Clase A, B, AB, C Which of them mean hi-end?

[dvjorge]

If my amplifier is not a clas A design, It means I don't have a hi- end amplifier? Has the amplifier clase design some influence on its sound quality? Is it better a clase A than a clase B or C ? What should I buy to have a really state of the art amplifier? Thanks guys, this is a very important topic to select an amplifier. Please, All explanations are welcome.
Jorge.

[Garrardman]

Jorge,
The class of operation of an amplifier has very little to do with whether it is high end or not - it is all down to the design of whatever circuit it uses and the quality of the components used.
It is true that Class A amplifiers tend to be more expensive and thus percieved as high end because they need heavier cases and better quality metalwork to act as a heatsink for all the heat they produce.
By all means go for Class A if you want to score buzzword bingo points, but if sound quality is what matters to you most, then ignore what is written on the amplifier case and go for the one that your ears like the best!
Adam.

[skeptic]

The class of an amplifier operation has nothing to do with whether or not it's high end. Class C amplifiers are very efficient, have very high distortion and can produce very high power. They are reserved mostly for high power radio transmitters where their distortion components are filtered out and don't matter.

The class of operation of an amplifier has to do with what percentage of each cycle of the input signal, bias current flows. I'm sorry if this gets too technical but unfortunately, this is a highly technical subject. In class A operation, bias current flows all the time through each active amplifying element (a vacuum tube or transistor.) This makes it very inefficient and as a result, most class A amplifiers are low power output units. There are exceptions and most of these are solid state. Extreme measures however must be taken to dissipate heat and they are still very inefficient. Unproven advantages in sound quality are claimed for this particular design and I have a feeling that some manufacturers are now marketing them just to get entry into this niche market because it has become a consumer buzzword.

Class AB amplifiers share the burden of providing power by using pairs of active amplifying devices, each one of the pair drawing bias current and providing output on slightly more than one half of each cycle. How well these approximate halves match up determines how seamless the transition will be. Here's an old engineering tip for making a judgement by ear. Listen to music at a low level with very high efficiency loudspeakers and since most of the signal will be around this transition area, the distortion produced by class AB operation will be most evident. Most design engineers have learned how to successfully eliminate distortion caused by improperly biasing class AB operation. The proof is in the harmonic distortion specifications. BTW, even though class AB amplfiers are much more efficient than class A, they can never be more than 50% efficient. That means that if they produce 100 watts to a load, they must draw at least 200 watts from the wall outlet. Current draw depends on output but even at zero output, they still draw idle current. When properly executed, the state of the art for low distortion, high power, high accuracy, reliable power amplification combines the attributes of power Mosfet transistors, negative feedback, and class AB design. These types of amplifiers can produce hundreds or even thousands of watts of electrical power into anything other than a dead short circuit with practically non measurable noise and distortion, very wide flat frequency response and virtually zero output impedence. This makes them ideally suited for general high fidelity use if you don't know what type of loudspeaker you will buy or may change from time to time. Fine examples in the 60 to 100 watt per channel range are relatively modestly priced and very reliable. They usually show no signs of aging even after decades of use and may just occasionally require some cleaning, tweaking, or replacement of relatively inexpensive parts. At the other extreme is the SET class A amplifier. These low powered amplifiers, generally about 10 watts per channel or less strongly resemble the very first electronic amplifiers ever designed in many ways. They of course have the benefit of more modern parts and occasional novel twists but they are basically the same as those designed in the 1920s. By comparison, their measurements typically indicate low maximum power output, relatively high harmonic distortion, high output impedence (undesirable) and of course, because they are vacuum tube amplfiers they may slowly deteriorate over time. Furthermore, because they have no negative feedback, their operating parameters such as gain are not stable and may vary with changes in input voltage from the power company. A voltage stabalizer transformer or high quality UPS is probably a good idea with these especially if they don't have a well regulated power supply of their own. Despite this, there are a fair number of audiophiles who claim that they are the best sounding amplifiers and power output is quite satisfactory when paired with very efficient loudspeakers. The need for high efficiency loudspeakers is the main limitation in their use.

[cam]

The class of an amplifier operation has nothing to do with whether or not it's high end. Class C amplifiers are very efficient, have very high distortion and can produce very high power. They are reserved mostly for high power radio transmitters where their distortion components are filtered out and don't matter.

The class of operation of an amplifier has to do with what percentage of each cycle of the input signal, bias current flows. I'm sorry if this gets too technical but unfortunately, this is a highly technical subject. In class A operation, bias current flows all the time through each active amplifying element (a vacuum tube or transistor.) This makes it very inefficient and as a result, most class A amplifiers are low power output units. There are exceptions and most of these are solid state. Extreme measures however must be taken to dissipate heat and they are still very inefficient. Unproven advantages in sound quality are claimed for this particular design and I have a feeling that some manufacturers are now marketing them just to get entry into this niche market because it has become a consumer buzzword.

Class AB amplifiers share the burden of providing power by using pairs of active amplifying devices, each one of the pair drawing bias current and providing output on slightly more than one half of each cycle. How well these approximate halves match up determines how seamless the transition will be. Here's an old engineering tip for making a judgement by ear. Listen to music at a low level with very high efficiency loudspeakers and since most of the signal will be around this transition area, the distortion produced by class AB operation will be most evident. Most design engineers have learned how to successfully eliminate distortion caused by improperly biasing class AB operation. The proof is in the harmonic distortion specifications. BTW, even though class AB amplfiers are much more efficient than class A, they can never be more than 50% efficient. That means that if they produce 100 watts to a load, they must draw at least 200 watts from the wall outlet. Current draw depends on output but even at zero output, they still draw idle current. When properly executed, the state of the art for low distortion, high power, high accuracy, reliable power amplification combines the attributes of power Mosfet transistors, negative feedback, and class AB design. These types of amplifiers can produce hundreds or even thousands of watts of electrical power into anything other than a dead short circuit with practically non measurable noise and distortion, very wide flat frequency response and virtually zero output impedence. This makes them ideally suited for general high fidelity use if you don't know what type of loudspeaker you will buy or may change from time to time. Fine examples in the 60 to 100 watt per channel range are relatively modestly priced and very reliable. They usually show no signs of aging even after decades of use and may just occasionally require some cleaning, tweaking, or replacement of relatively inexpensive parts. At the other extreme is the SET class A amplifier. These low powered amplifiers, generally about 10 watts per channel or less strongly resemble the very first electronic amplifiers ever designed in many ways. They of course have the benefit of more modern parts and occasional novel twists but they are basically the same as those designed in the 1920s. By comparison, their measurements typically indicate low maximum power output, relatively high harmonic distortion, high output impedence (undesirable) and of course, because they are vacuum tube amplfiers they may slowly deteriorate over time. Furthermore, because they have no negative feedback, their operating parameters such as gain are not stable and may vary with changes in input voltage from the power company. A voltage stabalizer transformer or high quality UPS is probably a good idea with these especially if they don't have a well regulated power supply of their own. Despite this, there are a fair number of audiophiles who claim that they are the best sounding amplifiers and power output is quite satisfactory when paired with very efficient loudspeakers. The need for high efficiency loudspeakers is the main limitation in their use.

you mine as well explain all you know about class D. I'm certainly interested.

[skeptic]

I know virtually nothing about class D amplifiers. They didn't exist when I went to school. Sometime I think in the mid 1970s as I recall, somebody, maybe Mitsubishi introduced to the market what they called a class D switching amplfiier. In principle, it is possible to emulate or create an equivalent analog signal by switching a DC power supply on and off fast enough at just the right moments with switching transistors. Also in principle, you could make this type of amplifier very efficient and very accurate. Just a guess, but for real info about it, I'm afraid I'm not the one to ask.

[cam]

I know virtually nothing about class D amplifiers. They didn't exist when I went to school. Sometime I think in the mid 1970s as I recall, somebody, maybe Mitsubishi introduced to the market what they called a class D switching amplfiier. In principle, it is possible to emulate or create an equivalent analog signal by switching a DC power supply on and off fast enough at just the right moments with switching transistors. Also in principle, you could make this type of amplifier very efficient and very accurate. Just a guess, but for real info about it, I'm afraid I'm not the one to ask.

I thought for sure you would ramble on for a long time but I guess I left you speechless. Skeptic informd us on classA,B,C designs, Anyone out there that could explain class D. I know class D is usually used in sub designs, but quit frankly I would like to know how and why all there is to know about class D.

[skeptic]

Is that what you call my pearls of wisdom, rambling on? Sheeeeesh, and to think I waste my time trying to edjamakate yoooze guyz.

[cam]

Is that what you call my pearls of wisdom, rambling on? Sheeeeesh, and to think I waste my time trying to edjamakate yoooze guyz.

Wisdom comes with age, You are just not old enough. I'm not saying I'm as old as you or as wise. You have given your limits of wisdom, now it is time for someone wiser, and someone who would like to ramble on about class D.

[Mash]

Class D amps are switching amps and Skeptic is "on". These class D amps are used with (and only with) servo subs because as the servo feedback circuit corrects the cone motion to match the preamp input signal sent to the sub, the servo feedback circuit at the same time effectively cancels out the distortion generated in the super-efficient class D amp. In other words the servo feedback circuit adds the inverse of the class D distortion products into the signal fed to the sub's amp as required to make the the cone reproduce (only) the preamp input signal.

Skep- most speakers will sound little different with good examples of the various desireable amp classes because most speakers have significant inductance (i.e. cone voice coils wound around bobbins and ES have matching/stepup transformers). Capacitance is usually also significant. The Magnepans have "voice coils" that are linear conductors laid in the plane of the membrane like singular wires so they have rather low inductance & capacitance. Class A amps usually sound best on Maggies. I have a Panasonic SA-HE100 (Mosfet) in the kitchen that I will try on Maggies one of these days... the Mosfet output stage has me curious.

[skeptic]

I seem to remember that the Mitsubishi class D amplifier was advertised as a general purpose high fidelity amplifier. I think it was around 150 wpc. Perhaps it didn't live up to its advertising hype.

[skeptic]

"Wisdom comes with age, You are just not old enough."

Remember the 2 million year old man? I'm his father.

[cam]

[QUOTE=Mash]Class D amps are switching amps and Skeptic is "on". These class D amps are used with (and only with) servo subs because as the servo feedback circuit corrects the cone motion to match the preamp input signal sent to the sub, the servo feedback circuit at the same time effectively cancels out the distortion generated in the super-efficient class D amp. In other words the servo feedback circuit adds the inverse of the class D distortion products into the signal fed to the sub's amp as required to make the the cone reproduce (only) the preamp input signal.

Skep- most speakers will sound little different with good examples of the various desireable amp classes because most speakers have significant inductance (i.e. cone voice coils wound around bobbins and ES have matching/stepup transformers). Capacitance is usually also significant. The Magnepans have "voice coils" that are linear conductors laid in the plane of the membrane like singular wires so they have rather low inductance & capacitance. Class A amps usually sound best on Maggies. I have a Panasonic SA-HE100 (Mosfet) in the kitchen that I will try on Maggies one of these days... the Mosfet output stage has me curious.[/QUOT
You say class D amps are used with (and only with) servo subs because as the servo feedback circuit corrects the cone motion to match the preamp input signal sent to the sub. But what about a sub such as the Paradigm pw-2200 v2 400 rms 1500 peak ultra class D and various other non servo class D subs such as B & W has.

[mtrycraft]

I thought for sure you would ramble on for a long time but I guess I left you speechless. Skeptic informd us on classA,B,C designs, Anyone out there that could explain class D. I know class D is usually used in sub designs, but quit frankly I would like to know how and why all there is to know about class D.

How about a google search

http://www.google.com/search?hl=en&i...ss+d+amplifier

[cam]

How about a google search

http://www.google.com/search?hl=en&i...ss+d+amplifier

Stumping the mighty skeptic is WAAAAAY better then doing a google search. And besides I'd rather hear it from this board wether it is true or not.

[skeptic]

There are those things I know nothing about but can pretend to know and fake my way through and then there are those which I never even heard of and so I cannot even pretend.

What is a class "G" amplifier and what makes it different from a class "D" amplifier? I'll bet there are lots of seminars on switching amplifiers and other digital designs which don't even mention analog class A, B, and C or just give them a brief mention. What a strange experience that would be.

[filecat13]

I did a lot of research before settling on amps, and ended up getting some Class H amps. These used PCR800 MOSFET stereo amps were built in the mid 80s by Soundcraftsmen. I eventually found four of them in Cleveland and bought them.

I've also had a couple of H+ amps over the years.

Before anyone asks, my research involved reading, listening, and measuring. I'm not an EE, and I didn't have a clue what phase control relay (PCR) or "crowbar" meant until I read about it. I've never done any theoretical or laboratory experimentation with amps, though I have poked, prodded, measured, and listened to them under controlled circumstances.

For a general look at amp types, go here:

http://www.screensound.gov.au/glossa...r?OpenDocument

Class H is lumped in with Class G. Or here:

http://www.prosoundweb.com/install/tfw/amps.php

If these cursory lists are not enough, there are dozens more. Do a search.

Here's a parenthetical note from the audatious Web site:

[Historical note: Soundcraftsmen is credited with pioneering class H designs with their 1977 Vari-proportional MA5002 power a mplifier.]

[topspeed]

These class D amps are used with (and only with) servo subs

May I humbly submit the following for your perusal:
http://www.psaudio.com/products/hca.asp
http://www.belcantodesign.com/prod_evo2.html
http://www.spectronav.com/
http://www.carverpro.com/2003/products/zramps.html

Class D's are the future of solid state amplification. Consider their advantages:
1) Super efficient (95% in the case of the HCA2) thereby generating little to no heat even at peak levels and consuming no more than a night-lite in standby mode
2) Much smaller in stature as they aren't encumbered with rows and rows of heat sinks
3) Combine many of the best attributes of both tubes and ss amp, when done correctly of course.
4) Completely load invariant regardless of volume. They would love to drive your Tympani's Mash. Throw some Apogee's or Quad ESL's at them while you're at it. No biggie.

PS Audio uses an SDAT proprietary output stage and this article is one of the better explainations of switching amplifiers that I've encountered. The Spectron and Bel Canto both utilize a different design than PSA.
http://psaudio.com/articles/sdat.asp

The Reader's Digest version of Class D or "Switching Amplifiers" as they are now being coined is they work like a movie camera. They essentially switch the power on and off at varying rates depending on the volume required. The more volume, the longer they keep the switch open. Because they are always either on or off (as opposed to Class A where it is always on and the extreme heat generated is wasted energy) they are extremely efficient. Are there bad sounding switching amps? You betcha. Are there fabulous sounding switching amps? Feanor (Bel Canto), myself (PSA), and others here who use the Carver as a home amp seem to think so. FWIW, when I auditioned Albert Von Schweikert's $160,000 VR11's, they were being driven by a Spectron.

This is just the beginning. Listen for yourself.

[mtrycraft]

And besides I'd rather hear it from this board wether it is true or not.

LOL, you are killing me