On Monday, August 26, 2013 12:26:06 AM UTC+1, Dave Plowman (News) wrote:

It's the PS for a fairly esoteric moving coil pickup pre-amp which uses
balanced inputs. The quiescent current at least is very similar on each
rail. Basically was chasing the last residue of hum, and discovered (by
accident) if I disconnected the transformer centre tap it improved. The
scope showed the hum to be more on the negative rail. Changing the neg reg
to a different make improved things to the point I doubt I'll better.

Sounds like a symmetrical load. Adding resistors can help deal with small imbalance. For low current loads like that, passive power rail filtering is often enough, and can often help. IME though poor grounding layout and lack of IC decoupling are as often the problem with homemade preamps.


NT