Listening
I put the PDX 4.150 in trunk and connected channels 1-4 to the outputs 1, 2, 5 and 6 from the Alpine PXI-H990 Multi-Media Manager. The speaker outputs were connected to the front separates and rear 6" x 9"s in the Buick, and I ran through the automatic Time Correction and Road EQ setups to set the stage for listening to this diminutive D Class. When I fired up the head unit, there was an odd phasing thing going on and a strange noise from the rear speakers. The amplifier was connected properly and all the speakers worked--the weirdness was coming from the Media Manager. About an hour later, I discovered that one of the kids had turned on the surround sound from the Alpine DVI-990 head unit for watching a DVD, but set it up for a non-existent center channel. I was listening to four ambience channels and a sub, pretty strange. Darn kids! I reset the Media Manager, ran the automatic setups again and finally started some serious listening.
First up was "Snowbound" from Kamakiriad by Donald Fagen. The front separates were popping a little at high volumes, so I raised the crossover point to 100Hz to protect them. The Rhodes crunch and everything else in the intro to this track was there as well as I can remember hearing it. The cymbal work and hi-hat from "Tomorrow's Girls" were simply stunning. Listening to Michael Ruff's "Eyes of Love," I actually noticed a triangle chime in the first chorus for the first time. The lower percussion and bass at the beginning were a little subdued, but everything from there up was very good. From Mary Chapin Carpenter's Come on, Come on album I listened to "Rhythm of the Blues" and "I am a Town." Carpenter's voice was very up front, well centered and clear as a bell. The cello in the latter track was very well defined. Listening to several tracks with some bass beat, like Yello's "Oh Yeah," continued the clarity theme, but revealed less-than-perfect control in the bottom end. It is my opinion that this is due to the lower damping factor of this amp, like any Class D amp. Remember that damping factor is a calculation of output impedance to load impedance and higher is better, at least up to 300 or so. Putting resistance between the output devices and the speaker itself will decrease the number and results in a softer, slower, less powerful sound. (All you guys using teeny-weeny 18-gauge speaker wire for your subs, take note.) Class D outputs necessarily use inductors between the output device and the speaker terminals, which raises the impedance of the circuitry and lowers the damping factor.
Conclusion
All in all, I was very impressed by this amplifier. Although lacking a little in low-frequency performance, it had stunning sound quality in the low-mid to high frequencies, which is probably what it was designed for. The fit and finish of the amplifier is very good, and though I shorted, overpowered and overheated it on the bench, it came back to life every time. I'm not sure it will work if I ever figure out how to put it back together, but that's my problem. The only other item I can knock this for is the confusion with the speaker connectors and bridging.
This amplifier is very small and stackable. The "Power Density" name makes perfect sense. At a retail price of $750 and maximum power output of 986 watts, this amp will cost you about 76 cents per watt. I think it's a good value, and perfect to drive a higher-end 4-speaker system.