What is a Record Player Preamp

Turntable Preamplifiers

The phono preamplifier—or preamp, as it's commonly known—is a crucial component of a record player that is often a source of confusion for those new to vinyl. While many enthusiasts focus on the turntable, cartridge, and speakers, the preamp plays a pivotal role in ensuring your records not only sound their best, but are actually audible at all.

In this article, we’ll delve into what a preamp does in relation to a record player, how to determine if your turntable has one, and whether a preamp is necessary for your setup.

What Does a Preamp Do?

A preamplifier’s primary function is to boost the signal from your turntable to a level that can be processed by your amplifier and speakers. Turntables produce a very weak signal called a phono signal, which is much lower in voltage than the standard line-level signals produced by other audio sources like CD players or DAB radios. This extremely weak audio signal needs to be raised up to line level to be useful to an amplifier, and that's where the preamp comes in.

Beyond amplification, a preamp also performs an important task known as equalisation. The audio signals produced by vinyl records are not naturally balanced; the bass frequencies are recorded at a drastically reduced level and the treble frequencies are boosted considerably. This is done to ensure the grooves on the record can be cut more efficiently and to reduce its susceptibility to surface noise during playback.

Be it built-in or an external device, the preamplifier uses active circuitry to reverse these extreme bass and treble adjustments and restores the original tonal balance of the recording, making your music sound as intended. This balanced signal is then fed into a gain stage which increases its low voltage to a level that's suitable for the input of a Hi-Fi amplifier or stereo system.

What is a Record Player Preamp? - External Phono Preamp Wiring DiagramWhat is a Record Player Preamp? - External Phono Preamp Wiring Diagram
What is a Record Player Preamp? - Built-in Switchable Phono PreampWhat is a Record Player Preamp? - Built-in Switchable Phono Preamp

How do I know if my Turntable has a Preamp

Identifying whether your turntable has a built-in preamp can be a bit tricky to the newcomer, but there are a few tell-tale signs. The simplest way is to check the back of your turntable.

If the record player includes any form of digital connection such as Bluetooth or USB for recording, it’s got a preamp. This is also the case if the player includes built-in speakers or a headphone option, as all these require a preamp or analogue-to-digital conversion circuitry in order to work.

A separate grounding wire if present is always a sign that there isn't a preamp. Most Hi-Fi turntables don't include built-in preamps as the use of better quality external units is preferred by enthusiasts, and they use a separate ground for the metal parts of the player which connects to the body of a preamp or amplifier to remove any hum. Line-level record players generally either don't have a chassis ground, or they incorporate it into the signal ground of the RCA plugs, so you won't have this extra wire.

If you're still unsure, you can connect your turntable directly to a pair of active speakers or any line-level input on an amplifier. If you hear music at a normal volume, your turntable has a built-in preamp. If the sound is very faint, then it very likely does not have a preamp, and you will need an external one.

Is a Preamp necessary for a Record Player?

Put simply yes, it's a required component. The type of preamp however depends largely on your audio setup. If your turntable has a built-in preamp, you can connect it directly to powered speakers or an amplifier with line-level inputs without any additional equipment. However, if your turntable lacks a built-in preamp, you will need an external preamp unit to boost the phono signal to line level.

Even if your record player has a built-in preamp, using an external preamp can often provide better sound quality (providing it can be bypassed). External preamps are generally of much higher quality than the built-in ones, offering more precise equalisation and lower noise levels, and some Hi-Fi-specific preamps will include settings for different types of turntable cartridges and gain settings to get the most detail from the signal.

As another option, some Hi-Fi amplifiers feature a dedicated ‘Phono’ input stage which can accept the low signal level from a turntable directly and would be accompanied by a grounding point. This built-in phono preamp was standard on stereo amplifiers for many years, though the drop off in vinyl popularity during the 90s meant they disappeared for a time, and are now only found on higher-quality amplifiers and audio receivers.

What is a Record Player Preamp? - PDX010 Phono PreamplifierWhat is a Record Player Preamp? - PDX010 Phono Preamplifier

Diving Deeper into Phono Preamps for Turntables and Record Players

Let's look further into the world of phono preamps, from the built-in types found in most modern record players such as the popular briefcase designs, to the external preamplifier units that are favoured by Hi-Fi lovers and vinyl enthusiasts.

Understanding the Phono Signal

Turntables produce what's known as a phono-level signal, which is significantly weaker than the line-level signals output by other audio devices. For the majority of turntables which use a moving-magnet cartridge design, it's approximately a 0.5-volt signal, which needs to be increased up to the 1.5-volt required for line-level use so that it can be processed by your amplifier. Without a preamp, the music from your vinyl records would be simply too quiet to hear properly.

The reason for this lower signal is simply the physics at play. A record player's stylus is a diamond needle attached to a metal tube. The needle runs in the moving groove of a record and is ‘reads’ the lumps and bumps in that groove. The small mechanical movements of that needle and tube are detected by a coiled magnet inside the cartridge which turns these movements into an electrical signal (a similar process is used in both microphones and electric guitar pickups). With no powered circuitry involved, this signal is electrically very weak, though very ‘pure’ in its source to signal creation, which is one of the reasons people love the sound of vinyl so much.

Why is it called Phono?

Phono comes from the Greek word Phonograph, which means ‘sound writing’ or ‘voice writing’. It originated from the first mechanical recording methods which were engraved metal cylinders, and was coined by Thomas Edison after he combined the existing phonautograph machine with aspects of the telegraph and telephone into a vocal recording device. The technical name for a vinyl record is a phonographic disc.

The Purpose of a Ground Wire on a Hi-Fi Turntable

With a turntable, you have two separate electrical operations happening simultaneously. Firstly you have the drive system, which is a mains-powered DC motor that is either driving the platter directly or via a rubber belt. This will be grounded to the chassis if it is metal, and to any other metal parts. The ground wire allows this chassis grounding to be connected to the external preamplifier or amplifier to tie them together, which reduces unwanted hum.

The other is the audio side, which uses a diamond-tipped needle (stylus) connected to a cartridge which uses either a magnet or coil design to convert the needle's vibrations into an electrical signal. This AC signal is extremely delicate and is highly sensitive to external electrical noise, so is kept separate from the mains and DC parts of the player. The signal from the cartridge is fed through the tonearm and out of the turntable either through an onboard preamp or directly out via a stereo pair of RCA/Phono connections which feature their own ground.

So you have two grounds, one for the ‘earthing’ of the mains to the metal chassis parts, and a separated grounding path or ‘negative’ side for the audio signal, kept apart to remove unwanted electrical noise from being amplified.

Most lower-cost record players and turntables now don't include the separate ground, either because they are a line-level output already, or because they feature no metal parts so they can't be chassis grounded. You will however still find it on Hi-Fi and professional DJ turntables.

Preamp Equalisation and the RIAA Standard

One of the critical functions of a phono preamp is to apply equalisation to the phono signal. Vinyl records are recorded with an equalisation curve that reduces the bass by 20 dB and boosts the treble frequencies by 20 dB. This technique, developed by the Recording Industry Association of America (RIAA), helps to minimise the required groove width on the record and reduce the impact of surface noise.

Along with raising the gain of the weak phono signal, the preamp reverses this EQ process, boosting the bass and reducing the treble to restore the music to its original balance.

Though all phono preamps will perform a form of this signal boosting and equalisation, some take it more seriously than others, which is why there is a large market for preamp stages aimed at the Hi-Fi enthusiast and Audiophile who prefer to use units with better quality components and specifications over built-in or low-cost preamp devices.

Types of Phono Preamps

Preamps come in two main varieties: built-in and external. Built-in preamps are integrated into most modern record players, providing a convenient all-in-one solution for casual listeners. These preamps are typically found in entry-level and mid-range turntables or those with on-board speakers. They allow these players to be connected with standard RCA cables into any line-level input that can be found on mixers, stereo systems, amplifiers, and active speakers.

As previously mentioned, some audio amplifiers have built-in phono preamps known as phono stages, which is incorporated as part of their audio preamplifier circuitry. This was standard on stereo amps of the 70s and 80s, though is now only seen on higher-specification Hi-Fi amplifiers.

External preamps, on the other hand, are separate devices that connect between your turntable and amplifier. They are often preferred by audiophiles due to their superior sound quality and greater flexibility in terms of upgrades and customisation. They come in many forms, from the latest DSP-driven digital circuits to all analogue purist devices, some even going as far as using valves in place of the transistors.

Benefits of an External Preamplifier

Opting for an external preamp offers several advantages. Firstly, external preamps will usually feature much higher-quality components and more precise circuitry, resulting in better sound quality. They can provide more accurate equalisation, lower noise levels, and greater dynamic range compared to cheaper built-in preamps.

Additionally, an external preamp allows for more flexibility in upgrading your audio system. You can experiment with different preamp designs to find the one that best matches your turntable’s dynamics and your listening taste.

Integrating a Preamp into Your Audio Setup

Integrating a preamp into your audio setup is straightforward. If your turntable has a built-in preamp, you can just connect it directly to your amplifier or powered speakers using standard RCA cables. If you're using an external preamp, you'll connect the turntable to the preamp, and then the preamp to your amplifier or active speakers.

External preamplifiers are active circuitry so will require their own power to operate. They are generally quite compact units so are easily tucked away out of sight in a Hi-Fi setup.

Preamp Quality and the Audio Experience

The quality of the preamp can significantly impact your listening experience. High-quality preamps are designed to minimise noise and distortion, providing a cleaner and more accurate amplification of the phono signal. This results in clearer, more detailed sound with better separation between instruments and vocals.

While the inclusion of built-in phono preamps has been a great plus in the comeback of vinyl, making this old technology more accessible to the more casual listener, some would say it has been at the cost of the very sound quality that makes vinyl desirable in the first place. Like anything, it's completely subjective to the user, and many people are perfectly happy with the sound quality as it comes.

For the more discerning music lover, however, investing in a good quality phono preamp can make a noticeable difference in the overall performance, and for the real Hi-Fi buffs it allows you the necessary gain adjustments when switching between moving magnet (MM) and moving coil (MC) cartridges.

Advanced Features in Modern Phono Preamps

Modern preamps come with a range of advanced features that enhance their functionality and user experience. Some preamps offer adjustable gain settings, allowing you to fine-tune the amplification to match your cartridge's output. Others include multiple input options, making it easy to switch between different turntables or audio sources. Some high-end preamps even offer digital outputs, enabling you to connect directly to a digital audio converter (DAC) for further processing.

Matching your Preamp to your Turntable and Audio System

Choosing the right external preamp involves considering your turntable's specifications and your overall audio system. The preamp should complement the characteristics of your turntable's cartridge, providing the right amount of gain and accurate equalisation. It's also important to ensure that the preamp is compatible with the rest of your audio equipment, particularly in terms of connectivity and input/output options.

If you're buying a record player with a built-in preamp system but are planning on upgrading to an external preamp at a later date, you must make sure the player's internal unit can be disabled.

Final Thoughts

The phono preamplifier is an indispensable component that ensures your records sound their best. By boosting the weak phono signal to line level and applying the necessary equalisation, a preamp enables your amplifier and speakers to accurately reproduce the music stored in the grooves of your records. Whether you choose a built-in or external preamp solution, the key is to ensure it matches your turntable and audio system for optimal performance.

High-quality phono preamps can make a significant difference in sound quality, offering clearer, more detailed audio with better dynamic range and tonal balance. For serious vinyl enthusiasts, investing in a good preamp is essential for enjoying the full potential of their record collection.