You know you're not going to get any help with a question like that right? If it's homework, do your own homework, if it's not, put in some effort into your project before asking for help.
Open browser
type in url www.google.com
in search field type 'preamp circuit' without the single quotes
click the 'Images' link at the top of page
Woohoo... there's circuit schematics !!!
@mister e : i need a subwoofer pre amp which has a low frequency control to boost its low frequency signal because my amp dont have its own crossover.tnx
@mister e : i need a subwoofer pre amp which has a low frequency control to boost its low frequency signal because my amp dont have its own crossover.tnx
You need a lowpass filter circuit which is half of a crossover circuit. It passes the low frequencies to the subwoofer's amplifier but blocks the higher frequencies.
You should also have the other half of a crossover circuit which is a highpass filter for the other speakers.