Consumer electronics lab manual 8th sem ECE

1. SIGMA
STEREO 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. INTRODUCTION
This trainer has been designed with a view to provide practical and experimental knowledge of a ge neral
circuit of Stereo cassette player on SINGLE P.C.B.
SPECIFICATIONS
1. 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 control
10. 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. PRACTICAL – 1
BLOCK DIAGRAM AND WORKING PRINCIPLE
Tape Recorder circuit consists of two identical sections and power supply section. These two identical
sections 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 of
these signals is very low . The preamplifier is, therefore, designed to introduce minimum of noise. A lo w noise
transistor 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 of
the head and at the higher frequency and by the gap width of the head. The magnetic tape generates high
frequency noise. To maintain a good signal -to-noise ratio at the high frequency end, the high frequency signa l is
boosted while recording and is attenuated during play.
The main function of the equalizer is provided the boost at lo w and high frequencies required during
playback Negative feedback is used for equalization.
(C) DRIVER: -
The driver stage further amplifies the signals obtained from the equalizer and gives these to the output
stage through volume control.
(D) OUTPUT AMPLIFIER -
This stage amplifies the signals available from drive to drive the loudspeaker. It also incorporates bass and
treble controls.
3

4. (E) POWER SUPPLY: -
The stereo cassette player can be operated on mains or car battery. The connections are made in such a
manner 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 filter
circuits 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 on
the tape from left side, is picked up by left channel head and is given to left channel preamplifier Similarly the
signals recorded on the tape from right side, is picked up by right channel head and is given to right channel
preamplifier.
(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 in
the signal.
(K) TAPE/DECK MECHANISM: -
Tape Deck/Mechanism is a main part of the stereo Cassette player. It is used for (I) Playback (II) Winding
the 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. Figure-1 Block Diagram of Tape Recorder Trainer
5

6. PRACTICAL – 2
TERMS, DEFINITION AND NOMENCLATURE USED
4.1 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. 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. 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. (4) DISK CAPACITORS: -
1. 220pf 2 C8, C27
2. 470pf 2 C24 C5
3. 1n 4 C15, C7, C26, C34
4. 4n7 2 C35, C16
5. 22n 2 C3, C22
6. 47n 2 C49, C50
7. 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, P4
2. 100K Lin 16mm 2 P3, P6
3. 1M Lin 16mm 2 P2, P5
4. 2P2W SW 1 S1
5. Toggle 1 S2
8
(6) COILS (L): -
1. Choke coil 1 L1
1
9

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 left
channel 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 Q1
through R7, R8, and C3 r6. The reactance of C3 increases at lo w frequencies reducing the feedback
progressively. Thus the gain at low frequencies increases providing the necessary boost. The feedback at high
frequencies 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). This
also provides D.C. Negative feedback over the two stages and stabilizes the operating point of both the
transistors. The amplified audio signals obtained at the collector of Q2 are given to the driver amplifier transistor
Q3.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 ac
bypass 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 unbiased
emitter configuration.
R12 is base bias resistor. R10 is input base current limiting resistor. R11 is emitter resistor. C8 is used for
high frequency roll off. R13 is load resistor for Q3. C9 is output coupling capacitor. The amplified audio signals
from 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 the
ground 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 signals
obtained from the transistor Q3 are given at the audio input (Pin 8) of the IC. The IC amplifies these and the
output is available at the Pin 12 of the IC. The feedback is given from the output to the emitter of preamplifier
transistor in the IC (through a resistor 4K provided internally) and also through R41 (1K8), P3, C10 and C47.The
feedback voltages develops over R6 (33E ), C12 being used for d.c.blocking. The gain of amplifier depends on
this feedback. The bass frequencies can be amplified by varying P3 as it provides negative feedback in such a
manner to increase to bass response. C47 is used for dc blocking. R41 is the minimum resistor in case of Zero
value of P3.R17 (10E - 1/2 w) and C17 (0.1u) provides negative feedback and reduces the gain of the amplifier at
10

11. frequencies beyond 15KHz (roll -off) 14 V DC supply is given at pin 1 of the IC. The pin 7 is ground through
C13, which decouples the power supply to the preamplifier stage in the IC. Pin 5 is used for frequency
compensation. This is connected through C15 (1n) and is connected to ground through C16 (4n7). The output
signal available from the IC is given to the lef t channel LS through the coupling capacitor C18 (1000/10). The
pin 4 (brought out as bootstrap terminal) is connected to output Pin through C33 (220/10). This provides negative
feedback from the output terminal to the bootstrap terminal and increases the i nput impendence of the output
stage. LED D5 to D9 is used to indicate the output level. R18 (10E, 1/2w) is the biasing resistor for LEDs. The
provision is also made to connect external speaker through EP2 socket. R14 (220K) decides input impedance of
the 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 and
driver 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 4E
impedance. 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 a
capacitor C43. Diodes - D1 to D4 rectifies A.C. voltages and the obtained pulsating D.C. voltage is smoothed by
C43. 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 C19
and C38 through leaf switch in the tape deck/mechanism. This filter removes 100 KHz ripple from the +14V
supply is also given to the motor. C44 (1000/16) across the motor is the ripple filter capacitor.
11

12. PRACTICAL - 5
TEST POINT VOLTAGES
All voltages measured actually are sho wn below: -
Voltage Point- Voltage at Voltage at
Zero Volume. Full Volume.
1. Xmer Secondary 12.0vAC 12.0vAc
2. C43 +Ve lead 15.0vdc 13.0Vdc
3. C46 +Ve lead 7.1vdc 6.0vdc
4. 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. PRACTICAL – 6
TEST POINT WAVEFORMS
1. INPUT SIGNAL AT TEST POINT I: -
2. AMPLIFIED SIGNAL AT COLLECTOR OF Q1: -
3. INPUT SIGNAL AT PIN 8 OF IC1
4. OUTPUT SIGNAL AT PIN 12 OF IC1: -
13

14. PRACTICAL - 7
TESTING METHOD
1. 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 should
be 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 across
loudspeaker should be approximately 12V at full load
4. PLAYBACK TESTING: -
Feed 200uV, 1 KHz signal at the input of preamplifier i.e. at the negat ive end of C304. Keep volume
control in the maximum position and treble and Bass controls in middle position. The full output at loudspeaker
should 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 dB
higher than the output at 1 KHz. Also check the output a 10 KHz. It should be 3 to 4 db less with respect to 1
KHz.
14

15. PRACTICAL - 8
ALIGNMENT METHOD
R/P HEAD ALIGNMENT: -
The head can be aligned with a special cassette tes t type. These test -tapes are precision recorded on
cassette 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. 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. (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. PRACTICAL - 10
GLOSSARY OF TECHNICAL WORDS
Aim: -
To study the Glossary of the technical words of Radio, Tape, an d Two - in - one technology
Aerial
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 the
signal.
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 radio
receiver constant within limits while the carrier signal picked up by the antenna is varying in amplitude over a
wide range.
Automatic level control (ALC)
A ci rcuit arrangement, to reduce the gain of the amplifie r in tape recorder, when recording level exceeds a
certain 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 a
circuit terminal and ground.
Balance control
Control used to adjust the gain of the stereo channel differentially so as to get balanced output from the
amplifier.
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 tone
controls as against tone controls using passive circuitry.
Beat
Audible fluctuation of amplitude when two audio signals are very close together in frequency.
18

19. Binaural
Heard with two ears, also applied to double mono headphone listening to distinguish from headphone
stereo.
Carrier
(a) The R.F. component of a transmitted wave upon which an audio signal or other form of intelligence
can 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 local
frequency 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 input
circuits. 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 and
C120.
Cycles per second
The unit, for measuring the frequency or pitch of sound. This has been replaced by Hert z (abbreviated
Hz)
Condenser microphone
A microphone in which the operation depends on the changes in capacity between a fixed plate and a
diaphragm. These require polarizing voltage for operation.
Ceramic
Manmade piezoelectric or permanent magnetic material used in some pickups and loudspeakers
respectively. Ceramic pickups have better performance and life characteristics compared to crystal pickups
available 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 the
input signal.
Coloration
Change in sound quality according to peculiarities of the audio system, a character imparted to
reproduced sound, often and mainly by loudspeakers. No two speaker enclosures sound the same the
loudspeakers 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 the
level of loud passages. The level of the quiet passages is normally raise d to obtain a better signal to noise ratio
for the system. Lo wering of the level of loud passages becomes necessary when the recording system can not
accommodate 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. Control Unit
Preamplifier part of the audio system designed to operate separate from power amplifier. It accepts
signals from sources such as pickup, Micr ophone, tuner, tape etc; applies equalisation as required and it
incorporates volume and tone controls.
Crossover Frequency
Frequency at which a loudspeaker CROSSOVER NETWORK divides the signal of crosses over from one
section 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 sound
intensity to another. One dB is the smallest change in sound that human ear can detect. This is a logarithmic
measure. 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 of
the type width, making it possible to record two tracks on tape. One of these tracks is recorded in one direction
and 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. Tape
recordings 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 without
undue distortion. This is usually measured in db.
Damping
Process of reducing resonant effects by use of resistance or mechanical or acous tic equivalents of
resistance.
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 audio
equipment.
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. Dual Cone
Loudspeaker drive unit with two cones driven from one moving coil, inner cone of smaller diameter
extends the high frequency response.
Erasing
Neutralizing the magnetic pattern on tape by placing it in a strong magnetic field, thereby removing the
recorded sound from tape.
Erase Head
The erase head automatically removes the recorded sound from tape. It may be given d.c. or more usually
high frequency A.C. from the bias oscillator. The erase head is placed before the recording head and while
recording the perused tape reaches the recording head.
Equalization
The manipulation of frequencies that is required to meet the recognized standards of recording and
reproducing techniques. This usually requires boosting of lo w as well as high frequenci es while playing back and
boosting 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 electrostatic
forces to actuate radiating diaphragms.
Elliptical Stylus
Designed to minimize tracing distortion by placing a small radius in contact with the groove walls as
viewed 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 mounting
and 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 low
distortion.
Filter
Combination of Coil, Capacitor and resistor which is used to block or alternate alternating currents at
certain frequencies while allo wing essentially unimpeded flo w of currents at other frequencies or of direct
current.
Frequency modulation
Modulation where the frequency of the sinewave carrier alters with the amplitude of the modulating
signal.
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 sually
to modify the overall characteristic.
Fast forw ard
Provision is a tape recorder to run tape rapidly forward for quick selection of desirred portion.
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22. Flutter
Very short rapid variations in tape speed causing similar variations in sound v olume and pitch not present
in original sound.
Frequency range
The range between the highest and lowest pitched sound which a tape recorder or other sound systems can
reproduce 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 contains
unwanted harmonics.
Hum
A lo w and constant audio frequency heard as unwanted signal in the background of a received radio
programme.
Head
The ring shaped electromagnet across which the tape passes. Three types of heads are normally used
recording, 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, third
harmonic is three times.
Har monic distortion
Whenever a single tone sign al is subjected to distortion harmonics are generated the level of distortion is
measured 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.
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23. Horn
Acoustic device with expanding cross -sectional area horm loading provides the best matching from the
loudspeaker cone to the air and resul ts in maximum efficiency of transfer of po wer from electrical energy fed to
the 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 ratio
in dB.
Image frequency interference
Also kno wn as second channel interference. Interference from a sig nal on a frequency differing from the
local oscillator by the I.F. It is always higher than the local oscillator frequency when the wanted signal is lo wer
and 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 difference
of the frequencies concerned appearing as distortion.
Impedance
Measured in ohms, it is the A.C. resistance of any electrical component, generally referred to as either
high or low impedance. For best results in connecting two components, output and input impedance should
match.
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 an
infinite 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 or
rectangular in shape.
Limiter
A device where the output is automati cally prevented from exceeding a certain preset value. A limiter
may 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 or
breaking 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 or
overloading 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 with
damping material to confine resonant effects to very lo w frequencies.
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24. Linear
When applied to transfer characteristic of amplifier or transducer, it indicated direct correspondence
between 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 some
characteristic 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 automatically
reducing 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 t
matches 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 oxide
particled (or particles of some other magnet ic material such as chromiumdeoxide). These are used for recording
in the tape recorders.
Magnetic Pickup
Phone Pickup employing an electromagnetic transducer; moving magnet, moving iron, variable
reluctance, 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 commercial
discs.
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25. Mechanical Impedance
Opposition to change o f position or velocity due to inertia (effective mass), stiffness, and mechanical
resistance (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 inefficient
transfer 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 used
in 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. Negative
feedback 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 and
coated 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 overloading
the system.
Padder
A small value variable capacitor connected in series with main tuning condenser to provide alignment at
the low frequency end of tuning range.
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26. Patch cord
A short cord, or cable, with a plug at either end used to interconnect equipment, such as tape record ers
and amplifiers.
Pinch roller
Also known as pressure roller a rubber roller, which engages the capstan and pulls the tape at a constant
speed 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 for
freestanding 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 desired
frequency 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 and
30000 KHz.
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27. Rarefy
To make less dense as opposed to compress, part of sound wave where pressure is below that of
atmosphere.
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 coupled
resonance 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 at
particular 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 all
other 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 of
the 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 of
dynes 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.
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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 the
original sound.
Watt
A unit of electrical power.
White Noise
Random noise covering all audible frequencies without coloration or emphasis sounds like rushing or
hissing. Pink noise is specially selected spectrum of random noise used for test purpo ses.
Woofer
Loudspeaker unit for use at low frequencies output speaker.
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