Zero Cross Detection circuit for review

Douglas Beeson · 2014-06-10T21:57:14+00:00

Hello all, I'm back again with an audio zero-cross detection circuit that I have desig ned based on valuable feedback from some of you (notably Jim Thompson and J ohn Fields). I am trying to gate an audio signal while avoiding clicks as i t switches on and off. I'm submitting the LTSpice file here for your comments and also to ask why one thing does not seem to be working as intended: The output from the two LM339 comparators seems to go all to hell once some part of input frequency goes over 1000 Hz or so. It all works fine at lowe r frequencies, and if there is just one comparator instead of two (but I ne ed two to handle zeroes at rising and falling). I haven't built the actual circuit in real parts (lab is a bit of a mess at the moment), but LTSpice i s usually far wiser than me, so I must have a flaw in the logic somewhere! Thanks for your comments and help. doug beeson PS: Links for the referenced libraries are here: Version 4 SHEET 1 1752 2420 WIRE -384 208 -384 192 WIRE -224 256 -224 240 WIRE -112 256 -112 240 WIRE 0 256 0 240 WIRE -384 288 -384 208 WIRE -224 288 -224 256 WIRE -112 288 -112 256 WIRE 0 288 0 256 WIRE -384 448 -384 368 WIRE -224 448 -224 368 WIRE -224 448 -384 448 WIRE -112 448 -112 368 WIRE -112 448 -224 448 WIRE 0 448 0 368 WIRE 0 448 -112 448 WIRE -112 480 -112 448 WIRE 624 672 624 640 WIRE 976 704 976 672 WIRE 320 736 320 720 WIRE 320 784 320 736 WIRE 784 784 768 784 WIRE 880 784 784 784 WIRE 1088 784 1072 784 WIRE -384 800 -448 800 WIRE -240 800 -304 800 WIRE 112 800 64 800 WIRE 288 800 192 800 WIRE 416 816 352 816 WIRE 624 816 624 752 WIRE 624 816 496 816 WIRE 672 816 624 816 WIRE 880 816 672 816 WIRE 288 832 208 832 WIRE -368 896 -368 864 WIRE 320 896 320 848 WIRE -704 912 -720 912 WIRE -624 912 -704 912 WIRE -448 912 -448 800 WIRE -448 912 -544 912 WIRE -400 912 -448 912 WIRE 320 912 320 896 WIRE -240 928 -240 800 WIRE -240 928 -336 928 WIRE -192 928 -240 928 WIRE -48 928 -112 928 WIRE 48 928 -48 928 WIRE 208 928 208 832...