What's the difference between Class A/B and D amps in the SS world?

[KentTeffeteller]

That RFI is something I've been warned about. Evidently one rather sacrifices radio function as a trade-off for having better sound in the pre-recorded function (USB Drive). Most HD posts on the subject have echoed the sentiment of some amps being worse than others. Supposedly the 'Stinger' amp is one of the best for NOT causing the radio to be worthless. Of the 5 amps I listed up in Post #14, the Stinger is the only one that has received any 'favorable' commentary regarding this RFI problem. As such, it may end up being the selection I make. However, I've had REALLY good results with JL stuff in the past...... going WAY back into early auto-audio history. There's also a Kicker amp that's in the running, and it too has history with me and past systems from years ago. I know both Kicker and JL have been around for a LONG time.....and I know nothing about Stinger, mmats, or Hertz (or the others). So....tough decision. Fortunately, I've got you guys to help guide me.

Is there any way to effectively shield the amp's RFI from being so invasive? Also, is this an 'emission' type RFI coming right out of the amp itself, or is this conducted on the power lines? One comment on the HD forum was to keep the amp as far away from the FM antenna lead as possible. If it's an emission RFI and making it's way into the antenna lead, what about doing something 'old school' like wrapping the antenna wire in tin foil......or something creative like that? I presume wrapping the amp would be an invitation for an thermal failure of some kind.

That RFI is not just affecting radio reception either. It's also injecting noise into gain stages, and another thing to cause hum issues. And affect sound quality thusly. A lot of SMPS units are not very well designed nor filtered against this junk.

 

[KentTeffeteller]

Only if they use a switching power supply. My PS Audio S300 does not.

It really depends.....

PS Audio also tends to build their gear without shortcuts, for it's topology, it is well built and executed.

 

[merlynski]

Having ridden many miles on 2 wheels, and many ears on music, I don't care for a sound system on my motorcyles. YMMV
For a motorcycle Class D is a better 'fit' by size, weight and power usage, IMHO, but here is a lightly technical explanation:
https://www.audioholics.com/audio-amplifier/amplifier-classes
Keep your knees in the breeze

EDIT: FWIW, depending on which model Harley you may be able to get a higher output stator and regulator for your scooter.

 

[guest139]

It really depends on execution. There is no ALWAYS in audio.

I have been impressed with the PS Audio S300 Amp. I just compared it to a recently repaired Denon POA-2200 and the Denon was veiled and tubby compared to the PS Audio. It was a real eye opener.

The original post was referring to car amplifiers. I’ve always had aftermarket audio components in my vehicles. From my experience I have yet to hear a good class D amplifier. The exception being class D subwoofer amplifiers which I do currently use an Alpine MRP-M350 monoblock amp with a 24dB/octave slope crossover. I can blast bass heavy music for hours on it and it will barely get warm. On the other hand I had a 4 channel class D Alpine amp powering the main speakers and it didn’t take long before I sold it because I just didn’t like the harshness. It doesn’t compare at all to my old school Alpine class A/B amp. I also use an Alpine CDA-9815 head unit which is 60Wx4 class D and even that one sounds harsh using the head unit’s built in amp. I have an older Alpine class A/B head unit that is clearly superior in sound quality. I also had a Yamaha RX-V371 5.1 surround sound receiver which I don’t even know what class it is but to my ears it sounded like a class D. I got rid of in favor of an older Yamaha DSP-A3090. Has it just been a coincidence that everything I’ve owned that is class D doesn’t sound as good as the class A/B stuff I’ve owned?

 

[FinalVinyl]

Class D sounds terrible for home audio

 

[Pio1980]

Without getting too technical, can anyone give me a rather nut-shell explanation of the difference between the Class A/B and Class D amps, and any benefits / detriments there-of? I'm looking at installing some upgrades to my Motorcycle's audio system, and I've been told that the Class D stuff is the way to go. I presume there's a reason for this recommendation, but I didn't get one. So, before I bite the bullet and buy the amp I'm going to use, I thought I'd do a bit more research on the subject. Obviously being a motorcycle, 'size' is an issue. Also there's a relatively limited supply of current available as well. I'm not sure what the total output of the Harley Davidson Charging system is.....but I've got to believe it's less than that of a typical automobile. Fortunately for me I have only a 2-speaker system, so I'll be running only one amp into some upgraded speakers using the factory head unit and a line adapter to connect the head to the amp. I'm told I'll also need a 'Flash' of the bike's head unit in order to compensate for some factory EQ settings that are recommended to be changed. But, I'm considering the addition of a 9-band EQ unit as well. As that's not a big current hog, I'm not too worried about powering it. But, back to the amps; if I can better understand the 'why?' of going with the Class D vs A/B, then I can probably pick a better amp for the bike. Any help is appreciated. Tom D.

To a direct practical answer;
Recent cool running class 'D' amps are sonically "clean", powerful, and efficient, meaning that you get the noise cutting intelligible sound levels required and have more electrical power reserve available for other accessories. The one thing to keep in mind is to ask about any issues with radio reception with the installation of the amp of interest.

 

[Pio1980]

To a direct practical answer, recent class 'D' amps are sonically "clean", powerful, and efficient, meaning that you get the noise cutting intelligible sound levels required and have more electrical power reserve available for other accessories. The one thing to keep in mind is to ask about any issues with radio reception with the installation of the amp of interest.

One websearch result:
https://www.hdforums.com/forum/tour...fix-for-fm-radio-loss-with-a-class-d-amp.html

 

[Ken Freeman]

Before I started into a different industry, I actually designed a handful of switching power supplies for DC outputs like PC power supplies (over a 12 year period), and RFI is indeed a problem for the designer. Cable-borne noise can also be a problem on input cables (aka "mains") and the output cables. A lot of research in the field of Electromagnetic Compatibility (EMC) has enabled designers to make products a lot quieter. EMC is a fancy term for knowing how much noise is being pumped out, and how much damaging or irritating effect it is having and how to bring the situation into an amicable and affordable balance. The research results guide the engineer to suppress the noise output and protect the (let's say) audio system from interference so that interference will not be objectionable or even detectable. BTW, preventing interference of AM radio can be a lot harder than for FM radio.

I also designed a few power drivers to control electric motors for small and medium applications in automobiles. The motor drivers for various car parts are technically no different from switching power supplies in other parts of industry, aerospace, and defense. The all have to pass requirements on interference, that may or not be related to "switching power supply shall not mess up my airy highs." The groups I worked in were able solve these problems for our products, regardless how stringent the requirements. I have not been in this branch of electronics for over 20 years, but everything I've read about Class D and others, is that the same concerns that create noise in tanks, space vehicles, the International Space Station and engine controls and throttle controllers, are inherent in the technology used in the audio industry.

If it's known that say, a QSC amp does not cause significant noise, hash, AM and FM interference, and does not make your computerized GPS navi/clock to go on the fritz (much worse is possible with RFI and conducted emissions), and less professional models do show listening problems, then the QSC is better-engineered in some way, and that should be a point in its favor. My experience with audio stores is that I will rarely find anyone I can discuss this with, but ... YMMV says a man with faith in humanity. Maybe we can all convince QWC to come to the home audio marketplace.

Sorry for all the technobabble, but we engineers are not in the weeds on this matter, but if product specifications do not imply the hashiness shall not interfere with airy highs and provide a requirement that can be measured, we will not be able to apply all this great research and make amplifiers with airy highs and don't heat, and don't need new circuit boards every 6 months. If the Ford Electronics group had sent products with those problems to be installed into new cars, heads would have rolled and jobs lost.

What new class D or other types of switching amplifiers do not sound questionable, overheat, have excessive fan noise, and do not sell for $10k/100 watts? Specifics are desired!