What a phono preamp actually does
A turntable cartridge produces a very small electrical signal, far weaker than the line-level signal a streamer, CD player or computer sends to an amplifier. The first job of a phono preamp, also called a phono stage or phono equalizer, is to raise that signal to line level.
The second job is tonal. Records are cut with the bass reduced and the treble boosted, and playback has to reverse that curve. The history of phono equalization at microgroove.jp explains that the RIAA curve was established in 1954, that virtually all records made today use it, and that the device applying the inverse response on playback is the phono equalizer.
Do you already have one?
The question is never whether you need a phono preamp at all, but where yours is. Look at three places: the turntable, the amplifier or receiver, and any separate box between them.
| What you see | What it means | How to connect |
|---|---|---|
| PHONO/LINE switch on the turntable | Built-in preamp that can be switched on or off | LINE into an AUX input or powered speakers; PHONO into a phono input |
| Amplifier input labelled PHONO | The amplifier has its own phono stage | Turntable output into PHONO, with any built-in turntable preamp off |
| No switch and no PHONO input | Nothing in the chain does the phono job | Add a separate phono preamp between them |
| Powered speakers only | They expect line level | Use the turntable's LINE setting or a separate preamp |
Manuals spell this out. The Audio-Technica AT-LP60-BT manual describes a built-in switchable phono/line preamp: use PHONO for a stereo's phono input and LINE for CD, tape or AUX inputs. The AT-LP8X manual states the opposite case plainly: that turntable has no built-in phono equalizer and must go into a phono equalizer or an amplifier with one built in.
How a wrong connection sounds
- No phono preamp at all: very quiet, thin sound with little bass, even at high volume.
- Two phono preamps in a row: loud, harsh and distorted, with exaggerated bass.
- Turntable set to LINE but plugged into PHONO: the same doubling problem.
- Low hum that changes when you touch the arm: often a missing ground connection.
The thin wire with a spade: grounding
Many turntables have a separate ground lead next to the audio cables. The AT-LP8X manual explains that connecting it to the amplifier's ground terminal helps prevent a low humming noise during playback. If your phono preamp has a ground post, the turntable's ground lead goes there instead.
Ground leads carry no mains power; they only tie the turntable's metal parts to the same reference as the preamp. Connect the lead only to the ground terminal of the amplifier or phono preamp, never to a wall socket, a radiator or household wiring. Our guide on connecting a turntable to speakers shows where the cables go in common setups.
Moving magnet and moving coil cartridges
Most turntables ship with a moving magnet (MM) cartridge, and most built-in and budget phono stages are designed for it. Ortofon notes that moving coil (MC) cartridges have lower output than moving magnet ones, so they need more gain, provided either by an MC phono preamp or by a step-up transformer.
If you change to an MC cartridge, check that your phono stage has an MC setting or enough gain for it. An MC cartridge on an MM-only input usually sounds quiet and noisy.
If you need a separate preamp
Match the cartridge type
Choose an MM preamp for an MM cartridge, or one with an MC setting if you use or plan an MC cartridge.
Check the connections
Make sure it has RCA inputs for the turntable, a ground post, and an output that suits your amplifier or powered speakers.
Switch off the other preamps
Set a turntable with a built-in preamp to PHONO and plug the separate preamp's output into a line or AUX input.
Place it sensibly
Keep the short turntable cable and the preamp away from power supplies, routers and phone chargers, which can add noise.