The new breed of Class D Amps

Sonnie

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There seems to be quite a storm over Class D amps in the past couple of years, particular the Ncore and Purifi based models. If I remember reading correctly, the same guy designed both, with the Purifi being his latest. I had not even heard of Purifi until the guys at NAD were telling me about them, which caused me to start looking around a bit.

After I sold my Emotiva XPA-1 monoblocks, thinking I'd be fine with one amp doing it all, then I got the bug to add Atmos wide channels and ended up diving right back into monoblocks. I got the HTP-1 processor, and having the extra channels to do wides and having some extra speakers, why not give it a try. So... I decided I wanted small and powerful monoblocks and went with the Wyred 4 Sound SX-1000R amps, which appeared to be a good fit for the Martin Logan stats, and would have more than ample power to drive them.

With all the buzz around the Ncore and Purifi amps, I've been tempted to try a pair, but I just don't think I'll notice any difference. Despite being skeptical of my hearing, I figured I'd ask around some of the manufacturers and here are some of the responses I received from four different manufacturers...

"The upgrade in the DAC’s and PURIFI amplification will be huge."

"the Sparkos are softer and will give you more bass and tonal density. They will drive the Martin Logan's just fine" (referring to deciding between which op-amps to choose)

"for your speakers I would recommend our NC1200SL with Sparkos op amps. I would not recommend Purifi for electrostats because of the minimum impedance that such speakers have" (contradicting the previous manufacturer)

"boutique buffers just don't offer any better performance than high quality options from the likes of Texas Instruments. Some of the boutique options actually perform far worse. They are all far more expensive. Its more about "up selling" and getting the customer to spend more rather than any actual technical or subjective improvement"

Some of you may remember our blind (and non-blind) amp evaluations we did back in 2015. We (Wayne, Joe, Leonard, Dennis and myself) evaluated the following amps:
  • Behringer EP2500
  • Denon X5200 AVR
  • Emotiva XPA-2
  • Exposure 2010S
  • Krell Duo 175
  • Mark Levinson 532H
  • Parasound HALO A31
  • Pass Labs X250.5
  • Sunfire TGA-7401
  • Van Alstine Fet Valve 400R
  • Wyred 4 Sound ST-500 MK II
While overall we felt there may have been some subtle differences, for the most part no one could 100% identify any differences. If I remember correctly we may have put a strain on the Denon receiver powering the stats at a ridiculously high volume. Otherwise, no one came away saying, "oh man I gotta have that amp". Okay... maybe Dennis was coveting my Parasound, but he didn't take it home.

We can easily blame it on the rest of the equipment not allowing us to hear any significant differences along with the fact we did not live with each amp over an extended period of time to get more accustomed to the differences. So none of us walked away being adamant that there are no differences in amps. However, we also kept in mind that ultimately if the amp is doing its job, it should be neutral and not color the sound.

I guess what I'm getting at with the new amps, are they using the op-amps to change the sound and does it really work? What's all the fuss about?
 

ddude003

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I guess what I'm getting at with the new amps, are they using the op-amps to change the sound and does it really work? What's all the fuss about?

OP amp rolling, like tube rolling, can change the sound of an amp, preamp or DAC... Various op amp designs, materials used and operating ranges mean there will be differences in the end resultant sound...
There are studies that can be found at https://www.aes.org/e-lib/browse.cfm?elib=16029 and https://www.aes.org/e-lib/online/browse.cfm?elib=17529

I don't know about the fuss... Like other components, Tubes or Capacitors for example, a Competitive advantage maybe...
 

Sonnie

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Interesting... although I did not read the full article since I don't want to pay $33 for the article or $1800 annually.

Differences in frequency response and noise are carefully controlled while the distortion characteristics of the op-amps are amplified.
 

Sonnie

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So similar to tubes, op-amps can add distortion, which I suppose some enthusiasts are fond of.
 

ddude003

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I don't think adding distortion is the goal... It just turns out that more or less distortion may be the result of many the variables between op amp devices and the variables in the various designs of amps, preamps and DACs they are employed in...

In these "new" class D amplifier System Integrators that use Purifi amplifier modules, what differentiates the sound or the value added for the consumer...
 

Todd Anderson

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I can't hear the difference in amps... at least I don't think I can. tubes, yes. I think that added distortion (warmth) might be identifiable in a blind setting. But, I'd imagine that listeners would have a hard time walking into a room and readily identify what kind of amp topology is in play.

Nice thing about Class D is that they run cooler. As for OP-rolling... not sure.
 

Sonnie

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The op-rolling idea seems kinda cool, if I thought my ears were good enough to actually hear a difference that would be substantial enough to cause me to prefer one over the other. The problem I have is my age and my ears, they simply can't hear much over about 11-12kHz, and then it's way down above 8kHz, so it has to be pretty loud for me to notice it. I have to get my wife to listen in our vehicles for rattles and noise... she can hear it, I can't.
 

bilboda

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I went with the stereo purifi from VTV Amplifier in the US. My speakers need power, Mark and Daniel Maximus rubies, and the Adcom GFA 5500 was sufficient but large and warm. Ordered with the standard NC500 buffers, I later added the buffers from neurochrome, not for op amp rolling but for better power regulation. Had fun times during the switch, Wayne at VTV help arrange an rma with Hypex ,sending me a new power supply for the cost of shipping, Purifi assured me I hadn't destroyed the purifi modules and Tom at neurochrome gave me the steady hand, necessary guidance, voltage regulators and correct part #'s I needed for a ribbon cable. It all works fine now. Can't say music is better now but it is cooler and size is reduced, which was also the goal. There is a great thread on diyaudio that can also assist with making the right choice for your speakers.
 

Luciano

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For op-amp rolling. It works for me. I could hear the difference between them. And I went a step further and also replaced the opamp with a opamp that is using jfets and is built with discrete components.

The thing I want from a class D amp is if I could find one that use Gallium Nitride (GaN) fets. That improve the sound quality and have higher switching frequencies that give higher efficacy. So it do not need a heatsink..

That is the next revulsion and a giant step in the development in class D amps.

Just that the sound quality will be at par and better than class A can produce is huge. But also when the units can even get smaller and or have greater performance is mind blowing. The GaN amplifiers have the same benefits in power supplies as in audio amplifiers.

So at the end we will get small/smaller and more powerful power supplies to our class D audio amplifiers that also have greater power output. Not that I care about power but it is impressive to see amplifier bords that of sizes that you are used to see and they give unbelievable high power output plus no heatsink is present. Yes it is no magic when the reason is that they work wit ~98% efficiency yes that is right when there is only 2% losses that may be transformed to heat.
 

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When you say you can hear the difference, what difference are you hearing? Not trying to poke holes in your statement - I believe you! Just curious!
 

bilboda

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A comparison of an available GaN amp from Orchard Audio and the standard Purifi Audio Eigentakt EVAL1 is on Audioexpress, can't seem to link it here It is titled "Fresh From the Bench: A Tale of Two Class-D Amplifiers Orchard Audio BOSC and Purifi Audio Eigentakt EVAL1" .
The GaN wins on size but measurements and ears are even. There are some caveats on the Orchard Audio for upstream components. One would have to research for the best fit for their speakers. This comparison does not go into that much.
 

doug2761

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I'm wondering if amp performance has gotten to a point where the differences are just not that significant. I've been swapping between my McIntosh 402 amps and a pair of the DIY Hypex NC400. Both are giving me very enjoyable listening experiences. Looking at the performance measurements on Hypex and Purifi amps it seems that noise artifacts are so far down in level, frequency response is so flat, and damping so high that these amps measured performance envelops are well beyond theoretical human ability to distinguish one from the other. I'm not saying folks aren't hearing a difference just that the measured amp performance is well beyond measured human hearing abilities so differences should be small at best.
 

Sonnie

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Here's that link (it may be you have to have a minimum number of posts to add a link to a thread - spam prevention).


Interesting size on the Orchard amp... 5.5" (14cm) x 4.8" (12.2cm) x 1.9" (4.8cm) ... although it would be short on power for me. I love the idea of small amps.
 

Sonnie

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I'm wondering if amp performance has gotten to a point where the differences are just not that significant. I've been swapping between my McIntosh 402 amps and a pair of the DIY Hypex NC400. Both are giving me very enjoyable listening experiences. Looking at the performance measurements on Hypex and Purifi amps it seems that noise artifacts are so far down in level, frequency response is so flat, and damping so high that these amps measured performance envelops are well beyond theoretical human ability to distinguish one from the other. I'm not saying folks aren't hearing a difference just that the measured amp performance is well beyond measured human hearing abilities so differences should be small at best.
That would be my thinking... very subtle differences most likely, but you need good ears to hear it too. My ears just aren't there.
 

TupuHiRez

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I'm wondering if amp performance has gotten to a point where the differences are just not that significant. I've been swapping between my McIntosh 402 amps and a pair of the DIY Hypex NC400. Both are giving me very enjoyable listening experiences. Looking at the performance measurements on Hypex and Purifi amps it seems that noise artifacts are so far down in level, frequency response is so flat, and damping so high that these amps measured performance envelops are well beyond theoretical human ability to distinguish one from the other. I'm not saying folks aren't hearing a difference just that the measured amp performance is well beyond measured human hearing abilities so differences should be small at best.

So for someone like me at 45 years of age with hearing working very reliably out to 16.5-17khz, I have to say I notice major differences between my various receivers (Pioneer, Yamaha, Denon), and my power amplifiers such as Emotiva XPA-2 Gen2, Arcam 8P, and D-Sonic M3a-800S. Upgrading my DAC to a Topping DX7-Pro was a huge improvement. Fine tuning my speaker placement and listening position afforded me even more detail, imaging, and simply a more refined presentation. Differences and changes in the system components are more easily discernable with the placement optimized.

So back to the amplification, receivers suck (haven't had to opportunity to play with a $5K+ Onkyo, Denon or whatever), even as a pre-amp so I run the DAC direct to the amp (I also don't hear the need to add more analog electronics to the signal path. I run toslink from my Kuro to the DAC for any audio from the video source. I use USB from a Lenovo TinyPC running Windows 10 and Roon to the DAC. While the Emotiva is a nice powerful amplifier it has some issues in the top end and is surprisingly not as capable in the low end as I thought when paired with my Tekton speakers, however it worked wonders for my Magnepan MMGs vs the Arcam 8P which is more musical (for lack of a better term), but lacks the power and I guess damping to manage the MMGs. With my Tekton Moabs I had to switch back to the Arcam 8P which sounded marvelous together. But I could tell there should be more refinement and while I love the stereo presentation from the listening position, headphones through the DAC which has an excellent amp said that there was more detail to be had. When I installed the D-Sonic M3a-800S (Pascal modules) and played music through it, I heard all the detail I experienced through the headphones and then some (the headphones are some mid range Sennheiser model) with all the marvelous sound staging and imaging you'd expect from a $4500 pair of speakers. One of the things that stand out to me is that you hear more of the finer details, leading and trailing information is much clearer, so you get more pop and definition in everything. The sound is smooth and rich, no etch. Tracks with complex passages with a lot of high frequency (or any frequency for that matter) can be navigated without fatigue.

I don't know how much better Class D gets from here within the $1000-$3000 price range, but I'm ready, but it needs to be another leap in performance. From what I can tell, reviews for the quality units in this range seem to review just about the same regardless of module type. When I say the same, things like the level of transparency, bass control, and this common trait where the midrange is slightly dark. The BOSC amp was on my radar but I'm not spending $1600 for 16db of gain and short change myself if I move into a bigger space, actually the lack of a trial option was the bigger problem. GaN on paper seems like the way to go, but I don't recall reading an audible leap in performance over the quality ICE, Pascal, Purifi implementations.

So to doug2761's point, I think since we've gotten to the point where amplification is exceeding the capabilities of Redbook audio, distortion is essentially non-existent, and pretty much uniform response from near DC out to 20khz and beyond, we're reaching the point of diminishing returns. I don't think the module type is going to matter much. How they are implemented, the quality of the power supplies and input stages will make the difference (probably leaving something out but certainly not just the module). I'll have to read something extraordinary about a Class D amp for me to want to upgrade again. I'm having way too much fun listening to music. Oh and those "poor" recordings? They sound great.
 

Luciano

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@Todd Anderson NP.
I have a RIAA amp stage. That comes with a op-amp named OPA2111KP.
I read about a audiophile grade op-amp. And I got to great lengths to see that I got original ones (their is a lot non original even they falsely claimed that it is original ones on eBay) directly from the manufacturer/supplier.
It sounded better but when I swapped to a totally different RIAA amp (that has a totally different op-amp) I noticed that I got a octave lower bass on that amp (that I did not know that I were missing!).
I lend the new RIAA amp out to a friend and started to use my old one again. (Had forgot about the bass issue.)
I then got the discrete op-amp because I heard they were among the best and I were intrigued to compare it to my audiophile op-amp one.

I installed the discrete one and it sounded as good as the audiophile one. It is hard to determine if one sounds better than the other they at booth good. (Potato potato.)

But here is the big one.. With the discrete ones I got the bass back! And I remembered the same story about when I switched to the new RIAA amplifier above. (And it had to been the audiophile op-amp that was not up to the task).

So the op-amps sounded differently.
Now I got a discrete op-amp that sound good or maybe i whould say great and is playing the whole frequency range (the lowest octave and that comparing against a audiophile op-amp that are praised by many muses01).
 

ddude003

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It will be interesting to see where GaN FETs go in the next few years...
 

Bill Shenefelt

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Home built Jbl 4343
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home built usingJBL 1 LE 85 horn and lens
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JbL L-300 home built cabinets
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two corner bass traps and 4 wall sound absorbers
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As we pass the years with Class D, there seem to be jumps of some kind in the reproduction quality of the amps.
Where in this generational improvements do the Crown XLS 1502 amps fit?
 

Sonnie

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I know a couple of guys that love their Crown amps and use them in their main system without hesitation.

They probably wouldn't get much attention from the high-end elitest crowd.
 

ddude003

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Yamaha RX-A850 Pro (the other 5 channels lol)
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MacBook Pro, Custom i7 7700k De-lid 2xAsus1080ti GFX build, Audirvana+, LiquidSonics, SoX
DAC
Chord Electronics Ltd. Qutest
Universal / Blu-ray / CD Player
Sony UBP-X700 /M Ultra HD 4K HDR
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Martin Logan ElectroMotion ESL
Center Channel Speaker
Martin Logan Motion C2
Surround Speakers
Martin Logan Motion 4
Surround Back Speakers
Martin Logan Motion 4 (yes, another set of these)
Subwoofers
Martin Logan Dynamo 700
Other Speakers or Equipment
Cifte 12AU7 NOS & Genalex Gold Lion Tubes in Pre
Video Display Device
Samsung The Premiere LSP7T UST Laser Projector
Screen
Elite Screens Aeon CLR3 0.8 Gain 103-inch
Remote Control
PrimaLuna & Lumin iApp
Streaming Equipment
Netgear Nighthawk S8000 Streaming SwitchLumin U1 Mini Streamer/Transport
Streaming Subscriptions
QoBuz Studio Premier, Roon, Amazon Prime & Netflix
Other Equipment
ThrowRug, SaddleBlankets, WideBand & BaseTraps...
Where in this generational improvements do the Crown XLS 1502 amps fit?
The Crown XLS 1502s are so so spec wise... And a hell of a bargain at that price point... If you have better specs for your up stream sources you probably don't want one of these in your stereo system... Maybe driving your subs... Otherwise, this seems like a very nice live stage venue kit... The other thing I see that I don't like with this amp is appears all analogue input goes thru a Analogue to Digital step and back from Digital to Analogue output... Maybe an extra step or two for a class D amp... Aren't these things all essentially Delta-Sigma DACs anyway?
 
Last edited:

Bill Shenefelt

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Aug 19, 2017
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6
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Anthem MRX 1120 receiver
Main Amp
Audire
Additional Amp
Yamaha
Other Amp
Crown 1502
Universal / Blu-ray / CD Player
Oppo 203
Front Speakers
Home built Jbl 4343
Center Channel Speaker
home built usingJBL 1 LE 85 horn and lens
Surround Speakers
Jbl le85 with horn and 12 inch JBL
Surround Back Speakers
JbL L-300 home built cabinets
Front Height Speakers
2-6 inch coax Klipsch in-ceiling atmos
Rear Height Speakers
2-6 inch coax Klipsch in-ceiling atmos
Subwoofers
Two SVS 16 ultra sealed box units
Other Speakers or Equipment
two corner bass traps and 4 wall sound absorbers
Video Display Device
Sony 4k projector and sony 65 inch tv.
Screen
119 inch Dalite
Remote Control
ARC MX-780
Streaming Subscriptions
Dish Network receiver
I willlikely only be using the two Crown 1502 amps for my 4 atmos speakers. Right now I have some older Heathkit amplifiers running the front mains and and my current Athem 1120 processor/amp running the ftont center and the front right and left sides and the rears are on a Heathkit amps. I also have my sides on the Anthem 1120 internal amps. I have an Anthem 525 amp on order and coming when they start sending out their Gen 2 units. Supposed to bea really good 5 channel amp It will run the front three and two side speakers on my future (depending upon shipment dates) Anthem 15.4 processor. Even PS audio is using a new class D amp section in a pair of their monoblocks. I was just wondering what the newer class D sections were in sequence of development and quality.
 

orchardaudio

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Succasunna, NJ
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Thanks to @jtwrace for introducing me to this forum. If anybody has questions about my GaN products feel free to post here or contact me.
 

dlaloum

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Integra DTR 70.4
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Anthony Gallo Reference 3.1
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Anthony Gallo Reference AV Center
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PSB Alpha
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Sony X90H
Some years ago, the Crown XLS Drivecore pro amp range made waves among audiophiles - at the time they were available for prices ranging from US$300 to US$500 ...

Many of us compared them to vaunted audiophile amps, and then switched to them.

Today they appear to have doubled in price - and where in 2014 they were fantastic value against the various audiophile option - today the picture may not be the same.... They are still great value if seeking a load insensitive high power amp... they still score in terms of $/Watt. - But I am not as sure as I was then, as to whether they are as competitive in value terms in todays marketplace.
 
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