As I understand it a zero crossing opto turns on just after the start of
a cycle. Like a good solid state relay. Your previous mail said you
want to modulate power, which assumes you are not switching at zero
crossing, but later. Which do you want?
I think one can make power modulation with both types. With zero crossing something like this: "switch on for one cycle, switch off for 3 cycles... and so on." Difference is only in timings. Am I right? I guess I go for the zero crossing type to produce less noise on the mains network, since I run audio equipments too.
Levente