Phono Preamps

A phono stage does two jobs that nothing else in a system does. It amplifies a signal thousands of times smaller than a line output without adding audible noise, and it undoes the equalisation every record is cut with. Records are cut with the bass reduced and the treble lifted, because a full sized bass groove would be enormous and quiet treble would vanish into surface noise. The RIAA curve puts it back, and a stage that gets that curve wrong gets the tonal balance of every record you own wrong with it.

The confusing part is that you may already have one. Plenty of turntables have a phono stage built in, plenty of amplifiers and receivers have a phono input, and some powered speakers do too. If a record player works plugged into a line input, something in the chain is already doing this job.

Your cartridge decides this, not your budget. A moving magnet cartridge wants roughly 40 dB of gain, and almost every phono stage on the market supplies it. A moving coil puts out a small fraction as much and wants 60 dB or more, which is a different design problem. A moving coil plugged into a moving magnet input sounds thin and quiet rather than obviously broken, which is why people live with it for months without realising.

If you own a moving magnet cartridge, the specification that matters most is capacitance, and it is the one least often printed on the front of the box. The cartridge is designed to see a particular load and the tonearm cable is already contributing part of it. A stage that lets you set the loading is worth more than a stage with a better distortion figure and no adjustment at all.

If you own a moving coil, gain and noise are the whole argument. The signal is small enough that the noise floor of the first stage is audible in quiet passages, and that is what separates a good design from an adequate one. Adjustable impedance loading matters here too, and unlike capacitance it is worth experimenting with by ear.

Built in, separate box, or inside the amplifier is a question about noise and convenience. A phono stage is amplifying microvolts, so it dislikes sitting next to a power transformer, a motor or a wireless router. A separate box can be put somewhere sensible and powered cleanly. A built-in one is already there and already works.

One last thing if you are starting out. If the stage inside your turntable is doing the job, a better cartridge or a proper setup will usually give you more than a better phono stage will.

RIAA accuracy is the specification that actually describes the sound and it is rarely advertised. A stage whose curve is off by half a decibel across a broad range is a tonal tilt on every record you own, which is a larger effect than any distortion figure anybody prints.

Gain is not volume. The right gain is the amount that lifts your cartridge's output to line level, and more than that improves nothing. Too much overloads the input of whatever comes next on loud passages, which is heard as hardness in the peaks and then blamed on the cartridge.

Hum is the standard failure and it is almost always the ground. The turntable's ground wire goes to the phono stage's ground post, and if the hum survives that, the next things to change are which sockets everything shares and the order it was plugged in. This is a wiring problem and no amount of money spent on components fixes it.

Subsonic energy is the invisible one. Warped records, and the arm and cartridge resonance itself, produce energy below 20 Hz that you cannot hear and your woofers can. If you see cones flapping on bass notes, a subsonic filter, which some phono stages include, is the cure.

Where the money stops working is higher here than in converters and lower than in amplifiers. The step from a built-in stage to a competent separate one is usually clear. Past a few hundred dollars on a moving magnet cartridge you are buying adjustment, better power supplies and lower noise, which are worth having and are not transformations.