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I know that Parasound Halo amps provide the first ~20wpc in Class A power, what other companies/models do this? Thanks!
Who's misrepresenting it? My main contention is that amplifiers that have the ability to transition into A/B operation are not really Class A. That is a misrepresentation......IMHO.The OP didn't mention anything about Class A/B operation in his query.No worries.Dave.
Your definition of class A applies only to single ended amplifiers. These were the first amplifier ever made and with tubes of course, starting with the De Forest Audion in 1906. Virtually every tube table radio has a class A single ended output stage. Car radios of the 1950's, 60's and into the 70's had a single ended transistor, class A output stage consisting of one power transistor. The car radio makers were right on top of power transistors because it simplified the power amp of the radio enormously. If is quite common to find the name DELCO or Motorola on early power transistors in and out of car radios. The output transistor was prevalent for many years while the rest of the ratio was still tubed. When we get to push-pull the definition changes. In a push-pull amplifier class A is defined by having the transistor that is going toward cutoff never completely cutting off. Whether made with tubes or transistors the definition is the same. I believe Nelson Pass is the inventor, or first made popular, the notion of sliding class A where the bias level follows the signal and attempts to keep the transistor going toward cutoff from cutting off. This was in the early 1970s at Threshold. I recall the amp, it was big with a lovely large meter on the front. Finding out where a class AB amp leaves class A is very easy. Take the idle current (typically 50-100 mA), square it and divide by the load impedance. For a generous example lets use 100 mA which is typical of a cool running AB 100 watt amplifier. That works out to 0.08 watts peak, 0.04 watts RMS for the class A region. The power dissipated is 0.1 amps x the total rail of 100 volts turns out to be 10 watts per channel. The amp runs warm, imagine the heat if you raise the bias to 5 amps required for full class A operation. If the temp rise on the heat sinks is say 2 or 5 degrees while dissipating 10 watts it will be 50 times higher dissipating 500 watts. OUCH! Class A amps need lots and lots of heat sinks. This is why big ones are so rare.You would have to run 1 amp of idle to get 8 watts peak class A power. In a 100 watt amp that would dissipate 100 watts and need a lot of heat sinking.
Who's misrepresenting it? You're including push-pull configurations in the Class A category as well as single-ended. I don't have a problem with that, although it was a later development. My main contention is that amplifiers that have the ability to transition into A/B operation are not really Class A. That is a misrepresentation......IMHO.The OP didn't mention anything about Class A/B operation in his query.No worries.Dave.
I would love to hear these Valvet E1-R monoblocks someday : http://www.highend-electronics.com/img/Productinfo_VALVET-E1r.pdfThey are Class A, single ended, and use only one power transistor in the output stage. This seems like the cleanest/clearest way to go if you have efficient speakers. I wonder why more companies don't offer this kind of product in the solid state market. Why should low power single ended amps be limited to triodes and pentodes? +1 on that.
The OP didn't mention anything about Class A/B operation in his query.No worries.Dave.
Dave, you're right. Several in this thread, including myself, concluded that the OP was enquiring about push-pull class A amps. This thread started as a bit of an off-shoot of another thread regarding amps for home theater (also started by the same OP), when someone in that thread mentioned A/B amps that switch to class A. Hope this helps clear the air.
I guess 10wpc isn't enough power for the vast majority of speakers out there. I've played with the E1 with Von Schweikert DB-99 SEs. Extremely pure tone and very, very holographic. The designer of the E1 used to produce horn speakers but he's put that part of his business on hold. The A3 is one of the most natural SS amps I've had the privilege of owning. At 50wpc it can drive most anything. Inner detail is likewise excellent with these, the E1's big brothers. A client of mine uses his A3s on Avantgarde Trios.In Europe there're a lot of people using SS with horns. I witnessed the same in Tokyo when I attended the IASJ Tokyo Audio Show last year.
Thanks for that context. I missed that other thread.Cheers,Dave.
I agree with Dave fundamentally about class A. It's either running in class A or it isn't. Let's see if we can get some more "pure class A" solid state recommendations though.
Yeah, I understand your definition doesn't include Push Pull Class A
All I meant to say was class A is Class A. Class A refers to the quiescent current and operating bias point of the device under test. In this case a transistor (solid state). You can have single device, single ended class A, or multiple device parallel single ended Class A, or multiple device push pull class A. But it's either class A or not. If the devices are biased into class A in the amplifier, then the amplifier is running in class A.If it is not, then it is not. It has nothing to do with how many watts, pushpull, or single ended.Why not recommend an amp that runs in class A instead of debate the theory?
