Now we know...

[WikiBoy]

Richard wtf are you contradicting most everything ive said. I have said the current has been set high enough to allow it to work in class 'A' .The amp is a CLASS AB design, i don't care what you claim it is.If you wanna argue it furthur i will encourgae an 'A1 specialist to come on here & give it how it is.

You are talking out of your hat with complete lack of knowledge. A class AB design *IS* a class B design biased to keep both transistors switched on at the same time (class A) for a few milliwatts. It is a misnomer, it should have been called class A and B, that would have made more sense. Class is not a design it is an operational characteristic, you can have many designs of class A and many designs of class B that is why amplifiers are different, BUT you can only have a limited number of operational modes and if you invent a new one then you take the next letter available in the alphabet. If AB was a new operational mode then it would have had a new alphabet letter, which at that time (mid 60's) would probably have been D or E. It is NOT a new operating mode, it is a sometimes A sometimes B mode.

It really takes an extrordinary ego to argue a subject you have little knowledge in and cannot admit the false nature of.

[Vinyl Grinder]

It really takes an extrordinary ego to argue a subject you have little knowledge in and cannot admit the false nature of.

You know nothing of me.You have a great way of turning things around to sort yourself, i'll give you that, infact if i didn't know any better i'd think you were some other guy on here we all know.I've asked a friend to come on & tell YOU what the 'A1' is.

Class 'AB' amplifier is a class 'B' amplifier which has a small amount of "bias" current flowing through the output transistors at all times.

A/B

[greenhomeelectronics]

Richard, your bit about taking the next letter does not make sense - are you seriously saying that class c amplification came along after a and b? Not when I went to college it didn't. Wot about Technics' class H then? Have we hit a rift in the time / space continuum :-)




I'll get me coat..........

[Filterlab]

And then there's Class N which is based on the reduction of time-average dissipation in transistor power instead of state-of-the-art reduction of instantaneous dissipated power. This becomes possible due the influence of capacitance currents that produce a negative collector current swing during a part of AC-period. In this case, along with an always-positive collector-emitter voltage, the instant dissipated power also is negative.

[Marco]

I totally agree with that, *BUT* only on a Wednesday.

Marco.

[Filterlab]

And a Sunday morning.

[WikiBoy]

You know nothing of me.You have a great way of turning things around to sort yourself, i'll give you that, infact if i didn't know any better i'd think you were some other guy on here we all know.I've asked a friend to come on & tell YOU what the 'A1' is.

Class 'AB' amplifier is a class 'B' amplifier which has a small amount of "bias" current flowing through the output transistors at all times.

A/B

So now all of a sudden you are agreeing with me. So now you accept that this following statement of yours is wrong, as I said - "it runs class 'A' up to around 8watt/8 Ohm, after that it runs into class 'A/B'".

Thats good, job done. That is all I wanted - to correct ignorance and misinformation.

[spendorman]

This is from

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

There is much more there in detail. I will have a look at my amplifier design books what they say about classes.

"I look down on him because he is lower Class" From the Two Ronnies!

--------------------------

Class A
100% of the input signal is used (conduction angle Θ = 360° or 2π). Where efficiency is not a consideration, most small signal linear amplifiers are designed as Class A, which means that the output devices are always in the conduction region. Class A amplifiers are typically more linear and less complex than other types, but are very inefficient. This type of amplifier is most commonly used in small-signal stages or for low-power applications (such as driving headphones).

Class B
50% of the input signal is used (Θ = 180° or π). In Class B, there are two output devices (or sets of output devices), each of which conducts alternately for exactly 180 deg (or half cycle) of the input signal.

Class AB
More than 50% but less than 100% is used. (181° to 359°, π < Θ < 2π). Class AB amplifiers are a compromise between Class A and B, which improves small signal output linearity; conduction angles vary from 180 degrees upwards, selected by the amplifier designer. Usually found in low frequency amplifiers (such as audio and hi-fi) owing to their relatively high efficiency, or other designs where both linearity and efficiency are important (cell phones, cell towers, TV transmitters).

* Class AB1 applies to tube or transistor amplifiers in class AB where the grid or base is more negatively biased than it is in class A.

* Class AB2 applies to tube or transistor amplifiers in class AB where the grid or base is often more negatively biased than in AB1, and the input signal is often larger. When the drive is high enough to make the grid or the base more positive, the grid or base current will increase. It is possible depending on the level of the signal input for the amplifier to move from class AB1 to AB2.

Class C
Less than 50% is used (0° to 179°, Θ < π). Popular for high power RF amplifiers, Class C is defined by conduction for less than 180° of the input signal. Linearity is not good, but this is of no significance for single frequency power amplifiers. The signal is restored to near sinusoidal shape by a tuned circuit, and efficiency is much higher than A, AB, or B classes of amplification.

Class D
Main article: Switching amplifier
These use switching to achieve a very high power efficiency (more than 90% in modern designs). By allowing each output device to be either fully on or off, losses are minimized. A simple approach such as pulse-width modulation is sometimes still used; however, high-performance switching amplifiers use digital techniques, such as sigma-delta modulation, to achieve superior performance. Formerly used only for subwoofers due to their limited bandwidth and relatively high distortion, the evolution of semiconductor devices has made possible the development of high fidelity, full audio range Class D amplifiers, with S/N and distortion levels similar to their linear counterparts.

Other classes
There are several other amplifier classes, although they are mainly variations of the previous classes. For example, Class H and Class G amplifiers are marked by variation of the supply rails (in discrete steps or in a continuous fashion, respectively) following the input signal. Wasted heat on the output devices can be reduced as excess voltage is kept to a minimum. The amplifier that is fed with these rails itself can be of any class. These kinds of amplifiers are more complex, and are mainly used for specialized applications, such as very high-power units. Also, Class E and Class F amplifiers are commonly described in literature for radio frequencies applications where efficiency of the traditional classes deviate substantially from their ideal values. These classes use harmonic tuning of their output networks to achieve higher efficiency and can be considered a subset of Class C due to their conduction angle characteristics

[WikiBoy]

Richard, your bit about taking the next letter does not make sense - are you seriously saying that class c amplification came along after a and b? Not when I went to college it didn't. Wot about Technics' class H then? Have we hit a rift in the time / space continuum :-)




I'll get me coat..........

Yes I am saying exactly that, it used to and should follow a timing sequence, though the marketeers are now even taking over that province from the techies, so in the last few years letters have been taken out of order as in T amp, and also now electronic firms are patenting or registering circuits that have no unique mode of operation for marketing purposes. So the process is being corrupted. Reality is being replaced by marketing delusion like so many things in the modern age. Ego based amateur marketeers at forums just perpetuate this process.

Anyway a simplistic but accurate description can be found at Wiki - http://en.wikipedia.org/wiki/Electronic_amplifier

[spendorman]

Yes, I have a 80s Technics amp that calls itself "New Class A", that would have put me of buying it in the 80s. However, I was given it a couple of years ago and it is not bad. So in this case the "Class marketing thing" worked against them. I still do not know what New Class A is, if it ever exists. I guess it is class B and at low power operates in class A, just like the majority of transistor power amps.