On Mon, 26 Aug 2013 00:26:06 +0100, 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.


That's exactly the sort of job where a virtual ground is useful. You can
get a single, nice smooth regulated supply then split it using an op-amp
and 2 close tolerance resistors. Your ground is then bang on centre-rail
no matter what the loadings are (within the output capability of the op-
amp).