Rapallo's Amplifier Glossary

Estimated reading time: 13 minutes

This week is Rapallo’s amplifier glossary … the world of amplifiers is riddled with terminology that-unless you been wandering the audiophile jungle for years- does your head in.

It should come as no surprise really, considering amplifiers are complicated electronic devices where a lot goes on.

While we have no intention whatsoever to make this blog a highly technical piece of reading that belongs in an electronics course syllabus, we do want to give you an idea what a lot of the words that get thrown around mean in layman’s terms.

They are by no means scientifically accurate definition, but we really tried to keep it as close as possible to what a science purist could tolerate. So here’s the Rapallo amplifier glossary.

What’s in a name? Rapallo’s Amplifier Glossary

One amplifier is not the same as the next. They come in a variety of flavors and combos. While things are not set in concrete and there is definitely a certain amount of overlap and grey area, these are generally considered the different types of amplifiers in the shops. These are also the amplifier sub-categories you will find on the Rapallo webpage.

Power amplifier: A power amplifier or power amp is an amplifier in its purest form. It amplifies low-power audio signals to a level suitable for driving loudspeakers; that’s it. Power amplifiers contain large, heavy circuitry which can be seen when you open one up and look at the large transformers and capacitors. They can’t operate on their own and will require pre-amplification and volume control of some sort.
Pre-amplifier: A Pre-Amplifier takes a low level input signal and prepares it for amplification. A pre-amplifier usually contains not only amplification circuits but filters used for tone control (bass, treble, mid-range) and equalization circuits. Pre-amplifiers also contain mixing circuits, decoder circuits, crossover circuits and various other circuits. The main role of any pre-amplifier is to boost the signal level to the point where it can be fed to the power amplifier.
Integrated Amplifier: An integrated amplifier contains a pre-amplifier and power amplifier in one unit, as opposed to separating the two. Most modern audio amplifiers are integrated and have several inputs for devices such as CD players, DVD players, and the likes.
Stereo receiver: A stereo receiver or stereo amp includes an integrated amp and a radio tuner designed to power a hi-fi system.Stereo amplifiers were unchanged for decades, their analogue connections favoring music played on CD players and turntables. But with laptops, smartphones and streaming services gaining ground as music sources, the stereo amp had to evolve, with built-in DACs, USB connections and wireless streaming now becoming increasingly important.
AV Receiver: The amplifier all-in-one solution for the ‘home theatre’. A receiver is a power amplifier, a pre-amplifier and a radio tuner all built into one unit, but it also allows you to route image through the receiver as well. These days AV receivers service multiple ‘zones’ and come with a whole range of features and extra’s.
Headphone amplifier: A headphone amplifier is a low-powered integrated amplifier designed particularly to drive headphones instead of speakers. They are often combined with a DAC (Digital analogue convertor) and can be portable or desktop models. Some are found embedded in electronic devices that have a headphone jack, such as portable music players.

Basic amplifier lingo – Rapallo’s Amplifier Glossary

We have no doubt that you will be very familiar with these basic concepts. However, for the sake of being complete, we have included them anyway.

Current: An electric current is a flow of electric charge carried by moving electrons in a wire. The unit of current is the “Ampere”, and indicates a current flow of one Coulomb per second. A Coulomb is a unit of electron charge.
D/C: Direct current
A/C: Alternating current oscillates as a sine wave
Voltage: We define voltage as the amount of potential energy between two points on a circuit. One point has more charge than another. This difference in charge between the two points is called Voltage.
Resistance: the difficulty of a current to pass through a wire expressed in Ohm.
Impedance: This is kind of the same as ‘resistance’, but for an A/C current. Impedance is the amount of resistance plus the amount of reactance (the opposition of a circuit element to a change in voltage) typical to an A/C flow of current. It is the load value in Ohms that the speakers present to the amplifier. (‘Load’is the generic term for something in the circuit that will draw power; in this case speakers). While playing music, a speaker’s actual impedance constantly fluctuates; however, speakers are usually given a single nominal impedance rating for easy comparison. Low-impedance speakers (4 ohms or less) can cause problems with receivers or amplifiers that are not designed to deliver large amounts of current.
Ohm: A measure of how much something resists (impedes) the flow of electricity. Larger numbers mean more resistance. As can be expected, the prefix “k” is used for kiloOhms, or thousands of Ohms, and the prefix “m” is used for megaOhms, or millions of Ohms.

When describing voltage, current, and resistance, a common analogy to help explain this concept is a water tank. I’m sure you have heard it before, but it’s still the easiest way to make sense of these three principles. In case you haven’t, it’s explained here.

The bowels of an amplifier- Trans-what?

Moving on. An amplifier has a lot of components in its inners, all with different tasks. We sum up the ones you are most likely to hear about when reading forums or literature.

A Transistor: If you want to amplify a fluctuating signal, such as sound you’d generally use a transistor-based amplifier. A transistor has three wire connections called a base, an emitter, and a collector. When you feed a small input current between the base and the emitter, you get a much larger output current flowing between the emitter and the collector. Before transistors were invented in 1947, much larger electronic amplifiers called vacuum tubes (popularly known as “valves” in the UK) were used in such things as TVs and radios.

A Transformer: Transformers are mainly used to convert one voltage to another.

The benefit of this is to minimize energy loss over long distances. Higher voltages allow for lower currents, which reduces the losses caused by resistance. The process of increasing the voltage is called “stepping up”, while decreasing the voltage is called “stepping down”.

Most electronic equipment also need a transformer to lower the mains voltage to a usable level.

A transformer is based on a very simple fact about electricity: when a fluctuating electric current flows through a wire, it generates a magnetic field all around it. The strength of the magnetism is directly related to the size of the electric current. So the bigger the current, the stronger the magnetic field.

High-end amplifiers often boast ‘toroidal transformers’. These transformers have a donut shaped magnetic core and their main attraction is their superior electrical performance. Because of this, they are becoming increasingly popular.

A Transducer: Refers to any device that converts one form of energy into another form of energy, specifically when one of the quantities is electrical. Thus, a loudspeaker converts electrical impulses into sound, a microphone converts sound into electrical impulses, a solar cell converts light into electricity, etc.

Crossover: A component that divides an audio signal into two or more ranges by frequency. It kind of acts as a ‘traffic controller’. For example, it sends low frequencies to your woofer and high frequencies to your bookshelves. You might say it works as a filter, allowing certain frequencies to pass through to the speaker while blocking others.

An active crossover is powered and divides the line-level audio signal before amplification.
A passive crossover uses no external power supply and may be used either at line level or, more commonly, at speaker level to divide the signal after amplification.

A Resistor: A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor.

A Capacitor

A capacitator is a cousin of a resistor, but it presents a high resistance to low frequencies, and low resistance to high frequencies. Perversely, more capacitance means less resistance.

An Equalizer (EQ): All sound – everything you hear – is essentially vibration, which we can visualize as waves moving up and down at different speeds, or frequencies.

At its most basic, an EQ manipulates frequencies. Whether analog or digital, an EQ is used to adjust different elements of sound to achieve an end result that appeals to the listener. You may associate EQ with effects like reverb or echo, or popular EQ presets like “Rock,” “Jazz,” or “Concert.”

Reading amplifier specs, forums and literature

Are you still with us? This is where we are really start talking business when it comes to making sense of amplifier specs.

Amplifier class: Amplifier classes aren’t just grading systems, but descriptions of how an amplifier functions at a core level. The most common amplifier classes used in consumer home audio today are Class A, A/B, D, G, and H.

Although there are good amplifiers in each class, there are also important differences between each of these classes, particularly when it comes to cost, amplifier efficiency, and consequently weight.

Class A amplifiers although at one point the audiophile’s choice, have fallen out of grace because they tend to be large, hot, heavy, power-hungry, and inefficient. However, they generally provide the best output quality (the best linearity).
Class B offer poorer linearity but are cheaper, run cooler, and are much more efficient.
Class AB are a compromise solution, aiming for the output quality of class A and the efficiency of class B. They are still the preferred choice of audiophiles because of their powerful, clean sound but digital amplifier designs (Class D) have made significant improvements in the past few years.
Class C amplifiers have much higher efficiency but much poorer output quality.
Class D Digital amplifiers features a very efficient design compared to conventional amplifiers. They are ultra-quiet with very low distortion. They are small, create barely any heat yet pump out incredible volumes of power compared to more traditional class AB amps. Digital amps are popular in powered subwoofers and even in some receivers. The downside of digital amplifiers is that they tend to lack the musicality and weight of a traditional amp.

Flat response: An amplifier might work better with some sound frequencies than others; the range of frequencies over which it works satisfactorily is called its ‘bandwidth’. Ideally, it has to produce a gain that is pretty much constant across a range of frequencies. This is called a ‘flat response’ or ‘linear response’. So, although counterintuitive: flat response is good.

Harmonic Distortion: The presence of frequencies in the output of an amplifier that are not present in the input signal. The additional frequencies are multiples of components of the input signal.

THD: The ‘total harmonic distortion’ (THD) of a signal is a measurement of the harmonic distortion present.

SNR: Signal-to-noise ratio (abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise.

Noise Figure: Noise figure is a comparison between the output ‘signal to noise ratio’ and the thermal noise of the input signal. It is usually measured as the difference between the noise output of the actual receiver to the noise output of an “ideal” receiver with the same overall gain and bandwidth. It is a number by which the performance of an amplifier can be specified, with lower values indicating better performance.

Clipping: Clipping is a strong distortion caused when your amplifier exceeds its power output. It can severely damage speakers.

Feedback: Another problem amplifiers have is called feedback. People who use microphones on stage are very familiar with it. If a microphone is turned up too much or placed too near to a loudspeaker, it picks up not only the sound of a person’s voice or an instrument (as it’s supposed to), but also the already amplified sound of the voice or instrument coming from the speaker slightly after, which is then re-amplified—only to pass through the speaker once more and be amplified yet again. The result is the horribly deafening whistle we call feedback.

RMS: A term used to indicate the average level of power that a receiver or amplifier can sustain over a given period of time. Average power ratings (ex: 100 watts RMS) provide a more realistic assessment of your amp’s performance than peak power (ex: 400 watts peak/dynamic power) since an amp can only sustain peak power for a short period of time. (RMS stands for “root mean square,” which is one of the mathematical methods used to calculate an amp’s average power output, and is commonly used throughout the industry to represent the average power rating.)

Gain: Simply, it is the degree to which an amplifier actually amplifies the input from the preamplifier/processor. Often overlooked by those unaware of its importance, this one parameter can have significant implications on actual performance when an amplifier is introduced into an AV system.

Gain Range: The maximum and minimum voltage that can be used to amplify a signal.

Input sensitivity: which is the amount of voltage needed from the preamp to drive the amplifier to full unclipped power.

Slew Rate: This is a term used to describe how quickly the output of an amplifier can track its input. Slew Rate is usually measured in V / usec. The higher the value (up to a point), the better the amp is at potentially reproducing the subtle nuances and dynamics associated with music reproduction.

Damping Factor: This is a quantity which defines how quickly how quickly an amplifier can stop a speaker’s driver from moving, when no signal is present.

The higher the damping factor, the better the amp will control the woofer and help reduce overhang distortion (again to a point). The damping factor of an amplifier is mostly dependent on the output impedance of the power amplifier and the ability of the power supply which feeds the power amp.

And then some…Rapallo’s Amplifier Glossary

Bi-amp: Bi-Amp means using two amplifiers to power your speakers. This can be either using a separate amplifier for the low and high frequencies, or a separate amplifier for each speaker.

Bi-Wiring: A method of connecting an amplifier or receiver to a speaker in which separate wires are run between the amp and the woofer and the amp and the tweeter. This can only be done with certain types of speakers. We won’t get into this any further here as it would take us into rather technical explanations.

Tube Amplifiers: Tube amps are considered the most alluring and sexy of the amp technologies by some audiophiles. The glow of the vacuum tubes, the warm analog sound and the overall musicality make a tube amps something immensely appealing, despite certain disadvantages. One of the drawbacks is that they create a lot of heat. They also have very little power compared to solid state (class AB) amplifier for the same money. On top of that, tube amps need constant adjustments or they will perform poorly in a matter of weeks. They need time to warm up to sound good. And finally, they also need to have the tubes carefully replaced every few hundred hours of operation. But for the discerning audiophile this is all justified by the incredible sound they deliver.

Monoblock Amplifiers: Monoblock or mono amplifiers are often the preferred choice of audiophiles and used in the most demanding home theater playback systems. Mono refers to the idea that one physical amplifier is designed to power one audio channel. The main advantage of mono amplifiers is the concept that each channel of audio gets its own power supply thus can provide more accurately and effectively the power needed in an audiophile or 7.1 speaker system as the source material demands. Some audiophile brands make dual or even tri-mono amplifiers which house multiple mono amps in the same chassis yet retain the advantages of the mono design. This normally comes at a significant cost premium. Monoblock amplifiers are commonly found in all varieties of amplifier including tube amps, solid state amps and even class D “digital” amplifiers.

With this Rapallo’s Amplifier Glossary we hope to set you on your way to make a little more sense out of all the information that is available when it comes to amplifiers. When your time comes to upgrade to your next AV receiver or power amp, this might just give you the tools to figure out which option is the right one for and which one provides the best value for money.

Of course, we are always happy to help out too.