We've seen that the average SMPS (switching power supply) is really nasty on PF, averaging a low 0.2, relative to a traditional supply that is 0.7 (the perfect being 1) - but we've also learned that a properly designed SMPS can achieve a PF of 1, something not really possible with the standard supply. As you may remember, a PF of 1 is very gentle on the AC line and doesn't affect other components as a low PF does.
In fact, our original Gain Cell series of products used B & O ICE modules - which many Class D based power amps still do - and while they make a good sounding amplifier, their power supplies all have extremely low PF and so they negatively affect the other equipment in the chain. In hindsight, after these many years, I am convinced that one of the reasons so many PS customers loved this series - while we had less success bringing non-PS customers into the family with these amps - was that most non-PS customers didn't have a Power Plant to protect them from the PF nasties. So while our amps sounded good, they hurt the performance of other equipment in the chain. Obviously we all judge the overall system performance when we insert a new piece of kit in the mix for audition.
Of course the best thing we, as designers, can do is make sure our power supplies have a reasonable PF so we don't negatively affect the other components in the system. As much as we love selling Power Plants, truth is it would be great if equipment didn't make the already tough incoming AC worse and they weren't needed as much.
But continuing with the differences between traditional power amplifier supplies and SMPS, another downside to the traditional supplies is lack of regulation: something easily handled in a SMPS.
Power supply regulation is rarely ever seen in a power amplifier, but pretty much always seen in a preamplifier or source equipment of any kind. The reason for is simple: a power regulator is basically a power amplifier itself.
What is power regulation? It's basically making sure the voltage offered to the amplifier circuit from the supply remains steady, regardless of the demands the amp places on it. So, let's imagine our power amplifier needs 140 volts for its supply voltage. In a standard supply that voltage is never steady - because as soon as the power amp starts to deliver power to your loudspeakers - the 140 volts begins to drop to something less. In fact, if you were to look only at the power supply voltage in an amplifier, you could see the musical signal easily - right on the supply itself as the amp delivers power to the speakers - that supply moving up and down in perfect harmony with the signal.
This is not good, something that would never be tolerated in a preamplifier or source piece because it would cause all manner of poor sound - yet 99.99% of all classic power amplifiers out there have unregulated power supplies. Why? Because to fully regulate the supply would require another power amplifier of equal size and heat loss to be built into the amp! One power amp would be needed to regulate the power supply and the second one to deliver power to your speakers. Not an economical solution for a designer and from a consumer standpoint, you'd pay twice as much and your amp would be 50% larger.
To solve some of these issues, many older PS amplifier designs had the power supply split: we regulated the power amp voltage gain stage while keeping the output stage unregulated. That helped a lot but doesn't solve the problem.
Enter the SMPS which is (if designed properly) fully regulated. This, along with its gorgeous PF input, makes the SMPS a beauty for building a power amp. 'Tis a shame most SMPS don't have both of these built in - but some do - and these are the ones we're focusing on.
How does the SMPS regulate without adding an extra power amplifier?
Gotta wait till tomorrow.
