741

This circuit can be used to remotely monitor a loudspeaker, alarm, or audio source for presence of an audio waveform. It can also be directly connected across loudspeaker terminals used as a peak indicator.
If you need to monitor some audio signal at a location that is either soundproof are too far away to actually hear [...]

There will be instances where the currents from each supply will be unequal. Where this is the case, the resistor divider is not sufficient, and the +ve and -ve voltages will be unequal. By using a cheap opamp (such as a uA741), a DC imbalance between supplies of up to about 15mA will [...]

The amplifier gets quite hot while in use, so decided to use a fan to cool it. The fan, however, adds a lot of noise. To get the best of both worlds, I thought I’d turn the fan on only when required. The circuit shown uses two forward-biased diodes, one as a sensor diode (at [...]