I'm building a wired helmet to helmet intercom for me and buffy and if its successful I will sell them, estimated price is $40 a set which comes in a fair bit cheaper than some of he other options out there.

anyway, so its all working except the smaller microphones I use dont work, in fact, they sometimes pickup radio!

When I was testing I used a bigarsed un-powered microphone,

and it worked fine, but when I moved to smaller ones, out of a cellphone handsfree unit or a computer mic/headset unit it didnt work. I tested the mic's plugged straight into a computer and they work fine but dont work plugged into the amp,

whats the difference?

Cheers

edit: the big mike is a Philips SBC MD150, the small ones i tried were from a nokia handsfree set and a logitec headset+mic setup