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A. Ampere or amp. The unit measure of electrical current.
A/B Inputs. Two input connections under the control of an A/B switch. Such
switches permit the selection of either of two sources, such as tape or receiver
signals, for a given amplifier input signal.
A/B Switch. A two-pole selector switch permitting signal coupling from either
of two or devices (A or B) to a common device, such as from multiple audio sources
to a given speaker system.
AC. Alternating Current or the varying amplitude characteristic of an electrical
signal. All information-carrying signals, including audio signals, are AC, as it
is the signal's variation that contains the information.
Attenuation. Reduction, as in audio volume control. The converse of amplification.
Typically performed with a gain control potentiometer in amplifiers or with a switchable-tap
transformer for in-wall volume controls.
Autotransformer. A transformer having a feedback winding for improved signal
transfer accuracy, especially at higher power levels. When used in audio power amplifiers,
autotransformers greatly reduce the distortion otherwise introduced by output transformer
nonlinearities. Rarely required except for the highest of output power levels.
AUX Input. Auxiliary input to an amplifier for the addition of another signal
source such as a second tape deck or turntable.
Bass. The lower frequency range of the audio sound spectrum (drums, explosions,
etc.) spanning the frequency range of around 20 Hz to 200 Hz. Primarily reproduced
by woofers and subwoofers in audio systems.
Bass Boost. Increased bass response for greater low-frequency sound. Often
found in headphones where space restrictions limit the internal speaker size, restricting
bass response.
Binding Post. A versatile connector jack that accepts banana plugs and provides
screw-down wire connection for either wire lugs or a thru-shaft wire insert. Typically
located on the backs of speakers or amplifiers.
Bipolar. Bipolar junction transistor, as often used in the power output stages
of audio amplifiers for its superior high-power efficiency.
Boost. Signal gain generally supplied within a selected band of frequencies.
Often applied in audio to compensate for restricted bass response, as encountered
with headphones, or simply to accentuate bass response.
Bridgeable (Output). An amplifier output capable of driving loads such as
speakers that are connected in bridge configurations. Requires two output connections
to the load for each bridge drive. (See also Bridged Power).
Bridged Power. The output power of an amplifier when driving a speaker connected
in a bridged, as opposed to grounded, configuration. Bridged drive of a speaker
potentially quadruples the power drive to the speaker.
Center Channel. An audio sound channel derived from the combined signals
of the left and right channels for greater surround effect. A center channel fills
in the sound presence between left and right.
CH. (See Channel)
Channel. One signal path, such as one of the two composing a stereo signal
or one of the three containing the bass, midrange and treble segments of an audio
signal. Also, a broadcast frequency as in TV and CB transmission.
Channel Separation. Signal isolation between channels such as between the
two channels of a stereo system. Greater separation adds depth and spatial sense
to audio playback.
Class A Operation. Transistor operation with continuous bias under all load
and signal conditions for low distortion and greater bandwidth. While less power
efficient, this operating mode avoids the transistor turn-off distortion introduced
by the more efficient Class B operation. The reduced distortion of Class A operation
most often benefits amplifier output stages. There, wide ranging current demands
would routinely exercise the turn-off distortion of Class B bias.
Clipping. A form of distortion in which an amplifier limits or clips signal
peaks. Commonly occurs when an amplifier is overdriven beyond its rated output level,
resulting in output swing up to limit imposed by the power supply voltage. Results
is severe audible distortion.
Continuous Adjustment. A continuously variable or linear adjustment, like
that of a potentiometer, as opposed to the discrete step adjustments of a switch.
The continuous adjustment typically provides greater adjustment resolution since
switched adjustments remain limited by the number of switch positions practical.
Cut. Signal attenuation applied within a selected frequency range. An equalizer
tuning function much like a bass or treble control but spanning a more selective
frequency range. The opposite of Boost.
Current Feedback. A signal control technique that reduces distortion by sensing
an output signal current, comparing it with the input signal and supplying gain
to correct any distortion difference. The type of control realized with the feedback
winding of an autotransformer.
dB (decibel). A logarithmic unit of relative signal level. For signal power,
P(dB) = 10log(P1/P2) represents the power level P1 as compared with a reference
level P2. Differs from dBu in that the latter is referenced to a reference P2 level
of 0.775Vrms.
dB/Octave (dB/Oct). Frequency response roll off rate or slope. This slope
reflects the selectivity or response sharpness of equalizer passbands. 6 dB/octave
represents the basic single-pole response roll off and 18 dB/octave represents a
highly selective, three-pole response characteristic.
dBu. The dB signal level relative to a reference level of 0.775 Vrms. [dBu
= 20log(es/0.775).] Differs from dB in that the latter only provides a relative
measure of two arbitrary signal levels.
D-Bass. Dynamic bass. A boosted bass response producing increased low-frequency
content for greater woofer output. Produces a more dynamic and encompassing sound
for action videos. (See also Bass Boost.)
Discrete Output. Output stage(s) formed with individual discrete transistors.
For the higher-power output stages of amplifiers, discrete transistors provide greater
power handling and more performance alternatives than those included in integrated
circuit components.
Distortion. Signal wave shape deviation from the original. To some degree,
all electronic equipment inherently distorts signals due to non-ideal signal transfer
responses. For a given audio element, Total Harmonic Distortion serves as a quantitative
measure of such response deviations. (See also THD.)
Distortion, Harmonic. A measure of the distortion content of a signal as
represented by equivalent harmonics of that signal and specified as a percentage
of the signal amplitude. While the equivalent harmonics represented do not actually
exist in the signal, their summation would reproduce the distortion component of
the signal. Further, filter separation of the signal into its fundamental and harmonic
frequencies yields the harmonics for identification and measurement comparison with
the fundamental.
Double-Sided Board. A printed circuit board having components mounted on
both of its surfaces for increased compactness. Multi-layer boards increase the
number of interconnect planes for even greater compactness.
Dubbing. Adding a second audio signal to a first signal as in sound-on-sound
recording. The second signal does not override the first but rather adds to it.
Dubbing can, for example, add background music to a vocal dialog.
Dynamic Headroom. The separation between a maximum signal excursion and the
maximum allowable. For audio speakers, this defines the separation between the maximum-recommended
operating level and that at which excessive sound degradation occurs.
Dynamic Range. The span between minimum and maximum signal levels as determined
by noise and power limitations, respectively. The noise reduction of 16 bit DSP
potentially expands this range to 96 dB, however, speakers and headphone responses
then impose a final limitation.
Dynamic Range Compression. Low-level signal amplification and high-level
signal attenuation applied to raise signals well above the background noise level
without exceeding maximum amplitude levels. Used to reduce the significance of tape
noise. Requires signal re-expansion in the playback process.
EL. Electro-Luminescent. An illuminated display often found in auto radios
that employs electro-luminescence rather than an incandescent bulb to light the
display.
EMI. Electromagnetic interference. Electrical interference coupled by magnetic
fields like the car radio noise sometimes produced by the car's ignition system.
Can also result from parasitic coupling from transformers.
Equivalent Input Noise. Output noise divided by the circuit gain. This input
representation permits direct comparison of noise and signal levels for qualitative
evaluation.
Feedback. Supply of a portion of a circuit's output signal to the circuit
input for comparison with the input signal and the generation of an error correction
signal. Commonly used to reduce distortion in amplifier stages. The underlying principle
of the autotransformers sometimes used in amplifier output stages.
FET. Field effect transistor. A lower-distortion but lower-gain alternative
to the bipolar transistor. Often used for higher-power amplifier output stages and
higher-impedance receiver input stages. Less effective than bipolar transistors
in amplifier gain stages.
Freq. Frequency.
Frequency. The rate of repetition of a signal in cycles per second. Higher
audio frequencies correspond to treble tones and lower ones correspond to bass.
Radio frequencies define station locations within a broadcast band.
Frequency Range. A range of frequencies between high and low end points.
A passband or bandwidth. Individual speaker elements like woofers, midranges and
tweeters serve different frequency ranges within the overall audio frequency range.
(See also Frequency Response.)
Frequency Response. The range of output signal frequencies supplied by an
amplifier, speaker or microphone as specified by the upper and lower bounds of the
frequency range in Hertz (Hz). Typically, 20Hz to 20kHz encompasses the full range
of human hearing and separate audio speakers generally serve different segments
of this range.
Front/Rear Fader. A front-to-rear balance control, as commonly used in car
audio systems to achieve volume balance between front- and rear-mounted speakers.
This control simultaneously increases volume in one location while reducing it in
the other. Analogous to the more common Left/Right balance control of general audio
systems.
F&R. Front and Rear, as in car audio volume balance. (See also Front/Rear
Fader.)
Gain. Amplification factor. Gain increases signal magnitude for greater sound
volume or improved radio and TV reception. Commonly provided by an amplifier in
audio or by an antenna in radio and TV.
GND. Ground. The zero reference point from which a voltage or voltages are
measured. In the most basic case, earth ground. In electronic systems, generally
the chassis or case ground of the system.
Ground Loop. A crosstalk producing condition in which the ground line currents
from one signal produce voltage drops that add to a companion signal path. Star
connection returns of all grounds at a common point avoid such parasitic interference.
Headroom. The separation between a maximum rated signal excursion and the
maximum allowable. For an audio speaker, the power level separation between a continuous
operating capability and the higher level for which short term excursions can be
handled without damage.
Hz (Hertz). A measure of signal frequency expressing signal cycles per second.
(The audio frequency range extends from 20Hz to 20kHz where 20kHz = 20,000Hz.)
Impedance. The electrical characteristic of an electronic device that reflects
the voltage developed in response to a current supplied to the device. Speakers
typically display a low 4 ohm or 8 ohm input impedance to accept high power drive
from reasonably low signal voltages. Microphones typically present a high output
impedance to develop a sufficiently high signal voltage from their low internal
power generation.(See also Impedance Matching.)
Impedance Matching. Matching a driven load impedance to that of the source
for maximum power transfer, as often implemented through transformer coupling for
impedance transformation. A feature incorporated in many in-wall volume controls
through transformer tap selection. Becomes especially important where multiple speakers
share a given audio signal line, as each speaker added alters the net load impedance.
Input Impedance. That impedance presented by the input of an electronic device,
as commonly expressed in ohms. Amplifiers typically present high input impedances
to limit loading effects on their signal sources. Speakers most commonly present
low input impedances to accept higher drive power. Most speakers have an 8 ohm input
impedance, although 4 ohm and 16 ohm types exist for different applications.
In/Out. Input/Output.
Isolated Mounting Legs. Equipment support legs that electrically isolate
a case from unwanted ground connections that could introduce ground-loop interference.
kHz (kilohertz). A measure of signal frequency expressing thousands
of cycles per second.
kohm (kilo-ohm). A measure of electrical impedance expressing thousands of
ohms.
LCD (Liquid Crystal Display). An energy-efficient high-resolution display.
Most often produces black characters on a light green background in audio equipment
but capable of multi-color.
LED (Light Emitting Diode). A semiconductor diode that generally serves as
an electronic indicator light to display the on/off states of equipment functions,
usually in red, yellow or green.
Line Input. A high level signal input that bypasses an amplifier's initial
gain stage to accommodate line level signals (1 to 2 Vrms). An input that accepts
the higher output signal presented by another amplified source.
Line Out (Line Output). An amplifier monitor output that bypasses the amplifier's
variable and power gains. This output remains unaffected by volume control variations
and free of the distortion introduced by later power stages.
L/R. Left/Right.
mA. (Milliamp). 0.001 amp.
Magnetic Shielding. Electrical shielding against electromagnetic interference
such as that commonly produced by transformers. Commonly achieved with high permeability
metallic shields that intercept and conduct electromagneticly coupled signals to
ground.
Mic. Microphone.
Milliamp. One thousandth of an amp (.001A).
Mono (Monaural). Monophonic; single-channel audio.
MOSFET. Metal-oxide-semiconductor field-effect-transistor. Often used for
higher current or lower distortion in power-driving amplifier stages.
Multi-Channel. Supporting multiple signal paths or channels, such as from
an amplifier output to multiple speakers.
mV. (Millivolt). 0.001 volt.
Ohm. The unit of electrical impedance, equaling an element’s voltage drop
divided by its associated current.
Optically Isolated. Employing optical isolation between system components
to prevent ground loop interference. Particularly effective because the conversion
to optical transmission breaks all electrical conduction loops.
Output Impedance. That impedance presented by the output terminals of an
electronic device, as commonly expressed in ohms. Lower output impedances facilitate
higher power transfer to a load.
PCB. Printed Circuit Board. The board on which electronic components
are combined and interconnected to form an electronic circuit.
PCM. Pulse-Code Modulation. Signal encoding through modulation of a carrier
pulse width. A signal encoding technique used in digital audio and some switching
power supplies.
Phase Shift. Time delay introduced in an electrical signal. Produces phase
distortion in audio signals of higher frequencies. Most often the result of amplifier
bandwidth limitations.
Phase Shift, Variable. Control over signal phase shift in stereo playback
to vary the apparent image location. The associated time delay introduced in one
channel of a stereo signal varies the apparent location of sound coincidence or
the acoustic image. Phase delay in one channel makes its image further away than
that of the other channel to alter the composite image location.
Polarity Switch. An electrical switch included on some amplifiers that permits
phase reversal in a speaker drive to check for phase synchronization. Synchronized
speaker drive produces additive sound waves while unsynchronized waves tend to produce
canceling effects. In the absence of such a switch, simply reversing the wire connections
at one speaker produces the same effect but the time required then makes synchronization
more difficult.
Power. The amount of electrical energy supplied to or consumed by a device,
such as supplied from an amplifier to a speaker or from the power line to the amplifier,
as specified in Watts (W).
Power Amplifier. An amplifier dedicated to higher output power levels but
typically lacking preamp sensitivity and control functions. Generally used in conjunction
with a dedicated preamp to fulfill these other requirements. Such a combination
permits largely independent optimizations of input and output features to best serve
more sophisticated applications.
Power, Bridged. Power available to a bridge-connected load (speaker). When
permitted by the amplifier, the bridge connection of a speaker drives it between
two opposing output swings. This drive doubles the speaker's overall voltage swing
to potentially quadruple the drive power. Higher impedance speakers in conjunction
with higher power amplifiers most likely realize the full bridged-drive benefit.
However, amplifier output power limitations may independently restrict this benefit
to a drive power doubling, depending upon the specific conditions of the application.
Power, Full-Bandwidth. That power delivered over the entire specified bandwidth.
At higher frequencies, amplifier output power generally becomes restricted by a
large-signal bandwidth limit that is distinct from the commonly specified small-signal
bandwidth. Larger signals encounter a slew rate limit or maximum rate-of-change
that imposes this added restriction. However, the amplifier remains capable of delivering
the full bandwidth at a reduced power level.
Power Output. The maximum power output available such as from an amplifier
output. Higher power output is important for the accurate reproduction of audio
signal peaks even if not fully utilized at the average volume level.
Pre-Amp. Pre-Amplifier. A low-level signal amplifier typically used in conjunction
with a power amplifier. Pre-amps provide initial signal gain and often include response
tuning controls. They are generally capable of driving headphones directly, however,
they most often require the addition of a power amplifier for speaker drive.
Punch Bass. Bass boost. Increased low-frequency audio signal drive to accentuate
bass components and/or to compensate for restricted low-frequency speaker response.
Especially effective with headphones as size restrictions then preclude the use
of lower-frequency transducer elements.
PWM Power Supply. Pulse-width modulated power supply for high power efficiency.
A type of switching power supply that increases the power available in response
to power demand rather than consuming a high standby power.
PWR. Power.
Q Control. Response selectivity control. Varies the roll-off sharpness of
a filter passband to control the selectivity of the band. Higher Q sharpens the
response for greater frequency selectivity.
RCA Connector. An economical, coaxial cable plug/jack combination commonly
used for audio and lower-frequency video signals. Couples signal and ground thru
inner and outer conductors, respectively. Sometimes color coded by function such
as signal (red/yellow/white) and ground (black).
RCA Inputs/Outputs. Signal connections presented with RCA connectors. These
connectors are economical, plug-in coaxial types commonly used in audio and component
video applications.
Regulated. Controlled or stabilized, as in a power supply output having reduced
sensitivity to the varying load demands produced by signal variations. A regulation
specification quantifies the residual sensitivity as the percentage output variation
induced by a given load demand.
RMS. Root-Mean-Square. An amplitude measure of an electrical signal
that reflects the net power capability of the signal or a speaker. Note that this
differs from the peak power, which reflects the maximum instantaneous power capability.
Screw Terminal. A wire connection terminal having a center screw for compressing
a bare wire end against a flat metal contact. Used for speaker wire and antenna
lead connections. Sometimes grouped in the multiple terminals of a barrier strip.
Short Circuit Protection. Internal protection that prevents damage during
an output short or other current-demand overload. This protection may be
of the instantaneous, electronic type or the delayed, thermal type.
Signal-to-Noise Ratio. SNR. The ratio of signal to noise in their composite
signal, as generally expressed logarithmically by SNR(dB) = 20log (es/en) where
es and en represent the signal and noise components of the composite, respectively.
Higher signal-to-noise ratios indicate greater suppression of the noise signal's
significance.
Silent turn-on/off. A feature that avoids speaker noise associated with turn
on and turn off; typically by design limiting the rise and fall rates of power supply
voltages during power cycling. This avoids the speaker pop sometimes produced by
an amplifier's internal on/off bias transitions.
Slew Rate. The rate-of-change of a signal expressed in volts/second. Most
notable in the slew rate limiting that reduces an amplifier's bandwidth at larger
signal levels.
SMT. Surface Mount Technology. A high-density electronic component mounting
alternative used for compactness and automated assembly economies. This alternative
eliminates the wire interconnect leads and packages of conventional electronic components
by soldering unpackaged components directly to a printed circuit board.
S/N Ratio. Signal-to-Noise Ratio. A noise performance measure of a signal
or the electronic component that supplies it, reflecting the ratio of the signal
amplitude to that of the accompanying noise.
SNR. Signal-to-noise ratio. (See also S/N Ratio.)
Soft Start. Gradual enable of internal power supplies to avoid speaker "pop"
during turn on. (See Silent Turn-on/off.) The resulting gradual rise in an amplifier's
power supply voltages avoids the rapid transitions in internal biases that could
produce an erroneous output signal spike.
Soft Turn-on. (See Soft Start, Silent Turn-on/off.)
Spectrum Analyzer. An instrument that detects and displays signal amplitude
versus frequency. Provides a visual display of audio-signal amplitude versus frequency
to identify the relative contributions of bass, midrange and treble components and
subdivisions of these components by frequency.
Stable. For an electronic circuit, remaining in a controlled state with no
evidence of oscillation.
Stable, x ohm. Stable under a load condition as low as x ohms where x is
the load (speaker) impedance. Lower impedance loads conduct higher current levels
from an amplifier's output and those currents produce parasitic voltage drops on
the amplifier's power supply lines and at the power supply output. Those parasitic
drops can act as feedback signals to produce oscillation under low impedance loading
conditions.
Surround Sound. That sound produced by an audio system having separate left,
right and center audio channels and speakers. Basically stereo sound with the addition
of a center channel that combines left and right signals.
Switching Power Supply. A power supply that employs internal on/off switching
for high power efficiency. An economical and space saving alternative with the disadvantage
that the supply's switching operation produces high-frequency electrical noise.
Terminal. A wire or cable connection point. May be a socket, screw-down connection,
spring clip, etc.
THD. Total Harmonic Distortion. A measure of the distortion content of a
signal as represented by equivalent harmonics of that signal and specified as a
percentage of the signal amplitude. While the equivalent harmonics represented do
not actually exist in the signal, their summation would reproduce the distortion
component of the signal. Further, filter separation of the signal into its fundamental
and harmonic frequencies yields the harmonics for identification and measurement
comparison with the fundamental.
Thermal Protected. Having temperature-sensing overload protection, such as
sometimes used in amplifier output stages to protect against sustained high current
demands. Thermal protection is superior to simple current limiting because the thermal
alternative only activates when the high temperature consequence of an overload
occurs. In contrast, current limiting activates immediately even though the potential
for high temperature damage has not yet developed. Thus, a thermally protected circuit
still accommodates some signal transients that would be unnecessarily blocked by
simple current limiting.
Treble. The higher frequency range of the audio spectrum which requires mechanically
precise audio speakers, called tweeters, for the reproduction of shorter sound wavelengths.
Tri Mode. A speaker connection flexibility of an amplifier output that permits
grounded, floating or bridged speaker loads. Grounded speakers reproduce one channel
of a stereo signal. Floating and bridged speakers are differentially driven by both
signal channels for a center channel response.
UL. Underwriters Laboratory. A private institution that tests and rates electrical/electronic
products for safety. Generally applicable to AC operated equipment and indicated
by product labeling when certified.
V. Volt. The unit measure of electrical voltage.
VAC. Volts, AC.
VDC. Volts, DC.
Vp-p. Volts Peak-to-Peak. The excursion range of an AC voltage signal between
its positive and negative extremes.
Vrms. Volts, root-mean-square. A time averaged measure of an AC voltage signal
that more directly reflects the power delivery potential of the signal.
VU Meter. A meter providing a visual indicator of average signal level particularly
useful in adjusting recording levels.
W (Watt). A unit measure of electrical power equaling the product of voltage
and current.
X-Bass. Extra Bass. (See also XBS, Punch Bass.)
XBS. Extra-Bass-System. (See also XBS, Punch Bass.)
XLR. A three-pin, locking connector configuration commonly used in professional
audio and sometimes in consumer audio to minimize coupled noise interference. The
three pins accommodate the two stereo channels and ground.
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