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Balanced and unbalanced
A connection is balanced when the signal is carried by two conductors (hot
and cold) and a screening braid. The hot pin has the job of carrying the in-
phase signal, while the cold one carries the same signal, but out of phase.
This method enables to make transmitted signals immune to
electromagnetic interference even over long lines, thanks to the fact that
when the two signals reach the receiving device, they are algebraically
subtracted one from the other, producing a new signal with twice the
amplitude and eliminating the interference along its path.
Final stage
(output stage)
An electronic circuit which converts low power signals to high power
signals with sufficient current to move the coils and therefore the cones of
a loudspeaker.
Impedance (Z)
Represents the resistance offered to AC by an electric circuit. It is
measured in Ohms
and as opposed to the resistance, takes into
consideration the circuit's inductive components (coils) and capacitive
components (condensers). Audio signals' input and output circuits are
divided into low impedance (with a Z of less than 5 kOhms, such as
microphones and loudspeakers) and high impedance (when Z is more
than 10 kOhms, as is the case with electronic instruments, CD players and
tape recorders). When connecting different units, it is necessary to try to
keep OUT and IN impedances similar.
Ground
Electrical reference point for a signal travelling round a circuit or along a
cable. The ground generally has a value of zero volts and is carried by
audio cables by means of a metal sheath which also has the function of
screening the signal (i.e. protecting it from external electromagnetic
interference.
Mixer
An active electronic circuit able to mix two or more audio signals together.
A mixer can also feature audio effects, mixing them with the original
signals.
Pre-amplifier
This is an active electronic circuit which handles low power signals. The
unit's functions are: handling the incoming and outgoing audio signals
(excluding speaker enclosures), volume and equalization.
Ground
The ground (or earth) in an electrical device is represented by the physical
connection of the metal parts exposed to the user and a cable in the power
plug (the middle pin). By means of the mains power supply, the ground
cable (normally recognizable for its yellow/green colour) is connected to a
metal pole hammered into the ground, often in the basement of the
building itself.
The aim of the ground system is to disperse in the ground any current
which in the event of faults could electrocute a user when touching the
metal parts of the unit in question. The dispersion of energy is sometimes
also used to eliminate any audio hum, which can be achieved by means of
a capacitive connection between the signal ground and the amplifier
ground, or even a physical connection.
13
TECHNICAL GLOSSARY
THD
Total Harmonic Distortion. This value indicates the relationship between
the effective value of the spurious harmonics generated by the system in
question and the effective value of the fundamental sine wave used in the
test. THD is normally expressed as a percentage.
TIM
Transient intermodulation. Measurement of intermodulation distortion
during the most critical moments of an amplifier's operation: powerful
transients which must release high energy in a very short period are
generated.
Tone burst
The measurements carried out in laboratories to test amplifiers' power
don't take into consideration the constant electrical variations which a
complex audio signal can have through time. Nowadays power is
expressed in peak Watts (as far as the response of an output stage with
extremely brief transients states is concerned), musical Watts (which
indicate the hypothetical power on a stable sinusoidal signal) and RMS
Watts (which measure the real power, but referred to a stable repetitive
complex signal). The measurement technique with Tone Burst signals is
extremely significant as it cyclically recreates the possible dynamic range
which a normal audio signal can have through time. This system ensures a
control of the quality and capacity of the output transistors and above all of
the power supply contained in the amplifier being tested.
Watts RMS
This is a measurement which expresses the effective value of the power,
i.e. the real amount of power which a system is able to deliver. RMS (Root
Mean Square) is the mathematical method used to calculate the effective
power: the square root of the mean (average) of the sum of the squares of
the harmonics contained in the spectrum. The RMS Watts are exactly half
themusical Watts and an eighth the peak/peak Watts.
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