switching problems with bjt

Hi, i have a problem in using a C1815 xsistor,when d emitter is earthed it prevents my cct 4rom switching.Will a mosfet solve dis as i cannot put an emitter resistor to maintain my time constant.Can i gnd d source directly?The switching is to be at d same time with another switch,one to produce a siren sound and d other 4 wave shaping to make d sound perfect.Also what kind of mosfet do i use?

Please use proper English with complete spelling for all words.
Attach your schematic so we can see what you are trying to talk about.

you are probably talking about modulation of your siren sound, C1815 can do the job, but audioguru cannot help without a schematic.

d frst ting ya nd tu du iz cm un ik 8 wit ot he rz n a clr mn nr