Patent ID: 7266206

Claim:
A channel down mixing apparatus for a car audio system, which has a channel down mixing function for down mixing a sub-woofer signal to an L (left) channel and an R (right) channel when a user does not select a sub-woofer speaker on/off signal terminal, the apparatus comprising: a pair of buffers that amplify an L channel input signal and an R channel input signal to a designated gain, respectively, in which a resistor is serially provided before each respective buffer; a pair of FETs that mix the sub-woofer signal with the L channel input signal and the R channel input signal when the user does not select the sub-woofer speaker on/off signal terminal, and output a mixed signal to each of the buffers; a pair of parallel resistors connected in parallel to the serial resistors that are inserted between an output end of each of the FETs and an input end of each of the buffers; a first transistor being configured to be turned on when the user turns on the sub-woofer speaker on/off signal terminal; and a second transistor and a third transistor, which are configured to be turned off when the first transistor is turned on and turned off when the first transistor is turned on, thereby reducing the L channel input signal and the R channel input signal to a designated level, respectively.