can someone please give me the definition of Class A?

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Zoltar
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Re: can someone please give me the definition of Class A?

Post by Zoltar » Fri Feb 11, 2005 10:06 pm

Class C - only half the wave is amlified. This is most efficient. Radio transmitters that transmit in the MegaHertz range use this, otherwise they would be too expensive to operate.

Class B - Push/pull. For transisters, this means one part of the circuit amplifies the positive part of the signal, another amplifies the negative part. There is a small range in the middle (close to zero volts) where the signal is not amplified by either the push or pull parts. This causes some distortion.

Class AB - Same as class B except a diode is added to each part to match the voltage drop required to drive the amp. This reduces the distortion in Class B. Note that the push and pull circuits are different, and might sound a little different. This is also a source of distortion.

With Tubes, Class B circuits are a little different. Tubes saturate differently if they are pushing vs pulling. Electrons actually jump off the screen if the polarities match (I think), but they don't the other way. ( I can't remember exactly, but this leads to peaks being amplified differently than vallys)

Class A - This is all push. The whole signal is shifted up into the positive range before the amp stage, then back down after. This is called a DC offset.

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Re: can someone please give me the definition of Class A?

Post by soundguy » Fri Feb 11, 2005 10:27 pm

I should probably mention thhat Im not trying to downplay the relevance or magic of a well designed class A circuit, not by any stretch. This is all just my reaction to an industry that has taken a specification and turned it into a marketing term which a new generation of young guys is latching onto and filing as "important" wihtout understand the relevancy of its importance. Go ahead an advertise your product as Class A, knock your socks off. Might as well advertise the rest of the shit you sell as Class AB though, in the big scheme, works out to about the same relevancy. No reason for people to be saying "my shit is class A" and then NOT saying "my shit is class AB". The emphasis should be on the sound the box makes, not the mode the circuit is working in. A well designed class A circuit, depending upon how it is biased, can give you a really intensely saturated sounding signal that a class AB circuit is just not going to do. Not all class A circuits do that though. Well designed class A circuits tend to be a little more forward sounding, but this is not always a good thing, not by a long shot. I got a vintech X73i which is their copy of someone elses thing. It runs class A. It also sounds like shit. Whoppee. Not only couldnt they design their own thing, but they couldnt even COPY someone elses thing and make it sound right. So you read the hype, you convince yourself you need Class A, you go buy the thing and now you have a class A pre whch sounds just sorta OK. You have a class A thing, so you are happy, but there are class AB circuits out there that sound a million times better than that box. WHY does it sound bad IMO? No, not because it is running class A, its because of the components the audio is passing through, not how its passing through them. What is the point of being excited about a class A circuit if it uses 3 cent parts and makes a shitty sound come out the speakers? None if you ask me, but for all thhe kids believing the hype and listening to the internet dealers everyone is convinced this shit sounds fantastic. Maybe I have cardboard ears. All I know is that I have access to really good gear and its only ever important if the gear sounds good. Its not ever important if the gear is class A or whatever fucking catch buzz word the people are using to sell their gear.

I have lots of gear that I havent disceted yet and I have no idea wether or not the opamp is running class ab, running class a, or running class a up to a certain level and honestly nor do I really care. What I do care about is how good the boxes sound and continue to use them based on that alone. I have sold class A neve gear because it sounded bad. I replaced it with class ab neve gear which I thought sounded better. Nobody is ever going to give a fuck about what pre I used on any record I do if that record doesnt sound good in the first place. Its THEN that people care. You guys realize that a lot of really TERRIBLE sounding records have been made on class A consoles, right? Dont give a shit about that though, do you? Someone makes some shit like Abbey Road and you are dying to know every litttle detail though. What does this tell you about the real relevancy of the gear. So many more bad sounding records have been made on AMAZING gear than amazing sounding records. Just think about that.

Joel, btw, all the 33609's have class AB output stages. Some are discrete output stages and some use a hybrid opamp with a IC driver, but they are all operating class AB. The 2254 is the only limiter neve made that was class A (unless Im missing one).

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Re: can someone please give me the definition of Class A?

Post by psychicoctopus » Fri Feb 11, 2005 10:48 pm

Zeppelin4Life wrote:Class-D. digital in a sense. but thats all I know..this is also rare.
rare in pro audio likely, but not rare at all in the rest of the world. Class D amplifiers have the highest practical power efficiency, so they are used in new battery powered stuff. Like cell phones, some mp3 players, etc... i.e. lots of modern portable audio thingies.
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Re: can someone please give me the definition of Class A?

Post by Zeppelin4Life » Fri Feb 11, 2005 11:07 pm

psychicoctopus wrote:
Zeppelin4Life wrote:Class-D. digital in a sense. but thats all I know..this is also rare.
rare in pro audio likely, but not rare at all in the rest of the world. Class D amplifiers have the highest practical power efficiency, so they are used in new battery powered stuff. Like cell phones, some mp3 players, etc... i.e. lots of modern portable audio thingies.
yeah class-D I associate w/ cell phones..dont know much about it, but yeah rare in pro audio. never seen one. it would be cool if someone could point one out..but makes no difference to me
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Re: can someone please give me the definition of Class A?

Post by joelpatterson » Sat Feb 12, 2005 7:38 am

Well maybe ONE problem is that while specifications are specific and quotable, intangibles like "sound good" are always going to sound like subjective judgements. And while there's a specificity and an authority to details and circuits and sine waves, there's a vagueness and suspect quality to vague-sounding promotional terms like "sound good" which may be a lie, where there is no lie in describing what is Class A and what isn't.

So what everyone needs is an unbiased, honest capacity to evaluate gear and performance that is uncolored by its technical reality.

You can quote me on that... although not if you haven't paid for your ad in TapeOp!
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Re: can someone please give me the definition of Class A?

Post by joel hamilton » Sat Feb 12, 2005 7:56 am

"Joel, btw, all the 33609's have class AB output stages. Some are discrete output stages and some use a hybrid opamp with a IC driver, but they are all operating class AB. The 2254 is the only limiter neve made that was class A (unless Im missing one). "

Thats right. I knew there was one that was class A and one was A/B. I thought it was the 33609 rev's, but you are right, it is the 2254/33609....

Thank you for clearing that up. I hate perpetuating myth.. There is plenty of that going around without me...

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Re: can someone please give me the definition of Class A?

Post by versuviusx » Sat Feb 12, 2005 10:08 am

well guys glad we cleared all that up. i definitley learned something. thanks for taking the time to voice your opinions and facts.

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Re: can someone please give me the definition of Class A?

Post by MD » Sat Feb 12, 2005 2:58 pm

Zeppelin4Life wrote: yeah class-D I associate w/ cell phones..dont know much about it, but yeah rare in pro audio. never seen one. it would be cool if someone could point one out..but makes no difference to me
Image

I have one of these. It is small and loud. Sounds good too. It's class D:
http://www.acousticimg.com/products/prod_clarus.html

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Re: can someone please give me the definition of Class A?

Post by rolandk » Sat Feb 12, 2005 5:13 pm

Digital amp technology is advancing rapidly and starting to filter into the mainstream. In car audio there are a shitload of 1KW+ Class D subwoofer amplifiers out there for ~$400.00. These amps are noisy as hell and don't do high freqs but they are loud and cheap.

A company called Tripath has a proprietary digital output section IC that runs full range freqs they call Class T. The company I work for (Phoenix Gold car audio and Carver Pro) has class D and T car amps and Carver has this line of Class T amps: http://www.carverpro.com/zramps.html and they are audiophile quality according to the audio community. I believe Yamaha has a new line of bass amps using this technology too.
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Re: can someone please give me the definition of Class A?

Post by hulahalau » Sun Feb 13, 2005 8:42 pm

Within Class A, there is a distinction between Class A1 and Class A2. At this point, i can't remember the precise definition of each. Maybe Soundguy can help.

The theory of Class A that most amp designers are trying to achieve is to avoid cross-over distortions of various types. The most insidious is the "sticking" that occurs when the solid state device refuses to turn on or off cleanly at the zero point. This is, as I understand, not a problem in tube Class A/B push pull, and this is often attributed as the main reason why tube push pull stuff sounds better than SS. However, there are other distortion mechanisms at work, even in Class A ubes, which are attributable to the non-perfect nature of any real world device. So a poorly designed Class A amp using a poorly performing (for the specific audio application) tube will sound worse then a well-designed SS amp.

I will say this for my own tastes, given that every device/amp is inperfect, and given that most people such as i are limited in budget, one often is looking for the "best" set of compromises that meet the speccific need of the user. For me, well-dsigned and constructed tube stuff tends to offer what I want.

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Re: can someone please give me the definition of Class A?

Post by soundguy » Sun Feb 13, 2005 10:23 pm

hulahalau wrote:Within Class A, there is a distinction between Class A1 and Class A2. At this point, i can't remember the precise definition of each. Maybe Soundguy can help.
no clue. I only know this shit because I wanted a cool guitar sound and started to build shit, I dont actually know what the hell Im doing.

that's reassuring, huh?

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Re: can someone please give me the definition of Class A?

Post by nacho459 » Mon Feb 14, 2005 1:25 am

I heard once that the only reason Neve made A/B modules instead of class A was due to heat issues. Basicly Class A amps are always running and get just as hot on 1 as they do on 11.

As far as guitar amps I tend to believe Class A stuff sounds purer sounding (not necessarily better) although poorly designed Class A is worse then well designed push pull.

I think a great example of a class A amp is the good old single knob Fender Champ. I still think that is one of the greatest sounding amp circuits ever designed. Almost any high wattage guitar amp is push pull. The signal goes from the preamp, tone stack, etc. through a phase inverter that does exactly what it sounds like then the +/- signals go through the power tubes and then are recombined by the output transformer.

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Re: can someone please give me the definition of Class A?

Post by The Real MC » Mon Feb 14, 2005 10:51 am

Here's a good "layman's" explanation of the different classes of amplifers.

http://en.wikipedia.org/wiki/Electronic_amplifier

I only recently learned of class H amplifers, that's the design that Bob Carver used.

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