The Anatomy of an Audio Controller or Preamplifier

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The Anatomy of an Audio Controller or Preamplifier: Know Before you Buy

Preamplifiers or audio controllers are devices meant to prepare an electric signal, such as radio waves, for amplification. Often housed in integrated amplifiers, or boxed on their own, preamplifiers are an important part of a quality home sound system. Some media players, such as turntables, also feature their own preamplifiers, although this is not necessary for the player and not true across all models. Very cheap players usually feature a very small preamplifier, while high-end ones require a separate preamplifier.

Preamplifiers are normally built into amplifiers or other gear in lower-end audio equipment, but in high-end equipment, they are generally placed separately so that the owner can tweak the sound to maximise quality and listening experience. Important considerations include the type of preamplifier and the signal-to-noise ratio (SNR) of the preamplifier. Buyers looking for a high quality audio controller should pay attention to the specifications, the internal parts, and the value for the money before purchasing a preamplifier.

Preamplifier Function

The primary function of the preamplifier is to extract the signal from the source without degrading the quality. Essentially, the preamplifier is there only to reduce distortion between the origin and the amplification of sound. The preamplifier uses a detector to transfer sound, usually with a coaxial cable. Depending on the width of the band, the preamplifier either easily produces top quality sound or produces lower quality sound.

Preamplifiers Types

There are three types of preamplifiers or audio controllers. These include the current sensitive preamplifier, the parasitic capacitance preamplifier, and the charge sensitive preamplifier. While all three are used, parasitic preamplifiers are most commonly used inside of other devices, and thus their name. Each of the three types of preamplifiers can still be purchased, although many people simply choose to purchase any preamplifier rather than choosing a specific model.

Current Sensitive Preamplifiers

Current sensitive preamplifiers are used with fast rise output detectors, including photomultiplier tubes and microchannel plates. Usually connected to devices with high output impedance, current sensitive preamplifiers work to greatly increase audio quality when paired with a correctly timed amplifier, and are sometimes used instead of genuine powered amplifiers. Current sensitive preamplifiers include 50-ohm coaxial cables, which are capable of handling the maximum power level for the preamplifier, known as the 50-ohm impedance. Buyers wishing to pair current sensitive preamplifiers with timing devices should carefully match the rise of the preamplifier to the detector or audio source, or the amplifier may distort the sound rather than amplify it.

Parasitic Capacitance Preamplifiers

With photomultiplier tubes, electron multipliers, microchannel plates, parasitic capacitance preamplifiers are very fast rise preamplifiers with the ability to amplify a very high impedance level. Generally, the high impedance input is combined with the impedance output, thus resulting in the 'parasitic' part of the name, as the preamplifier feeds on itself to produce quality sound. These should be combined with high input impedance amplifiers.

Charge Sensitive Preamplifiers

The most common preamplifiers seen in live stage, including band and musician preamplifiers, charge sensitive preamplifiers are compatible with semi-conductors, which makes them excellent for many uses. The preamplifier works with either sound or power of audio, and can be used to deliver on both wattage and timing. In ideal systems, preamplifier rise is similar to the detector rise or power width.

Preamplifier Parts

Preamplifiers include input, output, and a variety of technical parts that affect sound quality to some extent. For most buyers, the input and the output are two of the most important factors, but information including resistors, capacitors, buffers, and transformers can be just as important. Buyers can research the individual parts present in a model they are interested in, or check up on the specs listed on the box or the online description of the model.


Meaning and Use

Box or Casing

The outer shell or casing; protects the components


The plug-in area and audio acceptance, usually rated in ohms, bandwidth, and power


Control the exact specifications of the audio; can be interior and automatic, or exterior and manual


Increases gain and power in preamplifiers, for use with high impedance systems


Minimise noise and distortion


Deal with power handling


Detectors to pick up sound


Power control and regulation

Power Transformer

Transfers power through circuits

While there are many different parts in the preamplifier, most people find that simply choosing a quality device can yield good results, and that pieces do not generally need to be replaced. Most audiophiles, however, research an affordable model with good specifications, and then replace the lowest quality parts such as the capacitor, which can greatly affect sound quality. All preamplifiers contain these parts, although some are made of different materials such as crystal or silicone diodes, and silver foil inputs or wires vs. copper ones. There are plenty of different materials used, although most depend on the exact model.

Factors That Affect Sound Quality

Various factors that affect sound quality include all of the parts in the preamplifier, although some make more of a difference than others to the audio sound. For example, the input and outputs are the most commonly highlighted for sound quality because they partially control the timing, as well as the impedance of the preamplifiers.


Buyers should look for high impedance when choosing preamplifiers. For example, with a microphone for an on-stage preamplifier, the impedance should be 1,500 ohms or higher. At-home devices can have lower impedance, but the higher the number the better. Impedance is more important than many beginners to the audio world would think because it can actually result in an overheated amplifier or in complete distortion of audio. The impedance rating is the rate of power resistance, and the preamplifiers impedance rating should be high enough to handle the impedance of the audio source. For instruments rather than speakers, professionals recommend a preamplifier rating about four to five times higher than instrument impedance.


Gain is very important in preamplification because it determines the rise in amplification. Usually the higher the gain, the louder the final sound is without distortion. However, too much gain can be too loud for a space, or too distorted if the gain overloads the amplifier. Generally, it is a good consideration to purchase a preamplifier based on the gain and output of the amplifier or the speakers. Gain is measured in decibels and can range from very low numbers to more than 70 decibels.


Noise, commonly called distortion, is something that every preamplifier buyer wants to avoid. Sometimes measured in signal-to-noise ratio, the lower this rating the better, and the louder the gain, the more noise there is. Some preamplifiers are also rated with THD (Total Harmonic Distortion), which is the total distortion of harmonics without gain. Usually noise and gain ratings marked as 'ultra-low noise' are desirable, but very expensive. Most users should look for preamplifiers with the lowest noise rating within their budget.

Tubes vs. Transistors

Tubes and transistors are both optional methods of handling power in preamplifiers and amplifiers, and mostly they are a matter of personal choice. Usually, transistors are very common in household preamplifiers, but vacuum tubes are also used in some higher-end models. Most tube preamplifiers are labelled as such, while many transistor preamplifiers are not, except perhaps in specifications for the device. Tube preamplifiers are often called vacuum state, which is an easy way to distinguish them from standard preamplifiers. Some people consider tube preamplifiers to be slightly richer in sound, while others believe that the richer sound comes with the cost of more distortion.

Buying an Audio Controller or Preamplifier on eBay

Anyone can visit eBay to search for a preamplifier of any kind. From stage preamplifiers, to in-home options meant for home sound, eBay is home to a great deal of different styles and qualities of preamplifiers. Budget buyers can choose to purchase a low-cost model, or to purchase a second hand model, while audiophiles and anyone with a large budget for this device can choose to purchase from high-end preamplifiers as well. Buyers can also look into purchasing replacement parts for automatic upgrades to a preamplifier system.

Local Sellers

One thing that you should consider when shopping on eBay is that some of the preamplifiers are not listed locally. If you want faster shipping and better post rates, you should look for a local seller and choose from options nearby. On the other hand, if you are more concerned with quality amplification, then you can look anywhere you like as there are plenty of models available.


Preamplifiers come in a variety of qualities and styles, including current sensitive preamplifiers, parasitic capacitance preamplifiers, and the charge sensitive preamplifiers. Not all models are listed by type, but most are listed according to specifications, which is an indication of what they can do. Buyers can choose preamplifiers based on the individual parts, which can often affect quality to the point that many audiophiles may want to switch out lower quality parts for higher performance ones.

The main quality-affecting elements or features of the preamplifier include the gain, the noise, the impedance, and the inputs and outputs. Generally, higher gain and impedance are better for sound quality while lower noise or distortion is of course, always desirable. Buyers can look in electronics stores, sound and vision stores, online stores, and on eBay to search for various preamplifiers and their parts. It is important to remember what goes into a preamplifier when searching for a high quality addition to a system, especially because small elements can greatly affect the quality of sound.

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