endover Posted January 20, 2004 Share Posted January 20, 2004 I know I'll never be able to afford one but I just wanna know......In general, what the heck is a "Class A" amp? I've been told that 50 watts from a Class A amp is better than 100 watts from any other amp(I guess they don't class 'em if their below an "A"). If I don't have $20,000 speakers(my Chorus II's were just a bit cheaper than that), would I even be able to tell the difference? Quote Link to comment Share on other sites More sharing options...
JohnA Posted January 20, 2004 Share Posted January 20, 2004 Amplifier classes describe the method of operation. While come classes are easier to make sound good, the Class is NOT a dependable method of determining quality. In layman's terms: Class A - the output devices (tubes or transistors) are on all of the time. It is the least efficient and runs VERY hot. Class A does not suffer from "crossover distortion" caused when an output device turns on from an off state. Class A amps often sound better that all others and the Hornies' favorite design, Single-ended Triode (SET) is Class A. Class B - perhaps the most efficient "topology". An even number of devices are required; one device amplifies the + side of the electrical wave and another device amplifies the - side. When not amplifying a device is off. Runs very cool, only very careful design reduces crossover distortion enough to sound great. Class AB - the most popular topology; the + and - devices are turned on for all of their half of the wave and a little of the others wave. This allows an AB amp to operate in Class A for small voltages (say to 1.5 watts) and act as Class B most of the time. This is a nice compromise and is quite efficient since all of the devices are not "On" but for a short time and at low wattage. These will often run warm, but not hot. Class D - is a sort of digital amp I don't fully understand. The devices are switched on and off with the input signal. this makes, I believe a bunck of essentially square waves that are filtered to cut out the ultra highs and return the output to a wave that looks like the input. This is sometimes said to be the most efficient amp design and easily achieves extrodinary power in a small, cool package. Normally used for subwoofers and cell phones. There are some other types that are highly exotic. One is Class H. It's sort of like Bob Carver's trick amps where the power supply tracks the input signal so the amp can only put out the power it has to at the time. Good audio amps are nearly always Class AB and Class A. However, I believe McIntosh made some very good sounding Class B amps. Notice I did not mention power? It is not directly related. A 50 watt Class A amp is a 50 watt amp; nothing else. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 20, 2004 Share Posted January 20, 2004 Hi, ENDOVER Forgive me, guys, I am going to make some GENERAL STATEMENTS about feedback and lack thereof, and these are ONLY my opinions, so take with a grain of salt: One simple thing to remember about amplifier operating "class" is that in most cases (except A), negative feedback is applied to reduce distortion at a given wattage output and promote a wider frequency response than would be possible without it. The relationship of frequency bandwidth, distortion level and overall output gain (wattage) are all modifiable via the use of feedback depending on the circuit type and design, so cannot be assigned as either good or bad. There are some cases where class A (which has no feedback) is not capable of 20-20kHz or wider response without producing more distortion than other classes of operation. This is not necessarily a bad thing; tube amp distortion is regarded as much more acceptable than other operating class distortion in some circles; however, in regards to Class A such as a Tube SET amp the distortion will typically be higher than another type of amp with the same bandwidth capability. These things all trade off. The AB class operation typically produces the most usable wattage with the widest frequency bandwidth at the lowest distortion for a given output stage and is therefore the most popular. It is also the most stable in that the stage is not driven beyond its operational limits in "normal" operation. I am not saying that one is better than the other, only that these elements make up an engineering compromise (i.e., a balance of things) that like all things in our hobby are more a matter of taste and application than "hard and fast" rule. DM Quote Link to comment Share on other sites More sharing options...
JohnA Posted January 20, 2004 Share Posted January 20, 2004 Hey D, There's no reason a Class A amp cannot have negative feedback. I've only known of one transistor Class A amp that does not have negative feedback, the Monarchy. It may have it in some stages. Amplifier design is a highly technical subject. I barely understand the simple parts, though. Quote Link to comment Share on other sites More sharing options...
endover Posted January 21, 2004 Author Share Posted January 21, 2004 Okay...you folks obviously know your stuff! ...so where does that put most decent quality a/v receivers (those in the $500 to $1,500 range). Do they tend to have the AB amps in them? Quote Link to comment Share on other sites More sharing options...
JohnA Posted January 21, 2004 Share Posted January 21, 2004 Yes. Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 28, 2004 Share Posted January 28, 2004 Thanks John, Didn't know that. DM Quote Link to comment Share on other sites More sharing options...
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