Class -A Amplifier

108 Pages·2016·10.46 MB·English

THE AUTHORITATIVE MAGAZINE ABOUT HIGH FIDELIT a FEBRUARY 1977 ä1.00
CONSTRUCTION ARTICLES
Class -A Amplifier
Wide Bandwidth Preamp
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ymer driver. A 2-1/2
be shaped neo3rene-impreg-
the HPM 200 nated cloth
,
weeter dome unit that,
frequency unlike most
ill 360º speakers, is
woofer, HPM- peripherally ... .... ..V ,".
two. One driven for low
ed for deep distortion. Also
he other unlike most
.f
ed for upper speakers, this p
7f^
s
)gether, they midrange unit is e
fe
ie frequencies accurate to within 3 dB, even at
to 700 Herz, 60° off axis. r#
i
nimum And, keep all five
7.o
mit and HPM-200 drivers in balance We believe the IPM -200
..im and working together, we've represents a new standard of
g. engineered a massive accuracy in loudspeakers. Its
ey crossover network that keeps dynamic range, transparency and
)k like all sound waves in phase overall lifelike impact are without
:ional over the entire listening area. precedent.
not But no design Ask your Pioneer dealer to
onal dissertation can fully describe play the super amplifier of your
High Polymer Molecular what the H[- M-200 actually choice through speakers similar
film produces sound
pecial directly seuf aocre. sounds like. to the ones you're now using.
rive voice coielossn ontrho magnets. Irving Kolodin wrote Then ask him to play it through
igidity for Saturday Review, after HPM-200s.
.zey hearing Berlioz' "Symphonie We assure you, you'll hear
transients, Fantastique" over a pair of things you've never heard before.
p. Even when HPM-200s "... such towering PMß00
H rM
.s amounts of presence that one could diagram
the disposition of the Chicago ClaPlONEEi
) also has a Symphony just from the repro-
midrange duced sound'.' U.S. Pioneer Electronics Corp.,
75 Oxford Drive, Moonachie, New Jersey 07074.
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IN THE LAST 24 MONTHS
COMPANIES
11
HAVE INTRODUCED
"SUPER AMPLIFIERS"
THAT YOU CAN'T FULLY
APPRECIATE UNTIL YOU
HEAR THEM THROUGH
THESE SPEAKERS.
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HPM-200. T
INTRODUCING
DESIGNED TO DELIVER ALL
HIGH -POWER AMPLIFIERS
Most speaker:: available today tran.i Tents, every last bit of Sin:e High Po
were designe i at a time when listening enjoyment your super r Iclecul=r film can
3
most of the powerful amplifiers amplifier is capable of giving you. into a 0° cylind r
you could buy prcducec .ender It's called HPvr2C0. "HPM" tweeter and supert
100 watts a channel. stands for"High Polymer produce equal high
Which means if you have Molecular" film, a material that dis-Dersicxn over a fi
invested in ore of the new super makes it possible to transform Instead of one
amplifiers, your speakers could electrical energy into 200 ha:
well be keeping you from acoustical energy with optimiz
appreciating the full extent of complete accuracy. bass. T
your investment. The HPM-200 optimiz
So Pioneer has developed a tweeter and bass. Ti.
speaker system that can bring supertweeter are made cover tl.
you all the peak levels, all the of this unique material, from 2E'
which with mi
produces distortic
sound directly maxim,
at the film dampir.
surface. The revolutionary High Th
Polymer Molecular film
There are no tweeter and supertweeter. may loo
They don't look, or work like
magnets. And conventional speakers. convene
no voice coils. So there drivers. But they're
are no mechanical made like conventi
moving parts to get drivers. The cone
between the sound your materials include s
amplifier puts out and carbon fibers that
the sound you hear. them exceptional r
And High Polymer and low mass. So
t1
Molecular film can can fully reproducf
handle an almost without breaking u
limitless range of driven by enormot
power. Without power.
distortion. Without any The HPM-20(
loss in linear response. specially -designed
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®U. S. PIONEER ELECTRONICS CORP .1976.
Check No. 29 on Reader Service Card
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February 1977 "Successor to RAW Est. 1917" Vol. 61, No. 2
Patented Feature 28 Construct A Class -A Amplifier/Nelson Pass
Articles 38 Construct A Wide -Band Preamp/W. Marshall Leach
48 Low TIM Amp-Part II/W. Marshall Leach
58 New Tests for Preamps/Tomlinson Holman
65 Cheap & Easy Inverse RIAA/Square Wave
Direction
Generator/ Dennis Bohn
Equipment 66 McIntosh MR -78 Tuner/Leonard Feldman
Profiles 70 Dual 1249 Automatic Turntable/George W. Tillett
Record 74 The Column/Michael Tearson & Jon Tiven
Reviews 80 Classical/Edward Tatnall Canby
FACT 82 Jazz & Blues
87 Folk Bag/Tom Bingham
Only 1h3 Zisr-washer 91 Theater Music/Donald M. Spoto
System -tas a micrD-
fiber "s:an_"-a
patented "direction"- Audio 4 Audioclinic/Joseph Giovanelli
to the absorbent pad. In General 68 TAaupdeio G EuTidCe/E/Hdewramrda nT aBtnuarsll teCina nby
16 Behind The Scenes/Bert Whyte
24 Dear Editor/letters
REQUIREMENT 94 Classified Advertising
98 Advertising Index
The Discwa slier brush
must be used -n a
Editor Eugene Pitts III AUDIO (title registered U.S. Pat. Off.) is published
direction_ :r-dicated bÿ Associate Editors monthly by North American Publishing Co., Irvin J.
the arrow zn the Edward Tatnall Canby BBourtloewr,s kVyic, eP rPerseisdiednetn;t sF; raRn.k K Nenenmeethy erB, aaxntedr , JaVyi ceL.
handle. Bert Whyte President/Production; Vic Brody, Promotion Direc-
Assistant Editor Eugene J. Garvin Jr. tor; Mary Claffey, Circulation Director.
NET RESULT MDeasrikgent inFgra nDki rMecotoorre S anford L. Cahn RffooArr T$$1E140S..00-0U0;; n 32i t yeyedea arSsrs ta ffotoersr $$2o10n8.l0.y00:0 ; ;1 oayunetdsa ird 3 efoy etrh a$er8s . U0f0o.S;r . :2 $ 12 y6ey.ea0ra0s.r
Circulation Manager Jean Davis Printed in U.S.A. at Columbus, Ohio. All rights
The Discwasrer system. Advertising Production Gloria Klaiman rAemseerrviecad.n EPnutibreli schoinngte Cntos. cSoepcyornigdh cteladss 19p7o7s tabgy eN opratihd
picks ap rather than at Philadelphia, Pa. and additional mailing office.
Senior Editors Back issues, $2.00 each. World Library Congress
lines up dirt and Othe: Richard C. Heyser Number: ISSN 0004-752X. Dewey Decimal Number:
:ontamir-ant3 Bascom H. King 6R2E1.G38IO1 NoAr L7 7S8A.L5E. S OFFICES: Jay L. Butler, Publisher
suspended in just a B.V. Pisha asonnd ASvaen.f,o Nrde wL. YCoarhkn, , NM.Ya. rk1e00ti2n2g, tDelierepchtoonr,e 5(4251 2M) a3d71i--
-ew drops of D3 fluid Contributing Editors: 4J1ay0 0M. artin, 2525 West 8th St., Los Angeles, California
Tom Bingham, Herman Burstein, 90057, telephone [phone].
Leonard Feldman, Joseph Giovanelli, REPRESENTATIVES: Europe, V. B. Sanders, Interna-
C.G. McProud, Dan Morgenstern, tional Publishers Advertising Service, Raadhuisstraat
24, P.O. Box 25, Graft-de-Ryp, Holland; telephone,
Howard A. Roberson, Donald M. Spoto, 02997-1303; telegrams, Euradteam-Amsterdam.
Michael Tearson, George W. Tillet,
Jon Tiven.
Directed Research Publisher Jay L. Butler
only from:
About the cover: Two big construction
projects this month, a 10 -watt class -a AUDIO Editorial and Publishing Offices,
discwasher, inc. aprmepalmifipe.r Tahned par owtoitdyep ebsa, nsdhwowidnth on the 4P0o1s tNmoa.s tBerr:o aSde nSdt .,F oPrhmile a3d5e7lp9 h tioa , thPea. a1b9o10v8e address.
cover, were built by the authors and
COLUMBIA, MO 65201 "sound great," says the editor. Kr6
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Two sources
of perfection
in
stereo sound.
Match one to your equipment
"The right Pickering Cartridge for your equip- Pickering's new XSV/3000 is a remarkable de-
ment is the best Cartridge money can buy." STEREO velopment. It possesses our trademarked Stereo-
We've been saying that for years; and tens of thou- hedron Stylus Tip, designed to assure the least
sands of consumers have profited by applying this LAB TESTS record wear and the longest stylus life achievable
principle in assembling their playback systems. in these times with a stereo cartridge. Its frequency
If you have a fine manual turntable, the XSV/3000 response is extraordinarily smooth and flat; its
is a perfect choice. n channel separation is exceptional; its transient re-
If you have a high quality automatic turntable, sponse affords superb definition. It represents a
then installing an XV -15/625E in its tone arm is a whole new concept of excellence in stereo
perfect choice. cartridges.
The summary advice of Stereo's Lab Test, in an Read the whole evaluation report. Send for your
unusual dual product review, we think brilliantly free copy of the Stereo "Lab Test" reprint; write to
states our position: "The XV -15/625E offers per- Pickering & Co., Inc.,
formance per dollar; the XSV/3000, the higher ab- FREE! 101 Sunnyside Blvd., PICKERING
solute performance level." That makes both of these Plainview, N.Y. 11803.
i
cartridges best buys! Department "for those who can hear the difference"
A
Check No. 28 on Reader Service Card PICKERING & CO., INC., COPYRIGHT 1977
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Empire's
Audioclinic
Blueprint For
Better Listening
No matter what system
Joseph Giovanelli
you own, a new Empire
phono cartridge is certain
to improve its performance.
Patch Panel by having one ground brought from
The advantages of
Q. My stereo system sits inside a the offending equipment to the pan-
Empire are threefold. cabinet for protection against dust el. Be sure to label each jack on the
One, your records will and other disturbances. However, panel with a label suitable for quick
last longer. Unlike other when making connection changes in identification. Any logical system will
magnetic cartridges, the rear of the components, it is diffi- suffice.
Empire's moving iron cult to remove the units and hold
them while making those con- Wake Up to Records
design allows our diamond
stylus to float free of its nections. I once read about a control Q. Is there harm in leaving either a
magnets and coils.This board or control panel, that can be belt -driven or a direct -drive turntable
easily constructed, enabling one to in the play position, with stylus on the
imposes much less weight make the various connections and record but no power applied, for sev-
on the record surface and hook-ups quickly. I cannot find the eral hours at a time? This is an attempt
insures longer record life. article, but, perhaps, you can shed to wake up to the sound of a record
Two, you get better some light on this subject.-John R. rather than FM. realize that this prac-
1
separation.The small, Garne, West Franklin, N.H. tice would flatten idler pucks on mod-
hollow iron armature we A. You can make up a "patch pan- els with such a drive system, but I
el" which will enable you to make all haven't encountered any warnings
use allows for a tighter fit the necessary connections to your with the other drive types.-Gary
in its positioning among equipment without having to remove Sunada, Honolulu, Hawaii.
the poles. So, even the it from the cabinet. There are com- A. see no problem in terms of
I
most minute movement is mercial devices which do at least damaging either your turntable or
accurately reproduced to some of this, and if your needs aren't stylus by using the setup you just de-
give you the space and too complex, they might solve your scribed. The only reservation I have in
depth of the original problems with a minimum of effort. mind is in terms of the dust which will
recording. The unit is a metal panel mounted collect on the surface of the record,
to the front of an equipment cabinet. so be sure to close the dust cover of
Three, Empire uses It contains rows of quarter -inch your turntable once the stylus has
4 poles, 4 coils, and 3 phono jacks, which are more durable been placed on the record and the
magnets (more than any than the little phono jacks used on the timer set. The discs should also be
other cartridge) for better rear of some high fidelity equipment. cleaned before they are put away
balance and hum rejection. Their use permits you to connect and which may be inconvenient when you
The end result is great disconnect equipment without worry- are preparing to go to work.
ing about the connectors becoming
listening. Audition one for
intermittent and loose. Back Cueing Wear
yourself or write for our
The exact number of jacks will de- Q. For precise cueing on record
free brochure,"How To pend on your present and future cuts when I am taping them, I have
Get The Most Out Of Your needs, and each input and output is been backtracking my phono cart-
Records:' After you com- connected to its own jack. Inter- ridge by rotating the turntable back-
pare our performance connections between the pieces of wards. Can this cause damage to the
specifications we think equipment are made through cables stylus?-Larry M. Bauer, Dayton, O.
you'll agree that, for the with phono plugs at each end. These A. I do not believe that back cueing
money, you can't do cables should be made of shielded your turntable will cause any damage
wire with the shield wired to the to the stylus, but it may cause ex-
better than ground, and the "hot" or center con- cessive record wear if any cut is cued
Empire. ductor wired to the "tip" side of the very often in this way.
plug. The shields from the various ca- Turntables of the belt -driven or di-
bles are connected at the end which rect -drive variety can be back cued
faces the input only, which means that very nicely. However, turntables
the shield is used as a means to pre- which employ an intermediate idler
vent hum from stray fields, rather than assembly will be difficult to cue when
as a means of signal return. the idler is engaged. Furthermore, this
Because all the jacks are mounted could ultimately damage these idler
on a common metal panel, it is some- pucks.
EIVPIFE times possible to have ground loops
which could give rise to hum, al- If you have a problem or question on audio, write to Mr.
Already your system sounds better. though this usually doesn't happen. Joseph Giovanelli, at AUDIO, 401 North Broad Street,
Philadelphia, Pa. 19108. All letters are answered. Please
Empire Scientific Corp. However, if it does, it is often cured enclose a stamped, self-addressed envelope.
Garden City, New York 11530
AUDIO February 1977
Check No. 12 on Reader Service Card
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Power Plus.
The Scott 8336 Receiver.
Power is important.
But power alone is not
enough. That's why the popular
Scott R336 gives you all the power
you need. Plus the performance features
you expect.
The Scott R336 provides 42 watts minimum contin-
uous RMS power output per channel. More than enough
for most listeners. And both channels are driven into 8 ohms
from 20 Hz to 20 kHz with no more than 0.3% total harmonic distortion.
Power? Sure. But check these important performance features many other
receivers in this medium price range have sacrificed.
IM distortion (lower than 0.15%). Far below the Three position FM de -emphasis switch. Permits
average. Provides cleaner sound and eliminates proper reception of domestic, Dolbyized or MSS
N-s--
listening fatigue. European broadcasts.
Signal strength and center channel tuning Two completely independent tape monitors.
meters. Provide simultaneous visual indication Allow two tape recorders to be used simul-
of correct tuning and o timum signal strength. taneously for direct tape -to-tape copying with-
Phase locked loop multiplex section. Maintains out passing through the receiver's electronics.
superior stereo separation. Remains in align- FM Muting. Silences interstation hiss while the
ment for the life of the receiver. tuner scans the frequency spectrum. Clutched bass and treble controls with detents.
FET RF stage. Assures higher sensitivity and Pretuned LC notch filters in the multiplex.
overload immunity. Reduce interference to a minimum.
Log -linear taper volume control with detents. Signal strength meter circuit. Employs two point
Spreads out volume levels. Provides finer control sampling for wider dynamic range.
at low -to-moderate levels. Over 120 db IF gain. Assures better limiting
Clutched bass and treble controls with detents. and better AM rejection.
Allow altering the frequency response of one Instantaneous electronic protection circuit in
channel without affecting the other. Systems the output stage. Employs voltage/current sens-
can be "custom balanced" to compensate for ing to prevent output transistor failure and Signal strength and center channel tuning meters.
room acoustics, decor or speaker placement. speaker damage.
Separate high -frequency noise filter. Permits AM section designed around a tuned RF ampli-
cleaning up of noisy tapes, discs or broadcasts. fier using J-FET.Inproves signal-to-noise ratio.
And the Scott R336 is backed by a three-year, parts and labor limited warranty.
Another very important plus.
For specifications on our complete line of audio components, write or call
H.H. Scott, Inc. Corporate Headquarters: 20 Commerce Way, Woburn, MA 01801, Two completely independent tape monitors.
[phone]. In Canada: Paco Electronics, Ltd., 45 Stinson Street, Montreal,
H4N2E1, Canada. In Europe: Syma International S.A., 419 avenue Louise,
Brussels, Belgium. SCOTT
s
The Name to listen to.
Receivers / Tuners / Amplifiers / Turntables / Speakers
Check No. 35 on Reader Service Card
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?NE
Taoe
ide
PROBLEM
Herman Burstein
SOLVER
MOM Cartridge-Cassette Quandry With good transmitting and receiving
Q. I am considering the purchase of equipment, FM noise and distortion
a tape player for my car as well as a can be kept lower than on discs. On
tape deck for home use. Many of the FM a dynamic range of 60 dB is pos-
dealers I have spoken to have recom- sible, whereas the typical range on a
mended cassettes, while others have disc is usually more nearly around 45
recommended cartridges. don't or 50 dB, also distortion can be kept
1
know what direction to take... cas- under 1 per cent on FM, but not very
sette or cartridge, and I don't want to easily on a disc. With respect to fre-
THE BGW 2506 sacrifice fidelity for convenience. In quency response, very few of us can
DOESN'T HAVE- the past I have been exposed to in- discern between flat response to 15
expensive cassette players and have kHz and to a higher frequency. Most
KFnuosbess been unimpressed with their per- adults hear little if anything above 13
formance.-Thomas Mantini, Haver- kHz or so, while many have difficulty
Meters
Current limiting town, Pa. distinguishing between an audio sys-
Hum A. If fidelity is uppermost in your tem flat to 10 kHz and one flat to a
Noise mind, then I suggest cassette, as things higher frequency.
Thumps now appear, since the performance
High price of the better cassette machines out- Selection Specs
6 BUT, IT DOES HAVE- distances that of most all cartridge Q. I am undecided between which
machines and rivals that of many good of two tape decks to buy. Both are
E(3n4o0u -gwha tmts*u)s cle to drive 2 -ohm loads open -reel tape decks. To get a good priced at $200.00, but one has 0.1 per
Absolute speaker protection home cassette machine, you will cent wow and flutter while the other
(exclusive BGW SCR crowbar) probably have to pay upwards of has 0.09.-L.D. Crow, Jackson, Miss.
Virtually unmeasurable distortion* $200.00, and perhaps double that, par- A. A difference this small in wow
Modular construction ticularly if the machine incorporates and flutter is trivial and not a basis for
12 rugged 150- watt output transistors the Dolby B noise reduction in order choosing one machine over another.
HTHToreiugtaaehvl l yoysp p%e -eantiepmc dltop hm sifcerakodg n rnhate ecetakinc td p s caiinnrkcesul it breaker tnoo isaec hraietivoe. a really good signal-to- Mfrraeotiqoreu, eainmncdpy od risrteatosnprtt oiaonrnese. t,h es digifnfearl-etnoc-neosi sien
660 -square inches of efficient heat Tension Choice
radiating surfaces Q. In shopping for a tape deck, Bulk Eraser Effectiveness
Rugged steel chassis
Mono -stereo switch which pressure mechanism is best, Q. I would like to know if a bulk
*Guaranteed specifications: pressure pads or tape tension?-Gary tape demagnetizer is capable of eras-
Stereo mode: 90-watts/channel into Thoburn, Lexington, Mass. ing tape to below erase head levels.
8 -ohms, 20 -Hz -20 -kHz with less than A. For the best combination of min- Are there any disadvantages to using a
.1% total harmonic distortion (THD). imum head wear, minimum flutter, bulk demagnetizer?-Joel Jevotovsky,
100-watts/channel into 4- ohms, 5 -Hz - and good treble response-tape ten- Brooklyn, N.Y.
15 -kHz with less than .15% THD. sion rather than pressure pads is gen- A. Ordinarily a bulk eraser does a
Mono mode: 180 -watts into 16 -ohms, erally the preferred means of obtain- superior job when compared to an er-
20 -Hz -20 -kHz with less than .1% THD. ing good contact between the tape ase head. However, there are some
w20it0h -wleaststs t hinatno .81 5-o%h mTHs,D 5. -Hz -15 -kHz and the heads. tapes which if recorded at a high level
may require extra runs past the erase
The perfect mate is our new model 202
stereo preamplifier featuring the in- - Fidelity Quandry head in order to permanently remove
dustry's most accurate phono system Q. Some time ago you stated that all recorded material. I don't know of
82 -dB S/N, .01% THD, active 18 -dB/ FM stereo is capable of higher fidelity any disadvantages to using a bulk era-
OCT. Hi -Lo filters, studio type graphic than discs. However, FM frequency ser, except that it erases the entire
controls. See all 6 BGW power amps response is limited to 15 kHz and discs tape instead of permitting one to se-
and our new preamplifier at your local can easily surpass this. Hence your lectively erase the desired tracks.
dealer.
statement is confusing.-Peter Neu-
BGW Systems haus, Los Angeles, Cal.
PB.eOv. eBrloyx H 3i7lls4 2 A. Requirements for high fidelity If you have a problem or question on tape recording,
include not only frequency response write to Mr. Herman Burstein at AUDIO, 401 North Broad
SYSTEMS CA 90212 Street, Philadelphia, Pa. 19108. All letters are answered.
[phone] but also low noise and low distortion. Please enclose a stamped, self-addressed envelope.
Check No. 7 on Reader Service Card AUDIO February 1977
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