You wrongly connected the emitters of the transistors together! Why?
Look at the original circuit from RED Circuits where the collectors are connected together and the grounds are connected together.
Maybe you don't know which pin is the collector or emitter on a schematic so I labelled them here.
The sound from the master's mic is fed through its transistor to the amplifier in the slave where it is attenuated a little with R10 and R11 then amplified so it will be fairly loud.
(The original circuit used the TDA7052 (39dB gain) which has more gain than the TDA7052A (35.5dB gain). Also the TDA7052 has an input impedance of 100k but is only 20k for the TDA7052A so the attenuation by R10 and R11 in Boncuk's circuit is more than with the TDA7052.)
The sound from the slave's mic is fed through its transistor to the amplifier in the master where it is attenuated a little the amplified so it will be fairly loud.
You are supposed to adjust trimpot R7 so that no sound from the Master's mic comes out of its speaker and you are supposed to adjust trimpot R7A so that no sound from the slave's mic comes out of its speaker.
Look at the original circuit from RED Circuits where the collectors are connected together and the grounds are connected together.
Maybe you don't know which pin is the collector or emitter on a schematic so I labelled them here.
The sound from the master's mic is fed through its transistor to the amplifier in the slave where it is attenuated a little with R10 and R11 then amplified so it will be fairly loud.
(The original circuit used the TDA7052 (39dB gain) which has more gain than the TDA7052A (35.5dB gain). Also the TDA7052 has an input impedance of 100k but is only 20k for the TDA7052A so the attenuation by R10 and R11 in Boncuk's circuit is more than with the TDA7052.)
The sound from the slave's mic is fed through its transistor to the amplifier in the master where it is attenuated a little the amplified so it will be fairly loud.
You are supposed to adjust trimpot R7 so that no sound from the Master's mic comes out of its speaker and you are supposed to adjust trimpot R7A so that no sound from the slave's mic comes out of its speaker.