From AKG, the HPA 4000 is a headphone signal amplifier with 8 inputs and a single headphone output. Up to 8 SR 4000 or SR 400 receivers can be connected and monitored via the single headphone output. The control dial enables input channel switching and muting for added control and isolation. The LED display provides channel signal status. The HPA 4000 is an ideal solution for monitoring multiple SR 4000 receivers in complex arrays.