Class A vs. AB

[Cheapshot]

I've been looking at amps for a pair of paradigm reference 60's (Max i/p 200W). I plan on running two more speakers off the amp also but havent yet bought them.

I was wondering which kind of amp is better a class A w/ lower o/p rating (50W @ 8 ohms), like mabye somthing along these lines;

http://www.stereophile.com/solidpoweramps/505coda/

or a class AB w/ a higher o/p rating something like this;

http://www.anthemav.com/NewSitev2.0/AnthemProduct/MCASeries/MCASeriesHome.html

 

[j_garcia]

Class A will generally still sound better, IMO. The class A yeilds a bit more depth and a bit more detail. The downside to a class A amp is that they generate a LOT of heat so you need to take into account ventilation for them. My PM7200 is switchable between class A (25w) and AB (95w) and I can tell you there is a noticable difference between the two modes. For normal listening though, I leave it in AB mode. Are you running the 60s alone for music? If so, I'd go class A. If it is part of an HT, I'd stick with a good AB like Anthem.

 

[Cheapshot]

No this is strictly for Audio not HT.

So if you have two amps of the same power rating (A vs. AB) obviously the A is better but is there a point where the wattage on the Class A would be too low to compare w/ an AB. Say your PM7200 (25W) vs. the MCA 50 (180W all channels driven). Would 25W continuous power really sound as good as 180W on an AB?

 

[highfihoney]

class a amp's & class a/b amp's are two entirely different ball game's,class a amp's will not alway's give you the best performance either,amp's are system dependant,unless you have an extremely revealing system the benifit's of running true class a are far out weighed by the drawback's.

class a amp's are far more suceptable to costly repair's & break down's plus their sonic's are greatly affected by the power supply,a well made class a/b amp will give you 90% of the performance of class a without any issues such as recapping the amp,big$$$

i have found that a well made class a/b amp with a decent damping factor & a fast slew rate will perform just as well as class a amp's.

 

[mtrycrafts]

I've been looking at amps for a pair of paradigm reference 60's (Max i/p 200W). I plan on running two more speakers off the amp also but havent yet bought them.

I was wondering which kind of amp is better a class A w/ lower o/p rating (50W @ 8 ohms), like mabye somthing along these lines;

http://www.stereophile.com/solidpoweramps/505coda/

or a class AB w/ a higher o/p rating something like this;

http://www.anthemav.com/NewSitev2.0/AnthemProduct/MCASeries/MCASeriesHome.html

You also have a choice of getting two Behringer A500, bridged mode for $180 each This will give you a lot more power than either of them you listed.

No, audio mythology never stops about the perceived sound. The specs precludes audible differences when operated in their design spaces with any of these amps. But, to be convincing, one needs to do the comparisons level matched, DBT listening protocol.

 

[j_garcia]

No this is strictly for Audio not HT.

So if you have two amps of the same power rating (A vs. AB) obviously the A is better but is there a point where the wattage on the Class A would be too low to compare w/ an AB. Say your PM7200 (25W) vs. the MCA 50 (180W all channels driven). Would 25W continuous power really sound as good as 180W on an AB?

No. The power is clearly less with when in class A mode, so it needs to be turned up a bit and it won't go as loud, as class A is much less efficient. In AB mode, I do get about 80% of the sound quality when in AB without all that heat. The manual says "the amp will get hot, this is normal" and I have plenty of ventilation but I'm still not comfortable with my gear running that hot. I use it mostly just for low level listening and background music, so I don't need it to be in class A the vast majority of the time.

 

[WmAx]

In AB mode, I do get about 80% of the sound quality when in AB without all that heat.

Either (1) this must be a very poor amplifier when operating in AB class mode. [or] (2) the amplifier was designed to alter frequency response or some other parameter on purpose when modes are changed [or] (3) this is an inaccurate observation by use of a non-controlled listening test.

The amplifier should not sound any different except for the difference in output power. Class A, or AB, neither has any distinct inherant sound quality difference.

-Chris

 

[mtrycrafts]

Either (1) this must be a very poor amplifier when operating in AB class mode. [or] (2) the amplifier was designed to alter frequency response or some other parameter on purpose when modes are changed [or] (3) this is an inaccurate observation by use of a non-controlled listening test.

The amplifier should not sound any different except for the difference in output power. Class A, or AB, neither has any distinct inherant sound quality difference.

-Chris

Have you seen this yet? Very interesting research
http://www.axiomaudio.com/distortion.html#

 

[Rip Van Woofer]

Questions about Class A amp topologies come up with some regularity so let me add my $0.02 once again to mtry and WmAx's good points:

The Class A superiority myth has some basis in reality and history. Back in the old days of solid state many Class B amps suffered from inferior sound. The underlying mechanism (which lead to increased and measurable harmonic distortion*) is called "crossover distortion" so called because it involves transistors switching on and off, with the trouble occuring as the signal "crossed over" between transistors. (This is a crude and simplistic explanation but it'll do.)

Anyway, 20-odd years ago engineers figured out how to eliminate the problem. The class AB amp is one good solution. It operates in Class A at low power and slides into Class B at high power. And even in pure Class B they've fixed the crossover distortion problem by various means.

Also: many amps advertised as pure Class A ain't. They're AB, maybe just more "A" than "B". That's marketing (and lax enforcement of truth-in-advertising). Caveat emptor.

So as far as any solid-state amps built, say, after 1985 are concerned: fuhgeddaboutit!

IMHO, I think Class A, B, and AB amps will be obsolete within 10 years as the much more efficient Class D amps are perfected. But that's another thread for another time...

---

*The distortion was especially nasty because it was largely composed of higher-order harmonics which are the worst kind. "Second-order" harmonic distortion is fairly benign and can even sound nice. In fact some people like a fair amount of it. Many tube amps do just that which partly explains their popularity.

 

[Irvrobinson]

You also have a choice of getting two Behringer A500, bridged mode for $180 each This will give you a lot more power than either of them you listed.

No, audio mythology never stops about the perceived sound. The specs precludes audible differences when operated in their design spaces with any of these amps. But, to be convincing, one needs to do the comparisons level matched, DBT listening protocol.

Would you seriously buy that piece of junk? $180 is no bargain for such cheap construction.

Why is it that a certain faction of the audio world thinks that the only valid response to the silliness of audiophiles is to advocate the cheapest crap that the market can produce? Amps with far, far better specs than the Behringer are available, and I would argue its shortcomings would have an excellent chance of being audible with some speakers.

 

[mtrycrafts]

Would you seriously buy that piece of junk? $180 is no bargain for such cheap construction.

Why is it that a certain faction of the audio world thinks that the only valid response to the silliness of audiophiles is to advocate the cheapest crap that the market can produce? Amps with far, far better specs than the Behringer are available, and I would argue its shortcomings would have an excellent chance of being audible with some speakers.

What exactly do you know about that amp? Have you tested it? Is its performance JUNK??? Really??? Or, you just don't like inexpensive components? You can tell us that you don't. Buying expensive is a valid choice, you know.

Oh, its shortcomings will be audible with some speakers??? Which shortcoming??? Please argue all you want, but you'd better have some real evidence in your hand, not speculations, innuendos. Thanks.

Oh, one more. DON'T buy it. Who said you had to.

 

[Irvrobinson]

What exactly do you know about that amp? Have you tested it? Is its performance JUNK??? Really??? Or, you just don't like inexpensive components? You can tell us that you don't. Buying expensive is a valid choice, you know.

Oh, its shortcomings will be audible with some speakers??? Which shortcoming??? Please argue all you want, but you'd better have some real evidence in your hand, not speculations, innuendos. Thanks.

Oh, one more. DON'T buy it. Who said you had to.

I have not "tested" one, meaning with test equipment, but I have seen it and heard it. An acquaintence is a big fan of the Audio Critic and bought one based on the webzine's review, and partially because of this on-going rhetoric that amps are pretty much commodities.

I was basing my junk comment on the mechanical properties of the amp. It is built more cheaply than a typical consumer A/V product, IMO, to be more specific. Unnecessarily so, I think.

As for sounding different, my friend wanted to see how it would sound in my system compared to my, admittedly, very expensive equipment. I was actually curious too, based on the AC review. It took about three minutes to hook it up, because I use spades for speaker connections, and even though I bi-amp both sets of spades fit on the posts. I have very efficient speakers (95+db/watt) and there was a difference in the audible hiss level in the room. No, I couldn't hear it during reasonable music, but you could hear it with the amp just sitting there idling. It would drive me nuts if I bought that product, hence my comment.

(The AC review said the S/N ratio was 99db below full output. Assuming 28db of gain (I've never seen a spec, but this is typical for audio amps) at full power, that means the noise level is probably in the range of 70-72db below 1 watt. Given the efficiency of my speakers I'm guessing I was hearing noise at about -50db. Just guessing. The noise was audible within 6ft of the speakers, inaudible at 10ft.)

Nonetheless, my "junk" comment was mostly based on the mechanical properties of the amp. Anyone that owns, say, a Denon or Sony AV receiver would be disappointed, IMO, if they saw one, no less a snob like me. Of course, I'm not the target market.

 

[WmAx]

I have very efficient speakers (95+db/watt) and there was a difference in the audible hiss level in the room. No, I couldn't hear it during reasonable music, but you could hear it with the amp just sitting there idling. It would drive me nuts if I bought that product, hence my comment.

This is potentially useful information. So, this amplifier is probably not best mated with highly efficient speakers.

Was the hiss still present with nothing connected to the amplifier inputs? Did the hiss at all change when you modified the gain controls on the front panel of the A500?

I also find hiss from hardware to be unacceptable, even when no music is playing.

[/QUOTE]

-Chris

 

[Irvrobinson]

This is potentially useful information. So, this amplifier is probably not best mated with highly efficient speakers.

Was the hiss still present with nothing connected to the amplifier inputs? Did the hiss at all change when you modified the gain controls on the front panel of the A500?

I also find hiss from hardware to be unacceptable, even when no music is playing.

-Chris

I'm sorry, I didn't do extensive testing. I actually didn't think much about it until mtrycrafts brought up the subject. It was just one of those things we did on a whim. If you'd like I can ask my friend to bring his amp back sometime and do another test, if he'll agree to it.

I should mention, in the interest of balanced reporting , that he thinks he got reasonable value from the A500, and says he's going to install it in a cabinet and never look at it again unless it breaks. He agrees the build quality and selection of some parts leaves something to be desired. His speakers are some older B&Ws 804's that I found for him on Audiogon, and they're quite inefficient by comparison, so the hiss is inaudible unless you stand right next to the speakers in his system.

 

[pearsall001]

I can only comment on my own personal experience w/ the A500 amps. I have 2 of them bridged mono running some pretty good speakers. They are a Phil Jones creation - the AAD 2001 monitors. They sound absolutely stunning being powered by the A500 amps. No hiss or anything audible caused by the amps. Maybe you are experiencing a ground loop problem that is causing your noise. As far as specs go, some people get all tongue tied trying to read into them. Use your ears, they are by far the best known device to measure sound. No electronic device even comes close. I have come to the conclusion that this hobby of ours is filled w/ plenty of snake oil salesman, fraud magazines that can't even give a honest review - if it's good say so, if it's not say so & the high priced marketing by these so called hi-end companies that have everyone snookered into believing that there stuff is the best, along w/ the high price that goes with it. After all somebody has to pay for their advertising. Bottom line - if it sounds good - guess what - it is good. I for one believe you don't have to spend a king's ransome on equipment to enjoy good sound. IMO the A500 amps are one of those products. Let's just enjoy the music!!!

 

[Irvrobinson]

I can only comment on my own personal experience w/ the A500 amps. I have 2 of them bridged mono running some pretty good speakers. They are a Phil Jones creation - the AAD 2001 monitors. They sound absolutely stunning being powered by the A500 amps. No hiss or anything audible caused by the amps. Maybe you are experiencing a ground loop problem that is causing your noise. As far as specs go, some people get all tongue tied trying to read into them. Use your ears, they are by far the best known device to measure sound. No electronic device even comes close. I have come to the conclusion that this hobby of ours is filled w/ plenty of snake oil salesman, fraud magazines that can't even give a honest review - if it's good say so, if it's not say so & the high priced marketing by these so called hi-end companies that have everyone snookered into believing that there stuff is the best, along w/ the high price that goes with it. After all somebody has to pay for their advertising. Bottom line - if it sounds good - guess what - it is good. I for one believe you don't have to spend a king's ransome on equipment to enjoy good sound. IMO the A500 amps are one of those products. Let's just enjoy the music!!!

Ground loops cause hum, not hiss. And I *was* using my ears. BTW, I completely disagree that our ears are "by far the best known device to measure sound". That is, I think, just flat out wrong.

 

[WmAx]

Use your ears, they are by far the best known device to measure sound. No electronic device even comes close.

Incorrect.

-Chris

 

[WmAx]

I'm sorry, I didn't do extensive testing. I actually didn't think much about it until mtrycrafts brought up the subject. It was just one of those things we did on a whim. If you'd like I can ask my friend to bring his amp back sometime and do another test, if he'll agree to it.

Thanks. What I would really like to know is if the hiss changes with the gain setting on the A500, and does the hiss reduce in level if you disconnect the amplifier from the pre-amplifier?

-Chris

 

[mtrycrafts]

Use your ears, they are by far the best known device to measure sound. No electronic device even comes close.

I need to disagree with you on this as it is inaccurate, totally. The ears have advantages, identifying sound but that is due to the huge computer it is hooked up to with vast database of past sounds.

As far as detecting new sounds, being fooled, not detecting sound that is in fact present is well know in the audio and acoustics world. If instruments could not do better, we could not investigate hearing thresholds and other characteristics in acoustics.
You may want to think about perceptual coding, why that is even possible???
Your brain masks much of the information presented.
Your brain through the ears cannot detect large levels of noise, totally contrary to what you just praised the ear for.

http://www.axiomaudio.com/distortion.html#

Or, the instruments ability to map the Just noticeable Detection of hearing.

Florentine, Mary, et al 'Level Discrimination as a Function of Level for Tones from .25 to 16khz. Journal of Acoustic Society of America, 81(5) May 1987, pg 1528-1541.

Zwislocki, J and Jordan H. 'On the Relations of Intensity JND's to Loudness and Neural Noise,' Journal of Acoustics Society of America, 79(3), Mar 86, pg 772-780.

Viemeister, Neal F., ' Auditory Intensity Discrimination at High Frequencies in the Presence of Noise,' Science, vol 220, 16 Sep 83, pg 1206-1208.


There are libraries full of data about psychoacoustics, what we can and cannot detect, all recorded with instruments.
No, the ear is very limited in its ability.

 

[mtrycrafts]

.... and partially because of this on-going rhetoric that amps are pretty much commodities.

Perhaps you should explore the possibility to compare amps under DBT, level matched conditions and see if it is still a rhetoric 20+ years of DBT comparison doesn't support what I think you are implying.

I was basing my junk comment on the mechanical properties of the amp. It is built more cheaply than a typical consumer A/V product, IMO, to be more specific. Unnecessarily so, I think.

Maybe, but it is the design that makes the amp and signal processing, not the faceplate's cost, etc. After all, for $180 you will not get the same craftsmanship of an exotic amp. Most here are concerned about $$.

and there was a difference in the audible hiss level in the room. No, I couldn't hear it during reasonable music, but you could hear it with the amp just sitting there idling. It would drive me nuts if I bought that product, hence my comment.

As Chris mentioned, maybe it was the way it was set up?
The spec shows a -72dB (.025%) THD+N at .1watt level at high frequency, 20kHz. much better as frequency goes down. Perhaps they should use a more audible high frequency, like 16kHz?

The noise was audible within 6ft of the speakers, inaudible at 10ft.)

Thanks. I guess the solution is to sit at 10ft+ If I decide to get one for my boombox, I usually sit at 13ft, so the noise will not be an issue. Great news.

Nonetheless, my "junk" comment was mostly based on the mechanical properties of the amp. Anyone that owns, say, a Denon or Sony AV receiver would be disappointed, IMO, if they saw one, no less a snob like me. Of course, I'm not the target market.


I don't see how they would knowing that it is a $180 component. But, if such a component is on display for others, A better, more presentable amp is in order