What's the Deal with Pure Class A?

Early B.

I've heard (and read) stuff about Class A amps being superior to virtually all other kinds of amps. For those of us who aren't technically inclined, what's the deal in layman's terms?

What I really like to know is for those of you who own or have owned pure Class A amps, what is your opinion of them? Also, what are the disadvantages (aside from the high price tag)?

Thanks.

BlueMDPicker

Basically, a Class A amplifier is operational through 360 degrees of input wave form cycle.

Here's what our old friend Rod has to say:

http://sound.westhost.com/class-a.htm

Joey_V

Brad,

Pure class A basically means that the amp is running at FULL potential all the time. There are no variabilities in the voltage or current as there is with Class AB in which the current and voltage rail of the amp is dictated (yes, DICTATED) by the signal that it is receiving from the preamp/source. In full Class A, there is less distortion and you get the FULL sound of the amplification topology of said manufacturer.

I personally think that Class A is the way to go as it exposes exactly what the amp manufacturer has designed the sound reproduction to be, to a "T".

Bad part, as Sean mentioned, in order for the amp to run at Class A, it needs to run at maximum all the time, meaning so much of the energy it is grabbing from the outlet will be released as unused (sonically) energy in the form of HEAT.

Hence, I got the Plinius. My Plinius has a switch in the front that allows me to choose between Class A or Class AB operation. I normally have the Plinius set on Class AB, but when I listen critically, I go full Class A.

And the difference in sound is tremendously pleasing to my ears. Just better everything.

Joey

Early B.

Thanks for the responses, fellas. I like the idea of the switch on the Plinius.

Early B.

Here's another read -- Pass Labs offers a great explanation of its design philosphy and Class A. It's a bit too technical for me, but some of guys may enjoy reading it.

http://www.passlabs.com/downloads/articles/seclassa.pdf

heiney9

I think a good compromise is going with an amp that is heavily biased towards class A. It's still a class AB amp but good ones will run in class A for up to 20-30 watts and unless you are listening at very high levels this is usaually sufficient. I will also throw in that a very well designed class AB amp cam be just as sonically pleasing at a pure class A amp and it won't have all the disadvantanges covered by others in this thread.

The advent of power Mosfets has really allowed for more class A operation because the heat generated don't really affect Mosfets like Bipolar transistors. True single ended class A is certainly nice, but I've really been wondering if it's absolutely necessary. It's cool to talk about how an amp or a pair of amps can heat a small room, but..............

Having said that my next upgrade I'm going to be considering a pair of Monarchy mono blocks which run single ended class A. The reason.......just because . Not because it's necessary

H9

heiney9

Zero wrote:

H9,

For information’s sake; CC Poon’s amplifiers are not pure class-A. Only the first 5 or so watts run in this operation, switching over to A/B afterwards. That is why they draw so little power and run at only modest temperatures. Still, they sound great for what they are. It will be an interesting combo with your new Lsi-9’s… keep us updated..

I probably knew that and forgot. Thanks for pointing it out/reminding me. However it doesn't matter to me, I still want to give them a try, but the pre-amp is going to be an issue as I've heard they don't play nice with high gain preamps.

The Nelson Pass article, which I've read before but forgot about, is excellent. I agree 100% with his philosophy (always have) and some day I'd love to own some Pass Labs stuff. Lot's of great quotable stuff in that article. I know it's one mans POV, but he hits the nail squarely on the head on many reasons why ALL amplifiers DON'T sound the same.

This is my favorite quote

Appreciation of audio is a completely subjective human experience. We should no more let numbers define audio quality than we would let chemical analysis be the arbiter of fine wine. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not.--Nelson Pass

H9

zombie boy 2000

heiney9 wrote:

I probably knew that and forgot. Thanks for pointing it out/reminding me. However it doesn't matter to me, I still want to give them a try, but the pre-amp is going to be an issue as I've heard they don't play nice with high gain preamps.

My pre specs at 20db of gain and to be honest with you, it really hasn't been an issue. My noise floor is a little high, but this is to be expected and really doesn't concern me.

That and a slight hum that could never be detected with music playing. Ink-black silence? No way. But my set-up does so many other things right, that I believe it to be a fair trade.

Blownrx7

Early B.,
I had a Parasound JC-1 for a bit and it had a Class A bias switch. It was 10 watts in one position and 40 watts in the other. It always sounded better in the 40 watt position but I left it in the 10 watt position unless I was "really listening" to it and saved some energy.
I thought it was odd given that I noticed it even if I was listening at low levels, i.e. probably not sucking up more than 10 watts 95% of the time.
Go figure.

jakelm

My Hafler 200 (which I believe is a class A amp) has to be placed in an open area, (even my newer HK-635 AVR, which I beleive is a class A/B ). The heat it produces is amazing, curious hands beware. Driving my subs at higher dbs, I could almost cook and egg on it. But the sound when driving my 7b's (when running thru pre out of my HK) is amazing.

Jake

univera

Zero or anyone else, would you be so kind to explain the terms "triode" and "set" in layman's terms? I know they relate to tubes, but that's about it.