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whats the difference?

1350 Views 8 Replies 5 Participants Last post by  Dr. Isotope
what is the difference between class AB amps and class D amps?
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Class A/B amps use the "traditional" method of power delivery, in which an analog controller varies the amp's output voltage up and down to match the peaks and transients of the music being reproduced. The basic problem with this is that it limits this class of amps to around 50% efficiency, as the output stages are active all the time. So a good amount (actually half of it) is turned into heat-- hence the big heatsinks on AB amps.

Class D, sometimes referred to as digital, uses a PWM power output stage-- which is sometimes a digital switch, and explains the "digital" name. The PWM operates as an 0/1 switch: the power is either on, or off. This allows the amp to operate with as much as 90% efficiency. The better the output stage-- meaning, the more switching cycles it can produce per second, the more "lifelike" the music will seem.

Some purists claim that the Class D amps never sound as good as traditional A/B amps, but as we all know, perception is reality-- and I think Class Ds sound pretty damn good. They have serious advantages: smaller cases, lower power requirements, more flexible mounting options, because the amps produce less heat, and of course: more watts per dollar.

JBL and Alpine both make great Class Ds-- that are quite affordable. My Alpine MRV-F545 produces 125w RMS into each of 4 channels, with a peak amp draw of less than 50A... the whole amp can be run off of 8ga, and mounted in whatever cramped location you like, as they make so little heat. I'm something of a class D convert.
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Very excellent explanation Doc:)

I do however disagree on the SQ of A/B versus D class amps.

When you get into the higher end amps and have the matching high end source signal you start finding some very serious differences in the quality of the music being reproduced, even on sub amps.

I have used $900 Class D full range amps and still went back to A/B for the sonic improvement on my subs. I have tried the same 270 watt per channel D amps on seperates, still just not satisfied.

Then again, this was on a system with $7k seperates, outboard 20 bit ladder DAC with 20 volt outputs, studio grade and upgraded rack mount processors with 18 volts signals through them(trimed the input down a bit to 18v to prevent clipping)all balanced lines except input to the amps, etc, etc.

For the average joe system, D class may be all you need and if you are happy, that is all that really matters:)

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We now live in an era dominated by the mp3, satellite radio, and other forms of compressed digital audio... and as the output will only be as good as the source, the market for ultra high-end audiophile stuff is dwindling to an even smaller market share than it had before. How many people actually own SACD, or have a quality turntable? Compared to how many people own DAPs or satellite radio receivers...

...which is why I didn't think to make the clarification for the true audiophiles. I was talking to the other 99.5% of listeners out there.
Besides, you're a car audio guy. You know the painful reality, that making a great sounding setup in a car costs worlds more than making an awesome sounding setup in a living room. Most car audio guys (especially beginners), just want loud with the boom. Class D will give both of those, and respectable clarity to boot.

But I totally understand where you're coming from. My wallet is just much happier remaining an Average Joe.
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Class D amps are good for your subwoofers, they bring out the best bass and distortion is little to none.

AB amps are good for componets and interior speakers, since they give out a better sq quality. SPL you want Class D for your car a class d can range from 200 - 1,000 dollars. Mine cost about 500.00 but it puts out an amazing bass sound.

Car audio can be as cheap as 600.00 or as much as 10,000 dollars. On average my customers have about 2,000 dollars invested in their system. It's an expensive hobby but can be a fun one.
I knew there was more to the story on your part, why I said certain things, to get you to bring that out as well:)

I never use satelite, MP3, FM, etc, just not good enough for me, sometimes I wish my ears were not so spoiled, life would be simpler or at least less costly.

BUT, always a but, or is that butt, lol! I am going to be totally honest and going against the grain in what I will say next but first let me say, this has taken years to learn and from some of the best grand masters of the world in high end car audio. We can acutally accomplish the unthinkable and even surpass most super high end home audio in a vehicle. Even with the best techniques available there is no way to deal with road noise fully so when moving it is hard to have the same results unless just cranking it up really loud, something I love to do but my ears do not for long:(

True story:

My son that just turned 18 has heard some of the finest car audio installs ever done, one was mine(that opinion was shared by some of the finest ears in the world including a major symphony conductor)

Last January we were at CES, we only listened to a couple of installs as most are just show crap and sound horrible, I can take one quick look and see if it is worth listening to.

We went to all the rooms at Alexis Park, where most of the high end home audio companies set up in their suites some very very costly gear, including $10-20k amps, $10-50k speakers, etc.

My son was very disapointed and frankly I had not bothered listening to much in the high end home arena for many years. System after system just did nothing for us, I was astonished at the way they sounded. Finally we got to hear a really nice set of electrostats but now forget the brand, they were playing them far to loud and the distortion was painful when it occured, asked them to turn it down a tad and then it was very fine to listen to but I know I had heard much better.

My son wanted to leave but I told him we had one more, saved the best for last, to listen to. We took a break, went to our truck and turned on our current "budget" system, $2k retail in parts(the install for the era I competed was still there, just lower cost and fewer pieces of gear but carefully selected of course) One of our favorite audiophile CDs was popped in and within 10 seconds my son said this with quite an astonished look on his face.

"Dad, our system sounds alot better that all those we just heard, with the exception of the stats, once turned down they were very nice but I still like this better"

I agreed, now on to the best I saved for last, Doc Edgars Edgarhorns, the massive yet very cost effective Titans and the huge sub system that is they finest subwoofer I have ever heard. The price for all three is $13k, alot of money but far less than anything I could stand to even own from another manf.

We walked in and Doc gave me a very nice greeting, "Rick, great to see you here, this must be your son Richard:)
" Then we listened to a few tracks, you can crank these up to live listening levels with just no strain on your ears in the least, so real they are scary, I could use every adjective ever written and still not fully explain how these things sound, simply in a league totally of their own and better than any car system as well by a long margin.

Doc gave us the plans and we built a smaller set of his designs for now, later we will own the Titans and sub to go with it, need alot bigger room for them than we currently have.

By the way, the Titans are simply huge, kind of crazy looking with a huge tactrix mid horn, and superby effcient, they run them on a 3 watt per channel amp and only really need 1/8th watt to get as loud as you could ever need, I have heard them on 1/2 watt and it was deffening yet totally clean and articulate.

All that said, you can acheive amazing results in a vehicle if you know what to do and what gear will give the best bang for the buck, our comp system we are building now(last one was $20k in gear) will be around $6k for the drivers, amps, etc, at retail which we never pay. It will be around 98% as good as the $20k system though which is saying it will be incredible.

The most important part of car audio is install, proper electrical support, proper sound deadening, proper speaker selection and placement(exceptionally critical), a must is to have alot of tuning capability, excellent source unit(most are pitifull) and alot of time learning to tune.

I have had the most succesfull studio drummer in the world(probably one of the top three drummers to ever live) he is a mulitmillionair and made it all from the hundreds of albums he has appeared on, listen to the best recorded drum track ever done. Jim Keltner Improve, simply amazing recording and playing. This particular drummer really go into it and air drummed(as much as he could more around in the confines of a Tacoma) the whole track, obviously he knew it by heart. Once it was done he slowly turned my way and said "unbelievable, it felt exactly like I was playing this live, right now!"

That was the best compliment I have ever had in car audio:)

All that said, give me $2k, 100 or so hours, I can build a system that will blow away anything just about anybody has ever heard;) Not bragging in the least, this is not something I created, just something I have learned from the grand masters, all I did was put in the effort to study, build, rebuild, rebuild again, compete, learn, then have it tuned by one of the finest set of ears in the US and one from Asia as well. I can now tune very close but the finest details I just cannot get and once they are done it blows away my tuning by a landslide yet I have beaten world champs with my tuning, twice!

(I did not become a world champ though, should have, politics got in the way:(

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some people are picky about they way they want their setup to sound so they use class a/b for subs instead of D

but the other 99.99% of the people involved in car audio dont care
It all comes down to what you want to hear. I want clarity so I get some good hish and mids but I mostly want hard pounding bass so I get Class D amps and some good subwoofers. SPL is what I like. Others what to feel like they are actual listening to the band live, for that my set up would fail. So it really all just comes down to what you want to hear.

I would say the average joe just looks ats the wattage and the casing if they like that then they buy, me I look at actual specs and classes then I buy. and so do most car audio guys.

Get what makes you happy and what sounds good to you, your the one that has to listen to it and pay for it.
Originally posted by LaVaism@Jun 12 2005, 07:49 AM
Get what makes you happy and what sounds good to you, your the one that has to listen to it and pay for it.
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