A low hum or buzz from your speakers can come from the amplifier itself or from the way your system is connected. The good news is that the most common cause costs nothing to fix.
Step 1: find out where the hum comes from
- Turn the volume right down. If the hum stays at the same level whatever the volume, it’s likely coming from the amplifier’s power stage or a connected device.
- Unplug every input cable from the amplifier, leaving only the speakers connected. If the hum stops, the problem is in a connected device or cable.
- Reconnect devices one at a time to find the culprit.
Ground loops: the usual culprit
When two devices are earthed through different paths, such as an amplifier and a TV connected through a cable or antenna, a small current flows along the audio cable and you hear it as hum. Try plugging all the audio equipment into the same power board, and disconnect the TV antenna or cable box briefly to test. Never remove the earth pin from a plug to cure hum; it’s dangerous.
When it’s the amplifier
Ageing capacitors
The large filter capacitors in an amplifier’s power supply smooth out the mains. As they age, they lose capacity and a steady hum appears, getting worse over time. This is very common in amplifiers more than 15 years old and in vintage gear.
Transformer hum
A mechanical buzz from inside the case, which you hear even with the speakers disconnected, comes from the power transformer. It can be caused by loose mountings or by DC on the mains supply.
Noisy volume or tone controls
Crackling or scratching when you turn a knob is dirty or worn controls, not hum, but it’s often the next thing to go. Cleaning or replacing them fixes it.
Safety first
Amplifier power supplies hold dangerous voltages even when unplugged. If the hum is coming from inside the amplifier, don’t open it up.
Getting it repaired
We repair stereo amplifiers, AV receivers and powered speakers from Yamaha, Denon, Marantz, Onkyo, Pioneer, Rotel, NAD and many more. See amplifier repairs or vintage hi-fi restoration.