We consider a two-hop Multiple-Input Multiple-Output channel with a source, a single Amplify and Forward relay, and the destination. We consider the problem of designing precoders at the source and the relay, and the receiver matrix at the destination. In particular, we address the problem of optimal power allocation scheme at the source which minimizes the source transmit power while satisfying a given Quality of Service requirement at the destination, and a power constraint at the relay. We consider two types of receiver at the destination, a Zero Forcing receiver and an Minimum Mean Square Error receiver. Simulation Results are provided in the end which compare the performance of both the receivers.