Hi Joseph, apparently 301 underwent fairly substantive redesign since its introduction. Initially it was more similar to the 302 than 312. 302 is not my favorite amp by any stretch of the imagination. . . it lacks 'enthusiasm' for lack of a better word. More recent 301 units are apparently quite similar to 312, plus have their own unique designs. If you send me a PRIVATE EMAIL with the serial numbers of the used 301 you are being offered, I might be able to find out what's in them. Please do not post the serial numbers on this thread. Only their current owner is entitled to do that.
Model 312 is out of production, but you might find some dealers with still one in stock. The new amps are very close but have not been released yet. There will be a 625 mono in the $10K range per pair, a 925 mono in the $48K range per pair. I am moderately confident that these should be released before the 2nd half of the year. A model 825 stereo will follow. All these new amps will operate in low bias class A/B instead of class D, but will have advanced switch mode power supplies and power factor correction (PFC) like the 300 series.
I am lined up to take delivery of a pair of 925s, but I have not heard the new amps yet.. . . JRDG is in Colorado, and I live in Texas. Guido