Here's a simple microphone amplifier based around TDA7050 IC. There are many schematics, the choice fell on the amplifier chip TDA7050, the only downside was it that it was not appointed to the microphone. By adding a resistor R1 in the scheme by 4,7 kOhm - amplifier can no longer work with conventional condenser microphones.
If you remove the resistor R3 - the alarm will be put on a small speaker with an impedance of winding 32 Om'a.
Voltage amplifier is powered by 3 - 5 volts, but as the amplifier must be nourished from 12 in the scheme of linear stabilizer was added at 5 V.
This scheme was checked with headphones (current consumption was 50 mA) and connect to the line input of your TV.
Build Accurate LC Meter and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils. LC Meter can measure inductances starting from 10nH - 1000nH, 1uH - 1000uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging and reset function to make sure the readings are as accurate as possible ... [more]