In well designed SS class A power amps I was told that although power could increase to double in class AB mode from speaker demands of  8 ohms to 4 ohms, class A suffered to be cut in half.

For example a class A denominated amp rated at 50 watts class A into 8 ohms would double to 100 watts class AB  into a 4 ohm load but only have 25 watts of class A power before switching to class AB.

But I've noticed of late claims of manufacturers stating their amps double their class A power as impedance demands are halved.

So is the explanation that technology has advanced ?


Why not just buy a Sugden amp and end it. You will no longer have a yearning for anything up on Sugden, they were the first with SS Class A in 1967. No BS class A that transitions to class A/B....I had not even heard of Sugden, but a few years ago. My curiosity peaked, and I broke down and bought one. It set me back a decent penny

..but man I’m glad I did it.....A21SE Signature...once that was in place, I again broke down and purchased my Tannoy Speakers, now I’m in the poor house lol. I’ll tell you what, it’s one heck of a combo. You would not believe how good only 30 watts per channel can sound (40 watts into 4 ohm). I’m pretty much set for life, as I’m old.

The best class A amps have doubled their wattage into 4 ohms for at least 40 years.

I have a pair of mark levinson  33h mono blocks each one weighs over two hundred pounds they double every time the impedance  is halved and they are stable  to 1/2 an ohm. They stay class a all the time and when they were tested the output power was limited  by the input power. Each one the minimum  power requirements  are two dedicated  20 amp circuits.  They do not switch  to an ab amplifier  and there power doubles not halves as the impedance  is halved. 

@rost Wrote:


My understanding is a class A /AB amplifier will have a switch to differentiate between the two classes. The switch changes the amplifier's quiescent current. My amplifiers have a switch on the front panel in class A for 30 watts output, @ 8 Ohms the quiescent current is 250 watts and in class AB for 200 watts output, @ 8 Ohms the quiescent current is 80 watts. In my audio system my amps are always in class A mode. I hope that answered the OP question. 😎


I've got a Pass 250.8 amp that runs 25 watts in pure class A and then transitions into class AB and can generate 250 RMS into 8 ohms. It idles in Class A and sucks 400 watts of juice from the wall when not reproducing music- just turned on. It's about 110 pounds and when on is hot- not warm- hot- and will heat my dedicated room to 73 degrees after being on for a couple of hours. The power meter on the front which shows when it starts to move from Class A into AB mode never budges and I play it loud into a pair of Wilson Sasha 2. It's an incredible amp, super musical and dynamic and great bass. I've never been able to get it to come close to moving into AB, the first 25 Class A watts will drive the speakers louder than you can stand!