Hum Ham — Fixing mains hum and buzz in home and studio | humham.com
Five unplug-and-listen passes isolate the device that closes the loop; then you pick between a lift as a test and an isolation transformer as the fix.
A ground loop exists when two devices share earth at both ends of a cable, so the safety ground and the signal ground form a ring. Mains current flows round that ring and the audio wiring picks it up, which is why loop hum is a steady 50 or 60 Hz drone rather than a harsh buzz.
The isolation routine is mechanical. Power the system, confirm the hum, then unplug one device — starting at the far end of the chain — and listen for a few seconds. Reconnect if nothing changes and move one box closer to the amplifier. The moment removing a device drops the hum, that device completes the loop and the cable run attached to it is your worksite.
On narrow screens, swipe or scroll the plate sideways.
A ground lift on the signal line proves the diagnosis in seconds: hum gone, loop confirmed. It is a legitimate test and a poor lifestyle. Never disturb the protective earth on a mains plug; the lift belongs on the signal ground only, and even there it should stay temporary.
The durable fix is a 1:1 line-level isolation transformer placed in the offended run. It passes the signal while breaking the galvanic ground path, and it costs about 0.5–1.5 dB of insertion loss — inaudible at line level. Where the loop arrives on a coax TV or antenna feed, isolate that path instead.
Two habits keep loops from returning. Keep unbalanced runs under 10–15 m, because longer single-ended cable collects field-induced hum, and prefer balanced interconnections, which reject common-mode hum 50–80 dB better over the same distance.
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