Cgs synth

Hi...My name is Necip and I'm from Turkey...I wanted to make my own
modular...I'm fairly a newbie at designing and making synth
modules...I made DIY guitar effects for my bass before...so I know how
to solder etc. I need help to understand the electronic basics or
concepts about the filters,VCA's,and especially VCO's...so could
anyone help me??? Do you know a good web-page about electronic
basics...I need to know what a "current sink" is??? or why do I have
to compansate those transistors on most of the VCO
schematics???...Also if you know a book that I could buy on_line I'd
be really glad if you could tell me its name publisher etc...

Thanks