I was interested to note that David Hafler died this past week. Due to my long running audiophile obsession, I built a Hafler amp kit about 20 years ago. The amp is still running to this day as part of my brother's stereo system. I was so excited when I received the kit that I stayed up all night and finished it in one night. It worked from the first time I turned it on and continues to this day.
Hafler's influence in the nascent audio industry is right up there with the other greats such as Fisher, Marantz, etc.
It is also interesting that my latest preamp, the McCormack MAP-1, uses an Ambient Recovery Mode (ARM) that has some basis in the equally famous Hafler Circuit. I feel I was somewhat of a pioneer when I installed my first car stereo in my VW bug in the late seventies and built a rear speaker platform that used this Hafler Circuit. The crux of this setup is that you send the positive connectors of both the left and right amplifier channels to the third rear channel. The sound that is emitted from this third speaker is the difference between the two channels which is in essence the out of phase "ambient" information included on the recording. Needless to say I had one of the coolest car sound systems in my school and it led to a minor career in car stereo installation during high-school.
And to think that many think surround sound started with home theater and DVDs?