Hey everyone, Whelp, I've had this project dancing around in the back of my mind for a good six months now and I'm here to ask for some help. I'd like to build this biofeedback device from an old issue of Popular Electronics: http://220.127.116.11/~gbpprorg/mil/mindcontrol/Build_A_Brain_Wave_Feedback_Monitor.pdf The problem I'm running into is that the op-amps (Signetics N5556) are old and just about impossible to find. I've checked all of the electronics outlets I can think of for them, and the other parts were easy enough to source. Does anyone have a link to a shop that would carry something obscure like this? Barring that, could anyone suggest a substitute that's readily available? I'm just a hobbyist that enjoys building weird things so I apologize if this is a goofy question. Any expert advice would be GREATLY appreciated. Thank you!