Can someone define 'Class D' for me?
Registered User
Joined: Oct 2002
Posts: 7,584
Likes: 1
From: Baton Rouge, LA
Thread Starter
Registered User
Joined: Jun 2001
Posts: 1,659
Likes: 0
From: Brooklyn
Honorary Member
Joined: May 2001
Posts: 2,121
Likes: 3
From: Indian Land SC
You can check out this site, scroll down to #99 on the right hand side. It's fairly technical, so I'll add my own ramblings.
Class D means digital. Digital in this case really means digital, not like 99% of manufacturer's that use the word "digital" when they are looking for a word that will make their product appear to be better or different to the average consumer who has no idea what "digital" means. When given a choice of "digital" or "analog", people always choose "digital" because they think they are getting something special. Horse hockey.
For your use, the only advantage of a digital amp is that they generally use less power from your battery to produce the same output power to the speakers, and because of that they should run cooler, and may be packaged in a smaller box. In general they have higher distortion ratings and are more prone to failure (as shown by history) than analog or linear amps (most car amps are Class AB).
Don't buy a Class D amp just because it's digital. If it does something you need and can't get elsewhere, go ahead, but be sure of what you are getting. I bought a blaupunkt "plastic amp" for my subwoofer because I had very limited space and a sub is not as critical for distortion specs, and it has been fine. Blaupunkt calls it "Class X", which is pure marketing BS. It's really a Class D amp, but Class D amps have gotten some bad reps for reliability that they wanted to dissassociate themselves from that. Didn't help, I think they have pulled them from the market bacause of reliability issues.
Modifry's rant on "Digital" -
Digital means that something has been "digitized" - converted into a series of specific, discrete, individual parts. People think that digital means high-tech. This is not necessarily true. Digital, in many cases, means low tech. The only time digital is high tech is when we try to use digital methods to simulate an analog function.
Example - the communications industry, communicating over long distances. First there was smoke signals - guess what, they're DIGITAL!!!. Each signal was separate and distinct from the rest. There was no such thing as 1.2 smoke puffs, it's either one smoke puff or none. No in-between. Are smoke signals high tech?
Then came the telegraph - DIGITAL AGAIN!!!. The message was made up of individual dots and dashes - you'll never see a dash-and-a-half on a telegraph system. Eventually came the telephone - the first analog communication system. There are no distinct levels of tone or volume - the phone can carry unlimited variations in volume and frequency that can't be handled by a simple digital system.
That's the difference between digital and analog - digital has distinct levels with no allowable values in-between. Your speedometer is digital - it will never read 65.5 mph. Your temperature gauge is also digital. It has 6 distinct levels that can be shown, you'll never see 3 1/2 bars. An "analog" or "linear" temperature gauge or speedometer that has a needle and can indicate an unlimited number of values. You may not be able to tell the difference between 65.5 and 65.4 mph on your mother's '66 Buick, but the needle is capable of indicating it. That's analog.
Today, everybody has "digital mobile phones". These are high-tech, because they use digital methods to produce an analog signal (your voice). Your voice is broken up into thousands of tiny discrete voltage levels, transmitted through the system and re-assembled at the other end. But there is one more step after the re-assembley. The digital "voice" signal must be converted back to analog, otherwise it would sound like crap. We only use digital because it's a more efficient means to transport the signal. It still has to be analog on both ends for us to use it.
OK, now that I've gone off the deep end, back to Class D amps.
The ideal amplifier takes an input signal that does not have enough power to drive a speaker, and increases the voltage and current to a level that can drive a speaker without affecting the frequency of the signal. A regular analog amplifier is capable of handling the complete audio range of volume and frequency, with no distinct "steps" in the voltage output. Let's say we have an amplifier that increases the voltage by 10 times. If the input changes by .1 volts, the output would change by 1 volt. If the input changes by .0000001 volts, the output changes by .000001 volts (count the zeros, I think I did that right). No matter how small the change in the input voltage, an analog amp will create a corresponding change in the output.
A digital amp cannot do this. It must divide the input signal into distinct levels, so there will be a point where if the input change is so small it is not enough to "jump" to the next level, the output won't change. Just like your speedometer that won't respond to your speed change from 65.0 to 65.5, the digital amp has similar limitations. Very small changes in input voltage or frequency cannot be reproduced at the output. This creates distortion. How much distortion is dependent on how the amplifier is designed - the number of levels used and the methods used to convert the digital signal back to analog. Remember, the speakers are analog. No speaker on the planet is digital, no matter what the marketing department says.
A properly designed Class D amp can sound great, but just like analog amps, it all depends on the design.
.
Class D means digital. Digital in this case really means digital, not like 99% of manufacturer's that use the word "digital" when they are looking for a word that will make their product appear to be better or different to the average consumer who has no idea what "digital" means. When given a choice of "digital" or "analog", people always choose "digital" because they think they are getting something special. Horse hockey.
For your use, the only advantage of a digital amp is that they generally use less power from your battery to produce the same output power to the speakers, and because of that they should run cooler, and may be packaged in a smaller box. In general they have higher distortion ratings and are more prone to failure (as shown by history) than analog or linear amps (most car amps are Class AB).
Don't buy a Class D amp just because it's digital. If it does something you need and can't get elsewhere, go ahead, but be sure of what you are getting. I bought a blaupunkt "plastic amp" for my subwoofer because I had very limited space and a sub is not as critical for distortion specs, and it has been fine. Blaupunkt calls it "Class X", which is pure marketing BS. It's really a Class D amp, but Class D amps have gotten some bad reps for reliability that they wanted to dissassociate themselves from that. Didn't help, I think they have pulled them from the market bacause of reliability issues.
Modifry's rant on "Digital" -
Digital means that something has been "digitized" - converted into a series of specific, discrete, individual parts. People think that digital means high-tech. This is not necessarily true. Digital, in many cases, means low tech. The only time digital is high tech is when we try to use digital methods to simulate an analog function.
Example - the communications industry, communicating over long distances. First there was smoke signals - guess what, they're DIGITAL!!!. Each signal was separate and distinct from the rest. There was no such thing as 1.2 smoke puffs, it's either one smoke puff or none. No in-between. Are smoke signals high tech?
Then came the telegraph - DIGITAL AGAIN!!!. The message was made up of individual dots and dashes - you'll never see a dash-and-a-half on a telegraph system. Eventually came the telephone - the first analog communication system. There are no distinct levels of tone or volume - the phone can carry unlimited variations in volume and frequency that can't be handled by a simple digital system.
That's the difference between digital and analog - digital has distinct levels with no allowable values in-between. Your speedometer is digital - it will never read 65.5 mph. Your temperature gauge is also digital. It has 6 distinct levels that can be shown, you'll never see 3 1/2 bars. An "analog" or "linear" temperature gauge or speedometer that has a needle and can indicate an unlimited number of values. You may not be able to tell the difference between 65.5 and 65.4 mph on your mother's '66 Buick, but the needle is capable of indicating it. That's analog.
Today, everybody has "digital mobile phones". These are high-tech, because they use digital methods to produce an analog signal (your voice). Your voice is broken up into thousands of tiny discrete voltage levels, transmitted through the system and re-assembled at the other end. But there is one more step after the re-assembley. The digital "voice" signal must be converted back to analog, otherwise it would sound like crap. We only use digital because it's a more efficient means to transport the signal. It still has to be analog on both ends for us to use it.
OK, now that I've gone off the deep end, back to Class D amps.
The ideal amplifier takes an input signal that does not have enough power to drive a speaker, and increases the voltage and current to a level that can drive a speaker without affecting the frequency of the signal. A regular analog amplifier is capable of handling the complete audio range of volume and frequency, with no distinct "steps" in the voltage output. Let's say we have an amplifier that increases the voltage by 10 times. If the input changes by .1 volts, the output would change by 1 volt. If the input changes by .0000001 volts, the output changes by .000001 volts (count the zeros, I think I did that right). No matter how small the change in the input voltage, an analog amp will create a corresponding change in the output.
A digital amp cannot do this. It must divide the input signal into distinct levels, so there will be a point where if the input change is so small it is not enough to "jump" to the next level, the output won't change. Just like your speedometer that won't respond to your speed change from 65.0 to 65.5, the digital amp has similar limitations. Very small changes in input voltage or frequency cannot be reproduced at the output. This creates distortion. How much distortion is dependent on how the amplifier is designed - the number of levels used and the methods used to convert the digital signal back to analog. Remember, the speakers are analog. No speaker on the planet is digital, no matter what the marketing department says.
A properly designed Class D amp can sound great, but just like analog amps, it all depends on the design.
.
Registered User
Joined: Oct 2002
Posts: 7,584
Likes: 1
From: Baton Rouge, LA
good writeup there modifry... given the choice, i'd stay away from class D and class T (essentially class D amps, but using a gimicky style of error correction to compensate for distortion issues) amps. about the only way i'd consider using a class D amp would be for a subwoofer application...
oh, and beat you to the linkage... lol.
actually, i went by his shop and bought his CD a couple weeks ago. he's located out here in the BR area. pretty interesting guy...
Thread
Thread Starter
Forum
Replies
Last Post
Triple-H
Southern Ontario S2000 Owners
12
Dec 22, 2003 04:07 AM