[time-nuts] Looking for a low power very low noise DC/DC converter (100 - 200 ma 10VDC or 15VDC)

[ed breya]

Yes, for best quietness, you definitely should "can it up" in a metal 
box, and use feed-through caps for all the I/O, including the commons or 
grounds. You have to figure out also where all the currents flow, and 
contain the loops. With sufficient L-C filtering on the input and output 
(all inside the can along with the converter), you should be able to get 
whatever degree of cleanliness is required. The in and out ports should 
include common-mode filters (also inside the can). When it's all said 
and done, there should be the input power port +/- via feed-throughs, 
and the output +/- supply port via feed-throughs.

The can should not carry any current except that which flows through the 
common-mode filtering, so don't connect it internally to the either 
input or output "common," even though ultimately they are tied 
externally. This will help to keep the ripple and displacement current 
loops contained within the can. The can should be solidly connected 
(mounted) on the system ground chassis, and the feed-through caps will 
give the final degree of RF suppression. The I/O ports then can be 
connected as required.

Ed