ZX-Spectrum +3's amplifier connection
If it is needed the +3 can be connected to an amplifier using the TAPE/SOUND socket. This is a 3.5mm jack socket producing 200mV pk-pk at approximately 5 Kohms impedance. When using an amplifier, it is worth remembering that if you have connected a cassette unit to the +3, the tape 'load' and 'save' signals are also fed to the TAPE/SOUND socket (and therefore the amplifier's volume control should be turned down when performing these operations).
Input (not used) | | ___ ___ _ v | --_ (not used) \/ | | _ _____| -.___________ | | ()[_[_____| |___________ Audio output _/\ |_| ^ | | _-' | | | |___-- GND (common) _______| | | Audio GND output (common) TAPE/SOUND socket
Source: [The Hardware Book]