Audio Amp

110 Pages·2015·11.93 MB·English

TESTIÑG AND ALIGNING FLOPPY DRIVES
APRIL 1997
-Power
A Nigh
Audio Amp_
For Your Car
Build this high -quality digital amp and
get up to 200 watts of music power
Build a
Fuel Gauge 41J` 0
For your Batteries
Avoid unpleasant surprises
with this versatile circuit that
keeps an accurate eye on the
state of your batteries
High -Tech
Battlefield
Medicine li
Technologies used to
n
keep soldiers alive in
the field could soon find
their way to the home front
Microphone
A
Primer 04 >
Learn which microphone / PU6LIGATIOAGERNSBRAC¡pKq.-
to use, and how to use it $3.99 U.S.
$4.50 CAN. Ar226'2 7 4878 3
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CircuitM
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Electronics
,.
Vol. 68 No. 4
CONTENTS
A P R L 9 9 7
1
I
ON THE COVER TECHNOLOGY
45 TESTING AND ALIGNING
FLOPPY DRIVES
BUILD A 200-WATT DIGITAL AMPLIFIER
FOR YOUR CAR
Nothing beats a high -power amplifier for adding zip
and excitement to your mobile audio experience.
The problem is that
once you get to serious
wattage levels, the size
and heat issues asso- lectro\n ics Modern software makes it
easier than ever to pinpoint
ciated with standard
NOW drive problems, and this article
amplifier designs be- A High -Power shows- yo u what to do about
come difficult to over- Audio Arnp
them. Stephen J. Bigelow
come. Not so with For Your Car
class D switching WgeWt o pt h1is0 1h0lg0h 'weau&ttsa y 0lU mMuWsic ;Iurmre NrW
amps like the one de- NFeude la Gauge HIGH -TECH BATTLEFIELD
scribed in this month's FMwioothlrd yI nuonn up%rle waBeseaanntitte emO rceicenusslt e tsha t MEDICINE
cover story. That amp lsetaa le of your hatierres the
IV. tech
can deliver up to 200 Battlefield
Medicine
watts into a 4 -ohm Technologies used to
kwIsoldiers alive Infi nd
load, or 100 watts into Owls way`lefthe home
A Microphone
8 ohms, yet is relative- Primer
ly compact and effi- teaumse..d aIende hmowrc rnns, eeel e
cient. Even better, it
-de livers great sound with low distortion.
New technologies designed to
Alan Bayko
save soldiers' lives on the
-
battlefield will soon make their
way home. Bill Siuru
As a service to readers, ELECTRONICS NOW publishes available plans or information relating to newsworthy products, techniques and scientific and technological
developments. Because of possible variances in the quality and condition of materials and workmanship used by readers, ELECTRONICS NOW disclaims any
responsibility for the safe and proper functioning of reader -built projects based upon or from plans or information published in this magazine.
Since some of the equipment and circuitry in ELECTRONICS NOW may relate to or be covered by U.S. patents, ELECTRONICS NOW disclaims any liability for
the infringement of such patents by the making, using, or selling of any such equipment or circuitry, and suggests that anyone interested in such projects consult a
patent attorney.
ELECTRONICS NOW, (ISSN 1067 -9294) April 1997. Published monthly by Gernsback Publications, Ina, 500 Bi- County Boulevard, Farmingdale, NY 11735 -3931.
Periodicals Postage paid at Farmingdale, NY and additional mailing offices. Canada Post IPM Agreement No. 334103, authorized at Mississauga, Canada. One -
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1
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A P R L 1 9 9
I
B U L D T H S
I I
Electronics
NOW
58 "FUEL GAUGE" FOR YOUR
BATTERIES
Know at a glance just how Hugo Gernsback (1884 -1967) founder
much juice your batteries
LARRY STECKLER, EHF, CET,
have left with this Editor -in -chief and publisher
-ea sy -to -build project.
EDITORIAL DEPARTMENT
John Pivnichny
CARL LARON, editor
JOSEPH J. SUDA, technical editor
JULIAN S. MARTIN, associate editor
il TERI SCADUTO, assistant editor
í.. MICHAEL A. COVINGTON, N4TMI
1-4i:Tr, contributing editor
JEFFREY K. HOLTZMAN,
computer editor
LARRY KLEIN, audio editor
FRANKLIN J. MILLER,
audio editor
16 EQUIPMENT REPORT DON LANCASTER,
Olympus SYS.230 Magneto - contributing editor
Optical Drive. EVELYN ROSE, editorial assistant
ART DEPARTMENT
ANDRE DUZANT, art director
RUSSELL C. TRUELSON, illustrator
24 SERVICING PRODUCTION DEPARTMENT
New oscilloscopes blend the Rust M. YEE, production director
-be st of digital and analog. KATHRYN R. CAMPBELL,
production assistant
Bob Oblack
KEN COREN,
desktop production director
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28 COMPUTER CONNECTIONS CIRCULATION DEPARTMENT
How not to -be a JACQUELINE P. CHEESEBORO,
circulation director
bad coder. Jeff Holtzman THERESA LOMBARDO,
circulation assistant
REPRINT DEPARTMENT
80 AUDIO UPDATE MICHELE TORRILLO,
-A microphone primer. reprint bookstore
Franklin J. Miller Typography by Mates Graphics
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A REVIEW OF THE LATEST HAPPENINGS IN ELECTRONICS
are so essential in navigating the Inter- warpage. Boards that warp after expen-
On -Line Research Tools net. Institute of Physics Publishing and sive components have been added can
The Institute of Physics (TOP) and the INSPEC are certainly a perfect fit in this mean thousands of dollars in losses. An
Institution of Electrical Engineers (TEE) respect." experimental technique known as Ther-
have announced that, beginning this moire, developed at the Georgia In-
spring, users of IOP's Electronic Journals stitute of Technology and licensed by
on the World Wide Web will be able to Electronic Packaging Services (EPS)
select any journal reference and receive Electronic Delivery Ltd. Company, provides real -time data
the INSPEC abstract instantly, at no about PCB warpage. Research sponsors,
extra cost. Of Chinese Research who were brought together through
INSPEC is the information services Georgia Tech's Manufacturing Research
division of IEE, the largest professional Documents Center (MARC), include Motorola,
engineering society in Europe. The not - Aided by the University of Pittsburgh MICOM, Ford Electronics, IBM, DEC,
for- profit organization, with worldwide Library System, the Peking Univer- and AT &T
membership of more than 130,000, pub- sity Library became the first Chinese Thermoire developer Dr. Charles
lishes over 20 primary journals, as well academic library in the People's repub- Urne, an associate professor in the
as the INSPEC bibliographic database. lic to be able to electronically deliver re- School of Mechanical Engineering, ex-
The London -based Institute of Physics, search materials to libraries in the west. plains, "Electronic packaging companies
a professional society with more than This marks one of the first such services can use the warpage information to make
20,000 members worldwide, is a leader between a North American library and a changes in their PCB design early. That
in the electronic publishing of scien- library in China. way, there's no mass production of a
tific research journals. IOP's publishing The Pitt University Library System product that has a problem."
branch produces research journals and and Peking University Library success- Temperatures of up to 230° Celsius
graduate -level texts, as well as popular fully completed a test in which full -text are an integral part of PCB processing.
science books, magazines, and reference documents were transmitted on the The relatively minor heat generated by
titles. Internet using Ariel software. Document computers and other devices that contain
The IOP/ IEE project uses IOP delivery through cyberspace provides printed-c ircuit boards can also cause
Publishing's HyperCite service and scholars at each university with access to warpage. Small, thin, densely populated
INSPEC's database of scientific and the vast information resources of the boards are particularly susceptible to the
technical journal abstracts, which date other. problem. According to EPS manager
back to 1969. It will explore the efficien- Pitt University Library System direc- Dirk Zwemer, "It's not uncommon to see
cies of combining primary and secondary tor Rush Miller, who initiated the inter- losses of one to three percent in a mature
information services in a hypertext envi- national project while visiting Beijing product, and it can be much higher for
ronment, and is expected to become the last August, said, "the successful estab- some designs."
platform for a more extensive scheme in lishment of an Internet linkage between A special oven with a glass grating top
which HyperCite service will link IOP the [two] libraries ... is a milestone in the is used for the new process. A white light
Publishing references to all 32 of its long history of cooperation between the shines through the glass grating onto
full -text electronic journals. The sec- academic institutions of both countries. the PCB, and an inexpensive, compact,
ond phase of the project, planned for this Now that we have demonstrated for the charge -coupled device (CCD) camera
summer, will extend the concept to other first time that this technology can be uti- captures warpage digitally as it occurs.
important physics publishers. lized for resource sharing with libraries Equally spaced parallel lines are
"This is an ambitious project which in China, we plan to extend our partner- etched on the flat glass grating. When the
should have substantial tangible benefits ship to other major libraries in China." beam of light is directed at a specific
for researchers in physics," said Anne angle, the etched lines create a shadow on
Dixon, electronic publisher at Institute of the surface of the board. If warpage
Physics Publishing. Jim Ashling, director occurs, a moire pattern is produced by
of sales and marketing at INSPEC, Battling Heat -Induced the geometric interference between the
added, "We believe that integration of etched lines on the glass and the shadow
electronic journals with quality secondary PC -Board Warpage of those lines on the PCB's surface. The
information services is just what is need- During manufacturing, printed -cir- more the board warps, the greater the
ed to create the value- added features that cuit boards are vulnerable to heat -induced continued on page 30
6
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II
I
READERS' QUESTIONS, EDITORS' ANSWERS
it does so, the rms AC current through average voltage or current and then mul-
AC Current Mystery
the bulb will be the same as the DC cur- tiply it by 1.1 on the assumption that it's
QRecently, I was measuring the currents in rent would have been. a sinewave. A few meters are "peak
a simple rectifier circuit and found an responding, rms reading." Both kinds
anomaly. The circuit was a bridge rectifier 1P.E4A14K V 1.000 V read correctly only with sine waves.
with resistive load. I measured the AC cur- PEAK The moral? The rms current into a
rent before the rectifier and got 195 mA; the rectifier can be considerably higher than
DC current through the load was only 175 the DC current out, and the peak current
mA. I asked several technicians and then a going in can be even greater. Remember
Ph.D. in electrical engineering, who told me SI1N VE RWMASV E SQU1 AVR REM WSA VE that whenever you choose a power trans-
the discrepancy was due to the fact that the former; the current rating of the trans-
mibreateterd r eisnp ornmdss. toI sa vtheraatg ceo crruercrte ?n -tD bu.t Ji.s cBal.-, FpeIGak. 2a -nTd HrmEs RvoEltLaAgTeI OoNr ScHurIrPe ntb egtwreeaetlny fhoigrmheerr tsheacno nthdea rDy Cg ecnuerrraellnyt ntoee bdes dtoe livb-e
Uvongo, South Africa depends on the shape of the waveform. ered to the load.
A Figure 1 shows a circuit we bread- Because wattage depends on the VOL-TA-G-E ---
boarded that demonstrates the same square of voltage of current (P = E2/R = Capacitor voltage
effect, but the discrepancy is even bigger I2R), the rms value is obtained by squar-
(216 vs. 145 mA in our case). We used a ing the voltage, averaging the square,
true -rms multimeter. and then taking the square root. The
abbreviation rms stands for root of the
mean of the square. The average (mean)
of the voltage itself is somewhat lower.
The relation between rms, average, CURRENT
and peak voltage depends on the wave-
800 mA peak
form (see Fig. 2). With a squarewave, all
three are the same. With a sinewave,
which isn't at maximum voltage all the
time, the peak, rms, and average values
FIG. 1 -WHEN USING A TRUE rms mea- are in the ratio 1.414:1.0:0.9. If the wave-
suring meter, the AC current is considerably form consists of narrow spikes, the dis-
higher than the DC current in this circuit. crepancy is even bigger. Current works FIG. 3-AC VOLTAGE IS A SINEWAVE, but
exactly the same way as voltage. current only flows at the peaks where the
Why is the AC current larger? A quick Now back to the bridge rectifier. AC voltage exceeds the voltage already on
answer is that there's AC but not DC cur- Although the AC voltage at the input is a the capacitor.
rent in the filter capacitor. Thus, not all sinewave, the AC current waveform is
the AC current goes through the resistive not. We sampled it by inserting a 1 -ohm Finally, note that no energy is lost,
DC load. resistor and connecting an oscilloscope because the DC voltage out is higher
But that's almost too quick an answer; across it, and what we found is shown in than the AC rms voltage in. Except for
the question deserves a little more Fig. 3. Current flows only briefly at the diode drop and resistive losses, you get
thought. First let's review what we mean peaks, when the AC voltage is higher back in volts everything that you lose in
by rms. Because an AC voltage or current than the voltage on the filter capacitor. At amps.
is constantly changing, the only way to those times, the current flow is heavy
assign it a constant value is to use some (about 800 mA) because the capacitor has
kind of average. to make up all the charge it has lost since
The rms value is a special kind of aver- the last peak. Tube Substitution
age with the following property: the Because of the strange waveform, only QI need advice about replacing a 7199 tube
power (wattage) computed with rms AC a true -rms meter will give you the correct with a 6EA8 to revive my Williamson
is the same as with DC. For example, 6- rms value. Some multimeters are "aver- all- tube amplifier built many years ago.
volts rms AC will light a light bulb to the age responding, rms reading," which According to the RCA Receiving Tube
same brightness as 6 -volts DC, and when means that they actually measure the Manual, the 6EA8 is about the same as the
8
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