I designed this circuit to provide sound for my CCTV video surveillance system, as it will work over telephone wire or Cat5 cables.This avoids the need for long runs of coaxial cable or an always-on wireless link in an overcrowded radio spectrum.It uses an LM386 audio amplifier to drive two back-to-back audio transformers as part of a basic unbalanced phantom power circuit.It's powered from a 12V DC supply, with the supply voltage to the LM386 IC varying over a range of about 4-6V.A small lOkO potentiometer(VRl)is used to set the sound level.The electret condenser microphone is very sensitive, so continuous loud sounds will cause the amplifier to drop out, as its supply voltage falls too low if its current draw becomes excessive.For this reason, this circuit is not really suitable for music or any continuous high-level sounds, but it's fine as a baby monitor or CCTV microphone.
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