Late to the 350 party. I was living in Boston at the time and bought a lightly used 350 from a local dealer, but found it didn't sound substantially (any?) better than my then-highly-modded Advent 300, so I eventually returned it. Still regret that decision! It was such a solid piece of audio engineering and ergonomics.
At least I still have my 300, doing duty in the bedroom system, still sounding fine (though nowhere near my current big rig), never having missed a beat in 34 years.
I have two different 'preliminary' marketing brochures for the 350, written in the same matter-of-fact manner of other Advent copy of the day. It's clear all of its DNA came from the success of the 300.
The impetus for the 350 was as much to correct the 300's weaknesses:
1) marginal output power bumped up substantially;
2) FM drift cos they put some key passive tuner components right up against the power amp heat sink was cured with all-new layouts;
3) hard to read FM dial, much larger and nearly 360 degrees vs tiny 180 degree span of 300;
4) a tone defeat as the 300 tone controls couldn't be bypassed and clouded the preamp sound a little;
5) I assume some better components, a revisit of all the circuits, and a much cleaner layout rather than the random rat's nest of wires inside the 300, regardless of how brilliantly it worked. I've always wanted to take the schematic and lay it out properly with quality modern parts to see what such a fresh design was capable of.
If Jstaley (one of the designers who posted here) is still around, he may have more design briefs of the 350 to refine the 300...
