Originally Posted by arnyk
I've experimented with powering power amps with regulated switchmode power supplies and had what I consider to be reasonable success. This kind of amplifier has been widely sold to consumers for decades in the aftermarket high performance automotive audio business. None of the problems described above seem to have afflicted the commercial products or my own experiments.
The solution seems to be pretty obvious. In aftermarket car audio the solution is both built into the equipment and sold separately as "Stiffening" capacitors. The basic idea is to sacrifice the ability to filter a high frequency switchmode power supply with relatively small capacitors and put in energy storage capacitors that would do proud to any power amp operating off of 50/60 Hz. The transients are supported by the power main supply capacitors just as they are with unregulated power line based power supplies.
That's quite true but consider the automotive problem. How do you generate more than three honest watts without some form of DC/DC converter. You don't have a choice outside of an MG set or auxillary alternator. The stiffening capacitor is mainly for voltage drop from the engine to the trunk, it's on the amp's power input terminals after all. Remember that you are pulling 30-40 amps at only 12 volts over an 8awg, possibly #6 wire during transiets. The car battery is surely as stiff as it gets but getting that energy reserve to the trunk is another matter. But you are correct in that adding large rail bypass capacitors in an SMPS application is good provided they don't prevent the power supply from startup. But many SMPS's don't like a cold 50,000uf capacitor across their terminals. They see it as a dead short and abort startup.
Many of the zilliions of commercial variations on switchmode power supply technology seem to work best if they incorporate some kind of regulation. Must of this is revealed in modern pro audio and consumer power amps that already incorporate switchmode power supplies.
Crown's highly sucessful XTi series of power amps come to mind as a successful line of very powerful amplifiers that are based on switchmode power supplies and linear Class AB power amplifier circuits. They feature sufficient internal regulation that they are rated for use on power lines ranging from about 90 to 250 volts if memory serves. I've used them on 130 and 240 volt power no switches or adjustment required. I've had them on the bench and used them to amplify audio and they seem glitch-free. A 2KW XTi series amp weighs about 12 pounds, if memory serves.
Crown, QSC, are pro PA amps. That does not mean they sound any worse than good HiFi amps, in fact they often spec out even better. But the choice of a SMPS is for the exact reasons you, Self, and Sloan have stated. Weight, heat, and international usage are the primary reasons. And even on the HiFi front, if you have a 1kw sub woofer amp, you really don't have much of a practical choice. You can go class D or use a SMPS with class B. But once you get above 500-700 watts, that's the practical limit of a 50/60hz transformer in this application
. And thanks to the electronics industry as a whole SMPS's are cheap and fairly reliable these days.
Still bottom line, the QSC amps sound different in my system than the Haflers (and the tube amps as well but that's expected). They both are below 0.04% THD in the 10 watt range and that's the limit I can measure with my Heathkit copy of the classic HP330. As to which is better - that's subjective. I prefer the Haflers. I really don't like the QSC's even though many consider them "high end"
And consider I too am using SMPS's with my new class A amps. Here again I really don't have a choice. There is very poor PSRR in a class A amp so do I build a +/-24 volt 60hz transformer based bipolar regulated supply that can deliver 12-15 amps per rail?
P.S. The Hafler amps I am using here are the DH220's. There are before the buyout to Rockford / Fosgate. Wasn't it some of the Dynaco 400 team that designed these original Hafler amps?Edited by Glimmie - 1/29/14 at 4:45pm