Class A/B versus Class H amplifiers? what is the better choice? - Home Theater Forum and Systems -

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post #1 of 5 Old 02-07-10, 07:13 AM Thread Starter
Join Date: Jun 2009
Location: Edinburgh
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Class A/B versus Class H amplifiers? what is the better choice?

Hi all,

I was wondering what the benefits are of different amplifier topologies?

I recently borrowed a W-Audio DA-1300 power amp, and found it's sound quality a little rough compared to home audio amplifiers.

I am not sure what class of amplification the W-Audio is, its 2x420w 8Ω, 2x 650w 4Ω, 1300w mono bridged 8Ω.

The W-Audio is 200 the Behringer EP4000 is 300

The EP4000 is class H? The EP2000 is class A/B

So would the class A/B give better sound quality if used for the main channels or better fuller bass with less overall power?

I am now wondering if I should buy a W-Audio or Behringer, or get a more expensive better quality power amp, or indeed if there are any power amps with built in rumble/HP filters for 25Hz and under? (Yamaha do a series of power amps with a 25Hz filter)

Last edited by Parts; 02-07-10 at 07:47 AM.
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post #2 of 5 Old 02-07-10, 07:41 AM
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Re: Class A/B versus Class H amplifiers? what is the better choice?

Class H only refers to the power supply section - the output side of the EP4000 is still AB.
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post #3 of 5 Old 02-09-10, 09:03 AM
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Re: Class A/B versus Class H amplifiers? what is the better choice?

I was gonna write something but then I was fact checking on wiki and noticed it provides a much more detailed explanation:

but for the most part: the problem... when you are turning a transistor on or off you are wasting a lot of energy because you end up dissipating the energy not going to the load when the state of the transistor is changing (the speaker in this case) as heat (very oversimplified explanation)

The solution: High-efficiency amplifiers work on two primary principles: pulse-width modulation, or power supply rail tracking

Pulse-width modulation: since it is switching the state of an amplifier that is the main inefficiency, you can turn the transistor on/off between no power and full power many times (14-15,000 times/sec for 'car' sub amplifiers, 250,000+ times/sec for full range (20khz+ output) applications) The more power the amplifier has to output, the longer the transistor is on (with a shorter 'off time') and vice versa, this method can achieve 85-90% efficiency

Rail voltage regulation: for the most part these are class AB amplifiers that have their rail voltage regulated to be only a few volts over what is needed for a given output level, so say you *could* output 25 volts peak with a given amplifier, but your signal is only using around 10 volts, rail voltage regulated amplifiers would 'turn down' the voltage given to the amplifier to 'dim' so there may be 12 volts available when 10 volts is being output (so you have a 2 volt difference between what you are outputting and what your peak is rather than 15 volts, so there is less wasted energy) remember that the tracking (in better designs) is tracking the actual signal (very quickly) so in the end it is quite efficient

hopefully that gives you an idea how these things work
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post #4 of 5 Old 02-09-10, 01:36 PM Thread Starter
Join Date: Jun 2009
Location: Edinburgh
Posts: 74
Re: Class A/B versus Class H amplifiers? what is the better choice?

Sadly it does not tell me if a cheaper amp will sound better?

In my opinion although the Classe Audio power amp has less power, it's bass performance/quality is better, so it would seem many watts may help with volume but not bass slam and impact?

The W-Audio certainly seems a little rough and with a little less drive than I expected for a 600w (4Ω) per channel amp so could current have something to do with it?

The Classe is a 200w (4Ω) per channel hi fi amp.

I know you get class A class A/B and class B output amplifiers, so what sort of class are the output stages of some of these PA amps and what should I be looking at if I want quality as well as quantity?

And how do you know what class the output is? I am thinking I would like a decent power amp to drive a pair of subs in mono parallel, but also four similar models from that range to do the 7 main channels, with two identical speakers running centre mono parallel.

At the moment it is too expensive, but the Yamaha P7000s power amp for bass with it's 25Hz HP filter sounds good for the sub? But what sort of sound quality could I expect with four Yamaha P3500s for the mains?
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post #5 of 5 Old 02-09-10, 02:41 PM
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Re: Class A/B versus Class H amplifiers? what is the better choice?

If you read the manual or tech sheet for the amplifier it should tell you the output topology... however that is mainly going to affect the *efficiency* that the amp will have however more efficient means less heat generation... so the circuits will theoretically be less likely to burn out from heat related stress...

you mentioned that one amplifier sounded 'rough'... can you try to explain what you are trying to convey here? the only things I can think of is that one amplifier may 1)have a different dc filter implimented (most amplifiers have some sort of DC protection, a high pass filter probably between 1-15 hz to keep DC from the outputs), if both amplifiers have different values for this filter they may have a different very low end sound... 2)one amplifier may have been running out of power (thus increased distortion levels)... 3) (this is unlikely) if one amplifier had a very bad damping factor (damping factor is directly related to the output impedance of the amplifier) compared to the other one, you may have heard a difference in how 'tight' the transients were... for example, a kick drum would not punch so much as it would thud given a very low damping factor... for a well designed amp this should not be a huge issue though, the ear cannot hear the effects of damping factor (supposedly/word on the street) unless it is under ~25 (talking about the damping factor of the entire system... damping factor is *supposed* to be measured with a 8 ohm load directly attached to the amplifier output terminals (to get what the manufacturers list), speaker wire resistance and the impedance of the speaker can be used to find the actual damping factor that I was referring to.

you mentioned that the 600 watt amplifier seemed to have less improvement than you expected: remember,'doubling the watts' gives you 3 db more spl, since you are going from 200 to 600 watts, 10*log(600/200) = 4.77 db more volume with the extra 400 watts headroom: buying a more powerful amplifier should be (IMO) for the purpose of having headroom for peaks/transients, not necessarily to make things that much louder, to double the * perceived volume* (make things twice as loud) you would need to jump from 200 watts to 2000 watts (a factor of 10)

I have no experience with yamaha amplifiers so I cannot really say regarding that. I would say look at the specifications... thd at rated power, rms power, slew rate (has more impact on high frequency response), and damping factor: along with knowledge of the dc protections on the amp, should help in predicting an amplifiers performance/comparing between models and brands

Addition: depending on the speakers you were comparing amplifiers on, you may have been hearing power compression if the 600 watt amplifier was pushing the speakers near the maximum output they can produce... so you could have been hearing the speakers running out of steam more than a difference between the amps: it would have been prudent to use a db meter and a sine tone at a certain frequency to match the output levels on the amps for a good comparison
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