Thats correct. Amp designers always refrain from filtering before power supply. Filters do not mean they improve power supply everytime. They have diverse effects depending on original electricity condition. Normally they affect the dynamics of sound adversely. Not everyone will prefer them.Panditji, most amp designers believe that addition of rf and emi filters and surge suppressors mess up the sound. Which is why they don’t have this in their amps. Good designers focus on having large power supplies so that current can be delivered instantaneously on demand and that there is no lag. To them things like filters are band aids and not the right approach to a power supply design.