It’s amazing what application specific integrated circuits can do now. I never stop being surprised at what I keep seeing coming out of the pipeline. Audium Semiconductor recently gave me one such surprise with the hyper efficient AS1001 amplifier that can deliver 100 watts peak power, from a 1.5 volt (read single battery) power supply.
This is really cool, because it means more oomph from battery powered devices. Audium claims that this little sucker can run for about 1000 hours on 4 C batteries. That’s about 10 months at 3 hours of listening per day!
This chip is 50x more efficient than a Class D amplifier at moderate volumes. Depending on use, that's a lot less batteries per year in your portable boom-box! Photo from Audium Semiconductor.
Stepping back a bit, I’m a physicist by training. Most of us (except for the theoriticians) made some or all of our electronics as we learned our trade, and that meant that we knew all about power and distortion. This also meant that we liked really good stereo equipment that made true representations of what was pressed into our Mobile Fidelity Sound Labs master recordings of Dark Side of the Moon and the like.
This meant class A amplifiers, and for the really persnikity, tube amplifiers (for their richer sound at high volume, and gentle non-linearities as one hit saturation. Anyway, these things were power hogs and could heat the room even when doing nothing. Solid state amplifiers were looked down on, mostly because of how they distorted music as the crossed zero volts out. This sucked because all amplifiers cross zero at all volumes (Except for our friend the class A amp), so cheap solid state amps sounded bad, even when not being pushed.
But that’s not the case any more! Solid state amplifiers are now good, really good. (The highest end of the market is still the land of the Class A tube amp, but the size of this market keeps shrinking because of the advances in solid state analog electronics and the ever increasing price of the top of the line audio equipment). Signal reproduction is now so good in solid state products, that efficiency in one of the main areas of competition. This brings us to the class D amplifier. Class D amplifiers are kind of a cross between amplifiers and switching power supplies, but the details are unimportant. What is important is by using tricks with high speed switching of transistors (so they are either fully on or fully off), they are much more power efficient than “analog” waveform amplification. This is good for two reasons. One less power for the same volume is always good, and all the audio equipment is now just computers anyway, so getting closer to the binary world of CPUs makes integration easier.
The Audium product takes the Class D power efficiency and puts it to shame. As far as I can tell from what I can figure out from their web site, they do this by some form of “rail switching” where the internal power supplies of the chip only output high voltages when the amplifier needs them. Kind of switching squared…..
The AS1001 is 50 times more efficient than class D at a sound level between conversation and busy traffic. 20x more efficient between busy traffic and and old vacuum cleaner. The class D reashes parity with the Audium chip at about the volume level of a busy factory. Graphic from Audium Semiconductor.
The AS1001 is currently available in a 64 pin QFN package. For those not in the biz, that’s something less than 1 cm on a side, and about 1 mm tall! Compare that to a vacuum tube and it’s a tiny fraction of the space. The size and efficinecy means this chip is perfect for boom boxes, or wireless speakers that really are wireless because they don’t have to be plugged into the wall.
This is the development environment for the AS1001. The large plastic black thing is a battery holder. The AS1001 is a small square, less than 1cm on a side, somewhere in the dev system. Photo from Audium Semiconductor.
Anyway, what does this really mean? In green terms, it means a lot less batteries. (For details on the impact of batteries, look here.) But really, whether one uses disposable or rechargable batteries, it means using a lot less of them. And that’s a very, very good thing.
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