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Is there an actual difference between AB and A/AB ?

Almost all high end linear audiophile power amps which are not pure Class A sell some story about being Class A up until a certain power output, then switching to AB.

Excuse me, but isn't this actually AB to start with?

The whole point of AB is that you run with some bias current to prevent complete transistor shut off at the crossover frequency. This whole "our amp is Class A up until n watts" seems like hype.

Am I wrong?

Best,
E
erik_squires
kosst_amojan
2,095 posts
 
Wow... Pass class A amps are a scam, huh? Good luck trying to back up that claim. Typically his class A amps have a class A envelope double what they're rated at. 
yogiboy's avatar
yogiboy
2,678 posts
 
The last time I looked Pass amps are rated class A or class AB. Never seen them rated class A/AB!
batman1971
64 posts
 
In ss gear it’s all about bias current.   my 2 mono 100watt class a amps cost about 125 bucks a month towards the power Bill   Why.  Cuz that’s what it takes to have such high bias .   If it’s real class A they will be very heavy and get very hot.  It’s a horribly inefficient .  Mine are basically like having a hair dryer going 24/7. At idle.
In a Nelson pass design the A to  AB  kicks in once the output current goes more than double the bias current.     that’s right off passlabs web page as to how they explain their rating system.    ,It’s misleading to say they are class A,   They are AB.    Step up to  Amps like Boulder which are true class A and they weigh hundreds of pounds and will set you back the price of a sports car  for a small one or house for higher powered amps.   It takes heavier components to maintain such high bias current in ss gear. 

   Which is why tube amps amps are awesome and can be low wattage and give out true class A albeit just a few watts and still be in most peoples realm of affordability. 
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