The basic idea of this circuit was found in the American magazine Elementary Electronics 1980, but with some changes can be mounted easily today with a BC548 or BC549 transistors, for example. It is an active filter that amplifies only the bass for application in a separate amplifier with an output woofer. It is an interesting circuit for those who want to implement your home theater. The circuit can be powered with a 9 V battery, because its consumption is very low. The circuit can also be powered by the same source of the amplifier used for the woofer. We suggest that the amplifier is at least about 30 W for good results. Input signals and output cables must be shielded to avoid noises, mainly due to the fact that the circuit gain is high at low frequencies. One can add a switch that allows the signal to pass directly from the input to the output.