ABSTRACT
It is immediately obvious that the fi rst and simplest option will be the most cost-effective, but at fi rst glance it seems likely to compromise noise and ripple performance, and possibly interchannel crosstalk. It is therefore worthwhile to examine the pros and cons of each technology in a little more detail. I am here dealing only with the main supply for the actual power amplifi er rails. Many amplifi ers now have some form of microcontroller to handle on/off switching by mains relays and other housekeeping functions; this is usually powered by a separate small standby transformer, which remains powered when the amplifi er supply is switched off. The design of this is straightforward – or at least it was until the introduction of new initiatives to limit the amount of standby power that a piece of equipment is allowed to consume. The International Energy Agency is urging a 1 W standby power limit for all energy-using products.
