Class D FAQ

[anphex]

Hey guys, wanted to report back.
Reminder: I was wary of class d amos because of a subjective disappointing experience with an high end 2,5k class d amp and tried everything to dodge class d until I saw the Hypex NC400 kits.

Now they've arrived, are sucessfully built (of first try, yay), and wired. No electrical or sound issues whatsever, building them was a little weird but easy in the end.
I am kind of speechless. It's the best I've ever heard! Although that statement might not mean much with the 4 amps I compared so far. I was anxious about having aggressive sound and sharp highs again. The loudness eq (Dynamic EQ) of my Denon 6400 AVR paired with the old 2,5k class d am tended to extremely push highs above lets say 8 khz. Also some instruments like the sax in Anette Askvik - Liberty would hurt. Over all, the sound was aggressive, sadly.

The two NC400 monoblocks sound clean and balanced - even soft compared to the other class d amp. No complaints so far on my part. So yeah, thank you Hypex NC400 and ASR for restoring my faith in class d amps . But seriously, for this price a dual mono block setup at this level of performance is just insane.

Edit: After listening for a while the channel separation feels much wider. Dunno if this is euphoria placebo or due to the mono block setup.

 

[Koeitje]

Problem is most amplifiers specs (and ASR) ranks them by THD+N (SINAD) in 1 kHz, while everyone complaining about class D is because of harsh treble. That's why, IMO, it is very important to check the amplifier's power versus THD+N in 4 ohms especially the 6.67 kHz curve, exactly where sibilance is.

Or just buy NCore or Purifi, which have this perfected.

Yep, this is why I will always avoid ICEpower. Frequency versus distortion graphs at different output levels are really needed for class D reviews.

 

[DHT 845]

Class D sucks!

 

[snickers]

Hey guys, wanted to report back.
Reminder: I was wary of class d amos because of a subjective disappointing experience with an high end 2,5k class d amp and tried everything to dodge class d until I saw the Hypex NC400 kits.

Now they've arrived, are sucessfully built (of first try, yay), and wired. No electrical or sound issues whatsever, building them was a little weird but easy in the end.
I am kind of speechless. It's the best I've ever heard! Although that statement might not mean much with the 4 amps I compared so far. I was anxious about having aggressive sound and sharp highs again. The loudness eq (Dynamic EQ) of my Denon 6400 AVR paired with the old 2,5k class d am tended to extremely push highs above lets say 8 khz. Also some instruments like the sax in Anette Askvik - Liberty would hurt. Over all, the sound was aggressive, sadly.

The two NC400 monoblocks sound clean and balanced - even soft compared to the other class d amp. No complaints so far on my part. So yeah, thank you Hypex NC400 and ASR for restoring my faith in class d amps . But seriously, for this price a dual mono block setup at this level of performance is just insane.

Edit: After listening for a while the channel separation feels much wider. Dunno if this is euphoria placebo or due to the mono block setup.

Hey Anphex, nice to hear that you finally found the right solution for you. I'm also looking since a longer time to give a support to my AVR in the form of some Class-D amp's due do the much lover heat generated.

I would be really interested which ones were the other Class-D amp's which couldn't satisfy you, and maybe a short info why.

It's really not easy. I'm readying so much about different Class-D amp's and you can find for every one of them good and bad reviews.
Actually I'm looking a bit for TPA3255, Icepower and Ncore.

Would really appreciate some infos from you and wish you happy listening

 

[Koeitje]

Hey Anphex, nice to hear that you finally found the right solution for you. I'm also looking since a longer time to give a support to my AVR in the form of some Class-D amp's due do the much lover heat generated.

I would be really interested which ones were the other Class-D amp's which couldn't satisfy you, and maybe a short info why.

It's really not easy. I'm readying so much about different Class-D amp's and you can find for every one of them good and bad reviews.
Actually I'm looking a bit for TPA3255, Icepower and Ncore.

Would really appreciate some infos from you and wish you happy listening

He had a Nubert NuPower D. Don't know what kind of design that is. Looking at your options I'd say its like this: TPA3255 if you want a cheap solutions or NCore if you want an amplifier that really doesn't have any issues to worry about. I'd avoid ICEpower because of the increased distortion at 6.66khz (don't know how it is at higher frequencies, the data sheets don't show that....).

 

[EB1000]

Tbh people who intentionally buy Class A or Class A/B amps in 2021 are the anti-maskers of the audio world.

They measure worse (at the same price), they cost more (for the same wattage) and they consume more energy.

I'm a proud anti-masker and I'll take class-d over any other class, anytime.

 

[Matias]

Hey Anphex, nice to hear that you finally found the right solution for you. I'm also looking since a longer time to give a support to my AVR in the form of some Class-D amp's due do the much lover heat generated.

I would be really interested which ones were the other Class-D amp's which couldn't satisfy you, and maybe a short info why.

It's really not easy. I'm readying so much about different Class-D amp's and you can find for every one of them good and bad reviews.
Actually I'm looking a bit for TPA3255, Icepower and Ncore.

Would really appreciate some infos from you and wish you happy listening

I suggest you take a good look at the offerings from Buckeye amps here in ASR:
https://www.audiosciencereview.com/...amplifier-builder-line-up-announcement.16835/

 

[Matias]

He had a Nubert NuPower D. Don't know what kind of design that is. Looking at your options I'd say its like this: TPA3255 if you want a cheap solutions or NCore if you want an amplifier that really doesn't have any issues to worry about. I'd avoid ICEpower because of the increased distortion at 6.66khz (don't know how it is at higher frequencies, the data sheets don't show that....).

They usually show 6.67 kHz because the 2 main harmonics still fall inside the hearing range 20 Hz to 20 kHz. But 6.67 kHz is right there in the sibilance range, so low distortion in that curve means no harshness in the sibilance.

To evaluate even higher frequency distortion look at the 18+19 kHz dual tone IMD. But these are, imo, less audible and significant.

 

[anphex]

Well yeah, I had the Nubert NuPower D for a short while. I am hesitating to bad mouth this product because over all I hold Nubert high regard because the speakers are really really good for their price and their support and policy is super pro costumer. They even let me return the NuPower D despite being two weeks above the normal return policy. The design is propietary as it seems, made up from scratch and added the largest 3kw Hypex SMPS. It boasts about 900 Watt RMS at 4 Ohm with the claim that you don't have do worry about powering any speaker anymore. It's no secret that this was the main focus. Other specs read good as well. But when I tested it real life there was this small issue with very sharp highs that I didn't have with Hypex, Denon or Emotiva. TBH I didn't notice this really before I upgraded my speakers from 3 way to 4 way of the same Nubert speaker Line. Maybe it's just a small fix on their side or an oversight? I would be glad if they'd to a refresh of this amp because everything else was absolutely nice.

 

[snickers]

Thx so much guys for your fast answers. Manly I'm looking for a cheaper Class-D amp with 4 channels to help out my AVR. I really like the sound of my AVR would like, that he has only to power my 3 fronts and an additional power amp for my Surr. + Back-Surrounds.

I think in this price region it's more a decision between the TPA3255 and IcePower.
One good thing about the Ice amp's is, that they are "complete" module's. Meaning no extra PS needed and less connections means also less options for mistakes.

Would love to see some 4 channel finished amp's with TPA3255 or IcePower, but strangely never found some of them.
The Ncore has everything what I need and want, but for me it's a bit too pricey "only" for the surrounds. For the mains it would be something else, as there I would consider a higher budget.

 

[Matias]

Thx so much guys for your fast answers. Manly I'm looking for a cheaper Class-D amp with 4 channels to help out my AVR. I really like the sound of my AVR would like, that he has only to power my 3 fronts and an additional power amp for my Surr. + Back-Surrounds.

I think in this price region it's more a decision between the TPA3255 and IcePower.
One good thing about the Ice amp's is, that they are "complete" module's. Meaning no extra PS needed and less connections means also less options for mistakes.

Would love to see some 4 channel finished amp's with TPA3255 or IcePower, but strangely never found some of them.
The Ncore has everything what I need and want, but for me it's a bit too pricey "only" for the surrounds. For the mains it would be something else, as there I would consider a higher budget.

You can mix modules inside a build. For example, I chose 4 x 500W in 4 ohms for the front trio (2 x NC502MP modules) and for the surrounds "only" 2 x 250W in 4 ohms (1 x NC252MP module).
Or you can choose 3 x 250W in 4 ohms for the front trio (VTV for example has it for 860 usd) and use the AVR for surrounds.

 

[Rottmannash]

Hey Anphex, nice to hear that you finally found the right solution for you. I'm also looking since a longer time to give a support to my AVR in the form of some Class-D amp's due do the much lover heat generated.

I would be really interested which ones were the other Class-D amp's which couldn't satisfy you, and maybe a short info why.

It's really not easy. I'm readying so much about different Class-D amp's and you can find for every one of them good and bad reviews.
Actually I'm looking a bit for TPA3255, Icepower and Ncore.

Would really appreciate some infos from you and wish you happy listening

Can't imagine you've heard negative reviews on any Purifi based amps.

 

[Jim Matthews]

Can't imagine you've heard negative reviews on any Purifi based amps.

Complaints are buried in the 200 - 500 kHz bandwidth.

 

[snickers]

No not really. My only point in avoiding a bit the Ncores and Purifi's is, that I'm looking "just" for an amp for my surrounds. And wherever I look, the price reaches always at least 1000 or more for 4 channels of them. For my main channels I would spend this if needed, but for the surrounds I'm looking for a cheaper alternative.

 

[anphex]

Then how about an simple AVR? Prior to the Hypex revelation I was running my whole system on the Denon H6400X AVR amps and the sound was surprisingly good, even at high levels. I still use and will use it for my surrounds. Looking at the reviews the 4700 or even 3700 should be enough.

 

[Davide]

Sorry folks, I have a question about class D.
Is their modulator comparable in type to modern Sigma Delta DAC chips?
Because I was wondering if it was possible to build a unique device that through the current modulator of the DAC would drive the power switch, thus eliminating a lot of critical steps ..

 

[boXem]

Sorry folks, I have a question about class D.
Is their modulator comparable in type to modern Sigma Delta DAC chips?
Because I was wondering if it was possible to build a unique device that through the current modulator of the DAC would drive the power switch, thus eliminating a lot of critical steps ..

Switching speeds are not the same at all.
But there are class D amplifiers that directly convert the PCM into PWM, among them the (in)famous FDAs, the Axign chip, ...
Issue 1 is that in opposition to the instinctive belief, the conversion PCM to PWM is not linear. So instead of simplifying, it is adding one level of complexity
Issue 2 (the main one) is that the power stage is a complete mess of noise and distortion. So feedback is needed. Which is far easier to do in the analog domain than in the digital domain.
So trying to bypass the digital to analog conversion makes the process even more complicated.

 

[Davide]

Switching speeds are not the same at all.
But there are class D amplifiers that directly convert the PCM into PWM, among them the (in)famous FDAs, the Axign chip, ...
Issue 1 is that in opposition to the instinctive belief, the conversion PCM to PWM is not linear. So instead of simplifying, it is adding one level of complexity
Issue 2 (the main one) is that the power stage is a complete mess of noise and distortion. So feedback is needed. Which is far easier to do in the analog domain than in the digital domain.
So trying to bypass the digital to analog conversion makes the process even more complicated.

Okay, thanks for the clarification.
I actually understand...
But is the same also for the DSD?

 

[pma]

I assume it should be possible to decode DSD directly by using a LPF.

 

[boXem]

Okay, thanks for the clarification.
I actually understand...
But is the same also for the DSD?

Yes

I assume it should be possible to decode DSD directly by using a LPF.

You also need to add a power stage that will distort not very nicely.
B. Putzeys toyed with the idea of a power DAC taking DSD as input and without feedback. He ended with something like this:

Source: A true One-Bit Power D/A Converter