~ Glossary ~ Clavis ~ Vocabulary ~

~ An Explanation of some Terms and Abbreviations used on this Website ~

Continually under construction as the rest of this site grows

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A measure of square area = 4046.86m2 ~ Often used to describe a space which could be small <1m2 but has enough room for additional objects ~ Truly large areas are often described as "An area the size of Wales" which is part of the UK with an area ≈ 4M acres
A device for making a physical parameter larger ~ In electronics amplifiers increase Voltages or Currents by a fixed amount but only within the limits of the supplies used to produce the larger quantity ~ Audio power amplifiers rarely increase actual power ~ they convert a voltage to another voltage but with the capability to supply a greater current into a lower resistance load
Amp ~ Ampere
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Bandwidth BW
Is a physical constant k or kb named after the Austrian physicist Ludwig Eduard Boltzmann that relates the energy of atoms or molecules to absolute temperature ~ In electronics it appears in the formula for thermal noise voltage Vn-rms=√4kTBR where k=1.38062259 x 10-23 J/˚K



Comité Consultatif International Télégraphique et Téléphonique ~ Or in English the International Telegraph and Telephone Consultative Committee ~ as with many of these international groups the French based acronym was chosen to keep the Entente Cordiale ~ through the 1920s the terms CCI and CCIF were used and in the 1930s CCITT and ITU all of which is best explained here

Deci-Bel ~ Prior to 1924 telephone line quality was quantified by comparison against a 1 mile length of standard line at a frequency of 800Hz and the reference became known as the '800 cycle mile' ~ The attenuation of current or voltage along the line was found to be an exponential function of the distance d ~ Line loss being proportional to ed led to the CCI 1927 introduction of 2 measurement units ~ the 'Neper' using natural logarithms (ln) and the Bel using log base 10 (lg) which made calculations of powers related to line distance much easier ~ A Bel is defined as the logarithmic reference to a 10:1 power ratio where Bels = lg(P1/P2) or Nepers = 0.5 ln(P1/P2)

In 1968 the CCITT recognised one tenth (deci) of a Bel or the dB as the prime way to express signal transmission gains and losses where dB = 10 lg(P1/P2) such that positive dB values show signal path gain and negative dB values indicate a loss or attenuation and the dB values are simply added to give the overall transmission path loss or gain ~ dB is a relative measurement

Deci-Bel relative to a carrier signal ~ Often used in radio frequency measurement because the carrier signal is the only reference available

dBm or dB(mW) is a dB measurement relative to a power of 1mW ~ This requires the impedance in which the power is developed to be known and for telephone transmission systems this impedance was standardised at the average of early long cables and was 600Ω ~ Using a standard impedance amplifiers and transformers could be optimised for gain and frequency response and S/N and the measurement of power levels was done by simply measuring voltages where P=V2/R and R was 600Ω ~ 0.775Vrms across 600Ω is a power of 1mW and other voltages relative to this reference are expressed in dBs as 10 lg(V2/0.7752) or 20 lg(V/0.775) ~ For radio frequency transmission the cable impedances were standardised at 75Ω and 50Ω with the same 1mW reference ~ In all cases dBm is a measure of absolute power
Deci-Bel relative to something where the 'something' must be defined or made clear ~ The units and method used to measure the 'something' and what it is relative to must be the same ~ dBr prevents the need to creating a myriad of dB suffixes like 'dBov' which have to be defined in contex anyhow
dBu or dB(0.775V) is used to refer a voltage measurement to a reference of 0.775Vrms but unlike dBm the voltage is not necessarily across a 600Ω termination impedance and the suffix 'u' is used to denote 'unterminated' ~ dBu is an absolute measurement of voltage
dBV with a capital 'V' is used to refer a voltage measurement to a reference of 1.0Vrms it is simply a voltage without reference to any termination impedance ~ dBV is an absolute measurement of voltage
Direct Current or voltage ~ Used as a prefix or suffix to indicate that a Voltage or Current measurement is or should be steady with time as in d.c. to daylight ~ Also used for pulsed Voltages such as rectified a.c. where the direction of current does not reverse
Nowadays this could be a Transistor using Diamond as the semiconductor ~ From the 1990s diamonds have been used as photo–diodes for detecting and measuring high power ultraviolet light ~ The term Diamond Transistor as used by Burr Brown etc. refers to Voltage controlled Current sources that operate bi–directionally in all 4 quadrants of a V–I graph
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Noise Factor


The noise factor F of a system of electronic amplifiers and attenuators is defined as the S/N at its input divided by the S/N at its output and as such cannot be better than 1 ~ The radio frequency Engineers definition often states each S/N is derived from power measurments at room temperature but this is not practicle in many cases especially for audio but then neither is a noise factor for an audio amplifer often required ~ For low noise audio amps like pick–up cartridge inputs it is often nice to know how much additional noise is added by the amplifier or how near perfect it is and this is often expressed as a dB worsening of the output S/N which is referred to as a Noise Figure NF
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Gain Margin


Gain margin often abbreviated as Gm not to be confused with gm which is mutual conductance of a thermionic valve ~ There are various ways gain margin is defined and most assume perfectly monotonic open and closed loop gains but for valve power amps this may not be possible so it is best defined as the amount the normal closed loop gain can be reduced by increasing feedback before oscillation occurs ~ The test may give different results at various power levels and frequencies and where output transformers are used should allow for testing with an open circuit i.e. should be at least 7dB or >2x and not just calculated or modelled



Gain Bandwidth Product ~ Is the product of multiplying the gain of a device (which does not have to be an op-amp) by its bandwidth measured at –3dB or 0.707x points and thus the GBWP is a bandwidth ~ As with other similar parameters the device should be monotonic between –3dB points and these 2 points in the open loop response may be set by a 'dominant pole' so that the open loop is better defined before adding negative feedback ~ As the gain is reduced by NFB the bandwidth 'should' increases proportionally
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Intermodulation Distortion ~ Distortion due to signals "mixing" when passed through a non linear transfer device ~ IMD may be non desirable such as in an audio amplifier or intentional such as a diode mixer ~ The simplest form is the production of sum and difference signals of 2 desired signals and this is the basis of measuring IMD ~ In an audio amplifier the distortion will be from many signals over a 10 Octave BW and the IMD products will extend above and below the audio BW
Line Level
In telecommunications or broadcasting may refer to the nominal level of signal at an audio circuit node expressed in one of the dB formats ~ For domestic audio equipment it tends to imply an input or output of an amplifier between 100mV and 1Vrms that has a level or 'flat' frequency response
Long Tail Pair
A term derived from the layout of early valve analogue computers where pairs of valves used as differential 'operational' amplifiers had a common cathode resistor taken to a high voltage negative supply buss running below the platform supporting the valves ~ The cathode resistors were often several resistors in series to get a high value and high voltage rating and these hung below each pair of valves like 'long tails' ~ Beetles finding their way into these computers would often get zapped trying to climb the resistor chains causing errors or 'bugs' in the analogue output ~ Terry Gilliam in his wonderful film 'Brazil' had another take on this story
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Miller Effect
Miller Capacitance
The term Miller effect normally refers to a multiplication of the capacitance that exist between the output and input of an inverting amplifier stage that appears across the input of that amplifier ~ It can also be used for the change in any impedance connected between 2 nodes exhibiting inverting gain in a circuit ~ The effect was recorded by John Milton Miller in a scientific paper in 1920 when it was shown how the input impedance of single triode valve depended on the gain and the impedance at the output ~ Tetrode valves were already developed to 'eliminate' the capacitance multiplication problem in single stages but Miller made use of it with triode valves to create oscillators and stable amplifiers
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Noise Figure ~ Is the noise factor F of an electronic system expressed in dB ~ F is used mainly for radio systems or chains of equipment with common impedances ~ NF is best suited to audio amplifiers although not often quoted by manufacturers because it makes comparison of the best and worst designs obvious ~ The input and out impedances of audio amplifiers are often different and stating the decrease in S/N in dB is simpler because the S/N are often already in dB ~ For low noise amplifiers it is the source impedance that dictates the input S/N so the output S/N will always be worse than the thermal noise of the source resistance divided by the input reference voltage ~ The series input resistance of a standard QUAD 405 is 22kΩ and the input voltage for 1W output is 0.05V so the maximum possible output S/N with 0Ω source resistance will be 85dB at 1W measured in a 19980Hz Bandwidth
Abbreviation for Negative Feed-Back
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Abbreviation often used for an Out-Put Transformer ~ Easy to quote but not so easy to design or build
Order . . .
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Phono Connector
Abbreviation for Phonograph or record player or gramophone ~ Used to indicate inputs on audio equipment that accept signals from a record deck pick–up ~ With the birth of "Hi-Fi" at the time of the Williamson amplifier the Radio Corporation of America RCA introduced the connector now commonly known as the 'Phono' (and incorrectly as the Cinch) to connect the screened lead from a turntable pick–up to the sensitive 'phono' amplifier and was soon adopted world wide for other external screened connections ~ With the 1960s introduction of DIN plugs for audio connections separate 'RCA' inputs were often still used for the Phono inputs which set the term
Phono Stage
A Phono Stage is an amplifier placed somewhere between the output of a record disk pickup cartridge and the 'line level' input of a pre-amp and may be internal or external to the pre-amp ~ As well as amplifying the low level pickup signal ~ often more than 1000x or 60dB ~ the Phono stage provides up to 40db of gain variation across the audio frequency band to correct for the pre–emphasis equalisation used during the record process which has to be corrected during replay even if a non magnetic transducer like a strain gauge is used
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'q' is the symbol used for the charge of an electron which is 1.602176487x10-19 Coulombs ~ it ocurs in equations such as in=2qIdc  A/√Hz which is the rms 'shot noise' current in a conductor
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Root Mean Squared or Quadratic Mean ~ Used as a prefix or suffix to a regularly varying Voltage Vrms or Current Irms value to indicate that it will have the same effect as an equivalent V or I d.c. when producing power ~ RMS values are derived by squaring all values of the measurement waveform as a continuous function then taking the square root of their average or mean thus allowing for negative and positive values of a waveform producing power in a linear load such as a resistor ~ Wrms RMS power does not exist
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SI Units
Système International ~ The International units of measurement that form the 'metric system' which is ideal for people with 10 fingers and the hard of thinking ~ Although truly international the abbreviation SI is derived from French and most of North America ignores it ~ probably because 1.663x10–4ms–1 is more complicated to use than 'a furlong per fortnight' which is a unit of speed that crosses systems when expressed as '1cm per minute' with an error of only 0.2143% in Europe and damn close in the US
Signal to Noise ~ Most often expressed as a ratio SNR in dB ~ SNR=20xlog(Vs/Vn)dB or SNR=20xlog(Is/In)dB or SNR=10xlog(Ps/Pn)dB if measurements are Voltage or Current or Power respectively ~ In all cases the signal and the noise should be measured with the same equipment with the same bandwidth ~ A common mistake measuring S/N with a spectrum analyser is to reference the signal peak to the noise floor which gives much higher ratios and especially false figures for some audio equipment because the noise is not integrated in the 10 octave band 20Hz to 20kHz
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Total Harmonic Distortion ~ The sum of harmonic products produced by passing a sinewave through a non–linear system – Expressed as a percentage or in dB below the level of the fundamental i.e. 1% or –40dB THD ~ The measurement bandwidth or number of harmonics should be specified as should inclusion of any weighting filters but sometimes this is not done ~ Swept filter and FFT spectrum analysers can measure each harmonic individually and then mathematically derive the THD
THD plus Noise ~ Measurement of total harmonic distortion as above but including noise present in the non-linear system and the measuring equipment ~ Some THD meters have a sharp notch filter to remove only the fundamental frequency F0 leaving the harmonic and noise energy either side of F0 to contribute to a THD+N figure ~ This type of meter will measure the system noise when the sine input to the device under test is turned off so an approximation of THD alone can be made
Transient Intermodulation Distortion ~ A form of Intermodulation distortion induced or made worse by the inability of negative feedback amplifiers to correct distortion of transient or asymmetric signals due to time delay in the feedback path ~ TID may also be produced where amplifier stages nested within a feedback loop have a bandwidth much less than preceding stages ~ The output stage of a valve amp my be limited by the OPT at both ends of its frequency response
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A Zobel network is a "filter section" named after Otto Zobel of Bell Labs who developed the principle of "image impedance" for telephone line equalisation ~ The RC network across an audio amplifier output is referred to as a Zobel network but often it is not a calculated image and simply acts to provide a "more resistive" load at high frequencies where it is assumed loudspeakers become inductive

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