Hello, I wonder if anyone has seen this problem before, or can figure out what I am doing wrong: I am using an LM339 quad comparator to find zero crossings of signals from current transformers, at 60 Hz (circuit attached). I am using all four comparators in the chip, with each comparator using the same LM358 circuit schematic. The LM358 amplifying circuit works fine and using any one comparator of the LM339 produces a clean square wave output. The Problem: It seems that the two comparators on the low-number-pins (1 to 7) interract with each other and the two comparators on the high-number-pins (8 to 14) interract with each other. For example, if I put a CT input to AC1 and a CT input 180 degrees out of phase into AC3, the LM339 output for AC1 is zero, or a very narrow pulse. Those same two inputs applied into AC1 and AC2 (or AC1 and AC4) look just fine on the LM339's outputs. If the two inputs are in phase, the output is "normal" with maybe some distortion. If I connect the output of AC3's LM358 into a different LM339 chip, its output looks clean and normal. The circuit doesn't show that I've put .01uf to 10uf caps across the LM339's power and ground pins, with no effect. What can be done to prevent this interraction between the comparators on the same chip? Thanks for any comments.