What specific are you plugging into it?
The combination inputs on the QM4 can accept either low-impedance microphone lines (XLR) or high-impedance instrument lines (1/4"). A common mistake is treating these inputs identically. audio choice qm4 manual better
The QM4 supports remote wall plates for volume control in individual zones. The manual provides the exact pinout for the CAT5e wiring. By following the diagram on page 30, you can install a $20 potentiometer to control Zone 3’s volume from a waitress station. This is impossible to guess without the manual. What specific are you plugging into it
For more specific troubleshooting or parts, you can check enthusiast listings on replacement parts for this specific setup? The QM4 supports remote wall plates for volume
Are you experiencing any specific issues?
To help find the exact schematic or layout diagram for your specific unit, let me know:
Microphone feedback is a systemic loop where a microphone picks up its own amplified signal from a loudspeaker. You can configure the QM4 to minimize this risk entirely.