Wow, really interesting thread.
Atmasphere, I get the impression that what you're describing is simply the tendency of certiain topologies to present non-linear loads to their preceeding stages. If this is the case, then how is this substantially different than a tube output stage running in class A2 or AB2 whereby grid current becomes significant for part of the cycle?
Shadorne, yours is a great question . . . to me, it still may boil down to cost. Winding high-linearity audio magnetics is expensive no matter what; could it be that for the typical values used in a loudspeaker crossover, it's simply cheaper to get the same or better linearity using an air core?
Eldartford, the optimum load for the complete amplifier output stage depends on the load it's designed to drive, or vice-versa. A single pair of bipolar transistors in an emitter-follower output stage tends to be really comfy with loads of 8 ohms or above, but it's a simple matter to lower this by paralleling output devices, as is the case with virtually all the Mac autoformer-based amps. The autoformer simply gives the designer more flexibility to balance both the total current and dissapation requirements of the output stage.
Arthur, thanks for helping clear up some of the terminology . . . I have only superficial familiarity with transformer winding techniques. But I always thought that the process of splitting a single winding as you describe was called "interleaving", and that two separate windings wound together was called "bifilar winding". By this, the Acrosound/Dynaco transformers were interleaved but not bifilar, but the McIntosh transformers were both interleaved and bifilar?
And finally, I think that an autoformer would be an interesting addition to a Class D amplifier, as their output filters tend to give best transient response at a particular output load impedance. But most of these are designed to be small and lightweight . . . and an autoformer is of course a poor choice if those are major design criteria.
Atmasphere, I get the impression that what you're describing is simply the tendency of certiain topologies to present non-linear loads to their preceeding stages. If this is the case, then how is this substantially different than a tube output stage running in class A2 or AB2 whereby grid current becomes significant for part of the cycle?
Shadorne, yours is a great question . . . to me, it still may boil down to cost. Winding high-linearity audio magnetics is expensive no matter what; could it be that for the typical values used in a loudspeaker crossover, it's simply cheaper to get the same or better linearity using an air core?
Eldartford, the optimum load for the complete amplifier output stage depends on the load it's designed to drive, or vice-versa. A single pair of bipolar transistors in an emitter-follower output stage tends to be really comfy with loads of 8 ohms or above, but it's a simple matter to lower this by paralleling output devices, as is the case with virtually all the Mac autoformer-based amps. The autoformer simply gives the designer more flexibility to balance both the total current and dissapation requirements of the output stage.
Arthur, thanks for helping clear up some of the terminology . . . I have only superficial familiarity with transformer winding techniques. But I always thought that the process of splitting a single winding as you describe was called "interleaving", and that two separate windings wound together was called "bifilar winding". By this, the Acrosound/Dynaco transformers were interleaved but not bifilar, but the McIntosh transformers were both interleaved and bifilar?
And finally, I think that an autoformer would be an interesting addition to a Class D amplifier, as their output filters tend to give best transient response at a particular output load impedance. But most of these are designed to be small and lightweight . . . and an autoformer is of course a poor choice if those are major design criteria.