Dave and all,
This might sound redundant, but i usually place bypass ceramic caps like barry mentioned is quite helpful and also insert ferrite beads on the input to the converter, just like i do on other power supplies. reducing alot of noise heading thru to the output.Bad part about converters,etc is alot of them use a switching circuit which can produce harmonics which we call noise on the listening end of it all..1uf caps, ferrite beads,shielding and filters .depends on which section of the circuit giving you the problem is what solution you take.Some use ferrite core inductors to help filter stuff out too.
Just my own hillbilly take of it all. probably wrong but thats what i do,and look for.
Sounds like you all have under control
73
David
ac9xh
