An electronic vox (voice controlled switch)circuit can be designed using some electronic components, as in the diagram below.
The electronic vox (voice controlled switch) described in this scheme can be electronically connected to almost any audio device that has an external speaker jack. The threshold is set by potentiometer the amplifier volume control AF-VOX's. Signal from R2 is connected across the capacitively in the base of T1. Resistance R3 limits the current of the transistor, in cases where the input voltage exceeds 600 mV. Diode D1 blocks the positive excursion of the input signal so that it can not be more than about 0.6 V.
Relay output circuit is controlled by Darlington transistor T2. VOX Current consumption is mainly the amount of current through the coil and R5.