How do I tell what power an amp does in class A?

[Dumdum]

So I have taken several measurements of a car audio amplifier that’s claimed to be Class A to 30watts and then AB from there up to 165wrms per channel at 1%

It’s a four channel and has an idle current of 8a… I am very sceptical of the claims, I would expect a current draw of 20+a for class A up to 30watts so approx 120watts of power dissipated and a lot wasted (voltage is 15.4v in my car)

I’ve taken some measurements and they don’t look pretty either to me

 

[IAtaman]

I don't know if it is possible to tell
whether an amp is running as Class A from power vs distortion graphs or multi-tone measurements.

If we go from the power consumption, 8A at 15V is 120W or ca 30W per channel at idle. Sounds like Class A territory to me. Why would you expect it to consume 300W at idle?

 

[Dumdum]

Mainly because I’ve never seen an amp that was 100% efficient, so assuming 50-60% efficiency… 8a x 15v x 0.6 = 72watts at best?

I am also expecting low distortion due to the class a nature of the circuit at low outputs… which it seems to have until 1watt give or take

And at 5watts it definitely doesn’t seem clean enough to do 30watts in class A

 

[Dumdum]

This is what I expect from a class a…

Тест 2-канального усилителя Celestra Classe A35

Совсем недавно я делал отчёт о топовых усилителях Celestra серии VA, и в нём обещал, что отдельно рассмотрю модель Classe A35 – крайне необычную и нетиповую для автомобильной схемотехники. Для понимания, много ли вы видели серийных автомобильных усилителей, в которых упоминание в названии класса...

carmus.ru

 

[IAtaman]

Mainly because I’ve never seen an amp that was 100% efficient, so assuming 50-60% efficiency… 8a x 15v x 0.6 = 72watts at best?

You said 8A is the power consumption when the amplifier is idle didn't you? If that is the case, that is 0% efficiency - power is consumed, with no output. If you get about 30W power from them, then you can expect them to use about 120W each with ca 25% typical efficiency.

 

[Dumdum]

I also have other measurements which are less than favourable at 5watts that also question the class A, this is 4.5v into 4ohms with a 1khz sine wave

 

[Dumdum]

You said 8A is the power consumption when the amplifier is idle didn't you? If that is the case, that is 0% efficiency - power is consumed, with no output. If you get about 30W power from them, then you can expect them to use about 120W each with ca 25% typical efficiency.

I’ll take that as gospel brain not engaged due to Covid fog