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Topic: How do class D ampliers perform compared to AB? (Read 14814 times) previous topic - next topic
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How do class D ampliers perform compared to AB?

I am looking to buy an amplifier and would like to hear about class AB ampliers. How does the design compare to class AB?
How does class D amps perform when driving speakers: reliability, sound quality? How do they perform with dips in impedance or running 4 ohm speakers? I am trying to figure out if the technology has improved enough to consider this over class AB. I grew up with AB, so lean that way, but am willing to try class D if there is an advantage. Will be using this mainly for music listening.

Re: How do class D ampliers perform compared to AB?

Reply #2 –
I no nothing about this technology. I am just trying to learn something. I think you are a troublemaker

Re: How do class D ampliers perform compared to AB?

Reply #3 –
Class D amps use a high-frequency duty-cycle preload, making this a digital amplifier using PWM to output the actual audio signal. These amps are virtually everywhere these days. They're used to drive the speaker in phones, TVs, small kitchen radios, radio alarm clocks, etc. etc. They're also often used in virtually all Bluetooth headsets, Bluetooth speakers, and for pretty much all headphone socket amps, like the ones you find on phones, etc.

Class AB amps is a compromise between a class A, which is inefficient like crazy, and class B, which scales better in terms of efficiency. AB stays in the 'A' region, when the signal is quiet, so the inefficiency doesn't hurt the amp as much. When the signal is very high in amplitude, it is in the 'B' region, where the push-pull bridge takes effect, and technically introduces distortion on the crossover point. I practice this isn't audible, because that distortion is maske by the high amplitude of lobes to either side of the zero-crossing point.

Class D amps don't have any of those issues, but the main drawback is they don't scale infinitely high. I.e. they're great for small and medium amps, but if you need to amplify speakers for a live gig, it'd be difficult to use class D amps for the output stage. They're almost always used in some form of pre-amplification, though. What impedance and How many Ohms are accepted ad the inputs depends on the output stage of either amp. This is not something inherent to an amp class.

When it comes to buying advice, I'd simply either test them myself, or see if you can find customer reviews. Don't necessarily go by amplifier class, but by output power, and reviews. Also, if you absolutely don't like the amp, just return it.
Either class doesn't imply higher or lower quality. You can have AB (or A, or B) amps of crappy quality, and superb Class D amps.
There are entire industries geared towards people believeing things like that.

Re: How do class D ampliers perform compared to AB?

Reply #4 –
Well,

From my own experience there are class D amps that are very good in terms of quality.
I have a NAD C388. It has a Hypex amplifier stage from the Netherlands (Where I come from). From my opinion this is a very good amplifier, but that is just subjective.

Re: How do class D ampliers perform compared to AB?

Reply #5 –
IME, it's easier to get an inexpensive Class AB amp that specs really good but it will tend to be larger, heavier and less efficient.

Of the switching-type amplifiers, Hypex looked really good to me, but I was looking for something more compact and less expensive.

I finally settled upon an amplifier based on Texas Instrument's TPA3116D2 which seemed to offer a decent amount of power at well below 1% THD, with frequency response and noise figures also looking pretty good.

This is the amplifier that I purchased:
http://www.tpdz.net/en/products/vx3/index.htm

I like it: It seems nicely made, I can only hear the faintest amount of noise via headphones, and I can place an AM radio right on top of the housing and only hear a modest amount of noise. The same could not be said for amps based on Tripath's TA2022: I could not tame that EMI beast.

Re: How do class D ampliers perform compared to AB?

Reply #6 –
Quote from: 4season on
I like it: It seems nicely made, I can only hear the faintest amount of noise via headphones, and I can place an AM radio right on top of the housing and only hear a modest amount of noise. The same could not be said for amps based on Tripath's TA2022: I could not tame that EMI beast.
Well, this says more something about the AM radio, than the amp. RF shielding for Audio equipment is rather easy, compared to doing RF shielding for things like radar equipment and test equipment, which I'm more familiar with. An AM receiver which spews it's IF and output signal everywhere is kinda bothersome like that. If you really want to make a stress test: get a magnetron from a microwave oven and build a directional horn antenna, and then point that thing for a second or so into the running amp. if the am survives (which it should, given decent RF shielding), you're good. Noise will be audible anyhow, because power will be induced into all output cables after the amp, as well...

However, it's kinda fun shooting cheap boomboxes with a magnetron.

Re: How do class D ampliers perform compared to AB?

Reply #7 –
Quote from: polemon on
Quote from: 4season on
I like it: It seems nicely made, I can only hear the faintest amount of noise via headphones, and I can place an AM radio right on top of the housing and only hear a modest amount of noise. The same could not be said for amps based on Tripath's TA2022: I could not tame that EMI beast.
Well, this says more something about the AM radio, than the amp. RF shielding for Audio equipment is rather easy, compared to doing RF shielding for things like radar equipment and test equipment, which I'm more familiar with. An AM receiver which spews it's IF and output signal everywhere is kinda bothersome like that. If you really want to make a stress test: get a magnetron from a microwave oven and build a directional horn antenna, and then point that thing for a second or so into the running amp. if the am survives (which it should, given decent RF shielding), you're good. Noise will be audible anyhow, because power will be induced into all output cables after the amp, as well...

However, it's kinda fun shooting cheap boomboxes with a magnetron.
He probably meant the other way around - the AM radio picked up little noise from the amp.

Re: How do class D ampliers perform compared to AB?

Reply #8 –
Quote from: pdq on
He probably meant the other way around - the AM radio picked up little noise from the amp.
Oh, OK. Haven't thought of it that way. Using an RTL SDR for that sort of tests works actually pretty well.

Re: How do class D ampliers perform compared to AB?

Reply #9 –
Quote
Posted by polemon - 26 December, 2017, 04:48:46 PM

Class D amps don't have any of those issues, but the main drawback is they don't scale infinitely high. I.e. they're great for small and medium amps, but if   you need to amplify speakers for a live gig, it'd be difficult to use class D amps for the output stage
.

What size would they be good for; I was thinking of around 100 watts with class AB. The class D being more efficient, what would be comparable in power with class D?

What things should I be considering when buying a class D amplifier?

In my search of the NET I have seen a number of different design of Class D. What would be the better designs and models that would be good to look at?
Need imputs for computer and Blu-ray player, may add a tuner. 2 channel. Headphone amp would be good. Don't need wireless. Hoping to get something good, up to $600

I saw this article: 'Why We'll Soon Be Living In A Class D World'
http://audiophilereview.com/cd-dac-digital/why-well-soon-be-living-in-a-class-d-world.html
It talks about transistor technology called Gallium Nitride (GaN) that it says will replace silicon MOSFET Class D systems. I am wondering if this is real or hype or if it matters.

Re: How do class D ampliers perform compared to AB?

Reply #11 –
Quote from: JFS on
Quote
Posted by polemon - 26 December, 2017, 04:48:46 PM

Class D amps don't have any of those issues, but the main drawback is they don't scale infinitely high. I.e. they're great for small and medium amps, but if  you need to amplify speakers for a live gig, it'd be difficult to use class D amps for the output stage
.

What size would they be good for; I was thinking of around 100 watts with class AB. The class D being more efficient, what would be comparable in power with class D?
Well, like I said in my first post, class D amps are good for pretty much everything. In fact, class AB is more of a niche field at this point. Pretty much anything that makes sound, a class D amp is used to drive whatever transducer.

The power consumption scales with signals. Comparing AB to D is difficult, because there are several designs and several different grades of parts used. Like I said in my first post, there are cruddy AB amps and really good D amps, and you should go by reviews and tests. 100W (I'm assuming RMS) is well withing class D realm. Lots of car amps are available that have these specs, etc.
In fact car amps are a good example for a class D amp application with a higher power rating.

Quote from: JFS on
What things should I be considering when buying a class D amplifier?

In my search of the NET I have seen a number of different design of Class D. What would be the better designs and models that would be good to look at?
Need imputs for computer and Blu-ray player, may add a tuner. 2 channel. Headphone amp would be good. Don't need wireless. Hoping to get something good, up to $600

I saw this article: 'Why We'll Soon Be Living In A Class D World'
http://audiophilereview.com/cd-dac-digital/why-well-soon-be-living-in-a-class-d-world.html
It talks about transistor technology called Gallium Nitride (GaN) that it says will replace silicon MOSFET Class D systems. I am wondering if this is real or hype or if it matters.
Well, here's the thing: Don't read audiophile magazines and webzines, when you're looking for a product. When you're looking at the performance figures, try to get behind the actual signal path and electronic functions of designs like that. I suggest reading about the actual electronics engineering behind amp designs like that. What models are good? Well, again, you should go by reviews and tests, as there is no gold standard.

The article you linked is a little strange in that amplifiers where signals actually matter, i.e. RF input stages and communication systems, etc. actually provide test figures. The fact that these transistor are made with a substrate of GaN is just one of a great many range of substrates in PN-junctions, be it diodes, transistors, or other silicon dyes. Take a look at a dye shot of a CPU of the last 30 years and you see what I mean.

All of the sources you listed, are digital, except for the FM tuner (or perhaps DAB+ tuner?). From what you explained you're looking at an amp for a living room, or similar. So if all sources are digital anyhow, why not use an amp with digital inputs, and then simply send the data to the amp via HDMI or S/PDIF, or whatever it wants? A decent amp surely has a decent DAC for reconstruction inside the amp, rather than sending the analog signal to the amp from various sources. Some amps can be attached to a computer either via USB and acting like an ASIO interface. Often these amps also have a Bt receiver and can be remote controlled via an app. Many recent amps both have several digital and analog inputs, so even if you want to attach a classical FM tuner you'll be able to do that.

Re: How do class D ampliers perform compared to AB?

Reply #12 –
Quote from: JFS on
I am looking to buy an amplifier and would like to hear about class AB ampliers. How does the design compare to class AB?
How does class D amps perform when driving speakers: reliability, sound quality?

For Switchmode or class D amplifiers, reliability seems to be as good as anything.

I know of no reliable listening tests suggesting that sound quality of the cleanest switchmode amps is necessarily any different than classs AB amps or straight wire.

Quote
How do they perform with dips in impedance or running 4 ohm speakers?

Again I know of no issues.

This is not to say that every Class D amp and/or every class AB amp sound identical. As always, amplfiiers can fall prey to betging
being worn out or damaged, or poorly designed or built.

Quote
I am trying to figure out if the technology has improved enough to consider this over class AB. I grew up with AB, so lean that way, but am willing to try class D if there is an advantage. Will be using this mainly for music listening.

At this time Class D usually needs to bring some other benefit to the table such as efficiency or small size to be favored.

Measured performance tends toward having a bit more distortion, but not necessarily more audible distortion.

Re: How do class D ampliers perform compared to AB?

Reply #13 –
Quote
Need imputs for computer and Blu-ray player, may add a tuner. 2 channel. Headphone amp would be good. Don't need wireless. Hoping to get something good, up to $600
I'd look for a home theater receiver (AKA AVR).   It will most-likely be class D, but they may not tell you...  They may simply publish the specs.   Most (all?) AVRs can be configured for 2-channel stereo if you don't want surround.   These things are mass-produced, mass-distributed and sold competitively, giving you a LOT more bang-per-buck compared to a separate amplifier.

Re: How do class D ampliers perform compared to AB?

Reply #14 –
I'm sorry if my questions came across as trolling. I never meant them to cause a problem. Maybe I read too many articles on the Internet; that is why I was asking questions.

 

Re: How do class D ampliers perform compared to AB?

Reply #15 –
Quote from: DVDdoug on
Quote
Need imputs for computer and Blu-ray player, may add a tuner. 2 channel. Headphone amp would be good. Don't need wireless. Hoping to get something good, up to $600
I'd look for a home theater receiver (AKA AVR).  It will most-likely be class D, but they may not tell you...  They may simply publish the specs.  Most (all?) AVRs can be configured for 2-channel stereo if you don't want surround.  These things are mass-produced, mass-distributed and sold competitively, giving you a LOT more bang-per-buck compared to a separate amplifier.
Do you have any recommendations in looking for an AV receiver: how much to spend to get a decent one, or features that would be good to consider? All I know little.

Re: How do class D ampliers perform compared to AB?

Reply #16 –
Quote
Do you have any recommendations in looking for an AV receiver: how much to spend to get a decent one, or features that would be good to consider? All I know little.
As far a sound quality almost anything should be acceptable.  (With modern electronics it's cheap & easy to make a good-sounding amplifier, and "watts" are getting cheaper, probably due to class-D amplifiers.)

If you pay more you might get more power, more inputs, more features and better "build quality", etc.

I bought a fairly low-end one for about $300 USD.   I think mine is rated for about 80W per channel (more than enough for me in my living room, and the subwoofers have their own amplifier).     Even my cheap one has some kind of self-calibration and it came with a calibration microphone, but after running it I didn't notice any difference in frequency response and the documentation is sparse so I'm not sure if it's adjusting the EQ, or simply balancing the surround speakers.   And of course, they all have remote control and they all can decode any of the DVD/Blu-Ray audio formats (via HDMI).


Re: How do class D ampliers perform compared to AB?

Reply #17 –
Quote from: JFS on
I'm sorry if my questions came across as trolling. I never meant them to cause a problem. Maybe I read too many articles on the Internet; that is why I was asking questions.

Don't worry- you asked a fairly common question- and the article you linked had some good comments. Class D is pretty well taking over and any manufacturer of traditional solid state has to be worried if they are not jumping in with both feet.