My mfx is zoom g1xon... I just wonder how to bypass preamp and use my built in amp simulation..
It only has input and output. If i send it directly to d input it sounds terrible.
Without an fx loop in your amp you cannot bypass the preamp and so the main input is the only place you can plug the pedal into. Having said that you can still use the amp models if you want to. If you set your amp to completely clean with a flat Eq, you could use the zoom like it is running into the Fx return. Otherwise you could just use the effects on the zoom with your amp.
The G1Xon is designed to go between guitar and amplifier. In what way does it sound terrible? Try setting each effect in the patch to Off. Does it now sound as if it isn't there at all (it should!). Maybe you're just trying to make it add too many effects, or ones you didn't really want. It CAN be a 'multi' effect. It doesn't HAVE to be!