A Buying Guide for Preamps

Like if this guide is helpful
A Buying Guide for Preamps

Preamps prepare electrical signals, such as sound being produced by an instrument, recording, or voice, for further amplification and enhancement by an amplifier or speaker. When buying a preamp, buyers look at a number of qualities, such as cost and functionality. Depending on whether a preamp is used for personal or professional use, these devices may incorporate a range of advanced features that enhance sound transmission and quality. Ultimately, the desired characteristics and authenticity of the sound produced by the preamp will determine which device is purchased.

About Preamps

A preamplifier (preamp) processes or amplifies an electrical signal or sound. Preamps boost signal strength while reducing noise and interference. In music, amplifiers are used in combination with any device that creates an electrical signal or sound. Examples include instruments such as guitars and microphones for performers who are singing. Preamps may be used to increase the signal level (that is, the gain), change tone, alter the efficiency of the signal (that is, output impedance), and convert from unbalanced to balanced input/output. Gain is typically controlled on a preamp with a volume knob, whereas tone is generally changed using equalisation (EQ) controls.

Buying a Preamp

When buying a preamp, the choice generally depends on the individual user and the desired sound quality or character. Different types of preamps manipulate sound in unique ways. Understanding how sound is processed and manipulated using each type of preamp is important when choosing a device. Another key consideration is individual budgets and the cost of the device.

Types of Preamps

Although preamps may be subdivided into a variety of types depending on circuit design, there are two main categories. Colour preamps provide distinct characteristics to sound, while transparent preamps deliver a signal that is close to the original source. Many times, both types of preamps are used in combination when recording music. A colour preamp adds body and character, or ‘colour’, to a voice or instrument. They are often used for rock and pop recordings as well as dance and electronic music where the creation of unique sounds is desired. These preamps typically feature transformer-coupled designs with tube or solid state circuits. Transparent preamps reproduce a voice, instrument, and other sounds as close to the original as possible. Users who wish to create simple compositions with few components and realistic sounds often opt for transparent preamps. Transparent preamps generally feature a solid state circuit design without a transformer.

Circuit Design

Preamps are made with a variety of circuit designs. The table below compares the various types of circuit designs found on preamps.

Circuit Design

Description

Solid State

This type of preamp uses transistors to create increase signals (gain). This system creates less heat and is more efficient than a tube preamp. Distortion is very low and inputs are captured with high accuracy, even at maximum levels. Solid state designs are typically found in transparent preamps.

Tube

Tube preamps feature thermionic tubes or valves. These valves are used to create gain as well as add character to a sound. Most tube preamps are colour preamps. They are ideal for adding deep base and offer better upper frequency response than a solid state design.

Hybrid

This preamp combines solid state and tube designs. For example, a solid state circuit may be used for inputs while a tube design is used for outputs. These preamps combine the quicker response rates and clarity of solid state designs with the functionality of tube designs that add texture and character to sounds. A hybrid preamp is a cost-effective alternative to purchasing both a solid state and tube preamp.

Digital

Digital preamps combine analog input and digital output. This type of preamp is also characterised as a two-channel preamp. They typically incorporate a full digital analog converter (DAC) and may also feature USB input capabilities, helping to reduce the number of components in a sound system.

Modelling

Modelling preamps feature solid state circuit designs combined with digital and compressor components that add character and colour to sounds. With a modelling preamp, users can create similar sounds from both tube and solid state devices. A modelling preamp is generally an affordable alternative to buying both tube and solid state preamps.

Transformer Designs

Preamp circuit designs may or may not have a transformer. Transformer-couple designs provide richer and punchier sounds than a preamp without a transformer. Transformers help to colour or enhance a signal. The transformer bridges an input with the output and also increases signal voltage using magnetic coupling. A circuit design without a transformer tends to deliver a raw and more authentic sound. Preamp designs without a transformer have fewer components in a sound’s path, meaning sound is more transparent and less distorted. Transformer-less designs are generally found in solid state preamps, although they may be found in higher-end tube preamps.

Additional Design Features

In addition to the circuit design, preamps are manufactured with a variety of additional components. The following table provides an overview of common components commonly found on preamps.

Additional Design Features

Description

Sound Output

Preamps feature mono or stereo options. For personal or infrequent use, a mono device may be sufficient. By comparison, stereo provides a richer and more professional sound.

Channels

A two-channel or multi-channel device may be desirable for adding layers of sound or samples, especially when recording music. A single channel preamp typically suffices for casual or personal use, or for a single instrument.

DAW

DAW or digital audio workstation capability is essential for any preamp user planning to record, edit, or play back digital audio. Users who will not record their compositions can opt for preamps without DAW capability.

I/O Connectors

The type of input and output (Input/Output or I/O) connectors will affect functionality and sound quality. Balanced I/O is known for noise cancelling capabilities. Unbalanced I/O is typically used for instruments and mixers and when adding effects loops. Both types of I/O can be used in combination, although most users opt for a balanced I/O device because of the better sound quality.

Voltage

Generally, preamps feature a switch that allows users to select different operating levels or voltages. A -10dBV operating level is typically used for personal use, while professional users tend to opt for a +4dBu setting. The +4dBu setting permits the use of longer cables without compromising the signal.

Preamp Features

Preamps are designed with a wealth of features that allow users to manipulate and refine sound output. While for most preamp users the choice in device is determined by sound quality, others focus on the number and type of features used to manipulate sound. When buying a preamp, keep in mind which features are essential for individual use. The table below summarises common features found on preamp devices.

Preamp Features

Description

Variable Impedance

This feature allows users to control high-frequency content. A microphone’s performance can also be enhanced by increasing a preamp’s input impedance and to maximise the microphone’s output. This feature also allows for the equalisation (EQ) of the input signal without adding to the signal's chain, resulting in a more authentic sound.

Gain Control

Preamps may feature infinite or stepped controls for voltage gain. A stepped control allows users to return to a precise setting, which is useful when matching channels or the volume on tracks. Infinite controls are more precise, allowing for more exact gain settings.

Phase/Polarity Reverse Switch

A phase or polarity switch is typically used with preamps connected to multiple microphones. A phase switch is also useful for stereo recordings and helps add colour. A phase reserve switch is typically used when recording a direct signal from an instrument connected to a microphone.

Chaining

This feature permits users to combine or cascade two mono preamps into a stereo or multi-channel setup. Chaining is particularly useful for buyers who want to add a second preamp to an existing device.

Metres

Metres help users manage output levels. For example, VU (Volume Unit) metres provide a visual illustration of average volume levels. Certain preamps feature LED overload indicators rather than VU metres.

Pad

A pad is used to reduce the signal, especially when the input signal is at a high voltage. It will help calm the input to a manageable level and reduce distortion.

DI-Hi-Z Instrument Input

This front-panel input allows users to record directly from an instrument, such as a bass or guitar. This facilitates the recording of clean signals from the instrument.

Conclusion

The choice of preamp is often personal. Listening to various devices is one of the most important ways of selecting which preamp is right. Certain preamps may be designed for specific instruments, while others feature components such as transformers that will affect sound quality. If using a preamp to add body and character or enhance vocals and instrument sounds, a tube preamp is often desirable. By comparison, a solid preamp is generally used to create more authentic sounds with better transient and high-frequency response.

Have something to share, create your own guide... Write a guide
Explore more guides