FYI -- AMPLIFIER CLASSIFICATION For Those Not In The KNOW

[Gilbert]

Okay, this information is probably known and understood by most you guys, or at least I think it is. But for the guys and gals like me (prior to my reading this)...Here's a little education. Sorry, this is a rather long post that I used Cut-&-Paste to post here on this forum. It's not as long as some of Max's biography's (sorry max), but it's worth reading. I placed it here for future question and answer searchers like me.

---Watch Out Tube Boy's, I are educatin meself. I shall not remain IGNRANT---

Classes of Amplifiers

Amplifiers do not actually increase the strength of an electronic signal. What happens instead, the signal is copied and enlarged. There are different schemes for amplifying the signal. There are different classes of amplifiers. These classes are A, AB, and C. There have been some special classes such as G, created by Hatachi. Class H created by Soundcraftsman. Class D for the so-called digital amps and Class T for Tripath's digital amplifiers.

Class A amplifiers use one or more transistors that conduct during both the positive and negative cycles of the signal. This Class of amplifier has the lowest distortion but it is very inefficient and generates a lot of heat. A Class A amplifier requires that the amplifier generate the full current no matter what the output is. If you were simply listening to FM or watching a movie, the amplifier would be consuming as much power as if you had it turned up to full volume. Now I know why my krell runs so darn hot, even though I typically run her at about 5 or 6%.

In order to increase efficiency, Class B amplifiers use one transistor to conduct the positive portion of the waveform and another transistor to conduct the negative portion of the waveform. 99% of all audio amplifiers today are Class B. Class B amplifier can be built today so that its distortions are well below what the human ear can detect and nearly to the point where it is unmeasurable.

Many amplifiers call themselves Class A/B. In reality, very few are. Early Class B amplifiers had a problem known as switching delay. In a class B design, a transistor works 50% of the cycle while another transistor works 50% of the cycle. In early class B amplifiers, there was a distortion created between the time the devices were switching back and forth. Some people referred to this distortion as notch distortion because there was a notch appearance on an oscilloscope between the two waveforms.

Class A/B was created to leave the transistor conducting while the second transistor was conducting. This created an overlap between the two signals. The problem with this approach is that it created its own distortion called gumming. This means that the signal would get a little fatter where the two devices were both conduction.

Today, if you look at a properly designed Class B amplifier on a scope, you will see no switching distortion.

Class D amps are sometimes called digital amplifiers. There is really no such thing today as a digital amplifier. A Class D amplifier uses transistors that are either switched on or off to represent positive or negative values. The transistors are either on or off. The advantage of such a system is that it is highly efficient and generates very little heat. The disadvantage is that there can be a distortion caused between the switching of the positive and negative transistors as the positive and negative transistors can not be on at the same time.

Many Class D amplifiers are finding their way into Subwoofers. They are inexpensive to build and the logic is that the switching distortion is not important in a subwoofer.

Class T amps are a more refined switching amplifier developed by Tripath. It uses signal processing to eliminate the switching distortion of Class D. nOrh is currently working with parts from Tripath to determine the sonic merits using the Tripath parts. Our current view is that advantage to using Class T and Class D amps is not to achieve better sound than can currently be achieved with standard A or A/B amplifiers. Rather it is an attempt to create a lower priced amplifier that offers good performance.

TUBE AMPLIFIERS COMMING SOON To A Thread Near You.

[Zargathos]

That was very informative. Thanks!

[Audiokid]

I agree with you regarding the Tripath modules. The company I work for produces a Tripath based series of amps, from 2 to 6 channels. They are generally smaller, cooler (very efficient), but present other challenges to designers, such as broadband RF (radio noise).