Is it normal to hear hum when playing records?

No, a good, well-set-up vinyl playback system should be almost silent and exhibit no audible hum at rest or when playing records.

This is one of the great revelations about vinyl that many folks discover on the journey from basic equipment to more aspirational gear. The short version is that, if you haven’t listened to a serious vinyl rig, you need to, if only to have a reference point for how good vinyl can sound.

What is ‘Hum’?

The term ‘hum’ describes continuous low-frequency tones of a constant frequency or pitch, usually centred around 50/60Hz or 100/120Hz. Hum can be mechanical or electrical in origin and usually indicates a problem in the playback system. Whatever the origin, hum should be tracked down to the source and eliminated or minimised.

Electrical Hum

Electrical hum describes LF tones present in the electrical signal itself, typically injected at a specific point. Bad or missing earths/grounds are a common cause of electrical hum in vinyl playback systems. Poor quality cables and terminations are another common cause.

The high sensitivity and gain of a vinyl playback chain will take tiny ground currents that cause hum and amplify them to the point where they will become an audible problem. Any currents flowing in the ground system will be audible, and so we want to eliminate them.

Current flows between two points with a different potential or voltage. Ground currents that cause hum occur where two elements in the playback chain reference different grounds and therefore sit at slightly different potentials. Bad cables can play a part here, as some do not have an effective ground linking both ends of the cable structure.

The trick, therefore, to ensure a quiet system is to ensure the turntable/pre-amp/amplifier combination is effectively grounded together and that at least one piece is system ground-referenced. All grounds must be of a low impedance, made using clean, high-quality wire and connectors.

Cheap phono preamps, cartridges and cables will always be noisier than good ones, and active preamps will always be noisier than transformers. An English brand of turntables that shall remain nameless opts not to use a separate headshell/arm ground, instead relying on the return/shield of the signal cable for grounding. These decks are noisier than turntables with separated ground arrangements.

Equipment type, set-up and installation can all contribute to electrical hum.

Mechanical Hum

Mechanical hum describes LF tones that have a mechanical or vibrational origin and are picked up, typically by the cartridge itself, when playing a record. Mechanical hum can originate from turntable motors and mains transformers.

This type of hum can often be resolved with specific attention paid to damping and isolation. Transformers in turntables are typically suspended on rubber bushings, for example, and these can degrade and harden. Likewise, belt drive turntable motors usually have some form of elastic coupling designed to reduce the transfer of vibration in both directions.

Acoustic Feedback

Acoustic feedback is a process whereby mechanical vibration from the turntable itself or other equipment can be coupled through the turntable back into speakers, creating what’s called a positive feedback loop. These loops can occur through shelving, for example, shared by speakers and turntables, wooden floors and other resonant structures.

In these cases, hum and other signals make their way to the speakers, which energises the turntable, arm, and record at the hum frequency, which is then fed back into the signal chain and further amplified, hence the term positive feedback. You might have heard something similar at a live show where a microphone is placed too close to a monitor or PA speaker.

Positive feedback loops can very quickly go out of control and destroy speakers and even amplifiers, so if you have a hum that appears to be coupled through your turntable, resolve it or seek expert help immediately!

Rumble

Rumble is another source of low-frequency noise generated by a turntable’s spindle and/or motor bearings. This is typically a broader-spectrum LF noise than hum and may consist of several fundamentals or tones, and their harmonics.

Rumble intensity is generally inversely correlated with turntable price. In other words, the cheaper the turntable, the greater the rumble, and vice versa. This is because cheaper decks have poorer mechanical quality, looser bearing tolerances and greater bearing surface roughness. Consequently, cheap turntables are often rumbly.

More expensive machines have bearings machined to tighter tolerances, better bearing surface finishing, higher quality motors and other parts, heavier chassis, better lubrication, and so on. These elements contribute to lowering the noise floor of better gear, such that it becomes essentially inaudible.

Excessive Low Frequency Gain

Excess low-frequency gain is a more modern system issue, typically involving powerful subwoofers in vinyl playback systems. In such systems, the low frequencies may be boosted via electronic equalisation to compensate for amplifier and speaker non-linearities and room issues.

In such cases, where excessive bass boost is dialled in, especially at cartridge-tonearm resonant frequencies, with cheaper modern turntables that have significant rumble and are not well isolated, serious acoustic feedback may occur. This can break amplifiers, cartridges, and speakers, so again, great care must be taken when using subwoofers in vinyl systems.

Quiet

In well-set-up vinyl playback systems consisting of quality components, correctly connected, there should be no audible hum. The predominant noise in systems like this is groove noise, a residual component of the cutting lathe, the friction between the stylus and the groove itself.

There will also be some phono preamplifier noise in the form of a soft, gentle ‘rushing’ sound that will be inaudible during normal listening. Some white noise is present in all systems, but hum is absent from all good ones.

Mike, by “no hum” do you mean not much hum..?

No. I mean no hum – none, zero, nada! There should be no audible low-frequency components in a good vinyl system. If there are, the system has a weak link letting it down or a poor setup creating a problem, often both.

If you are curious about how quiet a vinyl playback system can be, let me know. If I’m not too busy, I may have a moment to demonstrate my reference system. Tell me then if you hear any hum… 🙂