[sdiy] Intro, and saving the 901?

[Richard Wentk]

Hi synth DIY people

I'm currently playing with the idea of building a Moog Modular clone - love 
the sound of that thing, even though it's obviously a temperamental design 
by modern standards. And it could be quite a cheap project.

I've been looking at the 901 oscillator, and wondering if there's anything 
worth saving in the design. Obviously it's a given that the exp gen in the 
901 has to be replaced with something more modern. But it also seems like 
the UJT oscillator is going to be inherently temperature sensitive no 
matter what you do to it. (The specs say Rbb varies by around 0.5%/K) And 
switching between capacitors for the octave setting doesn't look like a 
recipe for tuning accuracy. The triangle generation scheme is kind of 
eccentric too...

Meanwhile the 921 looks too complex to homebrew.

So I'm wondering three things:

1. Has anyone tried to revise the 901 design and somehow get it more stable?

2. Is the sound so much better that it's worth making the effort? I've 
listened to MP3s of more modern designs but they seem a little cold to me. 
(I have a suspicion this may be something to do with the op-amps. I built a 
3340 design a while back, and the difference between the sound unbuffered 
and buffered with a TL07x was surprisingly noticeable.) But obviously I 
haven't heard every single circuit out there. Has anyone tried an A/B 
between their favourite recent design - one that stays in tune and tracks - 
and an old 901 or 921?

3. Is the Minimoog osc design worth trying instead? How is that for temp 
stability?

Thanks for any answers!

Richard