Awesome info, thanks.
Ben
Alastair Reynolds wrote:Well Rick, it goes sort of like this, in a nutshell, when generating power by spinning a magnet in a coil, the faster you spin it , the more volts it generates, so to generate 400Hz. The windings, field coils etc can be smaller and hence lighter by virtue of needing less copper than one that generates 50 or 60Hz. Standard Voltages for aircraft were and for many still are 115V at 400Hz and 28V. Some aircraft have a 3 phase 28V generator. A problem that does arise using 400Hz though is losses due to impedance and transmission of the higher frequency current... Swings and roundabouts.... So at 400Hz , generators and transformers can be smaller, use less copper windings and need less iron in the cores. The small Ramjet (Ram Auxilliary Turbine or RAT) that you see usually in the tail of a passenger plane drives an auxilliary power generator to run the aircraft while the main engines are stopped.
My old Fuzz -Linear power amps from the mid 70s are rated at 50-400Hz, I think Crowns and SAEs were as well, but someone else may be able to comment on that.
Modern switch mode power supplies operate at high frequencies (e.g. 100KHz) for similar reasons, transformers can be far smaller and as such more efficient but you then need much higher speed diodes to be able to cope with the switching speeds needed without vaporizing, and good filtering to remove harmonics and prevent noise being injected back down the mains and turning up on something else that has inadequate filtering . Cheap switchmodes are one of the greatest sources of noise in the modern audio plant.If you're ever getting strange noise in audio paths, turn off the PCs and anything computer related first and see if it goes away.Of course this problem "never" occurs with a well made linear power supply using quality components, but they're far from cheap.
