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I believe that linear power supplies fitted to newly manufactured products have effectively been 'banned' as they waste too much power.

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Not being particularly technical a lot of the above comments go way above my head but if I read them correctly it appears as though a linear power supply is to be preferred over switched.
I think linear power supplies are generally preferred on SQ grounds. Switch mode supplies, because of the necessarily high switching frequencies and harmonics, tend to generate lots of high frequency noise and interference that finds its way into everything, no matter how much screening and filtering you do. Linear supplies run at mains frequencies, which cause less noise. However, the transformers are less efficient, and therefore have to be much bigger.

I believe that switching supplies are used because they`re smaller, lighter, cheaper and cool-running, not because of any legislative requirements. SMPS are usually also auto-ranging, so you can use one supply in all markets. By contrast my Denon A1UDCI uses linear supplies, and that`s pretty recent.

Extending my reasoning before, I`ve been looking at the PSUs in other M gear. Apart from the odd G07, 506 or 561, all recent players and processors seem to have SMPS`s. I don`t think the power requirements are ever too great, and there seems to be space available in everything except the combined players/controllers/receivers.

Therefore there might be a case for an enthusiastic owner to upgrade the supply in their transport as well as the controller - or even in the HD621 as well. The HD621 might not do any analogue conversion, but it`s still a source of digital audio that`s vulnerable to noise and jitter. Not wanting to get too carried away, I bet a suitably compact linear supply would help both the HD621, and the rest of the system.

Nick