Funny how this 948 thread has come up as I was just on the phone with Burmester this morning regarding an issue I am having with my 911mk3. I have noticed hum in the power transformer at certain times during the day. After Burmester recommended some experimentation to identify the root cause it turns out that it is due to a large amount of DC current in my mains. In my case when I have my TV on (or washing machine running) it raises the DC level to the point where the 911’s toroidal transformer reaches a point of saturation and this then begins to hum with a significant intensity; it is audible at over 5 meters away. When I turn off the TV and the hum stops. No problem for me as I typically do not have the TV on when I listen to music, although it is annoying when I want to watch movies. Although the hum is not harmful for the 911 it is not good either according to Burmester. This is apparently only an issue with very high end transformers which are ultra sensitive to DC; with my MC402 I never had such as issue.
The solution they recommended is one of their conditioners which were designed exactly for this purpose; the elimination of DC from the mains. Fabian from Burmester (who gave fantastic technical support) recommended two ways of using the device; either plugging everything from sources, preamps, TVs and power amps into the conditioner (he explicitly stated not to plug in a PC if this is used as a source), OR plugging everything into the conditioner APART from the power amps. As long as the power amps are plugged into the same socket circuit (group of plugs on the wall) to which a 948 is plugged the power amp will receive DC filtered electricity.
So looks like I will be adding one of these to the arsenal
