This paper describes an experimental study aimed at stabilizing the wake of a shedding bluff-body by means of closed-loop active flow control at low Reynolds numbers. A D-shaped (6.5mm thick) cylinder was used in order to allow a direct wake interaction rather than mixed wake-boundary-layer separation control. The internal fluidic actuators, installed inside the thin body, were ideally located at the separation locations, i.e., the trailing edges' upper and lower corners. The wake unsteadiness was estimated by a pair of hot-wires, while a single surface-mounted hot-film sensor was used as a frequency and phase reference for closed-loop control. The hot-film signal was contaminated by noise. Hence, a technique for real-time tracking of a low signal-to-noise ratio (SNR) signal was necessary. This was achieved by using Phase-Locked-Loop (PLL) algorithm, common in communications but applied here for the first time for flow control applications. The closed-loop scheme was based on real-time measurement of the wake-unsteadiness (using the surface mounted hot-film sensor), and control authority based on internal fluidic actuators. By using opposition control at frequencies close to the natural vortex shedding frequency it was possible to significantly reduce the wake unsteadiness. Applying the same approach, but sensing the wake hot-wire signal as the controller input, rather than the surface mounted hot-film signal, did not result in wake stabilization. On the contrary, the unsteadiness increased at all tested conditions. It is expected that a similar approach would work at much higher Reynolds numbers as well, as long as a clearly identifiable and nominally 2D vortex shedding occurs, even when the background flow is fully turbulent.