I m using the schematics from http://kitrus.com/projects/k49.pdf to build my receiver and i m using a 555 timer to drive the transmitter at 40KHz instead of the crystal oscillator circuit. Thing is my receiver is only sensitive to loud/sharp noises, even if the transmitter is not ON. the only changes to the receiver circuit is a BC547 in place of the BC639 and 1N4007 for the 1n4002/4. So... i need help, wat do u guyz think is wrong