As usual, I connected the amp to my reference system, in this case driving my reference speakers with the front channels in stereo mode, and my 4 ohm, 12” subwoofer with the rear channels in bridged mode. After the usual gain and crossover adjustments, I was ready to do some listening. The first note I wrote on my notepad was, “Sonically, there is no real indication this is a Class D amp.”
The IA6 sounded good, with no weird high frequency noise or apparent “hardness” that I have noticed in some other Class D amplifiers. The power was excellent, providing plenty of juice to run my system to really high volume levels without any sign of stress. I did, however, think that a remote level control for the rear channels would have been a nice added feature, as the IA6.4 had no remote method to change the level of the subwoofer.
Bass was smooth and tight, and had good low extension as I found out on Avril Lavigne’s “Sk8er Boi”. The IA6.4 sounded clean and natural in the midrange, and maybe had just a hint of sizzle on the top end. Musical details were easily discernable and overall clarity was excellent. I listened to the amp for more than 3 full hours, and while it did get good and warm, I had no thermal issues with it, thanks to the inherent efficiency of the Class D topology.
On the bench, the IA6.4 lived up to the “No BS” statement, and exceeded all of the published specs. I went through the amp with a fine tooth comb, and pretty much everything worked as it was intended to, and throughout testing didn’t so much as blow a fuse. The only deviation I noted was a slight rise in frequency response on 2 of the 4 channels. But because it only amounted to +2dB at 20kHz, most listeners will never hear it. Even a dead short applied to the outputs simply activated the protection circuit, and when the short was removed, the amp worked perfectly.
Signal to Noise was decent for a switching amp, and it easily exceeded the power ratings. Distortion was low, and stereo separation measured very good. Overall maximum efficiency occurs at full power into 4 ohms, and it was almost 85%. More importantly, efficiency was roughly double what a conventional amplifier provides at power levels where most of us listen to music. That means less strain on the cars charging system, and less energy lost to heating a heatsink.
Recalling Nick Wright’s quote about creating products with exceptional quality and performance, I have to say I think the IA6.4 is a great example of mission accomplished. If you were wondering how well a company that seems really focused on SPL would do building an amp that was meant to run for hours at a time instead of in 3 second burps, you can stop wondering and start listening.
For more information visit www.incriminatoraudio.com