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

: sigmatrainers@sify.com

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, power 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

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 low 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 lower 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 low 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.

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. I t consists of belts, idle wheels,

intermediate wheels, cams etc.

5

Figure-1 Block Diagram of Tape Recorder Trainer

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

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

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

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(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

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

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 have 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 low 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

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.

12

PRACTICAL - 5

TEST POINT VOLTAGES

All voltages measured actually are shown 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

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: -

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;

otherwise 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.

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 slowly on

one side and then to the other side till the maximum output is obtained should do this.

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.

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 wheel 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.

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 carrier 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 circuit 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 Switch

A switch, which simultaneously 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

Lower 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.

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. I t 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 quali ty 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. Lowering 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 surround

Strip or roll of compliant material fitted to the periphery of the loudspeaker cone.

20

Control Unit

Preamplifier part of the audio system designed to operate separate from power amplifier. I t accepts

signals from sources such as pickup, Microphone, 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.

Demodulation

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.

Diaphragm

Sound generating element in a loudspeaker.

DIN

Deutscher Industries Norman, German industrial Standards, now coming into common use for audio

equipment.

Dolby system

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.

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 low 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 allowing essentially unimpeded flow 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 forward

Provision is a tape recorder to run tape rapidly forward for quick selection of desirred portion.

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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

Lowest 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.

Harmonic Distortion

Distortion caused by non linearity e.g. by overloading an amplifier producing an output that contains

unwanted harmonics.

Hum

A low 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.

Harmonic

Multiple of the fundamental frequency. Second harmonic is twice the fundamental frequency, third

harmonic is three times.

Harmonic distortion

Whenever a single tone signal 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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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 power 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 known 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 lower

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 automatically 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 low 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 low frequencies.

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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 Amplifier

Power amplifier as distinct from preamplifier or control unit.

Mains

Domestic electrical power supply, 220230 volts, 50 Hz in India.

Matching Impedance

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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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 converting 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, microphone or pickup in which a coil of wire moves in a magnetic field.

Music Power

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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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 Arm

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.

Power Amplifier

Circuit element designed to supply audio 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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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.

Tweeter

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 describe 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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Wave form

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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