Portable stereo systems commonly known as boomboxes have been popular since the growth of hip-hop in the 1980s. Attaching a boombox to a microphone input on an amplifier or public address (PA) system is a simple way to boost the boombox volume or combine music from the boombox with a microphone or instruments.
Turn the volume on the boombox to zero. If the output is live when you connect it to the microphone input, it can cause a spike in voltage that could damage your equipment.
Locate the output on the boombox, likely to be a headphone jack with a 1/4-inch or 3.5-millimetre connection. Headphone outputs have a very low impedance due to the small quantity of power required to drive a pair of headphones, and the signal can be lost or degraded if connected to a system with a high-impedance configuration. A "line out" connector, if available, is a much better option because it has a higher impedance and is designed for connecting the boombox to other audio equipment. It will probably use a 1/4-inch or 3.5-millimetre jack, but could require a pair of RCA connectors like those used with hi-fi equipment.
Connect the cable to the output on the boombox, using an adaptor if necessary. If the amplifier or PA system has multiple microphone inputs, choose one and reduce its volume to zero.
Plug the free end of the cable into the input channel of the amp or PA system. Increase the volume on the microphone channel to the zero point. If using an amplifier, this will involve turning an "input gain" knob to the 12 o'clock position. Turn the master volume down to about one quarter.
Play music on the boombox and gradually increase the volume until it starts to sound distorted. Reduce the volume until you find the loudest level without overdriving the sound. If the overall volume needs further adjustment, use the gain or volume controls on the amplifier.