Class A versus Class A/B amps (any opinions?)

I'm just curious to see if anyone has any strong opinions on these 2 types of amps.
I've read that Class A maintain a more pure sound and that Class A/B is slower to respond to signals or possibly more distorting but this is somewhat speculative.
Ultimately i will be buying the A/B only based on the power consumption and heat issues. Call me crazy but that environmental side of me just kicks in.

I believe Mcintosh makes Class A amps but i haven't seen many other brands going down this road.

Alot of Class A amps only actually operate pure class a for the first few watts per channel. after thats its class A/B. of course there are a few that are rated 100wpc pure class A..but they also cost alot. what amp are you buyuing BTW.

chess, I thought that you did not like a hot-running amp.

A pure Class A amp will surely run VERY hot, even without any input signal. They will constantly consume up to 100W per channel of electricity, depending on the power rating and design details. Actually, the power consumption does not change much as the power output increases in a Class A amp.

Yes, in theory, a Class A amp provides the lowest open-loop distortion and no crossover switching distortion (which happens in Class AB and particularly Class B amps whenever the signal swing crosses zero). However, with a generous amont of negative feedback used in today's amps, I doubt that anybody can actually hear the difference.

In a related topic, I am curious about the current status of debate between the bipolar versus FET power stage. Does anybody have anything to say?

Doesn't Zoloft help with bipolar? I'm not sure about the other...

I was doing some reading on that very topic yesterday. I guess it depends on how much you believe that a FET power stage (tube based) modifies signal and sound.
I highly doubt i would ever tell the difference but i know certain audiophiles who would say otherwise.

Is a tube based amp the type that the one poster on this board has as a pic near his name?

Umm? Tube based??? No, I meant Field-Effect Transistor...

jbzngowest, Zoloft and other SSRI's are more effective in monopolar depression... LOL

In reply to:
I guess it depends on how much you believe that a FET power stage (tube based) modifies signal and sound.

You're a little mixed up brother.

By FET based he was refering to amps that use Metal Oxide Semiconductor Field Effect Transistors instead of Bipolar Junction Transistors.

Personally, I've been trying to find good literature on exactly how they employ the FETs in these designs for a few years and haven't had much luck (nor have I tried that hard...). A BJT amplifier is a fairly basic structure as the emitter output is the sum of the base and the collector. Simply add a little current to the base and you have an amplifier. A MOSFET is a true switch in that applying current to the gate merely opens a path for current to flow from drain to source with little gain.

Obviously, heat and power consumption should go WAY down (FETs only draw power when they switch from off to on and vice versa whereas BJT's draw power through their entire activity). But I've no idea what they're doing in the actual design or how this would effect signal integrity.

Semi, No. It is only the Class D amplifier that uses power FET's as pure switches like you said, thus drastically reducing power consumption and heat generation. Those designs are often used in the built-in subwoofer power amps and car audio, where a compact but extremely high-power amplifier is desirable.

An analog FET power stage (Class A or AB) uses the FET's more like a pair of "variable resistor" or "volume control" connected in serial between the power-supply rails. The source/drain resistance is controlled by the gate voltage. The gates of the "top" and "bottom" power FET's are driven out-of-phase, swinging them in the opposite direction according to the input signal. So, the FET power stage actually behaves much like a push-pull tube amp (hence chess's misunderstanding), but still having a very low output impedance just like the usual (bipolar) solidstate power stage. I remember that when the FET power amp started to appear in the consumer audio market in the early 70's, it was advertised as having "the best of both worlds" (meaning, the benefits of both tube and solidstate). Today, many manufacturers seem to stick to either bipolar or FET, while a few companies do use both technologies mixed in their lineup. But I have not closely followed up their pros/cons lately, and so got curious...

Ah. I understand. If you find more details on the benefits and such, let me know. I see it advertised everywhere as some random bragging point in marketing material which always struck me as... odd.

Lesson learned.
Never read anything in the wee hours of the morning.
There is no easier way to get one's facts brutally wrong.

So what does that say for someone like me that works in the wee hours of the morning? LOL...It's a good thing I'm tenured!!