Ground loop hum
TL;DR
A ground loop is an audible 60 Hz (US) or 50 Hz (EU) hum caused by multiple grounded devices creating a current loop through ground wires. Fixed with a ground-loop isolator on RCA connections or by using balanced XLR (which rejects ground noise).
A ground loop occurs when audio equipment is grounded via multiple paths (different outlets, cable TV coax, USB from a computer) creating a current loop. This loop picks up 60 Hz mains hum which becomes audible in your speakers.
Symptoms
- Steady low hum (60 Hz) or buzzing (120 Hz harmonics)
- Louder when volume is high; audible during silent passages
- Comes and goes when you touch chassis or move cables
Fixes
- Ground loop isolator – $15 device that goes inline with RCA cables
- Balanced XLR – Balanced connections reject ground noise inherently
- Cheater plug – 3-to-2-prong adapter breaks ground loop (safety concern, use only as diagnostic)
- Isolate cable TV coax – a common ground loop source
- Plug everything into the same outlet – single ground point
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