A Head-Mounted 24-Channel Evoked Potential Preamplifier Employing Low-Noise Operational Amplifiers

A simple circuit employing operational amplifiers yields an inexpensive low-noise biological amplifier. Design parameters are discussed and performance measured. When twenty-four of these amplifiers were incorporated in a head-mounted evoked potential preamplifier, noise increased while common mode rejection and stability decreased. These effects are explained and successfully controlled by minimizing source resistance and adding a simple feedback circuit.