sound activated circuit

hi guys and girls, im very new to electronics i only have minor experiance with it.

i would like some suggestions, this is what i need the circuit to do.

circuit must switch on with nois
switch off when nois stops
must be as small as possible(but big enough to make)
components must be available from local electronic store.
power supply is a 6cell AA battery pack
circuit runs a race motor

the application of this circuit is in a paintball loader(hopper)
the motor currently runs continuously which is noisy and draws alot of power.
i would truly appreciate any input or links to websites that could help.

You can amplify the signal out of a microphone, then use a rectifier to convert it to DC and then detect this DC value with a transistor which will drive your motor (with a relay if needed).

Here are some circuits:

http://www.rev-ed.co.uk/docs/picaxe_sound.pdf

http://www.alanovington.com/audio_detection_circuit.htm

Then the microphone hears the noisy motor and it keeps going forever.

thank you ill take a look at those circuit boards.

my consern at this stage is that it must turn off when there is no sound.