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Class A into Class AB

What is the goal of a designer who makes intergrated amps that have class A for x amount of watts before it goes into class AB? Are there any examples of this being implemented well? I get this feeling that it’s kind of just a marketing thing...where people think they are getting some quality class A without the very high price tag. I was particularly looking at the CODA CSiB amps where you have three choices of how much of your first watts are class A. I have since found a few other respectable brands that implement this as well. I have yet to come across anyone who has heard much of difference between AB amps and one’s that’s state "first X amount of watts..." Class A/AB. Anyone have any experience with these kind of integrated amplifiers? Just looking for a little bit of understanding as I’m trying to upgrade my amplifier.
tmac1700
erikt
270 posts
 
The Luxman L-509X is biased to be pure Class A for the first 6 watts.

I've got mine paired to Audio Note AN-K SPx/SE at 90db efficiency.

I do practically all of my listening in Class A - if you believe those seductive dancing meters :-)
holmz's avatar
holmz
2,328 posts
 
I do practically all of my listening in Class A - if you believe those seductive dancing meters :-)
I believe you and the others, including myself, that in an RMS sense… it is mostly Class-A.

Just the crest factor of a lot of music can be ~13dB. So that often jumps the peaks up to Class-AB.
Maybe at 60-65dB it is under/within Class-A.
But at 75-80dB those peaks will be above the meager level where the bias disappears it being qualified as “Class-A like” operation...”
And it has historically been in the louder sections of music where I have heard the grainy’ness, so maybe that was cross over distortion from Class-AB?
clearthinker's avatar
clearthinker
1,582 posts
 
Pure Class A if you please...
itsjustme
683 posts
 
6 watts is quite a lot of class A power.  Given that most decently recorded music has a peak:average ratio of ~ 10 or more, that means that peaks would be 60 watts if you were, on average running in class A.

And 6W is a lot of power! (surprisingly). As a designer i put a lot of experimental (read that: could blow up) stuff in my system with very expensive speakers.  So i have fused adapters pretty much all the time.  I use 1A fuses. Which means that they blow > 8W. They never blow.
itsjustme
683 posts
 
that in an RMS sense… it is mostly Class-A.

I think you mean in an **average** sense. RMS has to do with how we measure a wave:  peak, average, or "area under the curve" (root mean square or RMS).  It is quite different.  For a sine wave RMS = average. For complex waveforms you need to integrate to get the area.  Eek! calculus!


But your point, if i infer right, remains valid.
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