What freakdude explained is absolutely right. The same thing i was trying to explain but couldnt get the proper word the "lead". Our HU is not having this lead with the help of which the amp can switched on only when HU is ON. Now what is happening, whenever we switch on the ignition the amp start draining power from battery though HU is switched off and engine is not started. We have to be very carefull not switch on the ignition unnecessarily. All modern after market HU and amp comes with this facility. My dealer said if change the HU, there will not be any need of gain convertor.