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Different strokes

— By Paul McGowan —
No power amplifier is more sensitive to the incoming AC power as a class D and that makes it critical to run it off the best power you can manage whether that's from a Power Plant or perhaps you're lucky enough to live out in the country with out any neighbors mucking up your AC power. Whatever the case may be, sensitive is certainly a correct description of the class D power amp when it comes to the power supply. But not all class D power amp supplies are the same. I think the general consensus among high-enders is that a class D amp connected to a conventional linear power supply is the best approach for sonics. I am not sure if this opinion got formed because it's a little "safer" in that one is mixing only a little bit of new technology with a tried and true old technology, or if the best designs mostly have this arrangement. Certainly we are guilty of propagating this designphilosophyourselves; witness our original class D amplifier in 2002, the HCA-2 which sported just such an arrangement. But back in 2002 class D's were just getting going and, in the ensuing 11 years of work on these designs, we've learned a lot about what makes these sound effortless; and the classic linear supply can work but isn't necessarily the best. Let's review the differences between supply types. The traditional linear supply is a really simple circuit consisting of three components: a power transformer, a diode bridge and a set of power supply caps. What you get out of this supply is "sort of" DC, meaning it is dirty rippled DC. Here's a picture of what comes out. Just note the red line in this picture and ignore the rest. Ses how it is jagged and not smooth and steady as that from a battery? The size of those jaggies gets bigger as the power amp supplies more watts so that when you play something really loud, that ripple can be quite large. Now remember that a class D amp connects this power supply directly up to your speaker in little short bursts and you certainly don't want those ripples being sent to your loudspeaker. So what happens? Most modern class D amps have a special feedback circuit that "takes care" of this problem. Unfortunately, from a sonic standpoint, the more undesirable things we have to take care of, the worse the amp sounds. Adding a Power Plant to the mix, especially with MultiWave tuned on, reduces this ripple significantly and makes sure that under heavy wattage demands the ripple remains as low as possible - this is because a regenerator never varies its voltage even if the demand for power goes up. But, I digress. The second type of power supply is a lot more complicated and it is called a switching power supply. I know, it sounds nasty and certainly if not designed properly it can be more trouble than it's worth. Let's jump into this type of power supply tomorrow.

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