The API 3124+ is a high quality, compact, 4-channel mic preamp. It is equipped with the RE-115 K mic input transformer and the proprietary API output transformer found in the 512c single mic pre and throughout the API product line. The unit has an internal 48-volt phantom power supply, which is switchable for each channel, as well as -20dB pad switches that affect both the mic and Hi-Z instrument inputs, both located on the front panel.

Another feature of the 3124+ is that it can provide up to 65dB of gain to an output clip level of +28dBu. Additionally, the Hi-Z front panel inputs feed directly to the op amps, which allow a low level input such as a guitar or bass to be amplified without a matching transformer or direct box. These Hi-Z inputs can take input levels as high as +20dBu, making them perfect for keyboards and other high level devices. The mic preamp outputs are on rear panel male XLR connectors.