How to Buy a Used Audio Controller or Preamplifier

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How to Buy a Used Audio Controller or Preamplifier

A stereo preamplifier receives and switches analogue audio sources and boosts the line level signal from a source component like a instrument to an audio controller that sends the signal at a level that a power amplifier can use to power speakers. The preamplifier is an essential component in determining the overall tone an instrument can put out. Using separate amplifiers and preamplifiers became popular in the 1970’s. Audio controllers, or mixers, are necessary to create specific tones by mixing signals from the preamplifier. Integrated amplifiers have a stereo preamplifier and power amplifier in one case. The main difference between an integrated amplifier and a receiver is the lack of a tuner of some sort.

When looking for a used preamplifier or audio controller, look in guitar shops, or at online venues such as eBay. Preamplifiers and audio controllers are necessary components of an audio setup, and when looking to buy either of these items it is a good idea to research the types of audio controllers and preamplifiers, and the features needing to mesh well with existing components and musical instruments. eBay has a huge selection of used audio controllers and preamplifiers to choose from.

What Is a Preamplifier?

Amplifiers are divided into two sections, the preamplifier, which is the part one controls, and the power amplifier which is the actual amplifier, speaker and other related parts. The purpose of a preamplifier is to provide the musicians with options when it comes to shaping the sounds they create. There are only two types of preamplifiers available: onboard, or on the instrument, and those present on the amplifier heads.

Before the preamplifier came into being, passive electronics allowed the pickup to be sent directly to the amplifier without the aid of electricity. Passive pickups take the raw signal directly from the magnets to the amplifier head. However, with the advent of active pickups, musicians are able to use preamplifiers to change the strength of the signal and shape it by adding or subtracting treble or bass, thus creating the exact sounds they desire.

When a guitar string is plucked, a raw note is picked up by magnets in the pickups, runs down the pickup coils and is then pre-shaped by the controls on the preamplifier to provide more treble, less bass or different mid-range. The altered signal then proceeds to the mixer and then to the amplifier head, where it is processed by the controls on the amplifier, before emerging from the speaker. Preamplifiers may be incorporated in the amplifier case, contained in a separate housing, or mounted on a turntable, microphone, or musical instrument.

Types of Preamplifiers

Unlike power amplifiers, preamplifiers do not have specific wattage and can be built to each musician's specific requirements. The signal received from the preamplifier is boosted from between 30 watts to 1,000 watts, depending upon what the speaker is capable of handling. Preamplifiers can be categorised by whether they are ‘onboard’ or ‘on the head’. Each type of preamplifier has specific features and benefits, so it is a good idea to review the various options prior to buying.

On the Head

Preamplifiers situated on the amp head generally have master volume controls, gain, treble, mid range, and often an indicator that can show when clipping occurs. This is when the boosted signal is stronger than the amplifier can handle.

Solid-State Preamplifier

The most common type of preamplifier, the solid-state stereo preamplifier uses transistors to boost the signal from line level to a voltage high enough that a power amplifier can use it. The solid-state stereo preamplifier was the first model to be made with remote controls.

Tube Preamplifier

This type of preamplifier utilises a vacuum tube to boost gain in the audio system. Most tube preamplifiers have a remote control.

Digital Preamplifier

The digital preamplifier is a fairly new type and unlike the solid-state and tube preamplifier, can receive a digital signal, convert it to an analogue signal, and then boost it for use with a power amplifier.


Onboard preamplifiers generally have volume, tone, bass, boost (or cut), treble, and midrange controls, and often other knobs may be present depending upon the number of pickups on the guitar or bass being played.

Pedal or Stompbox

The stompbox preamplifier works with the magnetic pickups on electric basses and guitars. Pedal-type preamplifiers are extremely versatile and perform like an active circuit without having to permanently install them.

Rack Mounted

This type of preamplifier has either tube or solid-state input sections, and sometimes has the ability to switch between the two.

Instrument Mounted

Some onboard preamplifiers have the ability to boost or cut certain frequencies, while others can only boost.

Preamplifier Features

Some features of preamplifiers are necessary, while some are only used occasionally or not at all. Whether a specific features is used or not will definitely depend upon the user, the type of signal being sent, the desired sound, and the equipment being used.

Preamplifier Input and Output

One of the integral parts of a preamplifier are the connectors used for input and output. It is generally recommended to use a combination of XLR and 0.63 cm outputs, although some preamplifiers have digital outputs or output cards for digital audio interface. Keeping a balanced line out from the preamplifier will reduce noise and conduct a clean signal to the audio controller or mixing console.

Variable Impedance

The variable impedance switch is an important part of the preamplifier. Impedance is like water flowing through hose. If the nozzle is open wide, there is very low impedance. If the nozzle is closed, there is high impedance. High impedance reduces sound distortion. Variable impedance allows high-frequency audio to be dialled up or down as desired to equalise input without having another unit added into the signal chain. It also improves the microphones performance by increasing the preamplifiers input impedance.

Phase Reverse/Polarity Reverse Switch

This preamplifier switch is handy for working with multiple microphone setups to check for phase cancellation or an improperly wired microphone. However, if only recording with one microphone, this switch is not necessary.


A pad is needed to reduce high-voltage input signals that may cause the preamplifier to distort, bringing the signal to a more manageable level.

Direct Input or Hi-Z Instrument Input

Some preamplifiers have a front panel 0.63 cm input to directly record a guitar, bass or other musical instrument, although some high-end preamplifiers have no DI, because it is hard to get circuits that are capable of handling the low power requirements of an unbalanced instrument.


Chaining allows the combination or linking (cascade) of two mono preamplifiers or channel strips into a multi-channel setup. This is a good feature to have if multi-channel or stereo signal processing is to be added.

Gain control

Gain control is either stepped or infinite. Stepped gain lets the user go back to an exact setting. This is useful for matching volume to overdub on previously recorded tracks. Infinite controls allow more precise setting capability.


Preamplifiers have a visual feedback as well, to help manage levels. These can be LEDs that light up when a signal is near to clipping, or meters which respond to signals the way ears do.

Audio Controllers

Audio controllers, also known as mixing consoles, audio mixers, soundboards, audio production consoles, or mixers, are electronic devices used to combine or ‘mix’ signals. These controllers route and change the level, timbre, or dynamics of the audio signals. Mixers can generally mix analogue as well as digital signals, depending upon the type of mixer. The modified signals are then mixed to produce a final, combined output signal. Audio controllers are used in recording studios, public address systems, sound reinforcement systems, broadcasting, and television. A good example of the practical use of audio controllers is the audio signal from two microphones being combined and heard through one speaker.

Audio Controller Channels and Features

Every input source enters the audio controller, or mixer, through a channel. The greater the number of channels the mixer has, the more sources it is capable of accepting. Mixers can have different channel setups.

Channel Setup



12 input channels


16 input channels, two output channels


24 input channels, four subgroup channels, two output channels

Generally the input channels take up the most room on mixers. There are some features that are more commonly shared by mixers.



Input Gain

Level of the signal as it enters the channel and in most cases is a potentiometer knob; switch or pad to increase or decrease the signal level


Two equalisation controllers, for high and low frequencies.

Auxiliary Channels

Aux channels used to send a copy of the signal to another place, to separate channel feeds or add reverb effects

Pan and Assignment

Channel can be panned right or left; advanced mixers assign the signal to the main mix or to a particular subgroup


Switches to control how the channel is monitored; do not affect the channel output


Level of the channel signal as it heads to the subgroup or the master mix

Subgroup Channels

Means of sub-mixing groups of channels before the signal is sent to the main output mix.

Aux channels can be mixed on the main faders instead of on a row of potentiometers. Signal routing is more flexible than it would be with an analogue-based console. It is possible to save the console setup to be used when needed. This is very useful for live events as setups for many bands can be saved into the console in advance and loaded when appropriate.

How to Buy a Used Audio Controller or Preamplifier on eBay

To begin your search for a used audio controller or preamplifier on eBay, simply enter keywords that describe what you are looking for into the search bar at the top of any page on eBay. For example, if you enter ‘used preamplifier’ the local search engine will return a results page with hundreds of listings for used preamplifiers. Maybe you are looking for a used audio controller. Simply enter ‘used audio controller’ or ‘used audio mixer’ into the search bar. You can always sort the listings by seller, such that you only see listings by eBay Top-Sellers. These are sellers who have earned eBay’s top-seller status by successfully adhering to all policies and procedures in regard to selling and delivering merchandise.

After you have chosen the items you want to buy, you should read the listings carefully. If important information is not listed in the item description, you can ask the seller questions about the listing by clicking on the seller’s username and going to their member profile. Once there, simply click on the contact link and ask any questions you may have.


The right preamplifier and audio controller will greatly improve the quality of your performances and recordings. Any type of sound equipment can be quite costly if purchased new. A musician should consider buying used preamplifiers and audio controllers to save money. Simply choose the components that work well with any existing equipment by searching through the extensive listings of used preamplifiers and audio controllers on eBay. While searching for the perfect equipment, think about buying a new bass guitar as well. For a complete sound equipment setup, buy used preamplifiers, audio controllers and even speakers. There are many venues where you can buy used sound equipment, such as some second hand shops or charity shops, but for the best used sound equipment, you should turn to eBay first. It has numerous listings for used audio equipment to browse through to find that used audio controller or preamplifier to complete any home studio or performance setup.

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