beginner questions

[michael]

i have a few questions relating to designs on Tom's Synth Cookbook site (
www.geocities.com/efm_gc/cbook/cookbook.html ), and since the email link
there doesn't work i'm hoping that someone here can help me......

first, what are the trimmers on many of the designs for?

ie the balanced ring-modulator 
www.geocities.com/efm_gc/cbook/pics/brm1a_pc.gif

and the ms-20 filter
www.geocities.com/efm_gc/cbook/pics/vcf8b_pc.gif

second, would there be any easy way to run the designs here from 15V?

third, my past experience etching circuit boards didn't turn out so well,
but i've seen "professional" systems with heaters for the etchant. is this
worth the money? any advice about this?

i know this is alot to answer, but if someone could take the time i'd
appreciate it!

thanks,

michael