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class A,class A/B

goraman

goraman

Super Member
Banned
how dose keeping plate current 100% of the signal affect the sound differant than let's say 85%.What is the audible differance and why? and is it worth the money to go class A.:scratch2:Dose it affect the slew rate?Rise time ?or dampening factor? And is it more important with tubes than SS?
 
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A lot of it depends on the efficiency of your speakers. To go class A you need very efficient speakers because most class A amplifiers are under 30 watts per channel.
 
That did it for me,mhardy6647 That should be manditory audiofile reading and they need to see part 2 as well.Thank you what a great summery.
 
all i know is when i switch my Yammie amps from class AB to class A there is a discernable difference between to two differing topoligies in my ears (class A sounds better IHMO more clear and the imaging gets better)
 
slow_jazz said:
A lot of it depends on the efficiency of your speakers. To go class A you need very efficient speakers because most class A amplifiers are under 30 watts per channel.
Click to expand...

There are a lot of very high-powered class A amplifiers. The problem with class A is that you need a hell of a lot of heat-sinks because it is so inefficient, so high-powered amplifiers are MASSIVE, and quite expensive.
 
Cpt.Beaky said:
There are a lot of very high-powered class A amplifiers. The problem with class A is that you need a hell of a lot of heat-sinks because it is so inefficient.
Click to expand...
And they are usually (always??) very heavy and quite expensive, too.
 
yamahammer said:
all i know is when i switch my Yammie amps from class AB to class A there is a discernable difference between to two differing topoligies in my ears (class A sounds better IHMO more clear and the imaging gets better)
Click to expand...

I found the same on my CA-1000. I haven't tried the M-80 in class A yet.
 
A simple explanation of why Class A would sound better than Class A/B (for anyone who couldn't make it through that article) is that in Class A/B you get a small amount of distortion and offset in the waveform because of the pause created as the signal switches (the amps cannot react instantly to the signal as they switch on and off). The positive and negative side of the wave aren't quite properly aligned, so the sound is distorted. Class A is immune to that particular problem.

I included a very ugly illustration of what I mean...
 

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Cpt.Beaky said:
There are a lot of very high-powered class A amplifiers. The problem with class A is that you need a hell of a lot of heat-sinks because it is so inefficient, so high-powered amplifiers are MASSIVE, and quite expensive.
Click to expand...
But they make great space heaters! :D
 
How about MX's HCA power curve? This is from the MX-10000, the others follow similar power curve.
 

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Cpt.Beaky said:
I included a very ugly illustration of what I mean...
Click to expand...

'fraid you're just plain wrong about that. While what your illustration shows is indeed crossover distortion, what is depicted is more along the lines of what a Class B design would yield. Class AB is designed to have a little bit of bias current running so that the transistors do not have to turn on, as they are already idling. An optimally biased Class AB amplifier can have vanishingly low distortion.

The real problem is the transistor, which has a gain that changes with the amount of current flowing through it. In class A, this current is fixed, thus less variance in gain (and lower distortion). Modern audio transitors go a long way towards solving this problem, as they are more linear.
 
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