It is easy: almost all amps made today are direct-coupled with means that the output transistors are directly connected to the load (speakers). This is in contrast to a (solid-state) transformer-coupled amplifier in which a transformer buffers the load so that transistors are NOT directly connected to speakers anymore, but rather to a constant-impedance transformer.
Transformer-coupling has advantages: It is much easier on the output stage, thereby inceasing amplifier life span, and allows optimization of the output stage for certain loads for better linearity (lower distortion) among other things. The disadvantage is that it is very hard to wind a transformer for low losses and large bandwidth - both of which are needed to prevent altering the sound.
Despite the advantages, only McIntosh Laboratory uses transformer-coupled outputs (a patented design they have used for a long time) in their solid-state (and tube, of course) amps. The transformers use a special bifilar winding technique that doesn't easily lend itself to mass production but they figured out how to do it well. Seems like I knew of another company at some time that did it too but I can't remember now. Others may know.
Anyway, I can give you lots more technical details because I researched this topic for a while in another electronics application - just email me. Take care - Arthur
Transformer-coupling has advantages: It is much easier on the output stage, thereby inceasing amplifier life span, and allows optimization of the output stage for certain loads for better linearity (lower distortion) among other things. The disadvantage is that it is very hard to wind a transformer for low losses and large bandwidth - both of which are needed to prevent altering the sound.
Despite the advantages, only McIntosh Laboratory uses transformer-coupled outputs (a patented design they have used for a long time) in their solid-state (and tube, of course) amps. The transformers use a special bifilar winding technique that doesn't easily lend itself to mass production but they figured out how to do it well. Seems like I knew of another company at some time that did it too but I can't remember now. Others may know.
Anyway, I can give you lots more technical details because I researched this topic for a while in another electronics application - just email me. Take care - Arthur