The "tuning circuit" is probably a phase locked loop and a crystal oscillator controlling a microprocessor clock speed.
Believe me, if soldering a few pins to a board is beyond your scope then you haven't a snowball's chance in hell of redesigning an entire synth's operating system and hardware to go "boing" on command
Honestly, soldering a prototype board is no big deal. If you can follow simple instructions you can wire up a simple Arduino project without too much grief.
Start off with a couple of simple kit projects from reputable manufacturers to get a feel for soldering a board and by the end of the second one you'd be able to tackle a ribbon controller or an arduino mod wheel.
You might fry the first or second kit, but by the third you'll be designing your own mdoular synths with confidence.
Take a look at the search results I linked in my last post. They will tip you off to the sorts of pitfalls amateurs get into.
OR
HIRE A HIGH SCHOOL KID TO BUILD IT FOR YOU
Gary
