Your scope would need to be able to see cross-over distortion (or the lack of it). Signal generator on a line input. Channel A on the amp input, Channel B on the amp output. Use scope math to diff A/B, adjust gains for a scope signal null.I believe there are class A amps with more than one output transistor.
As per my OP, how can I check with scope juyst to be sure?
Unless it's horrible amp it will have minimal distortion. The blackbox way to tell is to look at efficiency under no and full signal load. A true class A power AMP it will be a hot, power hog all the time. A practical 50W amp might have a idle power of 100W and use 200W at max power. A low power class A headphone amp is unlikely to have this obvious amplifier class profile.Thank you for your suggestion. But maybe a good amp will have minimal distortion?
Can it also be done by observing the DC level of the amp's output, or using a meter to determine if the output current is mono or bipolar?
Not at the output, since it has a DC block capacitor.it would sit at half rail. Whereas A/B would be "0" volts.
No.At full volume, the current would therefore increase by about 25% for A as opposed to 50% for AB. Is that correct?
I think he got DC power conversion efficiencies for capacitor coupled and transformer coupled class A amplifiers confused with currents in amplifier class types....
Where did you get those 25% and 50% values?
Can you run your SIM with capacitor coupling to a load of 1K.Below is the LTspice simulation of a simple Class A amp:
Note that the average supply current (right box) is essentially the same as the quiescent current (left box).
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by Jake Hertz
by Duane Benson