Turntable Hum: Grounding, Ground Loops and the Fixes

The short answer: if the hum drops when you touch the tonearm, the deck is not earthed properly — land its ground wire on the ground terminal of whichever box holds the phono input. If the hum is there with everything earthed, suspect a ground loop and try removing that wire instead. If it only appears at volume while a record plays, it is not a grounding fault at all; it is feedback. Two of those three fixes cost nothing, which is why the diagnosis comes before any purchase.

Why a turntable is the one source that hums

A phono cartridge puts out a few millivolts — Audio-Technica publishes 4 mV nominal for the AT-VM95E against 240 mV from the same deck’s line output. That tiny signal then gets amplified by around 36 dB in a phono stage before anything else touches it. Anything that leaks into the cable before that amplification is amplified along with the music, which is why a CD player sitting in the same rack is silent while the turntable hums. It is not a flaw in your deck; it is the consequence of the smallest signal in domestic audio.

That is also why the earth matters. A cartridge sits inside a metal arm and a metal chassis which, if left floating, act as an aerial for the mains field in your walls and your equipment. Earthing the chassis gives that interference a path that is not through your phono input.

The three hums, told apart

Case one: the ground wire

Most turntables with RCA outputs have a thin separate lead, usually ending in a spade or a bare tail, whose only job is to earth the chassis. It goes on the box that contains the phono input, which is the part people get wrong. With an outboard phono stage, that is the stage’s GND post. With a receiver or integrated amp, it is the ground terminal beside the PHONO input. With powered speakers that have a phono input, it is their ground screw — Klipsch publishes a switchable phono/line input “with switch and ground screw terminal” on the R-50PM and R-40PM, and prints a connections page for a turntable in the manual.

Three practical details. Land it on bare metal, not paint or anodizing. Make sure it is tight — a spade resting against a post is not a connection. And if your deck’s built-in preamp is switched to LINE, you are bypassing the phono input entirely, so the ground wire has no useful destination on that path; switch to PHONO or use the line output consistently, not half of each.

Case two: the ground loop

A ground loop is the opposite problem: too many earth paths rather than none. Two pieces of equipment earthed to the mains and also joined by a signal ground form a loop, and a small circulating current in that loop appears as a steady hum. The signature is counterintuitive — everything is wired correctly and it still hums, or adding the ground wire made it worse.

The test is free and reversible: disconnect the turntable’s ground lead and listen. Some decks, particularly those whose power supply already earths the chassis, are quieter without it. If that is your system, leave it off and label it so nobody “fixes” it later. What we would not do is start cutting earth pins off mains plugs, which is how a hum fix becomes a safety problem — that is the one line in this whole topic worth refusing to cross.

Case three: induced hum from a power supply

This one is physical housekeeping and it is remarkably common in small systems. Wall-wart power supplies, the transformer inside an amplifier, and mains cables all produce a field. A phono cable carrying 4 mV that runs parallel to one of those for half a meter will pick it up. Audio-Technica’s own manual for the AT-LP120XUSB is published with the deck’s own supply and cabling in mind, and the same rule applies to any deck: keep the phono cables away from the power leads, cross them at right angles rather than running them side by side, and if a phono stage runs off a plug-top supply, put the supply at the amplifier end rather than beside the cartridge.

If you have an unshielded or damaged phono cable, the same hum appears for the same reason. A captive lead that has been bent sharply at the plug for years is a candidate; so is a cheap extension on the phono side. On decks with detachable output cables this is a five-dollar test.

The fourth noise: feedback, which is not hum

If the noise only appears when a record is playing and the volume is up — a low boom, a muddy bass, or a howl that climbs — that is acoustic feedback. Sound from the speakers is driving the plinth and the stylus is reading it, which produces more sound, which drives the plinth harder. No ground wire anywhere will touch it.

The fixes are mechanical: get the speakers off the same furniture as the turntable, put them on stands, and if the deck is on a flexing shelf or a suspended floor, decouple it — isolation products are ranked on published load rating for exactly this job. Starting from a deck that is level and on something rigid removes most of the problem before you buy anything. If the noise is a skip rather than a hum, the skipping guide has its own diagnostic order, and troubleshooting covers every other symptom.

What to look for if you are buying to fix it

If the conclusion is that you need a box with somewhere to land an earth wire, the published row to look for is simply whether the maker states one. Fosi publishes a dedicated ground post on the Box X5, which also offers switchable gain at 38, 48, 56 or 66 dB for moving-coil cartridges. Klipsch publishes a ground screw terminal on both of its powered monitors with phono inputs — and notably does not publish one for The Three Plus, which is the kind of omission worth catching before you buy. The Fluance PA10 we rank on our under $100 page is an excellent moving-magnet stage that does not publish a ground terminal, so it suits a deck that has no ground wire rather than one that does. That is the whole shopping rule: match the terminal to the deck you own.