A device for mixing the outputs of two sensors. The device includes a first input for receiving a signal from at least one first sensor, a second input for receiving a signal from at least one second sensor, a low pass filter for passing signal components of the first input signal below a first frequency, a high pass filter for passing signal components of the second input signal above a second frequency and a mixing circuit for combining the signals passed by the low pass filter and the high pass filter to form a combined output signal. The mixing device may be incorporated into a pre-amplifier for use with an electrified acoustic guitar, or other acoustic stringed instrument, having an under saddle sensor and a second sensor attached to a body portion of the guitar, such as the soundboard. In this way, lower frequencies are taken from the under saddle sensor and higher frequencies are taken from the body/soundboard sensor.