Automatic Charger for Battery Hi-Fi Preamps

Posted on Nov 25, 2012

This project is one for the experimenter, but as shown will work extremely well. The sensing circuit can be made so sensitive that a load of only 2.5mA is enough for the circuit to detect, and disconnect the charger. The idea is that the charger is left permanently connected, but of course that would normally introduce some hum into the supply lines.

Automatic Charger for Battery Hi-Fi Preamps
Click here to download the full size of the above Circuit.

The sensor detects that you have switched on the preamp (or small power amp for that matter), and immediately switches off the charger, so while listening, there is no connection to the AC. Although it is possible to use a "solid state" switch,

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