We're trying to build this intercom,
http://www.zen22142.zen.co.uk/Circuits/Misc/intercom.htm and the speaker amplifier section and relay switch works just fine but im having a hard time troubleshooting the mic preamp.
We used 2terminal electret mic instead of the 3terminal shown on the schematic, and an MPS2222a transistor instead of a BC109C. I've compared the datasheets of the transistors but i've no idea what to consider first.
http://www.zen22142.zen.co.uk/Circuits/Misc/intercom.htm and the speaker amplifier section and relay switch works just fine but im having a hard time troubleshooting the mic preamp.
We used 2terminal electret mic instead of the 3terminal shown on the schematic, and an MPS2222a transistor instead of a BC109C. I've compared the datasheets of the transistors but i've no idea what to consider first.
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