audio handbook

202 Pages·2016·16.31 MB·English

AUDIO
HANDBOOK
Technical Editor & Contributing Author:
Dennis Bohn
Consumer Application Engineer
Contributing Authors:
John Wright
Ron Page
Tim Regan
Thomas B. Mills
John Maxwell
Tim D. Isbell
Nello Sevastopou los
Jim Sherwin
National Semiconductor Corporation • 2900 Semiconductor Drive • Santa Clara, CA 95051
© 1976 National Semiconductor Corp. DA-A70M46/Printed in U.S.A.

Section Edge Index
Introduction
Preamplifiers
AM, FM and FM Stereo
Power Amplifiers
noobydusl
Appendices
Index
Manufactured under one or more of the following U.S. patents: 3083262,3189758,3231797,3303356,3317671, 3323071, 3381071,
3408542, 3421025, 3426423, 3440498, 3518750, 3519897, 3557431, 3560765,3566218,3571630,3575609,3579059,3593069,
3597640,3607469,3617859,3631312,3633052, 3638131, 3648071, 3651565, 3693248.
National does not assume any responsibility for use of any circuitry described; 00 circuit patent licenses are implied;
and National reserves the right, at any time without notice, to change said circuitry.

Table of Contents
1.0 Introduction
1.1 Scope of Handbook . 1-1
1.2 IC Parameters Applied to Audio. 1-1
2.0 Preamplifiel'S
2.1 Feedback - To Invert or Non-Invert 2-1
2.2 Design Tips on Layout, Ground Loops and Supply Bypassing 2-1
2.3 Noise. 2-3
2.4 Audio Rectification --or, "How Come My Phono Detects AM?" 2-10
2.5 Dual Preamplifier Selection 2-11
2.6 LM381 2-12
2.7 LM381A 2-15
2.8 LM387 and LM387 A 2-19
2.9 LM382. . . 2-20
2.10 LM1303. . . 2-24
2.11 Phono Preamps and R IAA Equalization 2-25
2.12 Tape Preamps and NAB Equalization 2-31
2.13 Mic Preamps. ..... 2-37
2.14 Tone Controls - Passive and Active 2-40
2.15 Scratch, Rumble and Speech Filters 2-49
2.16 Bandpass Active Filters 2-52
2.17 Octave Equalizers 2-53
2.18 Mixers 2-59
2.19 Driving Low Impedance Lines 2-61
2.20 Noiseless Audio Switching 2-62
3.0 AM, FM and FM Stereo
3.1 AM Radio . 3-1
3.2 LM1820 3-4
3.3 FM-I F Amplifiers/Detectors 3-8
3.4 Simple Limiters . . 3-8
3.5 Gain Blocks 3-11
3.6 Complete I F Amplifier and Detectors 3-13
3.7 LM3089 - Today's Most Popular FM-IF System 3-18
3.8 FM Stereo Multiplex - LM1310/1800 . 3-23
3.9 Definition of Terms 3-27
4.0 Power Amplifiel'S
4.1 Inside Power Integrated Circuits. 4-1
4.2 Design Tips on Layout, Ground Loops and Supply Bypassing 4-4
4.3 Power Amplifier Selection. 4-4
4.4 LM377 /378/379 4-8
4.5 LM380 4-21
4.6 LM384 4-28
4.7 LM386 4-30
4.8 LM389 4-33
4.9 LM388 4-37
4.10 LM390 4-41
4.11 Boosted Power Amps/LM391 . 4-42
4.12 Power Dissipation 4-43
4.13 Effect of Speaker Loads 4-45
4.14 Heatsinking 4-46
Table of Contents
(continued)
5.0 Fioobydust*
5.1 Biamplification 5-1
5.2 Active Crossover Networks 5-1
5.3 Reverb. . 5-7
5.4 Phase Shifter 5-10
5.5 Fuzz. . . 5-11
5.6 Tremolo. . 5-11
5.7 Acoustic Pickup Preamp 5-12
6.0 Appendices
A 1 Power Supply Design 6-'
A2 Decibel Conversion . 6-11
A3 Wye-Delta Transformation 6-11
A4 Standard Building Block Circuits 6-12
A5 Magnetic Phono Cartridge Noise Analysis. 6-13
A6 General Purpose Op Amps Useful for Audio . 6-16
A7 Feedback Resistors and Amplifier Noise 6-17
A8 Reliability 6-18
7.0 Index
*"Floobydust" is a contemporary term derived from the archaic Latin miscellaneus, whose disputed history probably springs
from Greek origins (influenced, of course, by Egyptian linguists) - meaning here "a mixed bag."
Device Index
LM171 3-9 LM390 4-41
LM377 4-8 LM391 4-43
LM378 4-8 LM703 3-9
LM379 4-8 LM1303. 2-24
LM380 4-21 LM1310. 3-23
LM381 2-12 LM1351. 3-13
LM381A 2-15 LM1800· 3-23
LM382 2-20 LM1820· 3-4
LM384 4-28 LM2111· 3-13
LM386 4-30 LM3011. 3-11
LM387 2-19 LM3065· 3-15
LM387A 2-19 LM3075· 3-15
LM388 4-37 LM3089· 3-18
LM389 . 4-33 MM5837· 2-56

1.0 Introduction
In just a few years time, National Semiconductor Corpora it must be done noiselessly - in the sun, and in the snow -
tion has emerged as a leader - indeed, if not the leader in forever.
all areas of integrated circuit products. National's well
Unfortunately, this IC doesn't exist; we're working on it,
known linear and digital ICs have become industry standards
but it's not ready for immediate release. Meanwhile, the
in all areas of design. This handbook exists to acquaint
problem remains of how to choose from what is available.
those involved in audio systems design with National
For the most part, DC parameters such as offset voltages
Semiconductor's broad selection of integrated circuits
and currents, input bias currents and drift rates may be
specifically designed to meet the stringent requirements
ignored. Capacitively coupling for bandwidth control and
of accurate audio reproduction. Far from just a collection
single supply operation negates the need for concern about
of data sheets, this manual contains detailed discussions,
DC characteristics. Among the various specifications ap
including complete design particulars, covering many areas
plicable to AC operation, perhaps slew rate is the most
of audio. Thorough explanations, complete with real-world
important.
design examples, make clear several audio areas never before
available to the general public. 1.2.1 Slew Rate
1.1 SCOPE OF HANDBOOK The slew rate limit is the maximum rate of change of the
amplifier's output voltage and is due to the fact that the
Between the hobbyist and the engineer, the amateur and
compensation capacitor inside the amplifier only has finite
the professional, the casual experimenter and the serious
currentsl available for charging and discharging (see Section
product designer there exists a chaotic space filled with
4.1.2). A sinusoidal output signal will cease being small
Laplace transforms, Fourier analysis, complex calculus,
signal when its maximum rate of change equals the slew
Maxwell's equations, solid-state physics, wave mechanics,
rate limit Sr of the amplifier. The maximum rate of
holes, electrons, about four miles of effete mysticism, and,
change for a sine wave occurs at the zero crossing and may
maybe, one inch of compassion. This audio handbook
be derived as follows:
attempts to disperse some of the mist. Its contents cover
many of the multidimensional fields of audio, with emphasis vo = V p sin 211 ft (1.2.1 )
placed on intuition rather than rigor, favoring the practical
over the theoretical. Each area is treated at the minimum dvo
depth felt necessary for adequate comprehension. Mathe - = 211fVpcos211ft (1.2.2)
dt
matics is not avoided - only reserved for just those areas
demanding it. Some areas are more_ "cookbook" than I
others, the choice being dictated by the material and d-vo = 211fVp (1.2.3)
Mother Nature. dt t=O
General concepts receive the same thorough treatment as do Sr = 211 fmax Vp (1.2.4)
specific devices, based upon the belief that the more
informed integrated circuit user has fewer problems using where: Vo = output voltage
integrated circuits. Scanning the Table of Contents will
indicate the diversity and relevance of what is inside. V p = peak output voltage
Within the broad scope of audio, only a few areas could be
dvo
covered in a book this size; those omitted tend to be ones Sr = maximum-
not requiring active devices for implementation (e.g., loud dt
speakers, microphones, transformers, styli, etc.).
The maximum sine wave frequency an amplifier with a given
Have fun. slew rate will sustain without causing the output to take on
a triangular shape is therefore a function of the peak
1.2 Ie PARAMETERS APPLIED TO AUDIO
ampl itude of the output and is expressed as:
Audio circuits place unique requirements upon IC para
meters which, if understood, make proper selection of a Sr
fmax = -- (1.2.5)
specific device easier. Most linear integrated circuits fall 211 Vp
into the "operational amplifier" category where design
emphasis has traditionally been placed upon perfecting Equation (1.2.5) demonstrates that the borderline between
those parameters most applicable to DC performance. But small signal response and slew rate limited response is not
what about AC performance? Specifically, what about audio just a function of the peak output signal but that by trading
performance? off either frequency or peak amplitude one can continue to
Audio is really a rather specialized area, and its requirements have a distortion free output. Figure (1.2.1) shows a quick
upon an integrated circuit may be stated quite concisely: reference graphical presentation of Equation (1.2.5) with
The Ie must process complex AC signals comprised of the area above any VPEAK line representing an undistorted
frequencies ranging from 20 hertz to 20k hertz, whose small signal response and the area below a given VPEAK
amplitudes vary from a few hundred microvolts to several line representing a distorted sine wave response due to slew
volts, with a transient nature characterized by steep, rate limiting.
compound wavefronts separated by unknown periods of As a matter of convenience, amplifier manufacturers often
absolute silence. This must be done without adding distor give a "full-power bandwidth" or "large signal response" on
tion of any sort, either harmonic, amplitude, or phase; and their specification sheets.
1 -1