[sdiy] Buchla 259 wave folder/Rail to Rail OPamps/CMOS inverts as opamps

[mark verbos]

A while back Aaron asked if the OP496 was a decent replacement for a  
CA3160/CA3130 as used in the Buchla 259 wavefolder circuit. The  
circuit has 5 CMOS opamp stages in parallel set with different gains  
so that they all distort at various volumes, and then stay at the  
power rail making the overall output zig zag and fold over itself 10  
times.

Aaron was looking for a dual or quad opamp that would distort hard on  
the rail, like the ones in the original design, to get the same  
result. The OP496 costs about $6, so I don't see it as a viable  
replacement. I began wondered if a CD4069 could work for that. I mean,  
it has a MOSFET output right? it's used in lots of distortion boxes...

Well, today I was doing a repair on one of my Buchla 259s and decided  
to try it out. I soldered some wires to the legs of a CD4069 and  
patched them into the module's sockets. It works, and it isn't  
noticeably  noisier. It does not sound the same as the original  
though, or look the same on the scope. It requires a bit more gain  
going in to hit all the folds. The thing is, this would be worth  
exploring more, since it's one chip instead of 5 and it eliminates 5  
caps and 5 resistors. In a quick & dirty situation, this may be the  
ticket.

Now I wish I had recorded a comparison....

Mark