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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
kayleerex1's avatar
kayleerex1
4 posts
 
Since amplifiers typically operate at lower output levels than their power ratings, the higher the class A wattage rating, the more it operates in class A, so there is or can be an advantage for higher class A ratings in an otherwise class A/B amp.
I have designed and constructed a number of power amplifiers, including one capable of pure class A operation at 100 watts into 8 ohm loads and one capable of class A operation up to about 20 watts into 8 ohms although it can output 120 watts at 0,1% THD.
Both amps sound fine.  However, it is nice to know that one can provide class A operation at 100 watts.
The price is that the power dissipation in the output stage of a class A amplifier is twice its power rating.  The 100-watt class A amp therefore dissipates 200 watts under no-signal condition, so heat-sinking is critical.  For that reason, that amp was constructed as two monoblocks in separate enclosures for stereo use.  The two get quite hot, but no failures in over twenty years of operation does mean it is practical to build pure class A amps capable of respectable output wattage.
fatdaddy2
398 posts
 
That's the definition of a class AB amp.  So what's the beef?
larry5729's avatar
larry5729
1,009 posts
 
I never hear the word ARCAM in this discussion group?  ARCAM makes a ARCAM 30 that is Class G.  It costs double the price of their ARCAM 20 a class AB amp.  However, when I heard class G, I really felt it sound better.  Not sure why.  It had plenty of power and headroom.  I am still thinking about owning one.  

One thing about a Class G is it runs cooler than a Class A which can get really hot and it is not suited for an enclosed cabinet.
riley804
1,224 posts
 
One thing about a Class G is it runs cooler than a Class A which can get really hot and it is not suited for an enclosed cabinet.

most members are aware that class a amps run hot and need to be out in the open.
itsjustme
682 posts
 
another agreement with @tom6897. **Pure** class A is tons of money, heat for what amounts to very little benefit. High bias Class AB works great.  There are way better places to spend money and get more sound improvement.

And i design these things.
The idea of subtle nuance while the amp is running at 100% of power is a contradiction.  The room is shaking.
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