Class d keeps improving

[markk02474]

Wow, global negative feedback, just like my 28 year old, 760 wpc (@8Ohms), 120db S/N, Crown Macro Reference. Global NFB on my amp gives it high damping factor even at high frequencies.

 

[boXem]

Wow, global negative feedback, just like my 28 year old, 760 wpc, 120db S/N, Crown Macro Reference. Global NFB on my amp gives it high damping factor even at high frequencies.

Global feedback on a class AB amplifier is easy and almost as old as amplifiers.
On a class D amplifier it's much more tricky in the analog domain, but still not new.
The novelty here is to execute the global feedback in the digital domain.

 

[mika91]

The citation amp is available directly on HK website (at least in France)
I put it in the basket, but can't decide if I finish the order or not ^^

I'd prefer to read some reviews before, but whatever it seems full featured for value (600€): compact, chromecast, hdmi arc, 125W 8ohm, sub and trigger out, basic eq (bass, treeble, sub crossover), even dolby night mode.
It only lacks "not disturbing" mode with all lights off (except on key press) and dynamic loudness (as on RME dac or yamaha/denon/marantz amp)
Direct contenders are Sonos amp and Bluesound Powernode 2i: hope the harman will measure better.

wait&see

 

[markk02474]

Global feedback on a class AB amplifier is easy and almost as old as amplifiers.
On a class D amplifier it's much more tricky in the analog domain, but still not new.
The novelty here is to execute the global feedback in the digital domain.

Global NFB is in DACs now. I forget where I saw it though. I think there is already local NFB inside some DAC chips.

 

[boXem]

Global NFB is in DACs now. I forget where I saw it though. I think there is already local NFB inside some DAC chips.

That is called delta-sigma, not new either

 

[markk02474]

That is called delta-sigma, not new either

Global feedback is new, however.

 

[Max]

The citation amp is available directly on HK website (at least in France)
I put it in the basket, but can't decide if I finish the order or not ^^

Tempting indeed . The all-in-box solution with good performing amp and plug-and-play out-of-the-box streaming (chromecast+airplay)... If your shipment could go through Amir's hands

 

[Max]

The chip should perform at its best when directly connected to the speaker's terminals. Very interesting to (possibly) enhance the in vivo (electro mechanical) response of the drivers. But it requires to access to the internal wiring of the speakers... The HK product is a tradeoff. I don't know if we could have some measurements with a such complex load but would be great

 

[Abcdav]

Just made an account to share my experience and give you some feedback about this amp.
context: I was looking for an airplay2 class d with enough power for peaks. HDMI arc is a big plus.
not much On the market as far as I know: the 2019 Sonos amp and the hk citation.
Speaker is a 3 way passive monitor rated 4 Ohms.
Dipping at 3.2ohms around 150-200 Hz topping at 32Ohms around 1.5kHz.

both tested with digital input hdmi and airplay 2.
after some times with the Sonos amp i can understand comments saying it is bright. This amp is very lean and lack some bass when listen at low level. I guess this could explain why loudness is on by default.

citation amp is much more composed and balanced.low to high and does not induce an overly bright sound
Maybe it is a bit too generous bass-wise.

end of comparison for now. Should you want some subjective statement feel free.

about the citation
on the plus side, sound was very good and clean. Like I didn’t need anything more. I wish I could have kept it but it will go back.

first, when played via AirPlay some piano key strokes provoke audible distortion. For example the very beginning of true Colors by Ane Brun. Le canon de pachelbel by Pierre-Yves Plat.
the issue is not present on the digital inputs. Tested via hdmi Apple TV 4k.
but I can’t justify this kind of work around.

second the volume control should be more linear. not enough steps. From step 3 to 4 is like more than twice the volume.
it certainly does not help that my speakers are 95dB/m/2.8v (or 92/1m/1w). Should be less of a problem for lower sensitive speakers.

third the random audio glitch
some plops and cracks appears. I could not specifically pinpoint what is the cause. Seems related to either a change of track or volume adjustment. This not repeatable. Aka random. at one point I was wondering if all of this was due to the axign processor not fast enough doing it’s thing.

last: the heat. When saying this amp should sound like a class A, I was not thinking it will go as hot as said class A.
this is winter. house temp is around 20 degree Celsius. After a good hour on a night session the amp is very hot. And I can hear a fan going on for 2 seconds every 5-10 seconds. placing something under to elevate the amp helps. Best trick is to put it vertically on its sides or on its front. Case gets much cooler quickly and fan stays off.
Seems not enough time was spent on cooling system.
it is quite a disappointment when compared to the Sonos that gets barely hot with a passive cooling system.

or the citation amp does not go well with the kind of load my speakers are, and the Sonos is okay.

i checked with Harman customer support and they confirmed the amp should not be used with loads under 4Ohms. Not sur about that as I think manufacturers often stat this to avoid some claim.

i really liked the product on its core purpose: a (very) good sounding device. But there are unfortunately too much drawbacks at the moment.

hope it helps in some way. Really sorry to log in and being mostly negative toward a product. But I think I had to share.
maybe we’ll know more when one of you will do a proper review

thank you all for your participation on this incredibly valuable site

David.

edit: added load chart for the speaker.

 

[Abcdav]

One more thing

the need to use google home to set up the amp and the need to access a menu via IP address that almost looks like a debug mode (in some pages) in order to set up “advanced features » like bass treble level and cross over, feels super chunky.
also you cannot adjust the left-right balance! only available for surrounds speakers if any.

hope they will work on Q.O.L features and improve ease of use.

 

[Max]

Just made an account to share my experience and give you some feedback about this amp.

Welcome and thanks for the feedback !

 

[dualazmak]

https://bits-chips.nl/artikel/axign-chips-at-the-heart-of-harman-kardons-beat/

In the web page, we can find;

“The result is a Class A audio performance at Class D efficiency, size and cost,” summarizes Langezaal.

Does this mean that the "performance" of this new Class-D amp wound be similar or identical to that of a Class-A Hi-Fi amp, and not exceeding the Class-A?

Furthermore, does he believe Class-A is better than usual Class-AB in "pefrormance"? I feel he would think so...

Even though I fully agree with "Calss d keeps improving", apart from "efficiency, size and cost", but in terms of "performance", Hi-Fi Class-A amps would be still a high above "target" for "this kind/rank of" new Calss D amps; his summary brought such impression to me.

 

[Emlin]

In the web page, we can find;

“The result is a Class A audio performance at Class D efficiency, size and cost,” summarizes Langezaal.

Does this mean that the "performance" of this new Class-D amp wound be similar or identical to that of a Class-A Hi-Fi amp, and not exceeding the Class-A?

Furthermore, does he believe Class-A is better than usual Class-AB in "pefrormance"? I feel he would think so...

Even though I fully agree with "Calss d keeps improving", apart from "efficiency, size and cost", but in terms of "performance", Hi-Fi Class-A amps would be still a high above "target" for new Calss D amps; his summary gave such impression for me.

You seem to be very class conscious. Transparent is transparent, and that is all that one needs to be aware of, however it is delivered..

 

[dualazmak]

You seem to be very class conscious. Transparent is transparent, and that is all that one needs to be aware of, however it is delivered..

Yes, I agree with your observation.

Now, I myself also feel a little bit more (or too much?) "class concious" than before since I have been intensively testing and evaluating several Class-A, Class-AB, Class-A(H)B and Class-D amplifiers in my multichannel multi-amplifier project, especially on and after the page-15 of the thread, during the past 6 months.

The SP drivers (i.e. sub-woofers, woofers, Be-squawkers, Be-tweeters and horn super tweeters) directly connected to amplifiers (with no LC-network nor attenuator) are now responding very sensitively to the characteristics of each amplifier. I am just on amplifer exploration to select preferable "Class" and individual amps for each of the five frequency regions of super low (15 - 50 Hz), low (45 - 500 Hz), mid (500 - 6,000 Hz), high (above 6,000 Hz) and super high (above ca. 9,000 Hz).

One of my current major concerns is which would be better (to my ears and brain), Class-A or Class-D, for dedicate drive of highly efficient Be-Tweeters plus horn super tweeters covering high region (above 6,000 Hz), especially in terms of phase perspectives (sometimes said to be "phase rotation"). Even though I cannot understand the engineering details of amplifier design, I learned at many places that the nature of NFB would more or less affect the "phase rotation" in high regions.

If needed, it maybe better to have further discussion on "class concious" on the specific thread.

 

[mhardy6647]

after some times with the Sonos amp i can understand comments saying it is bright. This amp is very lean and lack some bass when listen at low level. I guess this could explain why loudness is on by default.

So -- in the context of this forum -- how can this be? Has Sonos engineered frequency contouring into the front end of this amplifier to add "brightness" (MR or treble boost?) and/or "always on" loudness? I know nothing about this component, so I am genuinely curious.

This question is meant generically; not directed at the poster per se.

 

[boXem]

So -- in the context of this forum -- how can this be? Has Sonos engineered frequency contouring into the front end of this amplifier to add "brightness" (MR or treble boost?) and/or "always on" loudness? I know nothing about this component, so I am genuinely curious.

This question is meant generically; not directed at the poster per se.

Without knowing the guts of the amplifier, I would bet on an old style class D with out of control loop output filter, having a tendency to boost or attenuate the highs pending the speaker. Nothing engineered on purpose.

 

[Abcdav]

So -- in the context of this forum -- how can this be? Has Sonos engineered frequency contouring into the front end of this amplifier to add "brightness" (MR or treble boost?) and/or "always on" loudness? I know nothing about this component, so I am genuinely curious.

This question is meant generically; not directed at the poster per se.

might not be the place to discuss Sonos amp but that is absolutely on me since I mentioned this amp in this thread

<<In the Sonos S2 application for iOS (or android), there is a loudness toggle that is “on”by default.
Worth mentioning that the few frequency charts found on forums for the Sonos amp do not show any treble boost.
As far as I am concerned, playing with treble slider doesn’t change my appreciation>>

back on the citation amp,
beside all the nip ticks I still think that is a very fine sounding amp.
i can confirm that the vertical position should be preferred. After 5 hours listening session (not super loud mind you) , in vertical position amp is just warm and fan stays shut.

anyone can chime in about the load profil of my speaker? Is it that hard for an amplifier? Do you understand why harman doesn’t recommend this matching?
Ironically one of the selling point is that the amplifier is load independent!

 

[pma]

This is the "classD" application that I like. 20 years old photo, 20kHz switching, 300V/600A.

 

[pjug]

Without knowing the guts of the amplifier, I would bet on an old style class D with out of control loop output filter, having a tendency to boost or attenuate the highs pending the speaker. Nothing engineered on purpose.

The Sonos guts is Qualcomm DDFA. These kinds of amps do have deviation from flat at the high end, a shown in Amir's measurement of the Sonos Amp and also Stereophile measurements of NAD DDFA amps. However, someone posted measurements of Sonos vs another amp that show they overlay exactly, so at least with the right speakers there is no brightness problem.

https://en.community.sonos.com/components-228996/amp-freq-response-sonos-vs-peachtree-6822985

 

[Rottmannash]

Does anyone have any experience with this Class D amp?

https://hometheaterhifi.com/reviews.../starke-sound-ad4-320-power-amplifier-review/