super nice transconductance amplifiers

[POLARIS at VAX1.Mankato.MSUS.EDU]

{Since when was $6.20 low cost.  You can make a very fine ring mod
from two LM13700's and a couple dual op-amps and
$.73 + 2X $.35 + resistors < $6.20}

Hey man, it was Analog Devices' idea to call it their "low-cost" multiplier :)
Anyway, for a few more $ over the LM13700 (which I admit to knowing nothing
about), you get a single 8-pin dip that does it all. There's even a VCF
circuit on the app notes (see  http://www.analog.com/products/sheets/AD633.html)

Dave