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

I was just having a bit of fun. If class a operation was an actual concern for me I’d likely need to know.

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 :)

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.

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.

@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.

I actually sent an EMAIL to my amp manufacturer earlier today and they already replied back. They claim my Coda #8 V1 does 18 watts class A into 8 ohms and around 12 watts Class A into 4 ohms. This corresponds to what @swede58 said with his Pass amp. Thanks for everyone's help on understanding this.

And companies rate things differently. A for instance, I have a Hegel, class A/B amp. I’ve tried three times asking the company how many watts are class A and never got an answer!  The third time I asked, I was told that because of their design, it all sounds like class A!

@willywonka Wrote:

 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.

Yes! See article below:

Mike

https://www.sound-au.com/class-a.htm

So, my Cayin A88T, (8 ohms: 22 wpc triode/45wpc ultra-linear), using the 16 ohm taps yields ____? Class A amps.

https://6moons.com/audioreviews/cayin/a88t.html

btw: Only model 1 has 16 ohm taps, later versions are still the same 8 ohm rating, only 4 or 8 taps provided.

thanks for any enlightenment

Elliott

@swede58 I know Ohms law but it doesn't address all my questions. I am a retired electronic tech by trade. 

Interesting it does less class A into 4 ohms. I wonder if all amps do this or if they are all different. I'll have to contact the manufacturer of my amp and ask. Thanks for the reply. 

This is the reply I got from Pass Labs when I asked this question: ”The X260.8 does 34 watts peak in class A into 8 and will do about half that into 4”

Your amp will operate in class A up to 9 watts in 4 ohms