Paul McGowan writes: I think we all understand the importance of power supplies in audio equipment – as everything we listen to in our systems starts out as DC voltage in the first place.
Power amps are particularly sensitive to power quality for reasons I’ve detailed in past posts – and of all power amp types, class D is the most sensitive. In fact, many class D designs available on the market today sound significantly better when fed from regulated power – like that from a Power Plant or any regenerated source.
I would venture to suggest that of all the products in your system that benefit from a Power Plant, a class D amp would have to be at the top of the list, followed closely by a class A/B and then A. Why? Because no other piece of equipment in the audio chain depends so heavily on the power supply to do its job. As I mentioned yesterday, a power amplifier is probably better thought of as a power supply first and a valve to control that power supply second. That’s an important distinction to understand.
In a DAC or a preamplifier, power supplies are also critical but in a very different way. Take our PWD for example. We made major improvements in the PWD with the use of multiple spot regulators that improved the isolation between circuits that manage all the digital audio data, the analog stages etc. Here low impedance and lots of isolation between stages is the critical element a designer needs to worry about. Since all DACS and preamps start out with regulated DC supplies in the first place, the major task is keeping one part of the circuit from affecting the other part and this helps tremendously in an effortless presentation of the music.
A power amplifier, on the other hand, is a much less sophisticated device – something of a brute – whose task is to get as many watts into the speaker as possible while preserving all the hard work of the circuits that came before it. It’s instructive to remember what I wrote yesterday about how a power amplifier is really nothing more than a valve that connects the power supply to the loudspeaker. The quality of that valve is important but not as important as the supply itself.
So in a class D amp there have been numerous approaches to the problems of the power supply – the most popular of which, at least amongst high end companies, is to go linear and big. Linear, meaning a traditional power transformer and capacitor bank, big meaning a lot of headroom. This works well in many cases because if the supply is big enough, the ripple of the supply is lower than a similar approach straining to meet the demand.
The second most popular approach is to add another class D power amplifier in place of the linear supply – this approach, called a switching regulator, has the potential to be far better but inherent in its design is the potential for much worse sound. It’s a classic double edged sword.
Tomorrow let’s take a look at the two approaches to power supply implementation for power amps that we want to make effortless music.