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A back-and-forth movement of electric charge. The rate of change of direction is called frequency.

An undesired form of feedback, occurring whenever sound vibrations from the loudspeaker cause a turntable or pickup to vibrate, thus introducing noise into the system.

Frequency within the range of human hearing - approximately 20 to 20,000 cps. Applicable both to sound waves and the electrical signals to which the latter are converted for amplification, recording, broadcasting, etc.

A circuit which corrects for any inaccuracy in FM tuning by 'locking in' the station being tuned. In inexpensive tuners, it is often used to achieve stability. With the temperature compensation and wide-band design incorporated in Fisher tuners, AFC is only used to provide an extra measure of tuning convenience.

Modulation accomplished by varying the instantaneous amplitude (intensity) of the carrier. Since an AM receiver must therefore be able to detect amplitude variations, it responds equally well to naturally produced amplitude peaks: lightning, ignition interference, etc.

Any circuit or instrument which strengthens (or 'amplifies') a signal. Audio amplifiers, RF amplifiers and IF amplifiers are all used in high fidelity equipment. (See preamplifier, power amplifier and control-amplifier. )

Since FM broadcasts consist solely of variations in frequency, the response of FM tuners to changes in amplitude is undesirable. This
figure, expressed in db, indicates how well such unwanted responses are suppressed; the higher the figure, the more effective the suppression.

Used interchangeably with AF. Also, the science of sound recording and reproduction, including acoustics.

The range of frequencies occupied by a signal, or the frequency range which an amplifier can handle. (See power bandwidth and wide-band.)

Circuit device capable of storing electric charge. It also has the property of passing alternating current while blocking direct current and of presenting a greater resistance to the flow of alternating current as the frequency decreases. These properties are all used in electronic circuits.

Ability of a tuner to reject unwanted FM stations and interference on the same frequency as a desired one; measured in db. The lower the figure, the better the tuner's performance.

A steady RF alternating current radiated into space by a transmitter-and-antenna system. This signal, when modulated, is used in the transmission of all types of broadcasts. (See modulation.)

Circuit, designed around two triode tubes, which provides approximately the same amplification as a pentode, but with less noise. This makes it ideal for amplification of weak FM signals.

The flexibility of a speaker cone suspension. High compliance is important in a woofer, where a flexible cone suspension is required for accurate reproduction of low-frequency signals of large amplitude. (Also applied to the flexibility of a pickup stylus at the point of suspension.)

A preamplifier and amplifier combined on the same chassis. This enables both sections to be matched precisely for optimum over-all performance.

The number of back-and-forth vibrations of an alternating current in one second. (bei uns sind das Hertz)

Circuit for dividing the audio spectrum into two or more ranges before feeding the signals to separate 'specialized' speakers: woofer, midrange and tweeter.

Unit of measurement to indicate relative levels of voltage, current, power, or sound.

A movement of electric charge in one direction only.

Monophonic composite signal derived from the sum or difference of the left and right stereo channels, often fed to an extra speaker to fill in an aural 'hole' between the left and right speakers. The signal from a voltage-derived center-channel output must be fed to an external power amplifier before it can drive a speaker. A power-derived center channel can drive a speaker directly.

A tube or semiconductor device which converts AC to DC. (Teil eines Gleichrichters)

Correction for nonuniform recording of low and high frequencies. For valid technical reasons, disc records are cut with low frequencies attenuated and high frequencies boosted. Equalization compensates electrically for this imbalance and produces a uniform response.

Taking a portion of the amplifier output signal and 'feeding' it back to the input. Negative feedback tends to make an amplifier self-compensating; irregularities in the output signal (distortion) which are not present at the input are cancelled. This principle can also be used to reduce hum or noise and to correct a nonuniform frequency response.

A circuit which removes undesirable frequencies from power supplies and amplifiers. In power supplies, it removes virtually all traces of AC (to eliminate hum). In amplifiers, it prevents amplification of objectionable frequencies, such as record scratch or turntable rumble. (See high filter and low filter.)

Modulation of a carrier by changing its instantaneous frequency, rather than its amplitude, in accordance with speech or music signals. By designing the FM receiver to respond only to FM, and to reject AM (caused by lightning or auto ignition pulses), noise-free reception becomes possible. This is one of the advantages of FM which has helped make it popular for high fidelity.

A Fisher concept in loudspeaker design. Combines the advantages of high compliance and long-throw suspension design.

Number of back-and-forth vibrations of a sound wave or alternating current in a second. Expressed in cps, kc and mc.

The section of a tuner or receiver which is used to select the desired station from either the AM or FM band, and to convert the RF signal to IF. To do its job properly, a front end requires a high-gain, low-noise RF stage, a mixer and an oscillator. The degree to which a desired station can be received without interference and without adding noise is expressed by sensitivity, selectivity and signal-to-noise ratio. The Fisher golden synchrode and golden cascode front ends both excel in each of these respects.

Amount of amplification (in amplifiers or amplifying stages).

An exclusive Fisher-engineered FM front end which provides high gain at low noise, combined with superior image and IF rejection. It uses a single high-transconductance frame-grid triode, neutralized for stability and matched for low noise. It is used in conjunction with two Nuvistor triodes.

Undesired harmonics (overtones) which were not present in the original program material. Expressed as a percentage.

A metal structure which conducts heat away from heat-sensitive semiconductor devices, such as transistors and diodes. Heat sinks are therefore especially important for reliable, conservative operation of transistors handling large amounts of power, such as those in the output stages of power amplifiers.

A circuit designed to remove undesired high-frequency noise from the program material. Such noises include record scratch, tape hiss, AM whistles, etc.

An undesirable low-pitched, steady tone produced in an amplifier by the AC power frequency (60 cps) and its harmonics.

Difference frequency produced by mixing an incoming RF signal from the antenna with a signal generated in the set's oscillator. By varying the frequency of the oscillator, it is possible to keep this intermediate frequency constant, permitting its efficient amplification in fixed-tuned IF stages.

Distortion which results from the mixing of two or more pure tones in any nonlinear stage of the amplifier. The distortion elements, which (in contrast to harmonic distortion) are not harmonically related to the input signals, are expressed as a percentage. Because of its nonlinear nature, this type of distortion is particularly unpleasant to the ear, and therefore should be kept as low as possible.

Resistance to the flow of alternating current, expressed in ohms. In most cases, it changes with the frequency of the applied alternating current.

A thousand cps. (Kilohertz)

FM stages that, in addition to amplifying, reject unwanted amplitude variations (from atmospheric noise or ignition pulses) and leave a pure FM signal of constant amplitude. The FM signal fed to such stages must have a certain minimum strength for limiting to occur. As with IF stages, the more stages the better, other factors remaining equal. In order to maintain optimum limiting over a wide range of input signal strengths, several limiters with overlapping action are required.

A method of speaker design where the woofer moves freely through long excursions, providing excellent low-frequency response with low distortion.

Compensation for the ear's reduced sensitivity to low and high frequencies at low volume levels. It is achieved by boosting extreme lows and highs progressively as the volume level is lowered.

A circuit designed to remove low-frequency noises from the program material. Such noises include turntable 'rumble,' tone arm resonances, etc.

A million cps. (Megahertz)

Process of superimposing voice, music or other intelligence on a carrier wave. (See AM, FM, carrier.)

Pertaining to single-channel reproduction of sound. (See stereophonic.)

Transmission of two or more channels on a single carrier so that they can be recovered independently at the receiver; in FM stereo, transmission of left-plus-right (sum) signal and left-minus-right (difference) signal on main carrier and subcarrier, respectively. The multiplex decoder in the receiver recovers independent left and right stereo channels from the multiplexed signal.

The short-term power available from an amplifier for the reproduction of program material. The music power output exceeds the RMS power rating to a greater or lesser extent. Its measurement is standardized by the Institute of High Fidelity (IHF) and represents a practical means of stating an amplifier's actual capabilities for the reproduction of program material.

Unwanted random sound created in small amounts by electronic equipment, often heard as hiss. Good design reduces it to negligible levels.

A ruggedly built tube of unusually small size, originally developed for military communications in ground-to-ground and satellite systems. Because of its rigid internal structure, compact construction, good shielding properties and excellent heat dissipation, it is ideal for use as a high-stability oscillator and low-noise mixer in front-end circuits.

Electronic generator of alternating current. Produces the signal used to mix with incoming signals in a tuner. (See IF.)

Maximum instantaneous voltage or power. Also, a sudden, momentary burst of sound.

This figure is a theoretical one, used to express an amplifier's maximum short-term capabilities by taking twice the RMS power. It is not representative of the actual capabilities of an amplifier and has been superseded by the IHF music power rating.

The 'lagging' of certain frequencies behind others as they pass through an amplifier, due to delay characteristics which depend upon frequency. In an IF amplifier, high phase shift results in high distortion, especially in multiplex reception. In an audio amplifier, high phase shift tends to produce instability, which results in audible distortion, especially at very high and low audio frequencies.

A circuit configuration which produces an audio output large enough to drive a speaker. It may be built as a separate component, such as the Fisher SA-1000, or as part of a receiver, such as the Fisher 500-C.

A term which states the frequency range throughout which half the rated power of an amplifier is available at rated distortion. It is determined by using a measurement procedure standardized by the Institute of High Fidelity (IHF). This specification indicates how much power is available at the critical high and low frequencies. The wider the power bandwidth, the better the amplifier.

A device which takes a small signal, e.g., from a tuner or record player, and amplifies it to a magnitude where it can drive a power amplifier. Most preamplifiers incorporate controls, like the Fisher 400-CX. It may be built as a separate component, or as part of a control-amplifier or of a receiver.

The maximum power a given amplifier can produce without exceeding its specified distortion rating.

A circuit in an FM tuner which converts frequency variations to amplitude variations, i.e., inaudible IF to audible AF. It is superior to the 'discriminator' circuit (which serves - the same purpose) because it provides AM suppression and is more linear over a greater bandwidth.

A tuner, preamplifier and amplifier built on one chassis. This design approach permits precise matching of all sections for optimum over-all performance.

A device which changes AC to DC. (See diode.)

Circuit device that offers resistance to the flow of alternating or direct current. When current flows through a resistor, a voltage proportional both to the current and to the resistance exists across it. This property and the fact that a resistor absorbs electric power, dissipating it as heat, are used in electronics. Resistors are made of wire, metallic film, carbon, and other materials.

The range of frequencies to which a tuner, amplifier, speaker, etc., will respond, and the relative amplitude with which these frequencies are reproduced.

Repetitive reflection of sound (from walls, etc.). Also, the spatial effect created thereby, which adds brilliance and warmth to sound, and helps to convey the size of the studio or hall. It can also be created artificially.

Alternating current of higher frequency than 15 or 20 kc. Specifically, alternating currents transmitted and received for communications or entertainment.

A power measurement which provides an indication of an amplifier's sustained power capabilities, at a specified distortion level.

Low-frequency noise resulting from turntable vibrations and reproduced by the amplifying system.

The ability of a tuner or receiver to reject stations on channels other than the one being received. The higher the figure (expressed in db), the better the selectivity.

An electronic device (e.g., transistor, diode, etc.) which uses a solid material such as germanium or silicon (instead of a vacuum), as a medium to conduct electric charge. Unlike tubes, semiconductor devices need no filament to 'boil off' charges into a vacuum, and are therefore more efficient and generate less heat.

The ability of a tuner or receiver to provide usable reception of weak signals. For FM tuners, this is measured in microvolts (millionths of a volt) required for a given number of db quieting (noise suppression). The lower the number in microvolts, the more sensitive the tuner.

The degree to which two stereo signals are kept apart. Stereo effect depends upon preventing 'leakage' of program material from one channel into the other.

Figure in db, expressing the ratio of desired signal voltage to random noise voltage. Look for a high db figure; the better the signal-to-noise ratio, the less background noise there will be in the reproduced program material.

Pertaining to circuits and components using semiconductors.

Two or more speakers and a crossover network in one enclosure. This approach permits the designer to match speakers, crossover and enclosure for optimum performance.

Pertaining to sound reproduction by means of two (or more) channels. This technique recreates the spatial effects of the original performance.

A circuit which permits the checking of recordings by taking the signal directly from the tape, a moment after the recording is made. This is only possible on three-head tape recorders.

Controls that affect the overall tonal balance of the music, by varying the proportion of bass and treble frequencies. Their primary use is to correct for defects in the program material and to adjust the sound characteristics to the acoustic environment of the listening room.

Electrical device which steps up or steps down the voltage. A power transformer is used to 'transform' 117-volt AC power ('house current') into various voltages needed to operate a tuner or amplifier. An output transformer is used to match the high impedance of amplifier output tubes to the low impedance of speakers.

Ability of an amplifier, loudspeaker or pickup to follow accurately abrupt changes in volume, such as the sudden burst of sound when a drum or cymbal is struck, or a string is plucked. Good transient response is vital to 'clean' and 'crisp' over-all sound.

A solid-state device which can perform most of the functions of vacuum tubes, such as amplification, oscillation, etc. It offers certain advantages in performance. (See semiconductor.)

A component which receives radio broadcasts and converts them into audible signals (audio). It may be built on a separate chasis, or as part of a receiver.

A speaker designed to reproduce the treble (high) frequencies, such as the higher overtones of the violin and the tones of the piccolo.

Capable of passing a broad range of frequencies (said of a tuner or amplifier). This is especially vital to good multiplex reception, and for faithful audio reproduction.

A speaker designed to reproduce the bass (low) frequencies, such as those of a bass viol or tuba.

A wavering of pitch which is due to minute variations in turntable or tape recorder speed.

Es gab gerade die ersten vernünftigen Transistorgeräte und keiner dachte an Quadro oder gar Digitalgeräte.
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