I lifted the ground with an adapter and the hum stopped — why do people say that is wrong?

Lifting the safety earth at the mains plug removes protection, even though the hum goes. The safe version lifts only the signal ground; better still, a 1:1 isolation transformer in the audio run costs 0.5–1.5 dB and stays put. Use the adapter as a diagnosis, then wire the real fix.

Everything is unplugged except one box and it still hums — what now?

Then the hum is born inside that box or in the cable run entering it. Swap that cable first — especially a foil-shielded one whose drain may float — and if the buzz sits at 100/120 Hz, the box's own power supply is the suspect.

Will a better braided cable fix the hum?

Only if the hum is a shield-termination problem, and braid tops out at 60–90% coverage anyway. Foil reaches 100% but only with the drain wire terminated at one end; name the frequency first, then shop for cable.

My spectrum shows a peak at 50.1 Hz — is that really mains hum?

Yes — European grids hold 49.8–50.2 Hz, so 50.1 Hz is squarely a genuine mains peak. A suspect peak would wander wider than about 0.2 Hz, and a rectifier would stack 100, 150 and 200 Hz beside the base.

50/60 HzMains hum frequency, by region

100/120 HzRectifier buzz after a full-wave supply

50–80 dBExtra hum rejection on balanced runs

0.2 HzTolerance on European mains

Silence the speaker hum

Hum Ham — Fixing mains hum and buzz in home and studio | humham.com

A hum from your speakers is almost always one of two signals: mains frequency sneaking in through a ground loop, or the doubled frequency a power-supply rectifier sprays into the audio path. Name which one you have and the fix picks itself; skip the diagnosis and you can swap cables forever.

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Find the frequency, break the loop, quiet the speakers.

Three passes

The routine at a glance

0.2 HzTolerance on European mainsContinental grids hold 49.8–50.2 Hz, so a genuine mains peak stays within about 0.2 Hz of 50 Hz.

10–15 mPractical limit for unbalanced cable runsMicrophone-grade cable at 30–70 pF per metre starts losing high frequencies and collecting hum past this length.

-60 dBFSHum level that is plainly audibleReal converter floors sit at -110 to -120 dBFS, so a -60 dBFS hum towers over the noise on any monitor.

Symptom-to-fix table

Symptoms, frequencies and the first fix to try
What you hear	Peak on a spectrum app	Likely cause	First move
Low steady drone	50 Hz, within ±0.2 Hz	Ground loop or transformer field	Run the unplug-one-box routine
Harsh buzzing edge	100 Hz plus 150/200 Hz	Full-wave rectifier noise	Check the power supply, not the cables
Same buzz on a 60 Hz grid	120 Hz plus 180/240 Hz	Rectifier harmonics	Isolate or service the noisy supply
Hum with hands on platter	50 or 60 Hz	Turntable earth wire off	Reconnect the earth to the phono post
Hum that grows with cable length	50/60 Hz rising past 10–15 m	Long unbalanced run	Shorten the run or switch to balanced
Hum on an unbalanced patch	50/60 Hz at -10 dBV level	No common-mode rejection	Move to balanced XLR at +4 dBu
Buzz on a foil-shielded lead	100/120 Hz	Drain wire not terminated	Land the drain at one end only

Symptoms, frequencies and the first fix to try

Step 1 — Name the frequency before you touch a cable

A peak near 50 or 60 Hz is mains hum; a peak near 100 or 120 Hz is power-supply buzz, and each has a different cure.

Your grid decides the base frequency. Most of Europe, the UK and Asia run 220–240 V at 50 Hz; North America runs 120 V at 60 Hz; Japan splits at Nagoya, 50 Hz to the east and 60 Hz to the west. Anything humming along that grid enters at that base frequency.

A full-wave rectifier doubles whatever the grid delivers. On a 50 Hz system the buzz appears at 100 Hz with further harmonics at 150 and 200 Hz; on a 60 Hz system it lands at 120 Hz with 180 and 240 Hz above it. Buzz sounds harsher than hum precisely because of those higher harmonics.

Use your ears or a free spectrum app on a phone. A genuine European mains peak stays within about 0.2 Hz of 50 Hz, because continental grids are held inside 49.8–50.2 Hz in normal operation. A peak that sits at exactly 100 Hz with a friend at 200 Hz is the rectifier talking, not the grid.

Hum vocabulary, defined once

Mains hum: A 50 Hz signal (60 Hz in North America) that leaks into audio through magnetic fields or a ground loop. It sounds like a low, smooth drone.
Rectifier buzz: The doubled, harmonically rich noise a full-wave power supply adds: 100 or 120 Hz plus harmonics at 150/180 and 200/240 Hz. Harsher and more nasal than mains hum.
Ground loop: A closed ring created when two devices share earth at both ends of a cable. Mains current flows round the ring and lands in the audio.
Common-mode rejection: The ability of a balanced input to ignore noise arriving equally on both signal wires. Balanced +4 dBu runs reject hum 50–80 dB better than unbalanced ones.
Drain wire: The bare conductor running alongside a foil shield. The shield only screens when this wire is terminated at one end of the cable.
Insertion loss: Signal level lost by passing through a device. A 1:1 line-level isolation transformer costs about 0.5–1.5 dB.

Objections from the workbench

I lifted the ground with an adapter and the hum stopped — why do people say that is wrong?: Lifting the safety earth at the mains plug removes protection, even though the hum goes. The safe version lifts only the signal ground; better still, a 1:1 isolation transformer in the audio run costs 0.5–1.5 dB and stays put. Use the adapter as a diagnosis, then wire the real fix.
Everything is unplugged except one box and it still hums — what now?: Then the hum is born inside that box or in the cable run entering it. Swap that cable first — especially a foil-shielded one whose drain may float — and if the buzz sits at 100/120 Hz, the box's own power supply is the suspect.
Will a better braided cable fix the hum?: Only if the hum is a shield-termination problem, and braid tops out at 60–90% coverage anyway. Foil reaches 100% but only with the drain wire terminated at one end; name the frequency first, then shop for cable.
My spectrum shows a peak at 50.1 Hz — is that really mains hum?: Yes — European grids hold 49.8–50.2 Hz, so 50.1 Hz is squarely a genuine mains peak. A suspect peak would wander wider than about 0.2 Hz, and a rectifier would stack 100, 150 and 200 Hz beside the base.

How this guide was put together

This page was assembled as a procedure: frequency identification first, loop isolation second, then a choice between shield re-termination, balanced cabling and isolation. The numeric limits — grid tolerances, shield coverage, connector levels, insertion loss — are common reference figures in audio engineering, restated here without product endorsement.

Where the numbers come from

The figures are drawn from widely published grid tolerances, audio level standards and cable specifications; nothing here depends on a single vendor's datasheet.