This paper deals with the investigation of modified boost converter with improved voltage gain for automotive audio amplifiers. A new battery powered modified boost converter consisting of two phases used in automotive audio amplifier is presented. The first phase uses a conventional boost converter and the second phase uses its inverted structure. By the proposed technique, a high voltage gain is obtained compared to the conventional boost converter. A 120W circuit is designed with an input voltage of 12V and duty cycle of 0.67 to achieve an output voltage of 60V. The converter achieves voltage gain of five, conversion efficiency of 98.4% and the full load efficiency of 91.35%. A new type of class D amplifier is presented and analyzed. Class D amplifier has high efficiency and used when high audio frequency and low power consumption is required. Simulation of the amplifier for an input voltage of 60V to achieve an output voltage of 62V is presented. A simulation study of the proposed converter and full bridge class D amplifier is carried out in MATLAB/SIMULINK. The performance parameters such as Voltage gain Voltage stress of the switches Inductor current ripple Switching and conduction losses Efficiency Comparison of operation in CCM/DCM are computed and the results are compared with the conventional boost converter circuit. To regulate the output voltage closed loop average voltage and current control is implemented. A hardware prototype of the modified boost converter and full bridge class D amplifier circuit is built to validate the simulation results.