We propose a new approach for singer melody extraction, based on blind source separation techniques. The short time Fourier transform (STFT) of the singer signal is modelled by a Gaussian mixture model (GMM) explicitly coupled with a generative source/filter model. We then introduce a simplification of this general GMM and approximate the STFT of the music signal using Non-negative Matrix Factorization (NMF) techniques. The melody line is extracted from the explicit source component of the model thanks to a Viterbi algorithm. The results are very promising and comparable or better than those of state-of-the-art systems.