About Guitar Amplifiers

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Guitar Amps Terms Explained

Here you will find explanations of terms you will come across when dealing with guitar amplifiers complete with pictures and tips

Define: Aux Send
Define: Analogue
Define: Active
Define: Amp Head
Define: Balanced
Define: Banana Plug
Define: Band Pass
Define: Bi Amp
Define: Bias
Define: Bridged
Define: Bypass

Define: Capacitor
Define: Clipping
Define: Combo Amp
Define: Compressor
Define: 
Direct Box (DI)
Define: Dry Joint
Define: Gain
Define: Horn
Define: Impedance
Define: Insert
Define: Jack

Define: Line Level
Define: Lowpass Filter
Define: NOS
Define: Ohm
Define: Overdrive
Define: Passive
Define: Re-Cap (Capacitor)
Define: 
Resistance
Define: Rectifier
Define: Return

Define: Reverb
Define: 
Sag
Define: Send
Define: Voice Coil
Define: Watts
Define: XLR




to top of the page
 PDF showing connectors used with Guitar Amplifiers

to top of the page Aux Send
Aux is an abbreviation for Auxiliary. You will see Aux Send sockets on mixing desks or guitar amplifiers which supplies an output, which can be routed to an external (auxiliary) effects processor or monitor system.

to top of the page Analogue
An analog or analogue signal is any variable signal continuous in both time and amplitude.

to top of the page Active
Opposite of Passive. An active device has its own power and can, if necessary, add to or amplify a signal in some way. Active speakers, for instance have a built in amplifier. An active

to top of the page Amp Head
A head amp we're talking about here is the dedicated amplifier in a 2-piece amp/speaker cabinet set-up. Fender built most of the early 2-piece systems, but other manufacturers quickly follow. The most famous heads were those built by Marshall, and they remain a staple for rock super groups. You probably couldn't find a photo of Jimi Hendrix, Eric Clapton, or Pete Townshend on stage in the '60s without that amazing backline of Marshall heads and stacked 4x12 cabinets.

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to top of the page Balanced
Balanced inputs or outputs you will come across (usually XLR - for XLR description, look under 'X') have signals independent of ground (X). One is generally considered positive + (L) and the other negative - (R) unlike unbalanced audio, for instance an example of which would be a standard 1/4-inch guitar cable.
The main benefit of balanced signals is that any noise that gets ‘picked up’ in the cables or circuit will be common to both the positive and negative sides, but because they are effectively out of phase they will cancel each other out reducing noise making them much better for long cable runs.

to top of the page Banana Plug
An electrical connector designed to join audio wires such as speaker wires to the binding posts on the back of many power amplifiers. They are very often along side ‘Speakon Sockets’

to top of the page Band Pass
Refers to filters. A band pass filter will only allow a specific range of frequencies through.

to top of the page Bi-Amp
This configuration simply means two amplifiers. Very often used when an audio signal is divided into two frequency ranges via a filter network called a crossover into high and low (or sub) for instance, and then sent to two separate amplifiers, which in turn drive separate loudspeakers specifically designed to reproduce those frequencies.

to top of the page Bias
You will hear a lot talked about bias, especially in connection with tube (Valve) amplifiers although it is equally important with solid state or transistor amplifiers. A bias is applied to a transistor or tube to enable that device to operate within its most linear range. If the bias is too high or too low, the output signal will be distorted in some way or in extreme cases overheating will occur and cause the amplifier to fail.

In tube amplifiers bias can be adjusted to allow the amplifier to distort sooner, (which in turn will result in reducing tube life) or later to produce a cleaner sound at higher levels.

In all cases, the level of the bias must be carefully adjusted to achieve the best results.

to top of the page Bridged
Bridging is a term to describe a configuration where a 2-channel amplifier drives a single loudspeaker, effectively doubling the power available to that single speaker. For this to work the input which is normally connected to the amplifier input is connected via a transformer or circuit that will split it into two, but out of phase signals. The two signals are then connected to each channel of the amplifier input. The speaker is connected across the two positives of the speaker outputs leaving the negative terminals not connected to anything.
This may sound a little complicated but normally there are switches on amplifiers to do all this automatically for you. You must make sure you read the amplifier’s manual regarding the minimum load (minimum speaker impedance) that may safely be connected without causing damage to the amplifier, as this will differ from standard operation.

to top of the page Bypass
Bypass refers to allowing a signal to pass through a device without being affected or processed. This may take the form of a switch to bypass an ‘effect’ for instance A ‘raw’ or unprocessed signal is sometimes referred to as a dry signal.

to top of the page Clipping
A distortion which results in a off the peaks of audio signals. Clipping usually occurs in the amplifier when its input signal is too high or when the volume control is turned too high. A clipped signal contains lots of harmonics and energy which can easily damage speakers, even if the speaker has a power rating higher than the amplifier it's being driven by. This is why amplifiers have 'clip lights' to tell you when clipping is occurring

pure and clipped sinewave Close Window

to top of the page Combo Amp
Combo Amps (short for combinations) are self-contained units containing the amplifier and speaker in one cabinet.

to top of the page Compressor
A compressor in audio electronics refers to a device which reduces the gain and dynamic range of an audio signal which we call compression. Compressors are used while recording and in live environments to control excessive levels. The amount of compression is stated as a ratio of the original level for e.g. 2:1 or 3:1 etc. In the case of a 3:1 ratio, for every 3dB the original signal increases the compressor would only allow a 1dB increase in level.

to top of the page Direct Box (DI)
Very often abbreviated DI (Direct Insertion). This is a device commonly used to convert high impedance unbalanced signals from an instrument like a guitar or keyboard into a low impedance balanced signals. It changes the signal to the proper level for a mixer and prevents the instrument from becoming loaded down with too low impedance, which would cause a change in how your guitar sounded and the volume level. It also allows the signal to be transmitted over long lengths of cable without picking up unwanted hum and noise. A DI box is always used in ‘live’ situations to send a signal out of an instrument on stage to the mixing board, which can be as much as 500 feet away. A simple direct box consists only of a small transformer (a passive device), but more sophisticated designs use electronic gain stages (an active device), which more resembles the input of an instrument amplifier.

to top of the page Dry Joint
This refers to a solder joint that is of a poor standard or the solder around the cable, wire or component in physically cracked usually due to heat or stress. A Dry Joint is called 'dry' because it looks dull and matt where as a good joint looks shiney.

Picture of a Dry Joint with physical damage which was causing an very loud hum as soon as the
amp was switched on! The customer though it was going to be an expensive repair but was an easy fix.

dry solder joint image click to see larger image

to top of the page Gain
Gain is how much an electronic circuit amplifies a signal. Level controls on guitar amps are very often labelled ‘gain’. In specs or references you will see gain expressed as a decibel value i.e. Gain +3 dB.

to top of the page Horn
A speaker design using its own funnel shape to amplify its sound and driven by the internal diaphragm of the speaker.Insert
You will see these on mixing boards and are used to interrupt a signal path and "insert" another signal. You could bring the signal out of the mixer for some processing or the addition of an effect, and then return the processed signal to the same point. Common applications include applying compression, gating, or EQ to a particular channel.

to top of the page Impedance
A measure of the opposition to the flow of alternating current (AC) through a circuit. Impedance is measured in ohms.

to top of the page Insert
Insert sockets are similar to 'send' and 'return' but combined into one socket, very often a stereo jack. Most commonly use on mixing desks to send a signal to an external effects or processor and back to the desk again.
Tip These are notorious for causing intermittant output as they are switched sockets and their contacts become faulty. Replacing the socket cures the problem. Carry a stereo jack plug with the tip and ring shorted together and plug this into the offending insert socket - this will get you out of trouble until the socket is replaced.

to top of the page Jack input jack sockets on Fender Guitar Amplifier click to see larger image

A jack is the socket into which a plug is inserted. If you are plugging your guitar into an amp, for example, you will insert the 1/4-inch phone plug (very often referred to as a jack plug these days) at the end of your guitar cord into the jack on your amp.

to top of the page Line Level
While technically Line Level is any voltage over 25 millivolts RMS is considered line level, in the modern audio world we narrow the scope a bit to the two line level references in use today: Balanced "pro" gear runs at around +4 dBm (1.23 volts), while unbalanced "semi-pro" gear operates at approximately .316 volts (-10 dBV).

to top of the page Low pass Filter
A filter specifically designed to remove frequencies above the cut-off frequency, and allow those below to pass unprocessed is called a low pass filter. The effect of a low pass filter is to reduce high frequencies. The 'Low' can be any frequency. Common examples include the "treble" controls or "tone" controls on electric guitars.

to top of the page NOS
NOS tubes are old tubes that have never been used. They are "New" in the sense that they have never been used. They are "old" in the sense that they were manufactured very long ago. Hence the term "New Old Stock".

to top of the page Ohm
A unit of electrical resistance or impedance. The symbol for ohms is ohm

to top of the page Overdrive
In audio, overdrive is generally considered to be another word for distortion or clipping. When you overdrive your guitar amp with too much level it distorts. For guitarists, however, overdrive gives a character of sound and sustain. Technically though it’s just distortion.

to top of the page Passive
A passive audio device is one in which does not use amplification circuits. Because they do not contain amplifiers, and are "cut-only" or "subtractive" in operation. Passive devices tend not add noise or distortion to a signal. Typical passive devices include direct boxes, splitters, tone controls i.e. bass and treble, equalizers and crossovers.

to top of the page Recap (or Recapping)
In audio this refers to the process of replacing capacitors in equipment. You will come across this with reference to guitar amps, very often tube (valve) amps. The condition of capacitors will have a direct impact on sound quality as they degrade with use and time. As they breakdown they cause circuits to become unstable and noisy. Electrolytic capacitors can even explode! For more in depth information about capacitors take a look at article More than you need to know about capacitors.

Exploded Capacitor Exploded Capacitor Image

to top of the page Resistance
In electrical or electronic circuits, this is a characteristic of a material that opposes the flow of electrons. Speakers have resistance that opposes current. Resistance causes a change of electrical energy into heat or another form of energy. All electrical circuits and wires have some resistance. The unit of the resistance is the ohm (Ω), named after George Ohm, who formulated Ohm's Law. Impedance is also a type of resistance but for AC signals.
To find out about the Resistor Colour Code to identify resistor values go here

to top of the page Rectifier
An electronic circuit or component designed to convert AC (Alternating Current) waveforms into DC (Direct Current). Normally these are used in the power supply of all types of equipment to provide the DC power source required by most electronic components for operation.

Two types of rectifiers are half-wave and full-wave rectifiers, and are so named because of what they do with the negative portion of the wave. A half-wave rectifier literally lops off the negative portion and only sends along the positive part of the wave. This is basically what a single diode does. A full-wave rectifier takes the negative portion and "folds" it into the positive half, creating something closer to true constant current. Today all modern (including vacuum tube-based) audio equipment uses full-wave rectifiers; they are often a set of diodes in a special configuration located immediately after a power transformer.Some tube amplifiers still use tube rectifiers and although a rectifier doesn't directly affect the tone or audio quality of a signal, it can still affect sustain. Tube rectifiers 'sag' in power output slightly (semi conductor rectifiers don’t suffer from this) when the amplifier is used at high volume levels or there is a sudden increase in volume, which will affect the characteristic of the sound. Many musicians very often prefer this characteristic.

to top of the page Return
A return socket is the other half of the 'send' socket : ) A signal is taken out of your 'send' socket and into your effects or processor then out from your effects unit and returned to the 'return' socket. The effect is then in series with your guitar or vocals, or what ever is feeding through your amp.

to top of the page Reverb 
Reverb or Reverberation is term given to the sound that remains or lingers after the original sound has stopped. If you were in a church or a large auditorium and you clapped your hands you would hear the sound of your hand clap continuing after the hand clap had finished. Generally, the larger the building, the longer the reverberation will take to stop. Many factors influence reverberation apart from the size of the building such as the material the building is made from.

We very often add reverberation as an 'effect' to Voice and Guitars. Reverb enhances the sound with added presence. Many Guitar Amps include this feature as a built in effect either producing reverb digitally or by analogue means using a Spring Reverb Tray. I prefer the old spring reverb type as it sounds more natural, unless the digital effect is of a particularly high quality. The digital effects are however, more controllable.

 Click on the images for pictures of spring reverb reverb tray top reverb tray underside reverb tray close up

to top of the page Sag
This is a term given to a property exibited by Tubes (Valves) in this case rectifier tubes. Rectifiers convert AC (Alternating Current) to DC (Direct Current) which electronic circuits need to operate correctly. Tube rectifiers aren't acually as effective as semiconductors when the going gets tough : ) in other words, when your amplifier is turned up loud, more current is required by the amplifier, the rectifier tube has to work harder and the voltage the rest of the amplifier needs tends to drop. This is due to it's impedance, but all you need to know is that the DC supply voltage drops which causes a 'compression' in the sound. Now you would think this was a bad thing, but the effect is actually welcomed by musicians and becomes part of the 'easy on the ears' tube sound.

to top of the page Send
An output used in audio amps and mixers designed for routing signal to an external effects unit such as a reverb, delay, or other processor. Typically, sends are paired with returns, which accept signal coming back from the output of the processor. These sockets interupt the signal path when a plug is inserted. Tip A common fault with these sockets is a faulty contact on the switch built into the socket which can produces an intermittant sound output.

to top of the page Voice coil
The output from your amplifier connects to the voice coil and is the wire wound around the speaker former. The former is mechanically connected to the speaker cone. When a signal is fed into the voice coil it produces a magnetic field, which combined with the magnetic field produced by the permanent magnet causes the cone to vibrate. This in turn moves the surrounding air, transmitting pressure waves our ears interpret as sound.

to top of the page Watts
A watt is a metric unit of power defined as one Joule per second and is a unit of energy. The 'watt' we refer to in audio applications is used as a measurement of power. For instance the output power of your guitar amp might be 100 watts. The power used by your amplifier by be 350 watts, or the power handling of your speaker might be 60 watts.
Watts are determined by voltage, current and in the case of power output, by the resistance/impedance of the load.
Watts=Amps x Volts and (Volts to power of 2) ÷ Resistance

to top of the page XLR xlr socket and plug click to see larger image

"XLR" was originally Cannon's name for one of their connectors, which meant X Series, Latch, and Rubber. In fact you may still hear these connectors referred to as "Cannon" connectors. XLR has however become a generic term, rather like ‘Hoover’ did for a vacuum cleaner. They are extensively used in audio and are generally used for transmitting balanced signals.

Pin 1 of an XLR connector is always ground/shield. The connectors are designed so that pin 1 makes its connection first when inserted which ensures that the ground connection is made first which will helps to prevent unwanted noise.

Either pin 2 or pin 3 may be hot, depending on the gear the connector to, but normally 2 is 'Hot' and 3 is 'Return'. Pin connections are usually labelled on the connector so you know which is which.

1 = X = Ground/Earth
2 = L = Live/Hot
3 = R = Return

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