Behind The Sound^®: Will a phono preamp improve sound quality?

A McIntosh home audio system.

There’s nothing quite like coming home after a long day, putting on your favorite vinyl record, and letting the sound wash over you like an ocean. While dedicated audiophiles have always known the satisfaction of pristine sound quality, there’s a new wave of interest among listeners of all stripes. Even as the world at large has become more digitized, vinyl has experienced a resurgence in popularity.

There are a lot of reasons for the vinyl revival. For starters, there’s something deeply grounding about physically browsing through your vinyl collection before setting the mood. On top of that, many people are discovering the warm, immersive sound quality that comes from a turntable.

Not all turntable set-ups are going to create equal sound quality. For those dedicated to investing time and money into their home listening space, it’s important to understand what different components do, and how they can affect overall sound.

This brings us to the central question: will a phono preamp improve sound quality?

Before we dive in, let’s go over a refresher of what phono preamps are, how they work, and how different audio components affect the musical signal.

What is a phono preamp?
A phono preamp, which is also known as a phono stage, does the heavy lifting of translating the electrical signal from a turntable into audible music.

McIntosh MP100 Phono Preamplifier.

When a turntable cartridge picks up audio information from the record grooves, it produces a PHONO signal. A phono preamplifier converts the small PHONO signal into a LINE signal. A LINE signal is the standard signal level that can be played through home audio stereo equipment such as CD players and DVD players. A LINE signal can be plugged into the LINE or AUX inputs on amplifiers, active speakers and receivers, while a PHONO signal can’t be directly plugged into these inputs.

How does a PHONO signal translate into sound?
The path that connects a PHONO signal with our favorite music is all about translation. There are two major things that happen when the phono preamp converts a PHONO signal to a LINE signal. First, the small signal from the turntable cartridge is amplified to be robust enough to be connected to a LINE input. For this to happen, the amplitude (size) of the PHONO signal must be increased roughly 100x (for a moving magnet cartridge).

Secondly, in order to convert PHONO to a LINE signal, the bass notes are increased while the treble (high tones) are majorly reduced. This is necessary because when record grooves are carved, the bass is reduced to save space on the record. The phono stage amplifies the bass and decreases the treble to correct this and create an ideal listening balance. The process of a phono preamplifier balancing the bass and treble is called RIAA (Recording Industry Association of America) equalization.

What is the difference between a phono preamp for MC cartridges vs MM cartridges?
There are two main types of phono preamps: those designed for moving magnet cartridges (MM) and those designed to work with moving coil cartridges (MC). The differences between these phono preamps correspond to the different outputs of MC and MM cartridges.

Moving coil cartridges produce a lower signal, usually outputting around 0.2mV. By contrast, moving magnet cartridges create a signal level that hovers between 3mV and 6mV. Both MM cartridges and MC cartridges produce small signals that require amplification and RIAA equalization in order to be converted to a LINE signal.

In general, MC phono preamps have higher gain than MM phono stages, due to the lower signal output of MC cartridges. MC phono preamps tend to have more distinct noise characteristics than MM phono stages (this is also because of the lower electrical signal).

Moving magnet and MC phono preamps have different input impedance in order to match the different output impedance. MC phono preamps have adjustable gain and input impedance that manually adjust to meet the signal levels of your specific MC cartridge. MM phono preamps don’t require that, making the phono stage set-up easier.

The MP100 Phono Preamplifier includes both Moving Coil (MC) and Moving Magnet (MM) inputs.

Luckily, a few preamps will successfully work with both cartridges, those generally include a switch that adjusts the phono stage according to the cartridge type. The high-end McIntosh MP100 Phono Preamplifier is a great example of a phono preamp that’s compatible with both MM and MC cartridges. The McIntosh MP100 is not only compatible with MC and MM cartridges (with six settings each), but it also includes a mono switch to decrease noise while playing mono records. You can also use USB digital outputs, or opt to disable and power down the digital outputs for a purely analog experience.

Is a phono preamp necessary?
The answer to this varies based on your current set-up. If your record player includes a built-in preamplifier, then you technically don’t need to get a phono preamp (although many audiophiles prefer a separate one).

If you’re unsure whether your turntable has a preamp, you can check the back of it. If there’s a PHONO/LINE switch, then it has a built-in phono preamp. In order to activate the preamp, you must set the switch to LINE. If the switch is turned to PHONO, the built-in preamp is automatically bypassed.

How does a phono preamp improve sound quality?
Now that we have the full spectrum of context, we can return to the original question at hand: will a phono preamp improve sound quality?

The shortest answer is yes. In general, because the process of RIAA equalization works to balance the bass and treble for a more balanced listening experience, a phono stage improves the sound quality. Also, on a practical level, it’s harder to listen to LPs if the turntable can’t be connected to a variety of amplifiers, speakers, or home audio components.

While separate and built-in preamps both fall under the phono stage umbrella, there are some differences in their construction. This is why some audiophiles opt for a separate phono preamp even if their record player has one built-in.

The most obvious difference is that built-in preamps are part of the turntable, while separate phono preamps require you to connect them manually with power cables. In order to fit into the record player, built-in preamps often have smaller circuit boards and a more pared down construction. However, high-end models like the McIntosh MTI100 Integrated Turntable include a built-in preamp fine-tuned for quality and convenience.

McIntosh MTI100 Integrated Turntable.

Standalone phono preamps (such as the McIntosh MP100) are a great option if you want more direct control over your sound, offering high-end capacitors, resistors, and other parts. In general, the reason some vinyl lovers are drawn to a separate phono stage is the direct control over the sound details.

However, if you have an integrated turntable with a built-in preamp, it’s not technically necessary to add a separate phono preamp. At the end of the day, it’s all about your sound priorities.

EXPLORE: Phono Preamps and Turntables