Bio-signals are signals that can be measured from a living being. Electrical bio-signals are the result of depolarization and repolarization of the cells in a specialized tissue, organ or cell system. Accurate reading and analysis of signals such as electrocardiogram (ECG or EKG), electroencephalogram (EEG), electromyogram (EMG) etc. is very important as they are used clinically in diagnosing diseases. Hum interference is caused by magnetic and electric fields from power lines and transformers cutting across the measuring electrodes and patients. This type of noise seems to be ever-present, although the modern noise reduction techniques are successful in minimizing this in signal recordings. We discuss a method to minimize such interference using a pre-amplifier design with a very high common mode rejection ratio of 131 dB at 60 Hz and high input impedance. A comparison of the design with the commercially available Instrumentation Amplifier is also done. We verify our results using computer simulation of an ECG signal via the software Multisim.