TOPIC : HI FI AUDIO AMPLIFIER/ AUDIO SYSTEMS
Transcript of TOPIC : HI FI AUDIO AMPLIFIER/ AUDIO SYSTEMS
TOPIC : HI FI AUDIO AMPLIFIER/ AUDIO SYSTEMS
INTRODUCTION TO AMPLIFIERS: MONO, STEREO
DIFFERENCE BETWEEN STEREO AMPLIFIER AND MONO AMPLIFIER.
[Q] DEFINE AUDIO AMPLIFIER. STATE ITS TYPE. DRAW ITS
FREQUENCY RESPONSE CURVE.
An audio power amplifier is an electronic amplifier that increase the strength of
low-power audio signals (signals composed primarily of frequencies between 20 -
20 000 Hz, the human range of hearing) to a level suitable for driving
loudspeakers. It is the final electronic stage in a typical audio playback chain.
Types of Audio systems : Mono Amplifier system
Stereo Amplifier system
[Q] : COMPARE STEREO AMPLIFIER WITH MONO AMPLIFIER
BLOCK DIAGRAM OF HI FI AMPLIFIER AND ITS WORKING. CONTROLS
AVAILABLE ON IT AND THEIR FUNCTION,
[Q] WHAT IS HI-FI SYSTEM? LIST CHARACTERISTICS OF HI-FI
SYSTEM. The word „fidelity‟ means faithfulness. In audio system it is used to indicate
faithful reproduction of sound.
Hi-Fi system stands for high fidelity stereophonic reproducing system. Such a Hi-
Fi Sound can be obtained from the recorded stereo tape or live systems from the
microphones.
High fidelity reproduction is essentially sound reproduction such that the most
critical person can listen intensity to it without any distortion.
Characteristics of HI-FI amplifier:
1. Signal to noise ratio should be better than 50dB.
2. Frequency response should be flat within +-1dB.
3. Non-linear distortion should not be more than 1%.
4. The system should possess dynamic range of atleast 8dB.
5. Stereophonic effect should be provided.
6. Environmental conditions should be such as to eliminate the external noise in
listening room.
[Q] DRAW AND DESCRIBE THE BLOCK DIAGRAM OF HI-FI
AMPLIFIER.
Figure shows the block diagram of a high-fidelity stereo reproducing system.
High- fidelity sound can be obtained from the recorded stereo tape or in live
system from the microphones. (Stereo signal can also be obtained from the record
player.)
The stereo signal is fed to two independent amplification channels through a tape-
mic switch. The amplifier system consist of a low noise high gain preamplifier,
equalizer, well design amplifiers giving flat frequency response and little distortion
by using negative feedback circuit and then the matching transformer.(A balancing
circuit is incorporated to balance out any imbalance in the characteristics of
otherwise identical circuits.) The secondary of the matching transformer of each
channel is connected to the respective loudspeaker column. For Hi-fi, the
loudspeaker columns consisting of woofer, squawker and tweeter are used.
All the blocks are design so as to get fat frequency response (from 40 to 15000Hz),
little distortion (less than 1%), high signal-to-noise ratio (more than 50db) and high
dynamic range (100 db) to achieve the final output of high fidelity.
Balance control: Two amplifiers of a stereo system, although independent of each
other are built as matched pair to give equal output for the same input. In spite of
the two amplifiers being identical, there may be variations in the characteristics of
transistors and ICs and positioning of loudspeakers and furnishings with respect to
the listener. The circuit used to compensate for such variations are called Balance
control.
Loudness control: Sometime music is at low level of volume (as in case of the
background music). At low levels there is considerable loss in bass in
reproduction. It is therefore, necessary that there should be substantial boosting of
the bass at low levels. Boosting at treble may be only nominal because loss at high
notes is quite small. The control which provides desired big boosting at bass and a
little boosting at treble is called loudness control.
Bass and Treble control: It is provided to tailor bass treble as per personal taste of
the listener.
Master Gain control: a master gain control is used for adjusting overall volume
without disturbing the balance. This is achieved by using dual concentric shafts,
the inner shaft adjust the balance control and the outer shaft, the overall gain or
volume of the amplifier. A typical master gain control circuit is shown in figure is
adjusted for balancing the two channels and then R2 and R3 are adjusted for
increasing or decreasing the volume of the channels. R2 and R3 are ganged.
Blend control: The stereo effect is diluted by this control when it is too much left-
right effect. Diluting is done by disbalancing the two channels. It is shown in
figure. Blend control potentiometer is set at zero resistance for balance output. For
disturbing the balance, this is advanced further to reduce gain of the left channel.
Although blending can be done by balance control also, but once set, the balanced
control is not disturbed.
Quasi stereo switch: When any one channel signal is made to go into both the
channels, one can use both channels and their speakers for a monophonic source of
signal. This is done by a switch called quasi-stereo switch.
[Q] EXPLAIN THE FUNCTION OF FOLLOWING IN HI-FI AMPLIFIER:
I)BALANCE CONTROL
II)LOUDNESS CONTROL
III)BASS AND TREBLE CONTROL
IV)QUASI STABLE SWITCH.
Controls available on Hi-Fi system are :-
Balance control :- Inspite of the two amplifiers being identical, there may be
variations in the output of each channel due to variation in the characteristic of
transistors and ICs and positioning of loudspeaker and furnishing with respect to
the listener. The circuit used to compensate for such variation is called “Balance
Control”
When the balance control is moved down , the output of left channel will increase
while that of the right one will decrease, and vice versa when moved up.
Loudness control :- Sometimes music is at low level of volume (as in case of the
background music). At low levels there is considerable loss in bass in
reproduction. It is therefore, necessary that there should be substantial boosting of
bass at low levels. Boosting at treble may be nominal
because loss at high note is quite small. The control which provides desired big
boosting at bass and a little boosting at treble is called “Loudness control”. It boost
audio by +12 dB at 50Hz and +3 dB at 10Khz. Such a volume control also act as
loudness control and is known as „Contour Control‟.
Bass and treble control :- It is provided to tailor bass and treble as per personal
taste of the listener.
Quasi stereo switch :- This causes any one channel signal to go into all
channels. This way , one can use all channels and all speakers for a monophonic
source of signal
[Q] LIST VARIOUS CONTROL OF HI-FI AMPLIFIER AND EXPLAIN
ANY ONE
Ans:-
Various control of Hi-Fi amplifier:- 01M
Balance Control:
Master Gain Control:
Blend Control:
Quasi Stereo Switch:
Bass & Treble Control:
Loudness Control:
Balance Control:
Two amplifiers of a stereo system, although independent of each other, are built
as matched pair to give equal
output for the same input. In spite of the two amplifiers being identical, there may
be variations in the output of
each channel due to variations in the characteristics of transistors & ICs and
positioning of loudspeaker &
furnishing with respect to the listener. The circuit used is called BALANCE
CONTROL.
A simple circuit is shown in fig. The balance control is a potentiometer. When it
is set in the center, the current
through LED1 & LED2 should be identical, if the signals in the left & right
channels are equal. In that case both LED will be equally bright.
In case of any inequality, the two brightness level will also become unequal.
When balance control is moved down, the output of the left channel will increase
while that of right one will decrease, and vice-versa when moved up.
Master Gain Control:
A master gain control is used for adjusting overall volume without disturbing the
balance. This is achieved by using dual concentric shafts, the inner shaft adjusts the
balance control & the outer shaft, the overall gain or volume of the amplifier.
A typical master gain control circuit is shown above. R1 is adjusted for balancing
two channels & then R2 & R3 are adjusted for increasing or decreasing the volume
of the channels. R2 & R3 are ganged
Blend Control:
The stereo effect is diluted by this control when there is too much left-right
effect. Diluting is done by
misbalancing the two channels.
It is shown in fig. above; blend control potentiometer is set at zero resistance for
balanced output. For disturbing
the balance, this is advanced further to reduce gain of the left channel.
Although blending can be done by balance control also, but once set, the balance
control is not disturbed.
Quasi Stereo Switch:
When any one channel signal is made to go into both the channels, one can use
both channels & their speakers for monophonic source of signal. This is done by a
switch called quasi-stereo switch.
Bass & Treble Control:
It is provided to tailor bass & treble as per personal taste of listener.
Loudness Control:
Sometimes music is at low level of volume. At low levels there is considerable
loss in bass in reproduction. It is, therefore necessary that there should be
substantial boosting of bass at low levels. Boosting at treble may be
only nominal because loss at high notes is quite small. The control which provides
desired boosting at bass & at treble is called LOUDNESS CONTROL.
It boost audio by +12dB at 50Hz & +3dB at 10 KHz. The loudness control
should be used only when sound level is low
GRAPHIC EQUALIZER CONCEPT- CIRCUIT DIAGRAM AND OPERATION. (5-POINT
CIRCUIT DIAGRAM)
WHAT IS THE GRAPHIC EQUALIZER? WRITE ITS NECESSITY
Graphic Equalizer:
A graphic equalizer is a high-fidelity audio control that allows the user to see
graphically and control individually a number of different frequency bands in a
stereophonic system. A typical graphic equalizer consists of several audio
filter/amplifiers, each centered at a specific frequency in the audio range.
Most graphic equalizers have two identical sets of filter/amplifiers, one for each
channel in a stereophonic system.
The gain (volume) controls in most graphic equalizers are slide potentiometers
that are adjusted by moving a control button up or down. Gain is increased by
sliding the button upwards.
The slide potentiometers for each channel are placed side-by-side, with the
lowest-frequency unit at the left and the highest-frequency unit at the right. In this
way, the positions of the buttons appear to follow a graphical curve that represents
the gain as a function of frequency for each channel.
[Q] DRAW AND DESCRIBE OPERATION OF GRAPHIC EQUALIZER
[1] In five point configuration, the graphic equalizer breaks up an audio input
signal into five different bands covering the range of human hearing. Once this is
completed, the signal in each band can be adjusted to provide best sound.
[1]A : The center frequencies f1, f2, f3, f4 and f5 of the frequency bands of the
graphic equalizer are usually fixed at pre-set values. Once these bands are added
back together, they are passed through an amplifier which increases the amplitude
of the signal to the point where there is enough power that can be heard through an
ordinary speaker.
[2] The circuit diagram of graphic equalizer is shown in figure. The graphic
equalizer consists of an amplifier for every segment of octave band. Such
amplifiers are connected in parallel to cover the complete frequency range.
[3] The individual gains of these amplifiers are adjusted such that the required
frequency response is obtained. Using five amplifiers for five octaves of frequency
may be very expensive. Hence amplifier shown in figure is normally used.
The figure shows, there is only one amplifier with multiple feedback paths. There
are gain controls and LC tuned circuits in every feedback path. Thus the gain of
every octave band is separately adjusted by the corresponding feedback path gain.
[4] The center frequency of the octave band is selected by inductors L1, L2, L3, L4
and L5. The gains of individual octave bands are adjusted by potentiometer
controls in the feedback path.
[5] The combination of individual control setting for various octaves will provide
the required frequency response. The peaks at individual octave bands overlap
each other. Hence, phasing distortion needs to be avoided. This distortion occurs
due to interaction between the overlapping peaks. The slider controls of each
octave band can boost or cut the signals from +15 dB to – 15 dB.
[Q] STATE AND EXPLAIN THE CONCEPT OF GRAPHIC EQUALIZERS. Graphic equalizer is used to eliminate unwanted peaks in the frequency response
of audio systems.
In five point configuration, the graphic equalizer breaks up an audio input signal
into five different bands covering the range of human hearing. Once this is
completed, the signal in each band can be adjusted to provide best sound. The
center frequencies f1, f2, f3, f4 and f5 of the frequency bands of the graphic
equalizer are usually fixed at pre-set values. Once these bands are added back
together, they are passed through an amplifier which increases the amplitude of the
signal to the point where there is enough power that can be heard through an
ordinary speaker.
The graphic equalizer consists of an amplifier for every segment of octave band.
Such amplifiers are connected in parallel to cover the complete frequency range.
The individual gains of these amplifiers are adjusted such that the required
frequency response is obtained. Using five amplifiers for five octaves of frequency
may be very expensive.
DOLBY NR RECORDING SYSTEM
[Q] EXPLAIN DOLBY-NR RECORDING SYSTEM IN BRIEF.
[1] The Name Dolby is synonymous with Noise-Reduction Systems.(Here Nr
represents for Noise-reduction).
[2] Dr. Ray Dolby introduced a novel system so the name given.
[3] In practice, Dolby system is used for pre-emphasis of high notes and de-
emphasis of low notes by equalization. Dolby system provides 10-15 dB
improvement in SNR.
[4] In his system, weak signals below 40 dB, above noise are boosted before
recording. All signals which are 40 dB or higher, pass through Dolby system direct
without change.
[5] Signal in the absence of boosting is shown in Fig.(a) After boosting ,recording
noise remains unchanged but signal is boosted as shown in fig(b).During playback,
signal and nose both are reduced as shown in fig(c).
DOLBY A SYSTEM:
fig : Reduction of Noise by 10 dB in Dolby System
Boosting is done in 4 bands – 1) Below 80 Hz.
2) 80 Hz to 2999 .
3) 3 kHz and above.
4).9 kHz and above.
Bands 3 and 4 overlap above 9 kHz, so that the high frequency noise, in the form of hissing sound is considerably reduced. Each frequency band is processed separately by using low pass, band pass and high pass filters and limiters. Dolby B System: [1] Amore simplified system than Dolby A system has been developed for home
use and is known as Dolby B System.
[2] In Dolby-B system, the encoded signal covers a signal frequency band from
500 Hz upwards.
[3]Signal below a specified threshold value in level are pass through a variable
filter which increases the level by about 1 dB at 500 Hz. Curve shown by dotted
line as shown in fig.
The processed signal from the variable filter and the direct input signal are added.
The adder gives the Dolby output.
For playback, the signal is inverted and fed to the variable filter. The output of the
filter gives to the adder to give decoded output.
TYPES OF SPEAKER –WOOFER, MID-RANGE, TWEETER
Compare between woofer, tweeter and squawker on the basis of following
parameters.
i) Frequency response
ii) Cross over network
iii) Cost
iv) Application
CROSS OVER NETWORK CIRCUIT AND ITS FUNCTION
[Q] STATE THE NECESSITY OF CROSS OVER NETWORK.
Necessity of Cross over Network [1] A single cone type speaker is not able to provide uniform response and
adequate output power over the entire AF range.
[2]A loudspeaker mechanism with a heavy and large diameter called woofer can
reproduce low frequencies.
[3]A loudspeaker with a light and small diameter cone known as tweeter which
performs much better at the high frequency audio frequency range.
[4] For proper functioning of a dual speaker system, it is necessary that the
frequency range to be covered by the combination of speakers should be split into
two ranges at a frequency called cross-over frequency.
[5] Hence woofers & tweeters are used with cross-over networks, for getting a
uniform frequency response over the entire frequency range
[Q] DRAW THE CIRCUIT DIAGRAM OF CROSS OVER NETWORK AND EXPLAIN
ITS OPERATION IN BRIEF.
When a multiway loudspeaker system is used to get flat frequency response for the
entire range of audio frequencies, it is essential to have a crossover network to
divide the incoming signal into separate frequency ranges for each speaker.
In the absence of crossover networks, the speakers will suffer overheating and the
output will be distorted when full power at frequencies outside their range is fed to
them. The overall efficiency will be much reduced in the absence of crossover
networks.
Crossover networks make use of the fact that the capacitive reactance decreases
with increase in frequency [FC
X2
1]and the inductive reactance increases with
increase in frequency
(X1= 2 f L). A basic crossover network is illustrated in fig.
The circuit consists of a low-pass LC filter across the woofer and a frequencies (16
Hz to 1000 Hz) to go to the woofer.
The series reactance of L and shunt reactance of C for high audio frequencies
prevents these frequencies from going to the woofer.
The high-pass filter consisting of C in series and L in shunt allows the high audio
frequencies to pass to the tweeter and blocks the low frequencies.
The response curve of a typical crossover network (of Fig ) is shown in Fig. . It
gives an attenuation of 12 dB per octave
CIRCUIT DIAGRAM AND FREQUENCY RESPONSE OF THREE-WAY CROSS OVER
NETWORKGIVE THE VALUES OF L AND C
[Q] DRAW THE THREE WAY CROSS OVER N/W WITH ITS
FREQUENCY RESPONSE GRAPH
Where, R1 is the impedance of a loudspeaker in ohms and fc is the crossover
frequency in Hz, L is The inductance and C, the capacitance of LC circuits.
A commercial three-way divider network is shown in Fig. In this circuit the
capacitor C1 of 1μF in series with the tweeter prevents low and mid-frequencies
from reaching the tweeter.
Similarly, the inductance Lw of 5 mH in series with the woofer prevents high
frequencies from reaching the woofer. Inductances Ls1 and Ls2 of 0.5 mH and 5
mH, respectively in the squawker circuit allow only mid-frequencies and prevent
too low and too high frequencies from reaching the squawker.
A typical divider curve for a three-way network of Fig. is shown in Fig.
A single element in filtering gives attenuation of 6 dB per octave and double
element in filtering gives attenuation of 6 dB per octave and double elements give
12 dB octave.
PUBLIC ADDRESS SYSTEM: NEED AND USE, BLOCK DIAGRAM,
REQUIREMENTS OF A PUBLIC ADDRESS SYSTEM
[Q] EXPLAIN DETAIL PUBLIC ADDRESS SYSTEM WITH SCHEMATIC
BLOCK DIAGRAM .
A public address system (PA system) is an electronic sound amplification
and distribution system with a microphone, amplifier and loudspeaker.
The intensity of sound decrease with the distance to receive good intensity
of sound for comfortable listening.
The system fulfils this function is called public address system.
Or simply PA system.
BLOCK DIAGRAM :-
It is an electronics system in which converts into electrical signal by
microphone.
The electrical audio signals are amplified and fed into another transducer the
loudspeaker which converts the audio signals into the sound wave.
The block diagram consist :- Microphone
Mixer
Voltage amplifier
Processing circuit
Driver amplifier
Power amplifier
Loud speaker
Microphone:-
It is a electrical transducer it pick up sound wave and converts into the
electrical variations called audio signal.
• Mixer :-
The output of the microphone is fed into the mixer stage. the mixer stage is
to effectively isolate different channels from each other before feeding into
the main amplifier.
• Voltage amplifier :-
It further amplifies the output of the mixer.
rocessing Circuit :- These circuit have master gain control and the tone controls
Driver amplifier :- It is gives voltage amplification to the signal to such an extent that when fed
to the next stage the internal resistance of that stage is reduced .
• Power amplifier :-
it is gives desired power amplification to the signal. it is push-pull type of
circuit in general. the power amplifier connected to the loudspeaker.
• Loudspeaker:-
It converts electrical audio signal into pressure variation resulting in sound.
Requirements
Sounds from the loudspeaker should not reach the microphone, as a acoustic
feedback will result in a loud howling sound.
Distribution of sound intensity :- Loudness of the sound is contained in low notes and the intelligibility in high
notes. As high notes suffer grater attenuation with distance than the low note
intelligibility suffers at further distance.
Reverberation :-
In a reverberation medium the intelligibility is poor. The Pa system should throw
additional power in those areas where the direct gets submerged in the echoes.
Dynamic Range Limitation:-
The amplifier of a good PA system is equipped with a level limiter which keeps the
output level constant when the input level exceeds a certain predetermined value.
Matching :-
Matching of the loudspeaker impedance with the output impedance of the amplifier
is necessary for maximum transfer of energy from amplifier to loudspeaker.
Grounding :-
Chassis and shields of equipments and coaxial cables should be properly earthed
through water pipes Audio systems