We adapt this circuit of Radio Electronics - March 1990. The magazine no more exists, but the circuit can be assembled easily. Instead of Rx and a low impedance speaker can be used a small radio transformer. The power supply does not need to be symmetrical and is between 6-30 V. This is an improved version of the previous circuit, with better performance and stability. The advantage of this circuit is the use of a single power supply. The input impedance is high and the source must have excellent filtration.
