Hi Devil - no, I wouldn't recommend you chop the '20; it's one of the best decks around. You'd need a LOT of work to get an SL1200 up to that level!
Let me explain about the bass. If you think about the 'envelope' of any note; attack - decay; belt drive sounds like you're switching your lights on and off with a dimmer switch. So you don't get an 'instant on', rather it's like it starts dim and gets bright. LEDs of course switch on and off in thousandths of seconds, which is why I used them as an analogy. Direct drives (and indeed idler drives like the 301) are much more LED-like. Obviously if you've got a gently plucked bass note (as in Kate Bush's 'Moving'), a DD won't make it sound like Mark King slapping his Fender Jazz bass on a Level 42 song; it will sound just as it should be. But the difference is that a BD will slur it slightly, even when it shouldn't. You can really hear this with kick drums, for example, which have a very recognisable on-off 'thunk'...
Now, why this happens is a matter of much debate; I subscribe to the school of thought that says DDs respond much better to dynamic wow (when the stylus excerpts a sudden 'drag' on the record due to higher groove modulations). Basically, as soon as there's a tug on the platter by the stylus tracking heavy groove modulation, the DD servo pumps some more juice into the motor, so the platter doesn't slow down. What happens on a BD is of course as soon as they're a tug, the weakest link in the drive system 'gives' a bit - which is to say the belt stretches. This results in a slight speed instability.
One way of getting around this on a BD is to have a massive platter, like the EAT Forte (around 25kg IIRC) which is driven by twin belts. But still, my listen test show, it's not quite as tight in the bass. Much better than an Avid Acutus though, which is already excellent as belt drives go.
The downside is that DDs are constantly feeding in more, then less, power, into the motor. This caused the '70s hi-fi hacks to accuse DDs of 'hunting' for the right speed. This is absolutely correct, but what they failed to point out is that on the same track, BDs would be constantly slipping their belts, the turntable equivalent of (motor pulley) wheelspin, as the high torque pulley struggled to get traction with the belt, which itself stretches in and out all the time! So the point is that both systems aren't quite right; the point is that to my ears a well executed quartz-locked DD is a better working compromise. A high torque idler like a 301 is better still, but it has its own new problems of throwing lots of noise into the system.
As an aside, I think a stepped belt would solve a lot of belt drive problems, kind of like the transmission on a 1983 Kawasaki GPz305 (anyone remember them?). Why no one does this is beyond me, although I'd guess it's something to do with cost. Most belt drives use those nasty cheapo Philips Impex/Airpax AC motors, which I'm not a big fan of... (the new Linn LP12 Radikal uses a new, stronger DC motor and sounds way better, but it will cost you a pretty pennny!)
Better stop rambling - reached the bottom of the Jacobs' Creek bottle...
David
