Class D is just Dandy!

Wait, didn't we have a manufacturer participate in this thread?

I tried going to their web site but it seems down?


http://www.iceh2oaudio.com/index_htm.html

Just a few of the industry's heavy hitters of hi-end design give their opinion on the merits of Class-D in a round table discussion with Absolute Sounds.

http://www.stereo.net.au/forums/topic/110007-switching-noise-in-class-d-amps/?do=findComment&com...

Cheers George

@georgehifi

Interesting article, full of inaccuracies. One I may have helped propagate.

Class D vs. Digital Amplification

The article claims, erroneously, that Class D amps all have an A/D converter at the front. They do not.  It is actually more of an Analog to Analog converter with a switching voltage amplifier in the middle. :) Somewhere there is an article or paper by Bruno Putzeyes chafing at the use of "Digital" to describe his amps, which I can't find right now. Worth a read if you can find it

Class D amps (ICEPower/Hypex) generally rely on feedback to control the switching, which uses a linear comparator. There's no A/D conversion in the chain, it's not needed.

Here is a good short article on the subject:

https://en.wikipedia.org/wiki/Class-D_amplifier

Interestingly, George, the Technics Class-D amp you are looking forward to IS more of a digital amp than most Class D in that it DOES have an A/D front end, followed by a DSP engine to do the calibration and frequency/phase adjustments to the original signal before feeding the amplifier section. You are really trusting the amplifier with a great deal, because it will chew the signal up and digest it before spitting it out again. This is an approach not entirely unlike Theta and Meridian have undertaken.

Best,

E

So, to those confused by Class D vs. Digital, to be "digital" you have to convert or have the signal as an integer to describe the waveform. Like the digits in a CD track. This is "digitization" or converting an analog signal into a series of digits.

Class D does NOT do this conversion, but the amplifier IS switched on and off. :)

It’s confusing because what happens is that the comparator keeps the switch ON or OFF more or less in proportion to the incoming signal. This is why feedback is so important and completely different in a Class D amp vs. linear. The feedback IS essentially the only way the amp has to control the output signal, however this feedback takes different shapes. The more global the feedback, the more accurate the output.

It’s a subtle but important distinction.

Here is a list of Bruno's papers, I encourage you to read them, as I am sure I made mistakes, and the guy is one of the celebrated Class D amp designers of our time.

https://www.diyclassd.com/p/application-notes-white-papers/

Best,

E

George,

Nice try I've read it all many times before.

What are we going to do with you?

Bruno never calls his modules digital,class "D" was just the next letter in the alphabet that hadn't been used yet.

I know that tomorrow I will get too listen for 6hrs of wonderful non fatiguing class d amplified music.

Kenny.

I love the use of a page of 10 year old quotes about a developing technology.

Beyond that, the article may only prove that all those famous designers didn't succeed in producing a good Class D amp. Only shows that they couldn't do it - not that it can't be done. As Bruno points out, it's a different engineering knowledge and skill set that many audio designers don't have.

Kenny.

I’m afraid I’m guilty of saying "Digital" vs. "linear" when I should stick to Class D instead, so my bad. :)

And yes, those quotes and tech are stale as hell. No wonder George can’t enjoy digital amps, all the stories he reads about them are a decade old and he can't trust his own ears.

Erik

randy,

See if you can connect with @h2oaudio he makes Class D with linear power supplies. They sound pretty sweet.

Erik

Sorry, but there has NOT been significant strides in class D since then -- has there? If some of the legendary names in amp design aren't good enough, what would be?

That's not a valid argument. With a new technology, why would established manufacturers be better at implementation than those who helped develop the technology?

Madavid,

Sorry, but there has NOT been significant strides in class D since then -- has there? If some of the legendary names in amp design aren't good enough, what would be?

I don't think that you quite get it,

There hasn't yet been a perfect amp designed or probably will never be that satisfys everyone's ears in the Sonics that each of us individually desire.

I can fully assure you that I will always have great respect for these legendary names in amp design.

I will comment on Nelson's Amps,
Over the years I have owned many of his designs starting with the 400a and several other Thresholds,Pass Aleph 30 and Aleph 2 mono's, x-150,Xa-30.8 and then building the F5 from him graciously giving to the Diy community,The last owned and recently sold was the J2.I fully enjoyed every one of them,But the class D amps that I have now Satisfy my ears with the least shortcomings of any Amp I have ever owned in my 30 yrs in this hobby.

Comparing class a amps to class d amps is like comparing apples to oranges,which one is better is always going to be highly subjective.


At the end of the day,
It's all about the music and getting closer to it.

Kenny.

@madavid0 

I don't have to be nice to people who are being nasty, so I'm not being nice to you anymore. You are the most transparent hater in the long list of transparent haters, and I know haters.

You previously stated you know almost nothing about Class D but now you claim to be an expert and want to bashing all the contributions of almost everyone else in this thread. I take offense at you coming in here and deliberately starting trouble. I trust the contributors. I value their input, and clearly you want to ignore all of us or call us poor judges of music and sound, which I find a personal insult to me and everyone here.

I have two questions for you:

1 - What is your income source? Are you in the audio industry or do you own a store or sell audio equipment online?

2 - Why don't you just come out, make peace with whatever point you want to make and leave us alone.  You have put a tremendous amount of emotional energy contributing nothing but hatred and bashing a technology. 
What happened? Did a class D amp fall out of the sky and kill your dog as a child?


E

The gods must be crazy!

@kdude66,

"I have a new Red Dragon S500....

Kenny, I tried this amp recently with my B&W 800D2’s. While it sounded wonderfully adequate in low end and detailed in mid’s /high’s, it didn’t quite push the 800’s the way my current amp does from ATI 544NC. In addition to being detailed, the 544NC drives the low end with such brute force that I have not felt the need to use my JL sub.

I would have been more than content with S500 if I owned the B&W 802’s. When I spoke to Ryan Tew of RDA, he recommended using a pair of S500 in bridge mode to drive my 800D2’s.

Got one more amp on my list of audition before I happily settle with my choice of class D amp.  Getting closer to sit back and enjoy the music :-) 

lalitk,
I haven't used my s-500 dragon very much,I have week old speakers so I'm using my 600m's because I know their sound and they have plenty of hrs on them.

I think you would be happier with a pair of dragons with your 800 d2's.I'm not that familiar with the Ati amps,they look very good though.I think they need more pwr then one s-500 can provide.

I'm personally looking at the Ps audio 700's mono's and maybe the Bhk preamp.I will let the dust settle and see what more user impressions have to say.

Overall very satisfied with my canto's for now.

Kenny.

Todd,

"The gods must be crazy!"

I think all of us are a little bit.

Exactly what is Normal?

LOL

Kenny.

Toddverrone 5-1-2017
The gods must be crazy!

Great film! And as those who have seen it will realize, its mention was à propos.

Regards,
-- Al
 

Al,

I will have too check this movie out,never heard of it.

I'm more a music guy,don't watch many movies.

Kenny.

Anyone looking at trying the NC500 boards should look at Nord,
Kenny I am using a BHK pre with the Nord mono's and it is awesome
https://www.nordacoustics.co.uk/

When I was trying to the latest class D experiment, Nord was on my short list. I ended up going with D-Sonic because the latest Pascal modules are supposed have technology that lowers switching noise to levels lower than previously possible and they receive universally positive reviews (so do the nCores as a matter of fact).

Another factor, I hear claims that the NC1200 is subjectively greatly superior to the lower end modules, and if that's the case it would be like robbing from myself to go with less. Unfortunately, NC1200 products are in the 10k+ range...

But here's the thing, the D-Sonics crushed my soundstage and seemed to lend themselves to listener fatigue. Do they need class A preamping or a tube stage?

he can’t trust his own ears.

I do very much so Eric , maybe it’s you that needs an bi-aural Exostosis operation.

As I said before the only one of new breed of Class-D’s that I had any time for, was the latest BelCanto 600 monoblocks to which BC from what I understood by the presenter has done their own switching noise filtering, from what is standard from NCore.

But they had to be driving a benign 6ohm load, of a top line Raven tweeter’ed two way bookshelf, to get me to like them, on the other speakers they too didn’t sound very good.

Cheers George

Jtsnead,
I have been following the evolution of the Nord since the inception of them,Rollable op amps,very cool.Colin North has quite a following on audio shark forum.

The Bhk preamp looks like a good fit for me and there is several used up for sale.Thanks for the info.


Madavid,

You may want to try a warmer sounding solid state or tube preamp with your d-Sonics.
Let us know the details of your current system and what kind of musical presentation or flavor that you are looking for.

Kenny.

George,

Were can a mate get a bi-aural Exostosis operation?
Can it be accomplished in the states or would I have to go down under.

Kenny.

I have three Crown ITech 5000HD stereo amps (6 x 1250 watts) with incorporated active dsp crossover controlling 2 JBL M2 Master Reference Monitors and a JBL Sub18 (2500 watts bridged amp).  These are called class I by Crown and are a variation of class D.  Dynamic range, transient response, and headroom, are well beyond the traditional average "audiophile" system.  These characteristics are, in fact, staggering when compared to my conventional Classe/B&W 801N system.  No doubt, this is due in part to the extreme high wattage and active crossover of the  Crown amplifiers, something not easily obtained with conventional amps.  I don't sense any particular harshness with the Crowns, and, in fact, the system sounds pretty sweet, but I do constantly wonder if upper frequency refinement would improve if the Crowns were other than class I.   The totally outrageous slam and bass response of the JBL/Crown system, however, is quite fun.

Lots of great info and feedback on the "big boys" in class D (B&O, Hypex, Pascal).

I've been using the NuPrime IDA-16, which uses proprietary modules and I'm really liking what I'm hearing. So much so that I'm pretty sure it's staying (45 day trial period). 

Anyway, anybody else using class-D amps from manufactures "rolling" their own modules?

Cheers,

Scott

@samac

I looked at the NuPrime pages VERY briefly. NuPrime’s tech sounds a lot like the Yamaha EEEngine. Small class A amplifier sandwiched between Class D voltage rails.

Again, kind of goes back to Carver’s Magnetic Field amp and NAD’s switching rails technology.

Sure gets grate reviews. I would love to give them a serious listen to see what the benefits really are.

I mean, it’s quite different from Hypex/Pascal/B&O but I have no idea if it’s much better.

The challenge with this kind of hybrid approach is again, you rely on feedback to tell you everything about what you should do from instant to instant. With the voltage rails swinging at the same time the Class A amp is swinging it is like shooting an arrow from a moving boat.

Best,

E

@erik_squires

Thanks, Erik, great info. I had no idea it might mimic or be similar to other designs.

It’s my first adventure with class-D so I have no idea if it’s better or even as good as Hypex, B&O or Pascal. I do know I like everything about it so far. It’s the easiest amp to listen to since my octal pre/845 SET combo. Refined and smooth with no listening fatigue at all.

I hope you do check out NuPrime. Would love to get your thoughts on how they fare against some of the competition out there.

Keep it coming, guys. This is a great thread.

Cheers,

Scott

Yes, George, Bel Canto Ref 600Ms are very good.  I  am right now listening to absolutely splendid sound of Mozart Symphony #40 with them driving  Focal Alto Utopia Be speakers, sourced from Esoteric K-01 through an ARC LS 25 Mk II pre.

I could not be happier with the sound quality.

Guys,

I'm so very happy with all of the participation on this thread, I'm also learning a lot, since I don't get to go to shows and dealers and listen as much as I would like to.

Would it be worthwhile to put together a web site JUST for class D amplifiers? It might give me the chance to listen to a lot more gear as a regular review feature, and break the mega-linear-amp stronghold.

It's just an idea, a lot of work if I chose to.

Best,

E

@kdude66 

That's quite a coincidence...I just ordered a pair of Bel Canto's REF600M's to try them out. The ATI 544NC amp is equipped with dual NC-500 modules in bridge mode per channel, so plenty of power (900W in 4 ohms load) to drive any speaker out there. 

I didn't want to end my quest for a 'perfect' Class D amp without auditioning the REF600's. 

PS: I did find @georgehifi comment about REF600's little discouraging.  

Cheers! 

I am a big a fan of excess as anyone, but at this point I'm going to have to wonder if big power matters ? I mean, come on! :)  :) :)

I also worry, like Nelson Pass, if big amps are worse performers in the first watt.

What do you guys think? Have you heard "better" in digital as you got "bigger" ?

@guidocorona 

I'm glad you mentioned break-in hours again. I'm at 300 hours with my amp and it continues to settle in and get better.

Do you feel the lengthy break-in associated with class-D runs across the board? As I mentioned above I am running an amp that does not use the more common modules. So wondering if you believe it will also "season" and settle in past the 1000 hour mark. Honestly wouldn't surprise me if it does. Anything I've purchased fromDACs to speaker to amps have taken months to fully bed-in.

Thanks.

Cheers,

Scott

You know, I was just thinking of something. It would be really fun to marry a Nelson Pass First watt Class A amp to Class D voltage rails via transformers.

Sigh I wish I had more energy. :)

Best,

E

I love the idea of a class D website, but to what purpose? Reviewing, comparing, contrasting? Or all of that plus sales?

It sounds like fun, but also like a lot of work.. though getting a steady stream of amps to review could lessen the pain.

I’m curious now about the sound of lower power vs higher power amps at low volume. I may have to try a little Dayton audio class D one evening, though it may be meaningless to compare a $60 amp to a $1000 amp and expect any sort of meaningful conclusions.

Also - Al, glad you caught that reference! 

@guidocorona 

Thanks for the reply. Looking forward to what more hours will reveal. It's been a great ride so far. 

Cheer,

Scott

Class D skeptic. I was once, the latest from Merrill Audio, is excellent
The Thor mono blocks at $4800 are very musical and best in class under $7k
IMO.

audioman,

Skeptic,I once was as well.

I haven't had a chance to hear the Thor but I have heard many good things from them and I'm glad you are enjoying them.

We would like to hear about your current system and maybe what the Thor amps replaced.

Kenny.

lalitk,

Ive been using my set of 600m's for 14 months paired with a canto pre3 which I have had much longer.

I used the nc400 for 4yrs before I got the 600 and I have a red dragon s-500 that only has 100 hrs on it.

I have always been a fan of higher pwr amps even with higher efficient speakers,I started 30 yrs ago in this hobby with Khorns and a Mac 275.

I don't really know for sure and haven't seen any documentation yet that says higher pwr Class d amps don't sound as good as lower power class d amps.

Maybe someone with more knowledge and experience with class d amps only  than me could chime in.

Kenny.

I'm playing catch-up on the posts but thanks for the recommendation on the Wtred gear Scott. That STI has been on my short list as well, most likely the v1 since the used prices sre
mire in my budget. I just haven't been lucky enough to snag one on the forum yet....

Todd, thanks for the reply. Please pardon my ignorance but I'm  not sure what you mean by different input impedance. I'm still a bit of a rookie at the terms and what they mean towards the resultant sound. 

If I may throw in my thoughts on the sound quality of class D amps, I can sum it up in 3 words: I'm a fan!

@autre I won't pretend to be smarter than I am.. I don't understand why it matters either, but preamps have a characteristic output impedance and amps have a characteristic input impedance. If memory serves me right, the amp input imp should be 10x higher (or more) than the preamp output imp. Having them too close can apparently cause the system to sound off or cause an increase in noise.

Anyone with more detailed knowledge, PLEASE addend or add!

Hi Guys,

The biggest issue with input/output impedance is the change in frequency response. This is especially bad with tube pres as they usually have a high output impedance. Driving a low impedance input amp can affect the overall response and deviate from ideal. With purist tube pre's even the volume control setting can affect things because they lack additional buffer stages that would prevent this.

Good ways to see this is to look through the Stereophile archives and look at tube preamps. In the measurements section you will see the frequency response driving different simulated amps. Here is a link:

http://www.stereophile.com/category/tube-preamp-reviews

If you look at this particular preamp, youll see the FR changes a great deal when driving a 100k load vs. 600 Ohms.

http://www.stereophile.com/content/vtl-tl65-series-ii-signature-line-preamplifier-measurements#aVQTI...

High impedance inputs also tend to be noisier (I think).

Solid state preamps or op amp based preamps can easily be completely flat down to 600 Ohms.

So, wanted to make things a little more full.

One of the spec’s commonly sited is S/N (signal to noise) or related THD+n (Total Harmonic Distortion + noise). The problem with Signal to Noise is that it is often cited at full power, and not at a more reasonable amount, like 1 watt.

So, a 1000 watt amplifier can claim 10 dB more S/N than say a 100 Watt amplifier that sounds exactly as noisy. The full power S/N ratio becomes useless for comparing amps and how quiet they are. What I wish reviewers and manufacturers did more consistently is rate the S/N at 1 watt or 10 watts. Something small so we can compare what we’ll actually hear.

Distortion is also something that tends to go down as power goes up until the limit of the amp is reached. This is why these figures can be misleading. This is something stereophile does a little better, in showing graphs of THD vs. power output. Now we can at least look at charts to compare noise and distortion as more usable power outputs.

The other thing, I think that the amplifier community is having a hard time keeping it’s prices up to make boutique manufacturing possible. This makes it necessary to have big differentiation. For instance, having a 1,400 watt amplifier is cool and all, but in my living room, at my listening levels does it mean my sound is better than my 250 W amps?

I don’t really know all the answers to these questions at all. I’m just sharing where I start to scratch my head. :)

Best,

E

Good comments by Erik.

In the situation Autre described in his post dated 4-29-2017 it is very unlikely that impedance compatibility issues were present.  The Rogue Sphinx has a very high input impedance (more than 100K according to Stereophile's measurements).  And although I don't know what the input impedance of the Peachtree Nova 125 SE is, it is most likely much higher than the output impedance of the solid state Onix CD player which was driving it.

Impedance incompatibilities between line-level source components, such as CD players, and integrated amplifiers such as those, or between preamps and power amps, are likeliest to arise when a tube-based output stage is driving a solid state input stage.

Regarding the 10x rule of thumb guideline which Todd alluded to, I would state it as follows:

The input impedance of the amp (or other component that is receiving a line-level input signal) should be at least 10 times the output impedance of the preamp or line-level source component that is driving it, at the frequency within the audible range for which that output impedance is highest. Which in the case of preamps or source components having capacitively coupled outputs (such as the majority of tube preamps) will usually be at 20 Hz.  And the output impedance at that frequency will often be far higher than the specified output impedance (which is usually based on a mid-range frequency such as 1 kHz), because the impedance of a capacitor rises as frequency decreases.

That doesn’t mean that there will necessarily be a problem if the guideline is not met. It depends on how the output impedance **varies** as a function of frequency. What it means is that there **won’t** be an impedance compatibility problem if the guideline **is** met.

If Stereophile has reviewed the preamp or source component, the measurements section of the review will usually indicate the output impedance at 20 Hz as well as at other frequencies.  But if only a nominal impedance can be determined, such as a manufacturer's specification that is presumably at a mid-range frequency, to be safe I would suggest a ratio of 50x or preferably even 75x.

Regards,
-- Al
 

Whew. Thanks Todd, Erik and Al. That is a lot to digest but I think I understand it a bit more now. This does a lot to explain the basis for such terms "system synergy" and "system compatibility". 

And now, back to our regularly scheduled topic of Class D amps are Dandy!

@autre 

"system synergy" and "system compatibility".

This is one of the reasons I was more then happy to go with a class-D integrated.😀

Cheers,

Scott

The biggest issue with input/output impedance is the change in frequency response. This is especially bad with tube pres as they usually have a high output impedance. Driving a low impedance input amp can affect the overall response and deviate from ideal. With purist tube pre's even the volume control setting can affect things because they lack additional buffer stages that would prevent this.

This is mostly misleading or outright false.

Output impedance **might** affect frequency response (in some cases, certainly not if the output is direct-coupled) but also affects distortion.

Tube preamps do not necessarily have high output impedance. That depends a lot on the design of the circuit! If it employs feedback, its output impedance will be fairly low and driving a 10K impedance should be no worries- check with the manufacturer (our preamps don't employ feedback and 600 ohms or less is no worries)! In a purist tube preamp, the volume control won't affect things (other than volume) despite there being no buffer; its all about how well the design is executed!

As an example, we make two tube preamps that have balanced outputs (and were the first in the high end audio world with such) and the load that they can drive makes no difference- the frequency response is flat, owing to a direct-coupled output. They also support driving 600 ohms as they were intended to support the old school balanced standard. Yet because they lack loop negative feedback, their output impedance is relatively high (compared to most solid state preamps), yet their distortion is very low driving any amplifier made with a balanced input. I've used our MP-1 to drive loudspeakers directly; how many solid state preamps can do that? 

Just sayin'.