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SIGMASTEREO CASSETTE PLAYER TRAINER       MODEL - STRDM100       Mfd.by: -                   SIGMA TRAINERS               ...
INTRODUCTION        This trainer has been designed with a view to provide practical and experimental knowledge of a ge ner...
PRACTICAL – 1                               BLOCK DIAGRAM AND WORKING PRINCIPLE      Tape Recorder circuit consists of two...
(E)   POWER SUPPLY: -      The stereo cassette player can be operated on mains or car battery. The connections are made in...
Figure-1 Block Diagram of Tape Recorder Trainer                       5
PRACTICAL – 2TERMS, DEFINITION AND NOMENCLATURE USED4.1 PART           B      Battery           C      Capacitor          ...
4.2 SIGNALS/SECTIONS/STAGES: -           AF          Audio Frequency           ALC         Automatic level Control        ...
PRACTICAL – 3                     PARTS LIST WITH CODING INFORMATION   (1) IC/Q/D: -   1.    IC TBA810   2    IC1, IC2   2...
(4) DISK CAPACITORS: -1.   220pf           2    C8, C272.   470pf           2    C24 C53.   1n              4    C15, C7, ...
PRACTICAL - 4                                 TECHNICAL DESCRIPTION OF CIRCUIT       The Stereo Cassette Player Circuit ut...
frequencies beyond 15KHz (roll -off) 14 V DC supply is given at pin 1 of the IC. The pin 7 is ground throughC13, which dec...
PRACTICAL - 5                                   TEST POINT VOLTAGESAll voltages measured actually are sho wn below: -Volta...
PRACTICAL – 6TEST POINT WAVEFORMS1. INPUT SIGNAL AT TEST POINT I: -2. AMPLIFIED SIGNAL AT COLLECTOR OF Q1: -3. INPUT SIGNA...
PRACTICAL - 7TESTING METHOD1.     SHORT CIRCUIT TEST: -       Measure the resistance between +12v supply line and ground. ...
PRACTICAL - 8ALIGNMENT METHOD       R/P HEAD ALIGNMENT: -       The head can be aligned with a special cassette tes t type...
PRACTICAL - 9                                 FAULTFINDING PROCEDURE.(1) No sound on play back            (1)   Defective ...
(B) TAPE DECK MECHANISM FAULTS(9)   Tape does not move in the        (1)   Belt loose, broken or has come off      Playbac...
PRACTICAL - 10                                    GLOSSARY OF TECHNICAL WORDSAim: -          To study the Glossary of the ...
Binaural          Heard with two ears, also applied to double mono headphone listening to distinguish from headphonestereo...
Control Unit        Preamplifier part of the audio system designed to operate separate from power amplifier. It acceptssig...
Dual Cone       Loudspeaker drive unit with two cones driven from one moving coil, inner cone of smaller diameterextends t...
Flutter        Very short rapid variations in tape speed causing similar variations in sound v olume and pitch not present...
Horn        Acoustic device with expanding cross -sectional area horm loading provides the best matching from theloudspeak...
Linear        When applied to transfer characteristic of amplifier or transducer, it indicated direct correspondencebetwee...
Mechanical Impedance        Opposition to change o f position or velocity due to inertia (effective mass), stiffness, and ...
Patch cord      A short cord, or cable, with a plug at either end used to interconnect equipment, such as tape record ersa...
Rarefy      To make less dense as opposed to compress, part of sound wave where pressure is below that ofatmosphere.Record...
Wave for m         The shape of a wave obtained by plotting some characteristic against tone.Wow        Slow variations in...
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Consumer electronics lab manual

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Consumer electronics lab manual
8th sem ECE

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Consumer electronics lab manual

  1. 1. SIGMASTEREO CASSETTE PLAYER TRAINER MODEL - STRDM100 Mfd.by: - SIGMA TRAINERS E-103, Jai Ambe Nagar, Near Udgam School, Thaltej, AHMEDABAD - 380054. Phone : +91-79-26852427 /26850829 Fax : +91-79-26840290 Email : sales@sigmatrainers.com : sig matrainers@sify.co m Web : www.sigmatrainers.com
  2. 2. INTRODUCTION This trainer has been designed with a view to provide practical and experimental knowledge of a ge neralcircuit of Stereo cassette player on SINGLE P.C.B. SPECIFICATIONS1. Power supply : 230V Ac, 50Hz.2. Audio power output : 120 watts maximum.3. Frequency response : 100 to 8000Hz.4. Tape speed : 4.75cms/sec.5. Speaker size : 4"/8 ohm.6. Erase system : DC erase.7. Recording bias : AC Bias.8. Distortion : 5 to 10%9. Automatic level control10. Volume and Tone control.11. Speech/Music and Monitor switches.12. Built in condenser mike.13. LEDs for recording, po wer and output indication,14. Auto stop.15. Sockets : (a) Auxiliary input for tape to tape recording (b) External mike socket for connection of dynamic mike. (c) Extra speaker connection socket. (d) Remote control socket for Motor stopping for recording with mike.16. The parts soldered on the front side of SINGLE PCB with complete circuit diagram screen -printed in multicolor on front side with parts at the same place.17. The acrylic cover fitted on PCB to safeguard parts on front side in elegant wooden box having lock and key. The testing points must be provided with 1.25" tags to connect CRO probe.18. Standard Accessories : 1. A manual having practicals 2
  3. 3. PRACTICAL – 1 BLOCK DIAGRAM AND WORKING PRINCIPLE Tape Recorder circuit consists of two identical sections and power supply section. These two identicalsections are known as left channel and right channel. Each channel consists of following sections: - (A) Preamplifier (B) Equalizer (C) Driver (D) Output. (E) Power Supply (F) Motor Circuit (G) Stereo Play Head (H) Power Indicator (I) Output Level Indicator (J) Bass/Treble Controls (K) Tape/Deck Mechanism The functions of above stages are similar in both the channels and are explained as under: -(A) PREAMPLIFIER: - The preamplifier amplifies the signals obtained from the stereo play head during playback. The level ofthese signals is very low . The preamplifier is, therefore, designed to introduce minimum of noise. A lo w noisetransistor is generally used in this stage in R -C coupled or directly coupled circuit.(B) EQUALIZER: - The frequency response of the stereo play head is limited at th e lo wer frequency and by the inductance ofthe head and at the higher frequency and by the gap width of the head. The magnetic tape generates highfrequency noise. To maintain a good signal -to-noise ratio at the high frequency end, the high frequency signa l isboosted while recording and is attenuated during play. The main function of the equalizer is provided the boost at lo w and high frequencies required duringplayback Negative feedback is used for equalization.(C) DRIVER: - The driver stage further amplifies the signals obtained from the equalizer and gives these to the outputstage through volume control.(D) OUTPUT AMPLIFIER - This stage amplifies the signals available from drive to drive the loudspeaker. It also incorporates bass andtreble controls. 3
  4. 4. (E) POWER SUPPLY: - The stereo cassette player can be operated on mains or car battery. The connections are made in such amanner that the mains get disconnected whenever the battery is connected through dc input socket.(F) MOTOR CIRCUIT: - The power supply is also given to tape mechanism. As the motor is major source of noise, elaborate filtercircuits are employed to keep the noise level to the minimum possible.(G) STEREO PLAY HEAD: - It consists of two heads -left channel head and right channel head. During playback the signals recorded onthe tape from left side, is picked up by left channel head and is given to left channel preamplifier Similarly thesignals recorded on the tape from right side, is picked up by right channel head and is given to right channelpreamplifier.(H) POWER INDICATOR: - LEDS or Neon lamp is used to indicate mains power ON.(I) OUTPUT LEVEL INDICATOR: - LEDS or a small current Meter is used to indicate output level.(J) BASS/TREBLE CONTROLS: - The bass control boost the bass frequency in the signal and the treble control boost the treble frequency inthe signal.(K) TAPE/DECK MECHANISM: - Tape Deck/Mechanism is a main part of the stereo Cassette player. It is used for (I) Playback (II) Windingthe tape forward quickly. (III) Rewinding quickly (IV) Stop (V) Eject the tape out. It is a Mechanical readymade item available from the manufacturers. It consists of belts, idle wheels,intermediate wheels, cams etc. 4
  5. 5. Figure-1 Block Diagram of Tape Recorder Trainer 5
  6. 6. PRACTICAL – 2TERMS, DEFINITION AND NOMENCLATURE USED4.1 PART B Battery C Capacitor CB Cabinet CN Connector CONS Consumables CP Control panel CR25 1/4 watt Carbon Resistors CR37 1/2 watt Carbon Resistors D Diode DC Ceramic Disk Capacitor EC Electrolytic Capacitor (Aluminum) F Fuse FH Fuse Holder H Head HS Heat sink HW Hardware IC Integrated Circuit J Jumper K Knob L Coil LED Light Emittimg Diode. LS Loudspeaker M Motor MIC Microphone NP Name Plate P Potentio Meter PCB Printed Circuit Board POT Potentio Meter PP Pot panel Pr Preset Q Transistor R Resistor SKT Socket Styr Styroflex Capacitor SW Switch TDK Tape Deck/Mechanism. W Wire X Transformer Xmer Transformer 6
  7. 7. 4.2 SIGNALS/SECTIONS/STAGES: - AF Audio Frequency ALC Automatic level Control +B +6V DC Voltage supply to the circuit. B/C Bass Control BI Battery Indicator dB Decibel. EH Erase Head EZ Equalizer EZA Equalizer amplifier GND Ground Hz Hertz IP Input IPS Inch per second. O/P Output PS Power supply PA Pre Amplifier RF Radio Frequency R/P Record/Play RLI Recording Level Indicator R/PH Record/Play Head T.C. Tone Control. T.B/C Treble Control V/C Volume Control 7
  8. 8. PRACTICAL – 3 PARTS LIST WITH CODING INFORMATION (1) IC/Q/D: - 1. IC TBA810 2 IC1, IC2 2. BC 148B 4 Q2, Q3, Q5, Q6 3. BC 149C 2 Q1, Q4 4. 1N 4002 4 D1, D2, D3, D4 5. LED Red 10 D5 to D14. 6. LED Green 1 D15 23 (2) CARBON FILM RESISTOR (1/4 WATT): - 1. 10E 1/2w 4 R17, R18, R36, R37 2. 33E 2 R16, R35 3. 100E 2 R15, R34 4. 150E 2 R2, R21 5. 330E 2 R11, R30 6. 1K 3 R19, R40, R38 7. 1K5 4 R5, R24, R39, R41 8. 2K2 2 R4, R23 9. 3K3 3 R7, R26, R28 10. 5K6 2 R13, R32 11. 10K 2 R8, R27 12. 22K 2 R1, R20 13. 68K 2 R3, R22 14. 82K 2 R10, R29 15. 220K 4 R14, R25, R33, R6 16. 1M 2 R12, R31. (3) ELECTROLYTIC CAPACITORS: - 1. 2.2/10 2 C6, C25 2. 4.7/10 4 C1, C20, C9, C28 3. 47/16 2 C4, C23 4. 100/10 2 C52, C47 5. 220/10 4 C12, C14, C31, C33 6. 330/10 2 C32, C13 7. 1000/10 3 C37, C18, C46 8. 1000/16 3 C44, C19, C38 9. 2200/16 1 C4323 8
  9. 9. (4) DISK CAPACITORS: -1. 220pf 2 C8, C272. 470pf 2 C24 C53. 1n 4 C15, C7, C26, C344. 4n7 2 C35, C165. 22n 2 C3, C226. 47n 2 C49, C507. 0.1 16 C10, C11, C17, C2, C21, C29, C30, C36, C39, C40, C41, C42, C51, C48, C45, C47(5) POT AND SWITCH: -1. 100 log 16mm 2 P1, P42. 100K Lin 16mm 2 P3, P63. 1M Lin 16mm 2 P2, P54. 2P2W SW 1 S15. Toggle 1 S2 8(6) COILS (L): -1. Choke coil 1 L1 1 9
  10. 10. PRACTICAL - 4 TECHNICAL DESCRIPTION OF CIRCUIT The Stereo Cassette Player Circuit utilizes six transistors, 2 ICs and 15 Diodes.(1) PREAMPLIFIER & EQULIZER: - Two of the transistors Q1 and Q2 h ave been used in the preamplifier and the equalizer stages in the leftchannel Circuit. (Q4 and Q5 for the right channel Circuit). The first transistor Q1 (BC 149C) is the preamplifier.The equalization required during playback is applied from the collecto r of the transistor Q2 to the emitter of Q1through R7, R8, and C3 r6. The reactance of C3 increases at lo w frequencies reducing the feedbackprogressively. Thus the gain at low frequencies increases providing the necessary boost. The feedback at highfrequencies is decided by R8 (10K). DC voltage is applied to the base of transistor Q1 from the emitter of Q2 through a resistor R3 (68K). Thisalso provides D.C. Negative feedback over the two stages and stabilizes the operating point of both thetransistors. The amplified audio signals obtained at the collector of Q2 are given to the driver amplifier transistorQ3.R4 is the load resistor of Q2.R1 is the load resistor of Q1.C5 470pf) is used for high frequency compensation.C1 is input coupling capacitor. C22 and R5 are emitter resistors for Q1 and Q2 respectively. C2 and C4 are acbypass capacitor for R22 and R5 respectively.(2) DRIVERS: - The driver stage consists of transistor Q3 (BC 148B). It is a single stage amplifier working in unbiasedemitter configuration. R12 is base bias resistor. R10 is input base current limiting resistor. R11 is emitter resistor. C8 is used forhigh frequency roll off. R13 is load resistor for Q3. C9 is output coupling capacitor. The amplified audio signalsfrom the driver are given to the main amplifier using IC810 through volume control pot p1 and C11. C48 (0.1u)parallel to the output of volume control is used as ‘Hi Filter’ i.e. it shunts the high frequency noise signals to theground when ‘Hi Filter’ switch is ON.(3) MAIN OUTPUT AMPLIFIER: - The IC 810 performs the functions of the audio amplifier, driver and the output stage. The amplified signalsobtained from the transistor Q3 are given at the audio input (Pin 8) of the IC. The IC amplifies these and theoutput is available at the Pin 12 of the IC. The feedback is given from the output to the emitter of preamplifiertransistor in the IC (through a resistor 4K provided internally) and also through R41 (1K8), P3, C10 and C47.Thefeedback voltages develops over R6 (33E ), C12 being used for d.c.blocking. The gain of amplifier depends onthis feedback. The bass frequencies can be amplified by varying P3 as it provides negative feedback in such amanner to increase to bass response. C47 is used for dc blocking. R41 is the minimum resistor in case of Zerovalue of P3.R17 (10E - 1/2 w) and C17 (0.1u) provides negative feedback and reduces the gain of the amplifier at 10
  11. 11. frequencies beyond 15KHz (roll -off) 14 V DC supply is given at pin 1 of the IC. The pin 7 is ground throughC13, which decouples the power supply to the preamplifier stage in the IC. Pin 5 is used for frequencycompensation. This is connected through C15 (1n) and is connected to ground through C16 (4n7). The outputsignal available from the IC is given to the lef t channel LS through the coupling capacitor C18 (1000/10). Thepin 4 (brought out as bootstrap terminal) is connected to output Pin through C33 (220/10). This provides negativefeedback from the output terminal to the bootstrap terminal and increases the i nput impendence of the outputstage. LED D5 to D9 is used to indicate the output level. R18 (10E, 1/2w) is the biasing resistor for LEDs. Theprovision is also made to connect external speaker through EP2 socket. R14 (220K) decides input impedance ofthe IC. R40, C49 and Pot P2 decide the gain of high frequencies in the signal. P2 works as treble a control. R28 (3K3) and C46 (1000/10) provides decoupling to the +B supply given to the preamplifier, equalizer anddriver circuit. C47 (0.1u) is used to avo id sudden instability (oscillations).(4) POWER SUPPLY: - +14V supply is given to the Stereo Player Circuit to obtain 6W out - put in the loudspeaker of 4Eimpedance. This is obtained from rectifying mains or form external Car Battery. The mains operation circuit consists of step down transformer, bridge rectifier diodes D1, D2, D3, D4 and acapacitor C43. Diodes - D1 to D4 rectifies A.C. voltages and the obtained pulsating D.C. voltage is smoothed byC43. LED (D15) is used to indicate the presence of +B (+14V) supply. R19 is current limiting resistor for D15.This +B (+14V) supply is given to the player circuit through LC filter consisting of choke filter coil L1 and C19and C38 through leaf switch in the tape deck/mechanism. This filter removes 100 KHz ripple from the +14Vsupply is also given to the motor. C44 (1000/16) across the motor is the ripple filter capacitor. 11
  12. 12. PRACTICAL - 5 TEST POINT VOLTAGESAll voltages measured actually are sho wn below: -Voltage Point- Voltage at Voltage at Zero Volume. Full Volume.1. Xmer Secondary 12.0vAC 12.0vAc2. C43 +Ve lead 15.0vdc 13.0Vdc3. C46 +Ve lead 7.1vdc 6.0vdc4. IC1 810 –Pin 1 15.0vdc 13.0vdc & 2 X X IC2 810 3 X X 4 15.0vdc 15.0vdc 5 0.8vdc 0.8vdc 6 1.5vdc 1.3vdc 7 7.3vdc 6.0vdc 8 - - 9 0.0vdc 0.0vdc 10 0.0vdc 0.0vdc 11 X X 12. 5.3vdc 4.4vdc 5. Q1 - Emitter 0.0vdc 0.0vdc & Base 0.6vdc 0.6vdc Q4 Collector 1.3vdc 1.3vdc 6. Q2 Emitter 0.0vdc 0.0vdc & Base 0.4vdc 0.4vdc Q5 Collector 4.7vdc 4.2vdc 7. Q3 Emitter 0.8vdc 0.8vdc & Base 1.3vdc 1.3vdc Q6 Collector 5.9vdc 5.8vdc 8. +B Current 135mA dc 1.0A dc 12
  13. 13. PRACTICAL – 6TEST POINT WAVEFORMS1. INPUT SIGNAL AT TEST POINT I: -2. AMPLIFIED SIGNAL AT COLLECTOR OF Q1: -3. INPUT SIGNAL AT PIN 8 OF IC14. OUTPUT SIGNAL AT PIN 12 OF IC1: - 13
  14. 14. PRACTICAL - 7TESTING METHOD1. SHORT CIRCUIT TEST: - Measure the resistance between +12v supply line and ground. If it is not equal to 0 then go ahead;other wise check for short circuit of all p arts connecting +12V supply line.2. POWER SUPPLY TESTING: - Connect AC or DC supply. Power LED must glow. Measure voltage at C5 (2000/16) +ve END. it shouldbe 18V without load and approximately 13V at full load (2A).3. OUTPUT AMPLIFIER TESTING : - Feed approximately 30mV, 1KHz signal at the input of IC 4440 i.e. at pin No.6. The output acrossloudspeaker should be approximately 12V at full load4. PLAYBACK TESTING: - Feed 200uV, 1 KHz signal at the input of preamplifier i.e. at the negat ive end of C304. Keep volumecontrol in the maximum position and treble and Bass controls in middle position. The full output at loudspeakershould be 16 to 18 Watts R.M.S. Reduce the input so that the output is 45 to 50 mw. Check the output at 100 Hz. It should be 12 to 13 dBhigher than the output at 1 KHz. Also check the output a 10 KHz. It should be 3 to 4 db less with respect to 1KHz. 14
  15. 15. PRACTICAL - 8ALIGNMENT METHOD R/P HEAD ALIGNMENT: - The head can be aligned with a special cassette tes t type. These test -tapes are precision recorded oncassette tape -recorder. Align the R/P Head as follow with the Help of test cassette tape. 1. Place the test cassette tape on the recorder. 2. Connect an output meter across loudspeaker terminal. 3. Set V/C to mid way. 4. Adjust the head azimuth alignment screw for maximum reading on the meter. Tuning the screw slo wly on one side and then to the other side till the maximum output is obtained should do this. 15
  16. 16. PRACTICAL - 9 FAULTFINDING PROCEDURE.(1) No sound on play back (1) Defective power supply section (2) Broken battery leads. (3) Defective leaf switch. (4) Defective contacts in the remote control jack. (5) Fault in power supply section.(2) No sound on play back 1. Defective amplifier section. 2. Open Head. 3. Defective Head.(3) Weak Sound during playback (1) Dirty Head. (2) Defective amplifier section.(4) Poor high frequency (1) Dirty head response on playback (2) Worn out head. i.e. Muffled sound. (3) Defective amplifier equalizer circuit.(5) Poor high frequency response (1) Tilted Head. when pre-recorded tapes or tapes recorded on other records are played back.(6) Excessive noise on playback (1) Noisy preamplifier Ic. (2) Recording done at a very low level(7) Does not operate on mains (1) Defective mains input cord, operation normal on battery plug or socket. (2) Defective mains input socket. (3) Defective power supply.(8) Excessive current drain from (1) I.C. Short. From the battery with or (2) Decoupling capacitor across Battery short. (3) Excessive current drawn by the motor. 16
  17. 17. (B) TAPE DECK MECHANISM FAULTS(9) Tape does not move in the (1) Belt loose, broken or has come off Playback position (2) Defective motor (3) Supply not reaching the motor (4) Pinch-roller is not pressing the capstan. (5) Insufficient pressure of the Pinch -roller.(10) Tape motion is irregular (1) Layer of dirt or tape Resulting in wow or flutter material deposited on capstan (2) Worn hardened or dented pinch roller. (3) Insufficient pressure capstan. (4) Worn,dented or bent castan. (5) Defective motor. (6) Worn or loose belt. (7) Weak batteries.(11) Unnatural sound High pitched Tape moving at different tape at which it was recorder Sound, or low pitched sound (1) Pinch-roller not pressing the Plastic side is contacting the Head.(12) Unnatural sound is muffled Tape has got twisted and the Plastic side is connecting And is not at all intelligible. Plastic side is connecting the Head.(13) Some whistling sound is Heard (1) Due to CKt.defect Playback. (2) Due to sticking of tape on the supply spol, tape guides or heads. (3) Excessive pressure of the spring on the Head.(14) Tape is not wound on the take up (1) Take up shaft not pressing reel while recording or p laying (2) Oily or greasy take -up back. reel base. (3) If a separate belt has been used for take -up the same may be loose or broken. (4) Insufficient pressure of the clutch. (5) Defence Cassette tape.(15) No rewinding (1) The rewinding idler is not pressing properly on the idler and base of take -up reel. (2) The driven wheel not pressing properly on the the fly wheel. (3) Oily or greasy idler wheel or suppl y reel base. (4) If a separate belt has been used for rewinding it may be loose or broken.(16) No fast forward winding (1) The driven wheels not pressing the take -up reel base. (2) Oily or greasy idler wh eel or take-up reel. (3) If a separate belt has been used for fast forward winding (and rewinding ) it may have becomes loose or broken.(17) The tape moves up or down on (1) Pinch-roller arm is bent. the capstan and the edges are (2) The pressure-pad used for pressing the recording head missing wrapped. the spring is loose. 17
  18. 18. PRACTICAL - 10 GLOSSARY OF TECHNICAL WORDSAim: - To study the Glossary of the technical words of Radio, Tape, an d Two - in - one technologyAerial Part of an antenna.A.F. Audio Frequency is 20Hz to 20000 Hz.All Wave Receiver A receiver designed to receive stations on MW as well as SW bands.Amplitude Modulation (AM) The modulation of a sine wave c arrier by a fluctuating signal so that its amplitude varies according to thesignal.Antenna Arrangement of conducting wires or rods used for picking up radiating radio waves.A.V.C. Automatic Volume Control. A radio circuit which automatically maintains the output value of a radioreceiver constant within limits while the carrier signal picked up by the antenna is varying in amplitude over awide range.Automatic level control (ALC) A ci rcuit arrangement, to reduce the gain of the amplifie r in tape recorder, when recording level exceeds acertain limit. This avoids overloading and distortion.Band In radio frequencies, which are within two definite limits and are used for a definite purpose.Band Sw itch A switch, which simultaneou sly changes the tuning circuits of receiver for a desired band of frequencies.Bias The fixed voltage applied between the base and emitter of a transistor.Bypass condenser A condenser used to provide low impedance path of radio or audio signal a round a resistor or between acircuit terminal and ground.Balance control Control used to adjust the gain of the stereo channel differentially so as to get balanced output from theamplifier.Bass Lo wer frequency end of audio spectrum normally bel ow 150 Hz.Baxandall Inventor of notoriously simple tone controls using negative feedback commonly known as Baxandall tonecontrols as against tone controls using passive circuitry.Beat Audible fluctuation of amplitude when two audio signals are very close together in frequency. 18
  19. 19. Binaural Heard with two ears, also applied to double mono headphone listening to distinguish from headphonestereo.Carrier (a) The R.F. component of a transmitted wave upon which an audio signal or other form of intelligencecan be imposed. (b) Radio Wave having the assigned frequency of a Radio Station.Converter A transistor used both as a mixer and an oscillator in a super heterodyne receiver. It generates localfrequency and combines it with an incomi ng signal to produce an intermediate frequency (IF).Cross Modulation In a receiver Cross Modulation may take place if a strong unwanted signal overloads the receiver inputcircuits. The unwanted station will then be heard in the background of t he wanted signal.Cassette A compact plastic packet is containing cassette tape. These are available in four sizes C30, C60, C90 andC120.Cycles per second The unit, for measuring the frequency or pitch of sound. This has been replaced by Hert z (abbreviatedHz)Condenser microphone A microphone in which the operation depends on the changes in capacity between a fixed plate and adiaphragm. These require polarizing voltage for operation.Ceramic Manmade piezoelectric or permanent magnetic material used in some pickups and loudspeakersrespectively. Ceramic pickups have better performance and life characteristics compared to crystal pickupsavailable earlier, which made use of natural piezoelectric material.Channel Separation Isolation of the two stereo channels from each other in the pickup of the amplifier.Clipping When the electronic circuitry is overloaded, the output is clipped as the output no longer follows theinput signal.Coloration Change in sound quality according to peculiarities of the audio system, a character imparted toreproduced sound, often and mainly by loudspeakers. No two speaker enclosures sound the same theloudspeakers are therefore considered as the weakest link in the audio chain.Compliance Yielding quality due to springiness or elasticity.Compression Reduction in the dynamic range of a signal by raising the level of quiet passages and/or lowering thelevel of loud passages. The level of the quiet passages is normally raise d to obtain a better signal to noise ratiofor the system. Lo wering of the level of loud passages becomes necessary when the recording system can notaccommodate the dynamic range of the input signal.Cone Diaphragm of moving coil speaker.Cone surr ound Strip or roll of compliant material fitted to the periphery of the loudspeaker cone. 19
  20. 20. Control Unit Preamplifier part of the audio system designed to operate separate from power amplifier. It acceptssignals from sources such as pickup, Micr ophone, tuner, tape etc; applies equalisation as required and itincorporates volume and tone controls.Crossover Frequency Frequency at which a loudspeaker CROSSOVER NETWORK divides the signal of crosses over from onesection to another.Cross talk Breakthrough of signal between two stereo channels also see CHANNEL SEPARATION.De modulation The process of separating the original information from a Modulated Signal.Detector The stage in a receiver when the modulation or the desired si gnal is separated out from the RF signal.Distortion Unfaithful reproduction of sound.Decibel Abbreviated dB, it is relative measure of sound intensity or volume. It expresses the ratio of one soundintensity to another. One dB is the smallest change in sound that human ear can detect. This is a logarithmicmeasure. The ratio between two sound powers P1 and P2 can be expressed as 10 log10 P1/P2 db.Dual track recording Many tape recorders and practically all cassette tape recorders utiliz e a recording head that covers half ofthe type width, making it possible to record two tracks on tape. One of these tracks is recorded in one directionand the other in the opposite direction.Dubbing Making a copy of a tape recording by playing it back on one machine and recording it on another. Taperecordings are easy to duplicate by rerecording with minimum loss in quality.Dynamic microphone An electromagnetic type of microphone, which employs a moving coil in a magnetic field.Dynamic range The ratio between the softest and loudest sounds a tape recorder or other device can reproduce withoutundue distortion. This is usually measured in db.Damping Process of reducing resonant effects by use of resistance or mechanical or acous tic equivalents ofresistance.Damping Factor Ratio of loudspeaker impedance to amplifier source impedance.Diaphrag m Sound generating element in a loudspeaker.DIN Deutscher Industries Norman, German industrial Standards, now coming into common use for audioequipment.Dolby syste m Noise reduction system, it compresses a signal before recording on to tape and expands it again on replay.Drive Unit Loudspeaker unit as distinct from the enclosure or the cabinet. 20
  21. 21. Dual Cone Loudspeaker drive unit with two cones driven from one moving coil, inner cone of smaller diameterextends the high frequency response.Erasing Neutralizing the magnetic pattern on tape by placing it in a strong magnetic field, thereby removing therecorded sound from tape.Erase Head The erase head automatically removes the recorded sound from tape. It may be given d.c. or more usuallyhigh frequency A.C. from the bias oscillator. The erase head is placed before the recording head and whilerecording the perused tape reaches the recording head.Equalization The manipulation of frequencies that is required to meet the recognized standards of recording andreproducing techniques. This usually requires boosting of lo w as well as high frequenci es while playing back andboosting of high frequencies while recording.Electronic Involving use of active components like valves, transistors and diodes & ICs.Electrostatic Concerned with forces and fields associated with electric charges; lo udspeaker amplifying electrostaticforces to actuate radiating diaphragms.Elliptical Stylus Designed to minimize tracing distortion by placing a small radius in contact with the groove walls asviewed from above and a larger radius across the groove as viewed from front or the rear.Enclosure Cabinet or other structure containing an enclosed or partly enclosed volume of air and used for mountingand loading loudspeakers drive unit.Fading Rise and fall in radio signals due to variations i n transmission conditions in space.Fidelity The faithfulness with which signal is reproduced in a receiver. High fidelity is synonymous with lowdistortion.Filter Combination of Coil, Capacitor and resistor which is used to block or alternate alternating currents atcertain frequencies while allo wing essentially unimpeded flo w of currents at other frequencies or of directcurrent.Frequency modulation Modulation where the frequency of the sinewave carrier alters with the amplitude of the modulatingsignal.Frequency response The variation of transmission loss or gain in a circuit or device with changes in frequency.Feed back The process in which a fraction of the output signal of a device or system is returned to the input, u suallyto modify the overall characteristic.Fast forw ard Provision is a tape recorder to run tape rapidly forward for quick selection of desirred portion. 21
  22. 22. Flutter Very short rapid variations in tape speed causing similar variations in sound v olume and pitch not presentin original sound.Frequency range The range between the highest and lowest pitched sound which a tape recorder or other sound systems canreproduce at a usable output or volume level.Fundamental Lo west frequency component in a complex waveform. Basic resonance of a loudspeaker.Guard Band A band of frequencies left vacant between two adjacent channels to prevent mutual interference.Gap The fine spacing provided between the poles of the recording, playb ack or erasing heads.Ganged Controls linked for operation by a single knob.Har monic Distortion Distortion caused by non linearity e.g. by overloading an amplifier producing an output that containsunwanted harmonics.Hum A lo w and constant audio frequency heard as unwanted signal in the background of a received radioprogramme.Head The ring shaped electromagnet across which the tape passes. Three types of heads are normally usedrecording, playback and erasing heads. Most of the domestic recorders utilizes a common record playback head.Some professional recorders also employ a monitor head.Head alignment In tape recorders, the correct positioning of the head and gap with respect to the magnetic tape.Headphones Small sound reproducers in a suitable form for wearing about the head.Har monic Multiple of the fundamental frequency. Second harmonic is twice the fundamental frequency, thirdharmonic is three times.Har monic distortion Whenever a single tone sign al is subjected to distortion harmonics are generated the level of distortion ismeasured by monitoring the level of harmonics produced.Head Shell Detachable part of pickup arm designed to carry the pickup.Hertz Hz unit of frequency, cycle per second.High fidelity HiFi. High level of faithfulness in sound recording and the reproduction. 22
  23. 23. Horn Acoustic device with expanding cross -sectional area horm loading provides the best matching from theloudspeaker cone to the air and resul ts in maximum efficiency of transfer of po wer from electrical energy fed tothe loudspeaker and acoustic power available from the horn loaded enclosure.Interference Any from of unwanted energy of a sufficient level to degrade the reception of a wan ted signal.Image rejection ratio A measure of a receiver’s ability to reject unwanted image frequency signals usually expressed as a ratioin dB.Image frequency interference Also kno wn as second channel interference. Interference from a sig nal on a frequency differing from thelocal oscillator by the I.F. It is always higher than the local oscillator frequency when the wanted signal is lo werand vice versa.Intermediate Frequency (IF) The frequency resulting from mixing the incoming si gnal and the local osicllator output in a receiver.Intermodulation The modulation of the components of a complex wave with each other to produce the sum and differenceof the frequencies concerned appearing as distortion.Impedance Measured in ohms, it is the A.C. resistance of any electrical component, generally referred to as eitherhigh or low impedance. For best results in connecting two components, output and input impedance shouldmatch.Input An electrical voltage fed into an ampl ifier.Infinite Baffle Loudspeaker mounting where there is no air path between front and rear of speaker diaphragm. Ideally aninfinite plane surface, normally applied to acoustic suspension type of enclosure.Long Waves (L.W.) Radio waves longer than medium wave. These lie between 20 KHz to 550 KHz.Loop antenna An antenna consisting of the one or more large turns of wire forming a closed circuit may be circular orrectangular in shape.Limiter A device where the output is automati cally prevented from exceeding a certain preset value. A limitermay be used to remove incidental amplitude modulation and noise from a frequency modulated signal.Leader and timing tape Special though, nonmagnetic tape which can be spliced to either end of a tape to prevent damage orbreaking off of the magnetic tape ends.Level indicator Indicates the level at which the recording is being made and serves as a warning against very lo w level oroverloading while recording. It may be in the form of neon bulb, magiceye, a meter or a light emitting diode.Labyrinth A loudspeaker enclosure with a long convoluted path between rear of the drive unit and outlet lined withdamping material to confine resonant effects to very lo w frequencies. 23
  24. 24. Linear When applied to transfer characteristic of amplifier or transducer, it indicated direct correspondencebetween input and output over the signal handling capability of the amplifier, any deviation results in distortion.Distortion depends on the no linearity present.Long Play (L.P.) Long playing record.Loudness Subjective aural sensation related logarithmically to objective sound intensity.Modulation The process in which some characteristic of one wave (e.g. carrier) is varied in accordance with somecharacteristic of another (e.g. speech).Modulation Index A measure of Modulation depth in angle modulated transmitters.Modulated Continuous A carrier wave modulated by a steady frequency tone.Muting Also known as ‘Squelch’. The process of inhibiting the output of a radio receiver by automaticallyreducing its gain in the absence of an input signal.Matching Connecting two circuits in a radio with a coupling device in such a way that impedance of either circui tmatches for maximum transfer of energy.Motor boating Regeneration occurring at audio frequencies in a radio receiver.Monophonic sound Sound recorded and reproduced on one channel. Most of the recordings are monophonic.Monophonic recorder Recorders, which have capability of recording and playing back only one channel sound.Magnetic tape A high quality plastic tape, which has been precision coated with layer of magnet sable, iron oxideparticled (or particles of some other magnet ic material such as chromiumdeoxide). These are used for recordingin the tape recorders.Magnetic Pickup Phone Pickup employing an electromagnetic transducer; moving magnet, moving iron, variablereluctance, induced magnet, moving coil. The output signal voltage is proportional to the velocity of the stylus.Main A mplifier Power amplifier as distinct from preamplifier or control unit.Mains Domestic electrical po wer supply, 220230 volts, 50 Hz in India.Matching I mpedance When the load impedance matches the source impedance maximum transfer of power takes place.Matrix Shell or stampers carrying a negative imprint of record groove and used for pressing final commercialdiscs. 24
  25. 25. Mechanical Impedance Opposition to change o f position or velocity due to inertia (effective mass), stiffness, and mechanicalresistance (friction) or any combination of these three.Microgroove Groove of a long playing disc record.Microphone Transducer with sensitive diaphragm for conv erting sound energy into electrical energy.Mismatch Electrical or acoustic situation with widely different impedances coupled together resulting in inefficienttransfer of power.Monaural One eared. After used wrongly in place of monophonic (Mon o).Mother Positive shell used in disc record manufacture. A few are produced from a negative Master and are usedin turn to produce the negative stampers or matrices employed for actual disc pressing.Moving Coil Type of loudspeaker, microphon e or pickup in which a coil of wire moves in a magnetic field.Music Pow er Power rating based on no sustained tones.Negative Feedback Signal from output of an amplifier fed back to the input in antiphase to reduce distortion. Negativefeedback may also be used to shape frequency response as well.Noise Unwanted signal.Output An electrical voltage coming out from an amplifier etc. and fed to line -in or loudspeaker.Oxide A used in magnetic tape microscopically small particle s of ferric oxide dispersed in a liquid binder andcoated on a tape backing.Octave Pitch or frequency interval of two to one.Ohm Unit of electrical resistance or impedance.Omni directional Equally effective in all directions.Overload Where an equipment or recording medium has been driven beyond its signal handling capacity.Overload Margin Amount by which input signal to a device can be raised above the nominal sensitivity without overloadingthe system.Padder A small value variable capacitor connected in series with main tuning condenser to provide alignment atthe low frequency end of tuning range. 25
  26. 26. Patch cord A short cord, or cable, with a plug at either end used to interconnect equipment, such as tape record ersand amplifiers.Pinch roller Also known as pressure roller a rubber roller, which engages the capstan and pulls the tape at a constantspeed and prevents slip.Playback head A magnetic head pick -up signals from tape.Peak to Peak Magnitude of voltage or current as measured between extreme positive and negative excursions.Phone Unit used to express loudness level above standard threshold.Pickup A device converts mechanical vibrations in to the electrical signal.Pickup Ar m Mechanical assembly of arm, pivots, counterweights etc. for carrying pickup head across ad is record.Pitch Quality of a sound, its position can be found in the musical scale.Player Unit Combination of turntable and pickup designed as an entity. Often mounted on a plinth with lid forfreestanding use.Playing Weight Downward force applied at the pickup stylus.Port Opening or vent in bass reflex loudspeaker cabinet.Pow er Amplifier Circuit element designed to supply audi o power to loudspeakers, driven by a preamplifier or control unit.Preamplifier Circuit element designed to accept signals from pickup, microphone, tape head etc. applying the desiredfrequency correction. It also incorporates volume and tone control s.Prerecorded Applied to magnetic tape carrying a commercial recording.Presence Vividness in reproduced sound obtained by boost in the upper middle frequency band.Printed Circuit Layout of circuit interconnections as conducting lines p rinted on a rigid board.Psychoacoustics The psychology of hearing.Quadrophony Sound field created by signal recorded and reproduced from four different directions.Radio frequency A frequency that can be used for radio communication, us ually regarded as being between 15 KHz and30000 KHz. 26
  27. 27. Rarefy To make less dense as opposed to compress, part of sound wave where pressure is below that ofatmosphere.Recording Characteristics Generally agreed frequency response for commercial r ecordings.Reflex Loudspeaker Cabinet with an outlet, vent or port, permitting enclosed air to be tuned for a coupledresonance effect with drive unit cone, results in extended low frequency response.Resonance Natural tendency of a mechanical, acoustical or electrical system to respond, vibrate, oscillate or ring atparticular frequency.Reverberation Repetitive reflection of sound in a enclosed space, contributing to ambience.R.I.A.A. Record Industry Association of America commonly refers to record replay characteristics.Ribbon Electro acoustic transducer employing a thin ribbon of aluminum alloy suspended in a magnetic field.R.M.S. Root Mean Square.Rumble Unwanted low frequency vibrations transmitted to pickup by turntable.Selectivity Which shows the ability of a receiver to reproduce signals of one station while rejecting signals from allother stations.Sensitivity The minimum strength of signal input which is capable of producing a desired value of signal output.Which shows the ability of a radio receiver to reproduce weak signals with satisfactory volume.Turntable Accurate circular platter with a central bearing together with associated driving mechanism for rotation ofthe records.Tw eeter Loudspeaker unit for use at high frequencies output speaker.Volume An acoustic rather than electrical measurement, which refers to the pressure of sound waves in terms ofdynes per cm square.Virgin tape A term sometimes used to describ e a tape that has not been recorded.Vent Opening or port in bass reflex loudspeaker cabinet; hence vented enclosure.Voice Coil Coil in the moving coil loudspeakers.Volume Control Control to adjust the electrical power delivered to the loudspeaker and consequently the sound record. 27
  28. 28. Wave for m The shape of a wave obtained by plotting some characteristic against tone.Wow Slow variations in tape speed causing similar variations in sound volume and pitch not present in theoriginal sound.Watt A unit of electrical power.White Noise Random noise covering all audible frequencies without coloration or emphasis sounds like rushing orhissing. Pink noise is specially selected spectrum of random noise used for test purpo ses.Woofer Loudspeaker unit for use at low frequencies output speaker. 28
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