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
PDF showing connectors used with Guitar Amplifiers
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.
An analog or analogue signal is any variable signal continuous in both time and amplitude.
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
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.
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.
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’
Refers to filters. A band pass filter will only allow a specific range of frequencies through.
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
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.
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.
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.
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
Combo Amps (short for combinations) are self-contained units containing the amplifier and speaker in one
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
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.
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.
click to see larger image
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.
A speaker design using its own funnel shape to amplify its sound and driven by the internal diaphragm of the
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
A measure of the opposition to the flow of alternating current (AC) through a circuit.
Impedance is measured in ohms.
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.
Jack 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.
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).
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.
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".
A unit of electrical resistance or impedance. The symbol for ohms
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.
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
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
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
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.
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
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
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.
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.
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.
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
Watts=Amps x Volts and (Volts to power of 2) ÷ Resistance
XLR 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
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