Amplifier Specification questions


I understand the differences between different classes of amplifiers. Most common amplifiers are Class A/B. Does this mean that all class A/B amplifiers operate in Class A to some point then switch over to Class B when they hit a predefined threshold by the design of the manufacturer. Do some so-called Class A/B amps only operate in Class B? My power amp is designed to operate up to 18 watts Class A before changing class of operation. I assume this number is in 8 ohms. My amp is rated at 150 watts into 8 ohms and 300 into 4 ohms. Does this mean that Class A rating will double to 36 watts in 4 ohms or will it stay at 18 watts regardless. What's funny is I was thinking I needed more power because my meters were always pretty well deflected but after looking closer, I realized the meters were on the 5-WATT scale instead of the 150-WATT scale. I can't believe I never noticed that before.

willywonka

@curiousjim - well their answer is completely BS.  Sounds like Class A.  I have to laugh at what manufacturers actually say to their customers.

Happy Listening.

Interesting it does less class A into 4 ohms.

The amplifier bias current determine the output power of class A operation.

For example, an amplifier can provide up to 8 Watts of class A power @ 8 ohms load before it switch to class B operation, the current at the output is 1A (P = (I*R) * I ), if the output current over 1A it will switch to class B. Therefore @ 4 ohms load, the class A power is up to 4 Watts.

Most A/B amp manufacturers don't market how much their amps run class A. I wonder how bad it would effect my listening experience to have power meters and know when the transition happens. Personally, I'd probably have to turn the meters off to ever enjoy the amps again.

I wonder how bad it would effect my listening experience to have power meters and know when the transition happens

@steve59 If the bias point is properly set the transition is completely inaudible. I wouldn't worry about it :)