Posted on Jul 16, 2012

This circuit is a bidirectional amplifier that can amplify both signals of a duplex telephone conversation. It uses the principle of negative resistance. Obviously, such an amplifier could easily be unstable; however, you can adjust Rl for maximum amplification and the circuit will remain stable.

Click here to download the full size of the above Circuit.

The LM324 op amps can be replaced with op amps that would distort less, such as the LM1558, LF412, LF353, or LF442.

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