How to Buy a Used Preamp

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How to Buy a Used Preamp

A preamplifier or preamp is an important component of any music system. Preamps are essential when amplifying and enhancing sound, whether a user is recording sound or performing. The type of preamp purchased will dictate the quality and texture of the sound source, whether it is a singer’s voice or tunes being spun by a DJ’s turntable.

About Preamps

A preamplifier (preamp) helps control sound and manages sound input, generally in combination with an amplifier and a speaker system. A preamp is generally connected from a sound source, such as an instrument, turntable or CD player, and an amplifier. Preamps are used for lower level signals. The incoming signal or sound is amplified in the preamp before being transmitted as a useable signal to the amplifier. Preamps include input options for a variety of sources, including tuners and CD players. Most devices include controls for balance and tone (for example, bass and treble). They may also include a jack for a headphone. Other common features include muting, mono and stereo options, speakers, monitors, and a subsonic filter. On the back panel, preamps include outlets for the AC power cord and input jacks for signal sources. Another socket is available for connecting to a power amplifier. Certain devices may also have jacks for recording devices and additional preamps.

Buying a Used Preamp

For most buyers, a used preamp is a more affordable option than buying a new preamp. Considerations when buying a used device include the price, working order, design, and type of preamp being considered. One of the main considerations when buying a used preamp is whether or not it works. Depending on a buyer’s experience with electrical devices, inoperative or malfunctioning preamps can be repaired or upgraded at a lower cost than purchasing a new device. When selecting a used preamp, the desired sound created by the device is often the most significant consideration. Different types of preamps amplify sounds in different ways. They also feature different components that may alter sounds by adding texture or colour.

Preamps Types

There are two main types of preamps. Each type of preamp produces different sound outputs. Both types of preamps may be used for recording and offer similar functionality. The decision on which type of preamp is therefore often determined by individual needs and preferences, in particular the desired sound. Colour preamps add character and body to sound. As the name suggests, these preamps add colour to a signal such as a singer’s voice or a musical instrument. They are typically used to create distinctive sounds. Colour preamps tend to be designed with tube or solid state circuit systems that feature a transformer. Transparent preamps offer users a more authentic sound similar to the original input, whether it is a voice or musical instrument. These are ideal when creating simple compositions or recordings. Transparent preamps are generally designed with solid state circuits without a transformer.

Circuit Design

Preamps are made with a variety of circuit designs. Most preamps are either tube or solid state. Devices may also feature a transformer in their circuit design. Transformer-couple preamps offer sharper sounds with more texture, while preamps without transformers provide a more authentic sound. When purchasing a used preamp, buyers should verify whether the circuit board is original or if components of the circuit design have been replaced. For example, ask the seller if a transformer is present and if it was an original component or added post-sale. The table below compares common types of circuit designs found on preamps.

Tube

Built with thermionic tubes or valves that create gain, tube preamps are used to add colour and character. When buying a used tube preamp, ask the seller if the tube was replaced. For older preamps where a tube may need replacing, new tubes may be purchased at a relatively low cost.

Solid State

By using transistors or op-amps to create gain, solid state preamps offer low distortion and high transparency in sound transmission. Ask the seller if any transistor has been replaced and whether it was done by the owner or by a professional.

Hybrid

Combining elements of solid state and tube designs, hybrid preamps offer the quick response and clear sounds of solid state preamps and the ability to add character to sound offered by tube preamps.

Modelling

Built with solid state circuit designs, these preamps include digital and compressor components that are used to add character and colour. Modelling preamp allow users to create authentic sounds as well as richer tones since they combine the effects produced by tube and solid state preamps.

Digital

Mixing analogy input and digital output, these devices reduce the number of components required to build a sound system. Similar to hybrid and modelling preamps, digital preamps are cost effective alternatives to buying both tube and solid state preamps since they combine the best of both devices into one preamp.

Preamp Components and Features

Preamps are available with a variety of common and enhanced features. When buying a used preamp, ensure that all dials, sockets, and other components are functioning properly. A preamp that has been employed professionally may have greater wear and tear than one used primarily for personal use. Confirm with the buyer whether any components have been replaced or if features have been added on as enhancements to the original device.

Common Features

The table below provides an overview of the common components found on a preamp.

Sound System

Preamps are available with either mono or stereo systems. For personal use, a mono preamp may be sufficient while professionals typically opt for stereo systems that add richer sounds.

Channels

Units are available with either a single or multi-channel system. Single channel preamps are generally used for a single instrument or personal use, where as a multiple channel preamp with two or more channels are used for recording or for professional use. Multi-channel preamps allow users to add sound layers and samples while recording or performing.

DAW Capability

Digital audio workstation (DAW) capable devices are used to record, edit, and play back audio. Preamps with this feature are typically used by professionals and any user interested in recording sound.

I/O Balance

Input and output (I/O) balance affects sound produced by the preamp. A balanced I/O cancels noise and better sound quality, while an unbalanced I/O can enrich a sound with character or texture. Unbalanced I/O is often used when playing instruments or when adding effects such as loops.

Voltage

Professional preamps feature a +4dBu setting while preamps operating at -10dBV are ideal for personal use. Preamps feature a switch that allows users to alternate voltage settings, with the +4dBu setting often used when connecting the preamp to longer cables.

Metres

Metres assist users in monitoring input and output levels. Certain preamps may have VU (volume unit) metres or a LED overload indicator.

Gain Control

Preamps feature controls or dials to control gain. These controls are infinite or stepped, with infinite controls providing more precise settings.

Enhanced Features

Preamps may be available with a variety of enhanced components or features. These features add functionality to the device, allowing users to further enhance, amplify, or manipulate sound. Additional features may increase the cost of a preamp. The table below summarises some of the common enhanced features found on preamps.

Channel Strip

Certain preamps include an equaliser and compressor/limiter in one unit, referred to as a channel strip. Preamps with an equaliser and/or compressor/limiter provide additional functionality with signal processing tools all in one device.

Variable Impedance

Preamps with variable impedance allows user to control high-frequency content. This gives users the ability to directly equalise an input signal while maintaining an authentic and unaltered sound. It allows users to increase input impedance.

Pad

A pad is used to alter a high-voltage input signal to manageable levels. This may be useful when making a recording.

Frequency Range

Preamps are available with a variety of frequency ranges. High-end preamps typically feature ranges between 4Hz and 150kHz. Typically frequency ranges are 20Hz to 20kHz.

Phase/Polarity Switch

This switch provides users with the ability to work with multiple microphones without compromising sound quality or creating interference. This feature is not required when using a preamp with a single signal source.

Conclusion

Buyers looking for a used preamp must take into account a range of considerations, including the price and condition of the preamp. The main determining factor when buying a preamp will be the desired sound a user wishes to create with the device. A transparent or solid state preamp creates an authentic sound similar to the original voice or music, while a colour or tube preamp enhances sounds to add depth and character. In addition to sound quality, consider the device’s suite of features and whether the preamp’s components provide sufficient functionality and capacity for individual needs.

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