents in the listening room.

[Rivendell61]

Dr. Who..

In these PWM amplifiers, as we are referring to here, what is the input signal, and what is the output signal?

If you take an A/D feed it to a D/A it is both analog in and analog out... surely you are not going to tell me it isn't digital?

Shawn

I will! They are not....they are 'mixed signal' devices. Thinking of them as 'digital' gets people into trouble. You see comments like "don't worry about the converter: it's digital--either it works or it doesn't"--and there are many of varients of this.

A bit OT but the vast majority of the engineering problems which must be resolved to create a good converter (vs a middling one) are analog. Can the manufacturer find a good engineer with expertise in 'mixed signal' applications? And how many months can you afford to have him work on one circuit board?

Mark

[Rivendell61]

1. The bar is always set very low for these amps. Most people expect "nothing" for their $100 and when it plays at all they are astonished. So, you have to ask, if they paid $3995 for it, would they be just as astonished?

Certainly there is some wow factor in the tiny plastic thing sounding good.

Don't forget that not all are cheap. The same Class D modules are in amps that will cost well over your $3995 figure (some many times over) and these also get the rave audiophile subjective reviews (perhaps for the inverted reason!?).

Mark

[Rivendell61]

I wonder if those trying to say digital amps aren't digital (since their output is analog) are merely trying to avoid the audiophile notion that "digital is bad"?

Treating a fundamentally analog device like a Class D amp as digital can lead to some design problems and performance compromises (compare specs on the 'digital' ones vs the analog ones).

I think you mentioned that you were intending to play with some Class D amps so you might find some good info (there is lots) in this paper (given at AES last spring)--on Analog vs Digital in Class D amps. http://www.hypex.nl/docs/allamps%20hypex%20layout.pdf

The primary author designed the Hypex amps (analog) but he also designed the best performing (by spec) digital controlled Class D amp: http://www.aes.org/e-lib/browse.cfm?elib=11439

Mark

[DrWho]

Dr. Who..

In these PWM amplifiers, as we are referring to here, what is the input signal, and what is the output signal?

If you take an A/D feed it to a D/A it is both analog in and analog out... surely you are not going to tell me it isn't digital?

Shawn

I will! They are not....they are 'mixed signal' devices. Thinking of them as 'digital' gets people into trouble. You see comments like "don't worry about the converter: it's digital--either it works or it doesn't"--and there are many of varients of this.

A bit OT but the vast majority of the engineering problems which must be resolved to create a good converter (vs a middling one) are analog. Can the manufacturer find a good engineer with expertise in 'mixed signal' applications? And how many months can you afford to have him work on one circuit board?

Please define "mixed signal"

As far as the analog behavior of digital circuits - there is an entire subfield of Electrical Engineering dedicated to it. Sadly I think most of the audio industry is ignoring many of the huge strides being made in the computer engineering world....where the analog design of digital devices is at a totally different level.

Btw, just because every digital circuit in the world is created with analog parts, doesn't mean that it's not digital...

[DrWho]

Treating a fundamentally analog device like a

Class D amp as digital can lead to some design problems and performance

compromises (compare specs on the 'digital' ones vs the analog ones).

I think you mentioned that you were intending to play with some

Class D amps so you might find some good info (there is lots) in this

paper (given at AES last spring)--on Analog vs Digital in Class D

amps. http://www.hypex.nl/docs/allamps%20hypex%20layout.pdf

Did you actually read that article? It had nothing to do with digital amps being digital or not... []

If anything, it showed just how digital the amplification stage really is! The

author was just pointing out that digital circuits are implemented by

analog circuits and that digital circuits designers need to take the

analog behavior into account....ummmmm, "duh?" That's what digital circuit design is all about! Btw, those are my favorite classes here on campus [Y]

I think people freak out because the amplification stage is also a

part of the D/A. There are a lot of digital and analog considerations

to be made with every D/A and where you draw the dotted line to divide

the digital and analog realm is rather arbitrary. The article was

pointing out that the analog behavior of the digital signal coming out

of the amplifier needs to be kept clean because it is being fed into a

simple low-pass filter. Typically D/A chips do their own filtering of

the digital signal, but in a digital amp it's a bit more difficult due

to the power handling involved - so the engineers go with a basic LPF.

And the author of the article was just talking about the importance of

the quality of the digital signal so that the basic D/A (aka, the LPF)

works as intended - instead of just ignoring the quality of the digital

signal.

[maxg]

And the pendulum swings back - this one can run and run and these discussions are similar all over the net.

Could we get any milage out of calling them hybrids - or would that just upset everyone?

[DrWho]

That works if you want to read for what you want to hear and not for meaning...no skin off my back if people wanna put their head in the sand.

[NOSValves]

That works if you want to read for what you want to hear and not for meaning...no skin off my back if people wanna put their head in the sand.

Funny I think that is your exact problem........ buy a sand box shovel would ya!

[Deang]

Written in 2004.

http://www.audioholics.com/education/amplifier-technology/the-truth-about-digital-class-d-amplifiers

[maxg]

That's what I like about Dean - he doesnt say much - but he says it loud.

So - they're analogue after all then. Tee hee.

Till the next post from Shawn that is....

[Rivendell61]

. So, in amps which are essentially and fundamentally analog, if we erroneously assign them "digital characteristics" (that they don't deserve) we will be looking in the wrong places for improvements. I am pretty sure that is an essential part of the paper referenced earlier by the Hypex designers.

Mdeneen,

I agree...but the definition is fairly harmless in the context of the consumer world, and the misnomer of "digital' has won the day in marketing if nothing else.

The only 'downside' may be for DrWho--if designing a Class D amp "as though it was digital", i.e., no feedback--he will have an amp without output impedance control (none of the 'digital' Class D amps do). Hmm, why does that seem ironic?

DrWho, whether you choose to think Class D amps are digital or analog is between you and the sonic results of your amp building exercise.

Quote from article: "It stands to reason that the myth of the 'digital amplifier' would have never taken off if it had been as common to show current wave forms as it is to view voltage wave forms". And yet you say "it has nothing to do with digital amps being digital.....". Really?

Simply because an amp has a bit of digital 'looking' behaviour going on does not make it 'digital'--ref your own odd statement above re converters not being analog simply because they have analog components.

The question of definition is resolved by how they actually behave (here is a quote from the author of the previously cited article):

**** "OK. Back to electronics. You have a device with all sorts of signals in it which you're tracing a signal with a scope. How do you tell it's digital? It might look very digital, for example a square wave, but by now you know that form and content are not to be confused.

Well, simple. Add some noise. Amplitude-modulate it. Add a small amount of time-variant delay. And make sure you can vary the amount of error you introduce at will. Then look at the output of the device.

There are two possible outcomes.

1)The first is that the output of the device remains to-tal-ly unchanged for all types of error. The signal is digital. Only when you crank up the noise level, suddenly very dramatic errors occur in the output. That's when the symbols could no longer be read.

2)The second possible outcome is that no matter how small the error you put in, you'll see it in the output to some extent. Some errors may have very little effect (e.g. amplitude modulation) while other errors (e.g. jitter) may have a clearer influence. Of course, if you make the error smaller, its effect on the output is smaller too, but it is never completely gone. The signal is analogue, even if it looks like a square wave or a serial bit pattern." ****

End quote.

That definition may seem a little 'difficult' because it seems counter-intuitive re converters, etc. But it is formally correct and is an 'engineers' definition in that it forces a functional understanding of the behaviour of the circuit involved

Which.....brings me to DrWho's question: "Please define 'mixed signal' ".

In light of the above you can see the phrase 'mixed signal' is used as an obscuring term of art to avoid causing confusion for those who can not understand that Class D amps (and converters) are correctly described as analog.... :-)

Mark

[sfogg]

"Till the next post from Shawn that is...."

I thought Mark said this horse was dead?

Shawn

[maxg]

"Till the next post from Shawn that is...."

I thought Mark said this horse was dead?

Shawn

Rumours of its death had been exaggerated seemingly....

[DrWho]

The only 'downside' may be for DrWho--if

designing a Class D amp "as though it was digital", i.e., no

feedback--he will have an amp without output impedance control (none of

the 'digital' Class D amps do).

Not true. If DrWho were designing a digital amp, he would be employing

the skills he learned in college concerning the implementation of a

well behaved DAC while taking into account the importance of output

impedance. So if feedback is the best solution to the problem, then

that is what will be implemented.

However, feedback is most certainly not the only tool, nor is it free

from

tradeoffs, and finally nor does its presence negate the digitalness of

a circuit. I would love to share some of the cool tools DrWho has

learned about, but he's paid good money for that education and needs a

bit more experience experimenting with the various tools to see which

he likes best.

DrWho, whether you choose to think Class D amps are digital or

analog is between you and the sonic results of your amp building

exercise.

If you want to draw the box around the chassis of the "amplifier" then

sure, it's an "analog" device. You can use the same analogy for the

complete signal path of a CD too. Better yet...feed a digital signal

into a digital amplifer and draw the box around the chassis and now the

"digital amplifier" is really just a "digital to analog converter". I'd

like to draw smaller boxes though and have someone show me where the D/A

stage happens...you're going to find that it's after the

point where the digital signal is represented by a larger voltage

swing...

Quote from article: "It stands to reason that the myth of the

'digital amplifier' would have never taken off if it had been as common

to show current wave forms as it is to view voltage wave forms". And

yet you say "it has nothing to do with digital amps being

digital.....". Really?

I would be curious how many here have actually measured the current

behavior of digital circuits...the claim is far-fetched. Voltage and

current are directly related by the impedance of the load (Ohm's law anyone?).

Simply because an amp has a bit of digital 'looking' behaviour

going on does not make it 'digital'--ref your own odd statement above

re converters not being analog simply because they have analog

components.

I agree. All that matters is that you've got switches (*cough* switching

amplifier *cough*). The transistors are being operated in their

"switching mode" which is akin to saying they are being operated in

their "digital mode". On and Off - that's a digital circuit. The

largest significance of this description is that the digital signal is

subject to aliasing and timing errors...

**** "OK. Back to electronics. You have a device with all sorts

of signals in it which you're tracing a signal with a scope. How do you

tell it's digital?

. . .

Or simply described in one sentence as a switch. []

It's either off or on, 30V or 0V. A digital circuit does not allow the

output to fall at a voltage inbetween. A digital amp (PWM or SDM) will

only output one of two voltages. How many more different ways does it

need to be said? Or is the problem that the naysayers don't understand

the ramifications of the switching behavior? The ramifications are why the

description exists in the first place! To say that a digital amp is not

digital is to say that it is free of digital ramifications.

I would love to see how the analog model accounts for the aliasing that occurs when the sampling rate is too low.

Which.....brings me to DrWho's question: "Please define 'mixed signal' ".

In light of the above you can see the phrase 'mixed signal' is used as

an obscuring term of art to avoid causing confusion for those who can

not understand that Class D amps (and converters) are correctly

described as analog.... :-)

lol, you're fired []

[Rivendell61]

The only 'downside' may be for DrWho--if designing a Class D amp "as though it was digital", i.e., no feedback--he will have an amp without output impedance control (none of the 'digital' Class D amps do).

Not true. If DrWho were designing a digital amp, he would be employing the skills he learned in college concerning the implementation of a well behaved DAC while taking into account the importance of output impedance. So if feedback is the best solution to the problem, then that is what will be implemented.

However, feedback is most certainly not the only tool, nor is it free from tradeoffs, and finally nor does its presence negate the digitalness of a circuit. I would love to share some of the cool tools DrWho has learned about, but he's paid good money for that education and needs a bit more experience experimenting with the various tools to see which he likes best.

DrWho, whether you choose to think Class D amps are digital or analog is between you and the sonic results of your amp building exercise.

If you want to draw the box around the chassis of the "amplifier" then sure, it's an "analog" device. You can use the same analogy for the complete signal path of a CD too. Better yet...feed a digital signal into a digital amplifer and draw the box around the chassis and now the "digital amplifier" is really just a "digital to analog converter". I'd like to draw smaller boxes though and have someone show me where the D/A stage happens...you're going to find that it's after the point where the digital signal is represented by a larger voltage swing...

Quote from article: "It stands to reason that the myth of the 'digital amplifier' would have never taken off if it had been as common to show current wave forms as it is to view voltage wave forms". And yet you say "it has nothing to do with digital amps being digital.....". Really?

I would be curious how many here have actually measured the current behavior of digital circuits...the claim is far-fetched. Voltage and current are directly related by the impedance of the load (Ohm's law anyone?).

Simply because an amp has a bit of digital 'looking' behaviour going on does not make it 'digital'--ref your own odd statement above re converters not being analog simply because they have analog components.

I agree. All that matters is that you've got switches (*cough* switching amplifier *cough*). The transistors are being operated in their "switching mode" which is akin to saying they are being operated in their "digital mode". On and Off - that's a digital circuit. The largest significance of this description is that the digital signal is subject to aliasing and timing errors...

**** "OK. Back to electronics. You have a device with all sorts of signals in it which you're tracing a signal with a scope. How do you tell it's digital?

. . .

Or simply described in one sentence as a switch. []

It's either off or on, 30V or 0V. A digital circuit does not allow the output to fall at a voltage inbetween. A digital amp (PWM or SDM) will only output one of two voltages. How many more different ways does it need to be said? Or is the problem that the naysayers don't understand the ramifications of the switching behavior? The ramifications are why the description exists in the first place! To say that a digital amp is not digital is to say that it is free of digital ramifications.

I would love to see how the analog model accounts for the aliasing that occurs when the sampling rate is too low.

Which.....brings me to DrWho's question: "Please define 'mixed signal' ".

In light of the above you can see the phrase 'mixed signal' is used as an obscuring term of art to avoid causing confusion for those who can not understand that Class D amps (and converters) are correctly described as analog.... :-)

lol, you're fired []

LOL DrWho. I liked your (content free) attempt to criticize the Voltage vs Current argument. I hope you were not serious. You have not read the paper have you.

The secret knowledge bit (2nd para) was good too--the best way to avoid answering what you can not.

No comment--aside from my prior posts--on the rest.

Hope your amp works.... :-)

Mark

[DrWho]

I read the paper and all of the "oh so important" claims being made by the author and they are exactly the same thing they're teaching in the digital signal processing classes about the implementation of DAC's. And for some reason the author seems to think the current behavior of digital circuits somehow isn't digital because "it doesn't look digital". The digital amps I just got finished building and tweaking in my last lab had similar current behavior - trippy eh? I guess you don't see the significance of Ohm's Law...but that's ok.

Oh btw, the amp worked just fine... []

[sfogg]

"I read the paper and all of the "oh so important" claims being made by the author and they are exactly the same thing they're teaching in the digital signal processing classes about the implementation of DAC's."

Yeah, that part of the paper doesn't really make sense.

It shows that timing errors in the PWM (string of bits as the paper even calls them) to the LPF (effectively the D to A) will have errors in the analog domain.

And?

Timing errors in a PCM system (either in the data itself or between the three clocks feeding the DAC) will introduce errors in the analog domain too. There is nothing new there. The timing errors (or other errors) can effectively alter the value of bit as it is received. Since the bits make up the audio if the value of the bits gets corrupted/misinterpreted so to does the analog that it encodes. Look at how digital jitter (timing errors) is measured by Stereophile or whoever... by looking for noise artifacts in the analog output of the system. Does that suddenly make the system not digital?

That other factors such as slew rate, bandwidth and ringing can effect a digital signal... again... duh. Anything that distorts the analog representation of the digital bits (IOW square waves) can alter the interpretation of the bit. Bits are often clocked/determined on their leading or falling edges. You don't have the bandwidth to really pass the square wave (again.. square wave is a sine wave with lots of odd order harmonics) cleanly and you distort the leading/falling edges and you can cause the bit values to be interpretted wrong. I mentioned a couple times earlier about 'perfect amps' being either high or low... a binary state. This is why. Imperfect amps take time to transition from one state to the other, there is sort of dead time between states.

That analog power supply fluctuations can effect digital circuits... again.... duh! This why pretty much any digital chip out there is going to spec. decoupling caps on its PS input(s) and reference inputs for example.

That the LPF can have influences on the analog output... again... nothing new there. Why does pretty much every PCM system out there now oversample the digital signal? So one can move the analog reconstruction filter (LPF) further away from the content band so it has less and less effect on that band. The faster the digital amps get at switching the higher up the analog LPFs can be placed.

As far as the discussion about feedback that is just talking about improving the system. The presence of feedback or not does not make a process digital or not. Is a no feedback single ended triode digital while a push-pull tube amp with feedback analog?

Shawn (Kicking the horse.....)

[Rivendell61]

I read the paper and all of the "oh so important" claims being made by the author and they are exactly the same thing they're teaching in the digital signal processing classes about the implementation of DAC's. And for some reason the author seems to think the current behavior of digital circuits somehow isn't digital because "it doesn't look digital". The digital amps I just got finished building and tweaking in my last lab had similar current behavior - trippy eh? I guess you don't see the significance of Ohm's Law...but that's ok.

Oh btw, the amp worked just fine... []

Well, no. Again you seem to have mis-read or not read. But I'll let you have the last word. If you actually believe what you have been saying why not take the questions to his forum and ask him? As noted above he has designed the best performing digital control Class D amps extant (not to mention converters and analog Class D). You might learn something.....

I'm done.

Mark

[pauln]

The last record I played through the Trends was side two of Abbey
Road. Last night I swapped the Wright 3.5 SETs back in and played it
again.

I did this because after hearing the Trends exclusively for the last few weeks I wanted to do a comparision.

My observations:

1]
Consistent with my initial reaction to the Trends ("Wow!") is the
notice of the difference in appearent sound level vs the SPL meter. To
get the Trends to sound like the same level as the SETs the SPL says
the Trends needs to be running about 5dB louder than the SETs. I have
no explaination for this... maybe the appearent level is based on
hearing the midrange whereas the SPL is gathering the additional bass
from the Trends?

2] Abbey Road has a nice variety of sounds in
the songs' instruments and it sounded quite different between the two
amps. The Trends extends higher and lower and does so with a very
agreeable dynamic immediacy that sounds great. The bass is more
pronounced in a way that does not sound like the "bass" is just turned
up - more like the real bass signal is more present in the source.

3]
As has been mentioned in other posts, the mids of the Trends is clear
and the high end is fully extended if not a little too much in some
cases, but there is something going on in the midrange I can't quite
catch, but something is going on there... The very high end (drum kit
ride and crash cymbals, brushes, voice sibilance) and all sounds
natural and realistic; it is the midrange where voice and guitar sound
almost perfectly not quite right. It is difficult to separate my
thought of what these should sound like from what I am used to hearing
in the SETs, so I can't pin this down very well, but there is a subtle
difference that I notice (as a long time guitar player) that may just
be a quirk of my own origen.

4] Even though the Trends does so
much so well, a fresh listening to the SETs again has brought me back
to them. Maybe an analogy will suffice (no offence intended to either
young club dancers or libraians):

Hearing the Trends is like
being set up on a blind date only to discover that your date is a
flashy (fleshy?) young club dancer with all the right proportions and
paint eager to party; the effect is Wow! And she's lots of fun to show
in public. Self centered, always checking the mirror, dumb as a
doorknob, and endlessly chattering about nothing of subtance...
doesn't grasp anything you want to talk or think about... a
superficially attractive wasteland - maybe worth a tour but not a place
one might live...

The Sets are like a young librarian; intellegent, well read, and
thoughtful; and truly interested in what you think and say. No makeup,
naturally pretty, and happy to sit with you for endless hours at home
or in a quiet park or coffeshop just hanging on your every word.
Natural interest and intimacy for the long term. As the Irish poet
said, "I see a fine land where I may lay down my sword and rest".

Its got to be the off-duty librarian for me... I'll keep the
Trends around for parties or when someone questions that La Scalas have
bass.