[sdiy] Thomas Henry XR-2206 VCO Page Up

[Ian Fritz]

At 03:47 PM 6/29/2006, Scott Stites wrote:


>The TL072 flat just would not move things very far at all (perplexing to 
>me), and the TL052 would work for the most part, but at a certain 
>interval, would also start oscillating, which is equally perplexing.  The 
>LF442 worked just fine, and we really didn't go beyond that in trying 
>different op amps out.

You need to always check carefully for oscillations at the summer amp and 
at the servo amp.  I have had to cure oscillations at the summer -- a small 
parallel cap should work fine -- as well as at the servo -- increase the 
100 p some.

My favorite dual to use for these functions is the OPA2227.  You need low 
offset for the summer (because it attenuates so much) and you need good 
servo properties for the servo section.  It does, indeed, take a pretty 
good unit if you use a dual.

  Ian