newbie question: EMS diode ladder

[noddle]

Newbie circuit question follows:

Been thinking about building a modular synth lately, and I thought
I'd start with a VCF because I could use it immediately with some
other gear, and also because ladder-type filters are pretty mysterious
to me and I thought maybe I could learn something.

The other night I put together one of those EMS-type diode ladder
filters on some vectorboard...the schematics are in a few places on
the web, I don't recall where.  Anyway, to make a long story short,
it only sort of works.  It does show VC filter action, but the rolloff
is pitiful--and there are three major problems:

1) only works when the output is looking into less than about 200 ohms,
	otherwise it self-oscillates rail-to-rail at about 2 Hz no matter
	how little feedback is applied;

2) max input amplitude is about 1 V p-p before serious distortion
	sets in (bias dividers too mushy? see below);


3) when the cutoff is set at a useful frequency, the standing current
	in the ladder is such that the sourcing transistors go into
	thermal runaway after a little while...makes a nice slow
	sweeping effect, until it burns up :P

Has anyone here built one of these and had it work successfully?
I guess I didn't think about input/output levels and impedences
when I built it--what do these things usually expect?  I built
this thing primarily to try to understand how these
filters work in a circuit, since the analysis I tried was giving
weird results (not that I tried too hard :-).  Are there any
resources still in print that I can consult that will tell me
how to design these things without reverting to op-amps (not that
op-amps are bad)?  Email replies would be appreciated.

Thanks,

Rob
rrafac at pesto.phys.nd.edu