Posted by David Lee on January 16, 2001 at 01:54:21:
In Reply to: Re: Crown & Switching power supply Amps posted by Arthur J. Dock on January 15, 2001 at 17:46:53:
: ..the K1 and K2 are actually a fully digital topology rather than just being an analog amp stage with a switch mode power supply.
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According to Crown the K1 and K2 use a toroid transformer in their power supply. All the switching stuff is done after the supply.
From Crown about the power supply:
"The K1 and K2 use a toroid transformer in the power supply for increased reliability and efficiency. Compared to the switching power supplies used by some manufacturers, our toroid design consumes significantly less energy, creates less heat which must be dissipated and is more reliable than the complex switching designs."
From Crown about the output stage:
"The K Series utilizes novel, switched-mode power conversion that obsoletes conventional class-D designs which are hampered by two unsolvable problems: reliability and high distortion levels. There are three primary benefits of the Balanced Current Amplifier design:
250 kHz Switching Rate Generates Less Heat
Conventional design wisdom dictates that a 500 kHz switching rate is necessary for 20 kHz audio performance. The BCA design switches at 250 kHz, but because of this breakthrough innovation, it appears as a 500 kHz rate."
Etc. etc.
As for the CE4000, it has a switch mode power supply and the BCA output circuitry. It is pretty light, too. The only thing that concerns me is something I noticed on the one CE4000 we have. It produces what can best be described as a "halo effect" around sounds. We were playing piano music on it, at low levels, right after playing the same thing through two other amps. We heard this funny sound and looked at each other. "Do you hear that?" I said. Switched back to another amp: no noise. Checked all input switches: all OK. It almost sounded like there was something on the piano strings. We played other music. Still there. I called it a halo effect because the visual equivalent would be a ghost image, like light scattering around the actual image. There is something "scattered" in with the original sound. Noise. I don't know if it has anything to do with the power supply or if it's unique to this one amplifier. I'm not keeping the amp, though.
(snip): Switching power supplies do have advantages e.g. wattage to weight. They also do have those nice characteristics of being able to provide output voltage despite dropping line voltage...(snip)
Since I'm throwing my $.02 in, whenever I do A/B comparisons between amps I prefer the amplifiers without switching power supplies on the low end. For my money the MA5002 and the K2 are the best LF amps out there. Both have transformer power supplies. Crest also makes/made some awesome amps for LF. They, too, have transformers. I have heard some awesome switching power supply amps, but only when they've been playing tops. (above 100Hz) (Carver comes to mind, not that I would never own one again) Transformer power supply amps always seem to have more power to produce bass. I'm no amplifier designer, but my theory, if anyone cares, is no matter how fast or well you switch your power supply, when it is called upon to produce sustained LF current, it just isn't there. It seems to me the big power supplies with big power supply capacitors can supply more current for longer before "running dry" as it were. Maybe an amplifier designer will read this and explain why it happens. (If it happens.) Anyone else notice this phenomenon?
Perhaps, and I'm totally guessing now, but perhaps the K series make such good bass amps because they have transformer power supplies and an extremely efficient output stage. The best of both worlds: Plenty of power in the power supply to draw from + very little draw to produce the output = awesome ability to produce feel-it-in-your-gut bass.
My hat's off to Gerald Stanley and Crown for the K2 and BCA technology. Keep it coming. Where's my K4?
David Lee
Rhino Acoustics