Originally posted by mickky:
Thanks for the much more informed responseto the original post, Paul. Am I being misleading about one class of amp being transformerless, or is it a different animal altogether?
Glad to be of service.....
There is no specific link which requires any particular class of operation to use or not use a transformer to couple to the speaker. It's possible to build an amplifier in any of the three classes A,B, or A/B either with or without such a transformer.
With old tube amps a transformer was almost always used, as it's the easiest way to couple power from the high-impedance tubes to the low-impedance speaker.
Many early transistor amps also used a transformer. The higher-quality units ran class A or A/B. Class B was especially common in battery-powered portables, due to the higher efficiency & thus lower battery drain.
Because transistors are lower-impedance devices than tubes, direct coupling is also easily achieved, and is the norm in modern amplifiers. The absence of the transformer is said to remove a possible source of distortion, but another advantage is that transformers for high powers and bulky and expensive.
It's still possible for a transformer-less output stage to run as class A, B, or A/B, however.
There is also a class C, but this is not suitable for audio applications.
