Fbt symbol 12000 User Manual - page 11
10
TECHNICAL GLOSSARY
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.
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.
Earth- 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.
Bridge- Indicates an electrical configuration of two power amplifiers that makes it possible to double the output power delivered to a single
loudspeaker line. In this mode the "bridge" connects the two power amplifiers to the same input signal but with a 180 degree reversal in
phase. The loudspeaker is connected across the two positive binding posts on the amplifier output. Some amplifiers are able to assume this
configuration by means of a switch and dedicated mono output.
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.
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 the musical Watts and an eighth the
peak/peak Watts.