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Class "D" vs Class "H" amplifiers
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Author:  RLC [ Wed Apr 01, 2009 4:41 am ]
Post subject:  Class "D" vs Class "H" amplifiers
Here is one for the engineers out there.
I noticed that dB technoligies uses class H amplifiers in their powered subs.
Could you explain in laymans terms the difference, pros, cons of each class above?
Author:  mckyj57 [ Wed Apr 01, 2009 5:07 am ]
Post subject:  Re: Class "D" vs Class "H" amplifiers
RLC @ Wed Apr 01, 2009 7:41 am wrote:
Here is one for the engineers out there.
I noticed that dB technoligies uses class H amplifiers in their powered subs.
Could you explain in laymans terms the difference, pros, cons of each class above?

That is hard to do. Each are designs that make amplification more efficient than the old standard class A or class AB amplifiers. A amplifiers are pretty much not used any more, since they have a maximum efficiency of 25%. Class D amplifiers can be as much as 97% efficient.

I won't go into what the differences are technically -- basically class A amps are continuously variable and use only one amplification circuit for the entire signal. Class D (and their kissing cousin Class C, not used these days because of distortion at the crossover) use two amplification sections, one for the positive cycle and one for the negative, switching between the two. This is why they are called switching amplifiers.

Class H is essentially a class D which uses three different power supplies to generate the voltage at varying amplification levels. This improves efficiency and supposedly prevents distortion caused by hysteresis. These amps were not in use yet when I quit studying electronics, so I don't know much more.

I can't really say there are pros and cons. Class H will be more complex, I suppose, but might have a smoother sound. But the differences are not going to be audible in just that way.

Bottom line, I would listen to them and pick.
Author:  Bazza [ Wed Apr 01, 2009 5:25 am ]
Post subject:  Re: Class "D" vs Class "H" amplifiers
I found this info...not mine as I only know enough to be dangerous. :P

EZ-Explanation:

A - Very low distortion, but big, heavy & hot. Always at full power. Tubes amps are Class A. Class A amplifiers are very inefficient and produce lots of heat because there is a large amount of current flowing through the output transistors even with no audio signal.

B - Very efficient, but noisy. Mainly used in things that don't care about fidelity like megaphones & walkie-talkies. Class B amplifiers are more efficient but will have a 'notch' distortion.

AB - A mix of both...the most widely used in modern amps. Class AB amplifiers are moderately efficient (depending on bias current) but notch distortion is eliminated by the idle (bias) current.

C - Broadcast transmitters and motor controls mostly.

D - "Switching Amps". Very efficient. Hi power, lightweight. Good for PA use although purists may disagree. Until recently Class D amplifiers were generally used for non high-fidelity or subwoofer applications.

G - A variation of the Class AB design with improved efficiency.

H - An enhancement of the Class G with even better efficiency.

There are more. E, AB2, I, S and even a Class-Z. It's an alphabet soup.


All in all, I would choose the one that goes to "11". ;)
Author:  karyoker [ Wed Apr 01, 2009 5:51 am ]
Post subject:  Re: Class "D" vs Class "H" amplifiers
Here is an analogy. It is not quite this simple but shows the basics.

Lets say you were lighting a camper trailer with a 12 volt battery and a DC to AC converter. The light bulb used is 100 Watts. Somebody says hey lets pulse it so we are not providing power part of the time and it will take less power. Hey ok!! Next step is putting a sensor on it to regulate the amount of on time to provide the light necessary. During the day the on time will be very short.

Well shucks lets use 3 batteries A six volt, 12 volt and a 24 volt During the day it switches to the 6 volt. Cloudy days the 12 volt and at night the 24 volt. YEA!!
Author:  JD [ Wed Apr 01, 2009 7:20 pm ]
Post subject:  Re: Class "D" vs Class "H" amplifiers
The Class H is similar to the A and B types but the positive and negative output voltage rails are split by intermediate levels. You'd have a high and mid rail and a low and low mid rail. That's at least 4 rails. The losses occur toward the positive and negative peaks as they approach the rail voltages.

The Class D is a completely different animal. The output is a big switch that is pulse width modulated in proportion to the input analog signal level. The output is filtered with a coil and cap network and is applied to the speaker as an analog waveform. It is characterized by less loss, lower heat and higher efficiency with slightly more distortion.

There's Class BD also. Which only means there are two Class D switchers, one with a high rail and one for a low rail that extend the range of the output signal.

I suppose the Class D with 2 positive and 2 negative rails on the output would be a Class HD.
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