McIntosh C20 - User manual

$ffr:t*itt
rutGtltT0sH r[0DEI t 20
STEREI| C(lilIPEI{SATllRS
Seriol No. 6L70A ond Above
McINTOSH IABORATORy, tNC
2 Chombers St. Binghomton, N. y.
u.s.A.
T'' al
i
t
I
a

TABLE OF CONTENTS
(R.ading Tirne 30 Minutes)
Page
Description . . . . . . . . . . . o . . . . . . . . . . . . . . . . . . . . . . . . . Z
Facilities . . . . . . . . . . . . . . . . . . . . o . . . . . . . . . . . . . . . . . . Z
Mounting Instructions ......................,..... 5
Connecting Procgdure...................r........ 7
A. C. Connection . . . . . . . . . . . . . . . . . . . . . . . o . . . 7
Prograrrr Connections (Input) .... r..... o ?..... 8
Prograrn Connections (Output). . . . . . . . . . r . . . . . 1l
Balancing a Stereo Systern........,.......... o.... IZ
Using the C-20 After Connecting and Balancitg. . . . . . 13
Specifications . . . . . . . o . . . . . . . . . . . . . . . . . . . . . . . . . . . L9
Perforrrtance Curves..... o... o... r........... o... Z0
Guarantee . . . . . . . . . . . . . . . . . . . . . . . . . . . . o . . . o . r o . . 2I
Service Inforrnatiof:).. . .. .. ... ... .. .............. .. ZL
Voltage and Resistance Charts . o.................. ZL-ZZ
SchgrnatiC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . o . . . . . . . . . 23
t--
- l-

,
DESCRIPTION
The Mclntosh Model C-20 is a Stereo Prearnplifier designed for home entertainrnent sys-
tems and professional applications. The Modet C-20 offers extreme fiexibility for either
stereo or monophonic reproduction. The perforrnance and reliability offered bythe C-20 is
obtained through the use of advanced circuit design and top quality cornponents.
Input Se lec tor :
INPUT SELECTOR
PHONO I
SM
2,,41\.s
TUNER / \ PHoNo
(l
TAPE T /r
\ / TAPE l{D
Aux\_/2
Mode Selector:
FACILITIES
Selects any one of eight prograrrl sources. Also para-
llels stereo cartridges for monophonic operation:
Use Phono S position for norrndl stereo
Use Phono M position for normal rrlonophonic
Reve rse: conne cts left channel to right s peake r, right
Ertlrffii" left speaker, corrects for left-right rever-
sal of prograrn.
Ste reo: (norrnal ste reo rnode selector pos ition) left
channel to left s peake r, right channel to right s peake r .
Left: left channel to left speaker; no prograrrl to right
Effit"".
Right: right channel to right speaker; no prograrn to
left s pe ake r .
M Left: left channel only to both speakers .
M Right: right channel only to both speake rs.
Separate bass and treble cofirpensator switches includ-
i.g 'rRIAA", " LP", " TApE - HEA D" , flat pos ition f or
rnicrophone and other positions for rnonophonic re -
cords. (Turning "TREBLE" control to "TAPE" gives
flat response. Turning "BASS" to I I Or I give s f lat re -
sponse. )
Treble: boost l3 db
at 20,000 cycles. at 20,000 cycles, attenuate l8 db
Bass: boost 16dbat Z0 cycles,attenuate ZO db at Z0
cycles.
STEREO L R MLEFT
REv >1 M RrGHr
()
\_-.
Record Cornpensator:
RECORD COMPENSATOR
oou8oss*oo
:"2-\'*,. YAPE
-()
\/
\__-,
Tone Controls:
TREBLE
-lo -r2
-z-

Balance Control:
BALANCE
'-"5''"'
Phase Control:
:'.,orr .
5
Tape Jack Switch:
IN-ON IN-PLAYBAGX IN-TAPE
orr*REcoRpo
t'YI'?trt
o
High Fre que nc y C utoff Filte r :
HF CUTOFF FILTER
9KC
"^5-'
"".:*;:: '
23
,Q4
lll-or. l,rr" " switch:
To balance for unequal program source: Turning con-
trol to left reduce s right channel to No output. Turn-
i.g control to right reduces left channel to No Output.
Reverses phase in left channel to correct for speaker
or program phasi.g.
Three positions:
Flat, fi-Ite r dis conne cted.
9 KC, rolls off response sharply starting at 9 Kc.
5 KC, rolls off re sponse sharply starting at 5 KC.
Compensates for Fletcher-Munson hearing character-
istic as prograrn loudne s s is reduced.
Rejects low f requency noise below 60 cps s trh as
turntable rumble or acoustic feedback.
Controls front panel tape jacks. Portable or second
tape recorder can be plugged in frorn front panel, un-
nece s sary to unplug any othe r tape machine connected
to re ar pane I .
-3-

Tape Compare Switch:
TAPE
COilPARE
Volurne Control:
and 'rfffrr - rronrr Switch:
VOLUME
A
t)
\/
oFF\/
Low Fre quenc y Trim Controls :
(on back panel)
LOW FREOUENCY TRIT
oo
.St o3r,
To permit instantaneous monitoring of tape before and
after recording.
Controls volume for both channels. Switches line pow-
er to four black receptacles on back panel, 600 watts
total capacity.
Cornpensate for unequal response at low frequencies
due to position of speakers or differences in speake r
efficiency. Provides 6 db boost at 50 cycles starting
frorn 500 cycles or 8 db cut at Z0 cycles starting from
200 cycles.
-4-

MOUNTING INSTRUCTIONS
(Serial No. 6L001 and Later)
Your C-20 Stereo Prearnplifier rnay be rnounted in a cabinet of your own, in the Mclntosh
Cabinet Model L-66, ot on a rack panel.
MOUNTING IN YOUR OWN CABINET.
This prearnplifier has been designed to mount on a shelf or from the front panel if the
panel thickness is 3/8" or rnore. It is suggested that the instructions be read through com-
pletely before starting the installation.
Enclosed in the Instruction Manual envelope are two copies of the "WOODEN PANEL
CUTOUT TEMPLATE" and two copies of the "SHELF CUTOUT TEMPLATE'| for mounting
the C-20.
Prepare the cabinet for the mounting by first cutting the wooden panel to receive the pre-
arnplif ie r .
l. On the back of the wooden cabinet panel make a vertical center line on the exact center
of the area in which the preamplifier will rnount.
In the parts bag that was packed with the prearnplifier there are two metal mounting striPs
l/2" wide and 3 I12" Long. The "WOODEN PANEL CUTOUT TEMPLATE" shows how the
rnounting strip is used as a measuring guide to locate the two "LOCATION HOLES. ''
Z. Take the rnounting strip and with a pencil mark one length 13 LlT"l both to the right
and to the left of the vertical center line, approxirnately one rnounting strip length above the
sheIf.
Rest the end of the rnornting strip on the shelf and mark one length (3 l'2"1 vertically.
Where these rnarks intersect is the position of the "LOCATION HOLES. "
3. Drill these two holes with a 3/16" drill being careful to hold the drill as nearly per-
pendicular as possible so as not to transfer any error in location of the holes to the front of
the cabinet.
4. Transfer the "WOODEN PANEL CUTOUT TEMPLATE" to the front of the wooden
cabinet panel. Match the "LOCATION HOLES'| for the ploper positioning of the template.
Caref ully drill the s ix 3 I I6" rnounting hole s .
5. Cutout the openingin the cabinet keep-
irg within the line s . If the s aw doe s not quite
reach the line s, finish the opening with a file
or coarse sandpaper.
6 . Us ing two f lathe ad rnachine s c re ws
fasten the two mounting strips on the back of
the cabinet panel so that the edge of the mount-
irg strip is flush with the edge of the cabinet
hole, and that the rnounting hole s coincide with
the mounting s trip nuts . Two lengths of
s c rews are provided f or diffe rent cabinet pan-
eI thicknesse. (Flathead 6-32 x LlZ" and
6-32 x I Ll4"l.
IMPORTANT: The heads of the two flat-
he ad rnachine s c re ws holding the rnounting
strips in place rnust be flush with the front
s urface of the cabinet. If the s crews will not
p ull into the wood , a s light c ounte r s ink with an
oversize drill rnay be necessary.
,@
# 6-32
FLATHEAD
MACHINE SCREW
/#'
dIk
UNTING
STRI P
SPRING
CLI PS
CABINET PANEL
CUTOUT
-5-
MOUNTING HOLES

Next prepare the shelf for rnounting the Prearnplifier.
I. Measure the thickness of the wooden cabinet panel.
2. " FOLD LINES" have been s upplied on the "SHELF C UT OUT
ard panel thickness up to one inch. Fold on the correct fold line for
ness.
The chas sis is secured to the cabinet shelf by
plied in the parts b.g through the 1 14 inch hole s
(10-32 x 1")for thicker shelf material.
The C-ZO prearnplifier is shipped with the
panel end caps removed to prevent damage in
shiprnent. The end caps rnay be attached to the
panel by sirnply sliding thern onto the pins Pro-
jecting frorn the panel ends. The end caPs are
held in position by tpring tension.
TEMPLATE" for stand-
your wooden panel thick-
insertion of four l0-32 x 3 14" screws sup-
in the shelf . Longe r s crews are provided
END
3. Place the folded edge of the template against the back of the front panel. The ternplate
center line rnust match the center line extended to the shelf in step #l of the front panel cutout
instructions.
4. Carefully rnark the location and drill the lour l'4" holes. Next prepare the C-20 for
mounting in the cabinet by removing the pressed wood shipping pallet and the four plastic feet
from the bottorn of the preamplifier.
The cabinet is now ready for the installation of the preamplifier. Carefully slide the C-20
in frorn the front of the cabinet. Two lengths of rnachine screws are provided for fastening the
preampli{ier front panel in place depending on the cabinet panel thickness. (6-32x l/2" and
6-32:r1 l/4"1.
/CAP
--{>
PUSH ON
MOUNTING IN THE MODEL L-66 CABINET
Cornplete hardware and instructions for rnounting your C-20 stereo prearnplifier are pro-
vided with the Mclntosh L-66 cabinet. This standard cabinet measures 16 9l16 inches wide,
6 LL/L6 inches high (including the rnounting feet), and lZ 114 inches deep, exclusive of the
front controls.
RACK PANEL MOUNTING
For mounting on a standard 19 inch panel, a minirnum panel height of 5 l/4 inches is re-
quired. Width of the preamplifier is 15 518 inches. No supporting shelf is needed under the
chassis if it is rnounted with rnachine screws.
d>
-6-

CONNECTING PROCEDURE
A. C. CONNECTIONS: Five A. C. receptacles are provided on the rear panel of the C-20.
These receptacles are rated for a rnaximum of 600 watts. Four of the receptacles are con-
trolled by the switch on the volume control. The fifth receptacle is red for identification and
ie not ewitched. This red receptacle is used for powering a turntable or record changer. The
receptacle is not ewitched so that the turntable power will not be turned off while the turntable
idler wheel is engaged. With this arrangement it is necesaary to turn off the turntable with ite
own control switch ensuring that no darnage will result to the turntable drive system.
b-
TAPE
COMPARE
@
JTS
-r
I I 9* 9: ',,,*$og..,ff,,'FER
@@@@-
MclNTOst't
LABORATORY INC.
lili#' ;,.J1ff^,1.j^?,i';
CERAMIC 2-lOr,rv lO-7Omv CERAMIC Z'lOrrnv to'7Ouv ?'l0uv lo-7O,uv 2-l0r'r,v lO{Omv MADE lN U'S.A'
*rr*@@@@@@@@@@<-L
RGH'-*@@@@@@@@@@<--R
oto o o
olo O o
"l-

PROGRAM CONNECTIONS INTO THE C-20 (Input Connections)
Provision has been made for eight separate program inputs controlled by the Input Selec-
tor Switch, one input for tape comparison or monitor controlled by the 'rTape Compare"push
button, and a pair of telephone jack inputs located on the front panel and controlled bythe
'rTape Jack'r push button.
I
@I
@
(l) Auxiliary
(Zl Tape
(3) Tuner I
(41 Tuner Z
(5) Phono I
(6) Phono Z
( 7 ) Tape Head I
(8 ) Tape Head Z
@-
TAPE
COMPARE
INPUTS-r
@ @''
TUNER TUNER M0DEL czo
STEREO PREAMPLIFIER
@@
MctNTOSH
LABORATORY INC.
Low LEVEL |NPUTS 2 CHAMBERS ST.
r xrAL **E[lGrttonouiu*nJ I-rAPE HEADI I rrA' ll B;NGHAMT9N, N.y.
CgtiAt*tC e-ro"r- - lo-?O,- CenAmlC z-tO^,rJ lO-7Ouv ?louv lO-7O,nv 2-l0mv to'?Omv MADE lN U.S.A'
rerr*@@@@@@@@@@<-L
*'{r-*@@@@@@@@@@*-R
l. The auxiliary input has a sensitivity of .25 volts and aninput irnpedance of 470,000
ohrns (470 K), This input will accept any auxiliary service, such as a T. V. set, requiring
flat frequency response.
Z. The tape input has sensitivity and input impedance the same as the auxiliary input.
This input is designed to operate with self contained tape machines, that is, machines having
their own playback preamplifier. The high input irnpedance of this channel will not adversely
load any tape rnachine or tape deck amplifier. Note that when the Tape Jack switch on the
front panel is pressed in to the 'rlnrr position this input is disconnected so that the tape arnpli-
fiers in this circuit will not load the tape machine amplifiers plugged into the front panel jacks
on the C-20.
3 & 4. The two tuner irrputs each have a sensitivity of. Q.25 volts and input impedanoe of
470,000 ohrns (470 K). Two inpute are provided so that AM and FM outputs frorn a stereo
tuner or a pair of tuners can be plugged into one input, such as the "Tuner fl" pair of jacks,
and the left and right outputs of a multiplex adapter may be plugged into the "Tuner $2" paft of
jacks.
5 & 6. Each phono input hae been arranged in three groups of two jacks.
@
- 8-

t-pHoNo I ---.1[ pHoNo z -----_1 J-TApE
XTAL MAGNEIIC . XTAL MAGNFTrc
CERAMIC 2-lOr'rv lO'7Omv CERAl,llC 2-l0uv lo-7omv 2-'l0nv
The fir s t group is rrlarked 'r XTAL- CERAMIC I
and ie to be us e d with a c ons tant arnplitude c ar -
tridge such as a cr ystal, ceramic, or frequency
rnodulated device. The imput sensitivity for full
output is 0. I volt. The input te rrnination is a ?,20
rnrnf capacitor in series with 47, 000 ohms. This
arrangernent allows the record corrrpensator
switche s to be used with the se type s of cartridge s .
The second group is rnarked 'ilow' ' or"Z to l0
MV'f and is de signed to be us ed with rnagnetic car -
tridge s having an output of le s s than I 0 MV. The
input s ens itivity f or f ull output i s Z MV. The in-
put impedance is 47,000 ohrns.
The third group is rnarked "High'r or 'f I0 to 70
MV" to be us ed with rnagnetic cartridge s having
relatively high output. The input sensitivity for
f ull output is l0 MV. Maximurn inpr"t voltage for
this input is 7 0 MV. The input impedance is
47 , 00 0 ohrns .
If a cartridge reguires other than 47,000
ohrns load irnpedance, a re sistance can be added
acros s the terrninals of the cartridge to achieve
the correct terrnination. The following chart rnay
be used as a guide:
Desired Irnpedance:
47,000 ohrns (47K1
37,000 ohrns (37K)
?,7 ,000 ohrns (Z7Kl
I 5,000 ohms ( I 5K)
6,800 ohrns (6.8K)
Resistor Across Input:
No Resistor
180,000 ohrns (I80K)
62, 000 ohrns (62K1
ZZ,00O ohrns (ZZKI
8,200 ohms (8.2K)
Each phono input has been arranged to play
either stereo or rrronophonic. In the rnonophonic
position of the input selector switch the two channels of a stereo cartridge are in paralleI to
cancel all vertical output. Vertical output results in objectionable noise generated when play-
ing a rnonophonic recording with a stereo cartridge.
If both a 6tereo and a monophonic cartridge are to be used in the system, the stereo car-
tridge can be plugged into Phono 1 and the rnonophonic cartridge into Phono 2, either left
'or right channel. When listening to the monophonic cartridge turn the selector switchto Phono
2M to reproduce the prograrn frorn both speakers. Not that the sarne effect could be achieved
by switching the rnode selector to M left or M right depending on the channel used.
-9-

PHONO ?---l rTAPE HEADT -1 ITAPE HEAD 2-1
| ' -'- l,racr.rerrc I I
l0'7O nv 2-l0nv lo-7omv 2'lO,r,rv l0-70mv
7 & 8. TaPe Head.
The output of s te reo or mon-
ophonic tape heads can be fed di-
rectly into the inputs on the back
panel identified as '' Tape Head l "
and '' Tape He ad Z" . Note that
each input is arranged in two
groups of two jacks. The first
g roup is rnarked " Low" or " 2 to
l0 MV" and is for use with tape
he ad s having an o utp ut of le s s
than l0 MV. The second group is
rnarked "High" or " 10 to 70 MV"
and is used with tape heads hav-
irg I 0 MV or rnore output.
Tape Cornpare
The C- 20 pe rrnits the Inon-
itoring of a tape as it is being
recorded. This rnake s pos s ible
the instantaneous cornparison of
the recorded rnaterial with the signal source. Jacks marked'TTAPE-COMPARE" have been
provided on the back panel to accept the signal from a tape recorder equipped with a monitor
head and preamplifier. When the "TAPE COMPARE'| push button, located on the front panel,
is in the out position the prograrn source is fed through the power amplifiers and loudspeakers.
When the button is depressed (I'IN'r position) the signal source becomes the monitored prograrn
frorn the recorded tape and is fed through the power amplifiers and loudspeakers.
IMPORTANT: WHEN THE 'TTAPE COMPARE'i PUSH BUTTON IS DEPRESSED, SIG-
NAL FROM ANY OTHER SOURCES WILL NOT BE HEARD FROM THE LOUDSPEAKERS.
WHEN NOT IN USE LEAVE THIS PUSH BUTTON IN THE IIOUTII POSITION,
Tape Jack Front Panel Inputs.
The two telephone jacks on the frontpanelsupplyleftandrightstereoinputfacilitiesfor
playback or left and right stereo output facilities for recording on a portable tape recorder
without disconnecting a tape recorder connected to the back panel jacks. Theleft hand jack is
the left channel input and the right hand jack is the right channel input. The "TAPE JACK"
switch controls the signal to or frorn the front panel telephone jacks. When the push button is
"IN" then any prograrn originating at the portable rnachine can be heard by rotating the input
selector to 'TTAPE'|. Note, when the push button is in the "IN" position "TAPE" input is
switched frorn the rear tape jacks to the front telephone jacks. The "TAPE JACK" push button
rnust be rrOUTrr to connect signals from the rear tape jacks to the "TAPE" input selector switch
position. When the push button is "OUT" any prograrn being picked up by the C-20 is connected
to the portable machine to be recorded on it. (Note, with sorne recorders it rnay be possible to
feed a signal into the C-ZO vi.a the telephone jacks when the push button is "OUT. " This is not
a norrnal rnode of operation and a distorted signal rnay result. )
- r0-

Output Connections.
Two sets of outputs have been
provided . One s et is the " MAIN
OUTPUT" to feed the power arnpli-
f ie r s and the othe r is the ' ' TAPE
OUTPUT" to feed a tape recorder.
The 'rTAPE OUTPUT" is unaf -
fe cted by any adj us trne nts rnade with
the f ollowing controls : " MODE SE -
LECTOR, " "BALANCE,'|T '|rPHASE",
"LOUDNESS,'r '|BASS, " "TREBLE, " "RUMBLE FILTER, " and "VOLUME. " Any adjustrnents
made in the 'TINPUT SELECTOR, " "RECORD COMPENSATOR, " and the "HF CUTOFF FIL-
'TER" do effect the signal at the "TAPE OUTPUT" jacks if the signal originates in the phonoor
tape head inputs.
The rnain and tape output jacks are fed from cathode followers. The input irnpedance of
devices connected to these outputs should be 50,000 ohrns or greater, and the capacitive react-
ance of audio cables connecting these devices should not be less than 8,000 ohrns at 20,000
cycles. This is the reactance of a capacity of 1,000 rnrnf. Audio cable having a capacity of
25 mmf per foot rnay be 40 feet long, 13.5 mmf per foot cable may be 75 feet long.
C-20 Prearnplifiers Serial No.
6 L7 0 0 and late r harre an additional
left plus right output jack. A rnono-
phonic s ignal can be distributed to
other roorns by.onnecting this jack
to a powe r arnplifie r to drive the
ffronophonic louds peakers . The ca-
ble c onne cting to this o utput should
not have a capacity of rrrore than
3 00 rnrnf . The input irnpedance of
the powe r arnplif ie r c onne cting to
this output should not be le s s than
I50,000 ohrns (150 K). Thegenera-
tor irnpedance at this output is ap-
proxirnately 7,3, 000 ohrns (23 K).
Connecting Prograrn Source
Grounds.
A single ground post is provid-
ed. The chassis ground frorn turn-
table, r€cord change rs (rnotors
used with each), tape <iecks, etc.,
should be returned to this post. Do
not duplicate this ground circuit.
Unde s irable hurn will be he ard in
the systenr alrnost certainly if duplicate ground returns are used. The left and right prograrn
cables frorn each source should be twisted.together and the ground wire frorn each source can
be wound or twisted in with these cables. To avoid hum, rnake sure that the ground wire does
not make any connections to shields of the left and right channel cables except for the connec-
tion provided with the C-20 ground post
I
@I
@
..r;*@o'
,ro.'@);^
Rlen*@
o!o o\.
-ll-

BALANCING A STEREO SYSTEM
A properly balanced stereo system must be in phase, and each channel rnustbeequal in
loudness, and sirnilar in frequency response, The C-20 has been designed so that once pro-
perly balanced the 6ystern will rernain in balance through all rnodes of operation. A familiar
recording either stereo or monophonic should be used for balancing the stereo systern. The
following procedure has been outlined to assist you.
l. Turn the "INPUT SELECTOR" to "PHONO I M. "
Z. Turn each "RECORD COMPENSATOR'| control to "RIAA. "
3. Turn the 'iBASS" and "TREBLE" controls to "O".
4. Turn the "MODE SELECTOR" to "STEREO.'l
5. Turn the "BALANCE" and 'TPHASE" controls to "O'r.
6. Turn the 'THIGH FRECUENCY CUTOI'F FILTER" to 'rFLAT. "
7. Turn the "LOUDNESS'r control to 'TFLAT' "
With the controls set as above a rnonophonic signal of equal arnplitude will be fed to each
side of the preamplifier.
To Adjust for Amplitude Balance in the Treble Range.
Rotate the "BASS" tone control totally counterclockwise. The"PHASE" control rernains
in the "O" position. Wtrile the record is playing, switch the "MODE SELECTOR"between "L"
and "R". Adjust the control rnarked '|GAIN" on the input to the power arnplifier until the loud-
speakers are of equal loudness. (When using the Mclntosh MC-Z4O and connecting the C-20 to
the stereo input jacks rnerely rotate the "BALANCE'| control on the MC-240 untilloudspeakers
are of equal loudness.) Do not use the C-20 "BALANCE'| control for this procedue. The
C-20 'TBALANCE" control is used to adjust for any unbalance in the source rnaterial, the phono
cartridge or the tape rnachine.
To Adjust for Balance in the Bass Range.
Many factors throughout the sound reproducing systern can adversely affect the balance in
frequency response. Loudspeakers in particular are prone to be unequal as a result of enclo-
sure, placernent in the roorn, etc. Controls have been provided on the rear panel of the C-20
to compensate for these inequalities in bass response. The following outline will assist you in
achieving balance.
Adjust the "TREBLE'r tone control to the totally counterclockwise position, and the "BASS'l
tone control to the extrerne clockwise position, For an additional boost, if desired, the ''RE-
CORD COMPENSATOR" control rnarked '|BASS" can be rotated to the "TAPE" position. (Note
that the rnusic will have unnatural tone balance for this procedure. Bass sound will predorni-
nate. In some installations it rnay be necessary to reduce thevolurne to prevent acoustic feeti-
back. )
While switching the'TMODE SELECTOR'r between'rL'r and'rR'r listen carefully to the low
frequency response. Adjust the controls on the back panel marked "LOW FREQUENCYTRIM.'I
The 'rLOW FREQUENCY TRIM'r controls are independent of the front panel tonecontrolsand
- LZ-

will adjust only the low frequency balance. Ihis arrangement leaves the front panel controls
free to correct overall tone balance in the prograrn, correcting for recording or playback en-
vironrnent.
There is afurther feature to the lowfrequencytrim controls. If you find that your loud-
speakers produce rnore than adequate bass response when the C-20 is adjusted for norrnal
playback, you rnay turn both low frequency trim controls fully counterclockwise. Then bring
the system into balance by advancing only the trim control corresponding to the loudspeaker
producing less bass response.
If ontheother hand your loudspeaker systems produce less bass resPonse thanyoudesire'
the low frequency trirn controls rnay be turned fully clockwise. The systern is thenbrought
into balance by reducing the bass response on the loudspeaker producing the greater bass arn-
plitude.
Following a sirnilar procedure the bass response of your system may be adjusted within
thelirnits of fully clockwise to fully counterclockwise on these trirn controls and the systern
balance established by advancing one control more than the other.
To Adjust Phase.
Rotate both record cornpensator controls to RIAA. Adjust bass and treble tone controls
to zero.
Stand approxirnately l0 feet in front of and rnidway between the loudspeakers. The source
of sound should appear to be directly in front of your. Rotate the "PHASE" control between"0"
and',180,,. If the source of sound is not directly infront of you in rr0rr position reverse the
leads to one loudspeaker. The phase switch has been arranged to correct phase insource ma-
terial wheneve r neces sary'
USING THE C-20 AFTER CONNECTING AND BALANCING
To Listen to Stereo Records.
l. Set the 'rMODE'r selector to "STEREO'r.
Z. Set the "PHASE'i switch to zeto'
3. Set the "H. F. " filter to "FLAT. "
4. Set the "LOUDNESS'i control to "FLAT. "
5. Rotate the input selector to "PHONO lS" or "PHONO 25" whicheveris connected to the
cartridge you wish to hear.
6. Set the record cornPensator controls to 'rRIAA.'l
7. Set the 'iBASS" and "TREBLE" controls to zero.
8. Set the "RUMBLE FILTER'' to "OUT. "
9. Set the I'TAPE COMPARE" switch to "OUT. "
lO. Rotate the ,'VOLUME" and'rOFI'- ON" control to "ON" and adjust to the desired vol-
urne.
- 13-

You may now start to enjoy the rnarvelous instrurnent which you own. To give you sorrre
farniliarity with its complete design and flexibility here are sorne of the things it will do for
you.
l. If the recording has been rnade with left or right distribution of instrurnents reversed,
you rnay correct it by changing the "MODE" selector frorn "STEREOil to "REVERSE. " You
will fi.nd sorne stereo records that sound better played in Stereo Reverse because in this posi-
tion the I'MODErr selector returns the left-right distribution to norrnal.
Z. If the sound is louder on the left than on the right, adjust the "BALANCEI'control to
the right to bring the sound into r'left to right" balance. If the sound is louder on the right,
correct it by turning the'TBALANCETT control to the left. You will find records where the bal-
ance setting differs frorn other records.
If after balancing your systerr. as outlined in this manual you then find that nearly all re-
cords always require an adjustrnent of the I'BALANCE" control to one side of the center, the
condition indicates an unbalanced stereo cartridge. While this is no great disadvantage as
such, you can correct for it by offsetting one of the power arnplifier input gain settings. When
switching frorn I'STEREO" to "REVERSEil you will now experience a change in volurne as a re-
sult of this correction.
3. If the stereo sound seerns to corne frorn either side of the room instead of being distri-
buted between the loudspeakers, adjust the "PHASEil control to I80o. This listening effect is
due to reproducing sound that is out of phase frorn one channel to the other. You will find some
records differ from others in this respect and that sorne tapes differ frorn records.
4. If you wish to reproduce ota, Uaaty worn record.s, you rnay rninimi ze tle surface noise
by switching the I'H. F. CUTOFF FILTERil to 9 KC or 5 KC.
5.. If you are using a turntable or changer which has a low frequency rumble noise, you
rnay reduce this problern by operating the 'TRUMBLE tr'ILTER" push button in the "IN" position.
Undesirable acoustic coupling in the very low frequency bass range rnay also be reduced by
this procedure.
6. Music reproduced at very low volurne loses its bass and treble due to a selective shift
in sensitivity of the hurnan hearing. The farnily of curves on a graph showing this effect are
known as Fletcher-Munson curves. The loudness control on the C-20 corrects for this effect .
'When you wish to hear rnusic at greatly reduced loudness and yet hear bass and treble then turn
the 'TLOUDNESSil control, to reduce intensity, rather than the volurne control. Sorne users of
C-20's like to leave the "LOUDNESS|t control at positions I or 2 to correct for environrnental
conditions such as loudspeaker characteristics or roorn placement, etc.
7. If you wish to Iisten to rnonophonic records, switch the input selector to'TPHONO I MI
or ITPHONO Z M". Vertical output frorn stereo cartridges is cancelled by operating the input
selector to the'rM'r(rnonophonic) positions. When listening to rnonophonic records vertical out-
put consists only of undesirable sounds such as record scratch.
8. The tone balance which you hear when listening to an orchestra is affected by the con-
ductorrs instructions to his rnusicians, the acoustic environrnent in which you are listening and
your own subjective hearing interpretation. When you realize that tone balance will vary even
with the roolrr or haII location from which you listen to music it is not difficult to understand
why tone balance controls play a necessary part in correcting for the following factors:
- L4-

(l) Each personrs subjective idea of tone balance.
(21 Loudspeaker frequency response characteristics.
(3) Loudspeaker placement in the listening roorn,
(4) The conductorrs idea of tone balance at the time the recording was rnade,
(5) The rnicrophone frequency response characteristics.
(7) The recording process influences.
These factors can be considered as environrnent influences. The bass and treble controls
are designed to provide a degree of cornpensation for the effects of environrnent. Start Iisten-
ing to your system with each control at zero. Ifyou wish to reduce treble in relation to bass,
rotate the "TREBLE" control counterclockwise until the tone balance sounds correct to you at
this particular tirne. Do not be surprised if you find your preference changing from time to
tirne. These controls will rnodify tone balance without introducing any undesirable effects of
therns elve s.
Tone balance rnay be accented in the treble range by rotating the I'TREBLEil control clock-
wise. Sirnilarly tone balance rnay be modified up or down by use of the bass control.
9. The record cornpensation controls are used to correct for the necessary program
equalization which the recording process introduces. Recording requires a change in the dis-
tribution of intensity with frequency and practically rneans that without compensation a rnagnet-
ic cartridge would sound greatly deficient in the bass range and overly bright or shrill in the
treble range.
For several years record cornpanies used rnany different recording characteristics in an
effort to give rnaxirnurn entertainrnent value to listening to their records. The recornrnended
settings for Iistening to these records are given in the table following.
RECOMMENDED SETTINGS OF THE RECORD COMPENSATOR CONTROLS
OF THE C-20 FOR MONOPHONIC RECORDS
Manufacturer
Cornpensator Controls
Bass Treble
Speed (Trrnover) (Roli-Off) Manufacturer
Cornpens ator Controls
Bass Treble
Speed (Trrrnover) (Roll-Off)
Allegro
Arnerican
Re c o rding
Society
Ang e1
Atl ant i c
Audi ophil e
Bach Guild
B anne r
Bartok
Boston
Blu e N ote
Caedrnon
33 LP LP
33 RIAA . TZ
33 RIAA - IZ
33 LP
- 10
LP
LP
-rz
-rz
33
C apital
C apit al
Cany on
Capitol - Cetra
Colosseurn
Cetra-Soria
C olurnbia
C olurnbia
C olurnbia
Conternpor ary
Concert HaII
Coral
C ook
45 RiAA - IZ
33
7B
45
7B
400 -rz
33 400 -rz
RIAA
300
LP
LP
400
LP
33 LP
RIAA
300
400
Riaa
LP
LP
LF
-rz
-rz
,78
33
33
33
33
33
- 15-

Cornpensator
Bass
Speed (Tnrnover)
Controls
Treble
(Roli -off)
Con..pensator Controls
Bass Treble
Manufacturer Manufacturer Speed (T.trnover) (Roll-Off)
Decca
DiaI
Electra
Ern s
Epic
Esoteric
Eur ope an
Fe s tival
Folkways
Good
Tirne J az z
Handel Soc.
Haydn Soc.
London
London
Lyticord
Mercury
MGM
MontiIla
New Records
Oc e anic
Oxf ord
33
45
78
33
33
33
33
33
78
33
33
33
33
33
7B
33
33
45
7B
33
45
7B
33
33
LP
LP
-rz
LP
-rz
-5
LP
LP
-r2
LP
-i0
-5
LP
-rz
-rz
-rz
LP
LP
LP
400
LP
RIAA
300
LP
LP
400
LP
LP
300
LP
400
RIAA
RIAA
LP
Period 3'3
Philh arm oni a 33
Rachrn anin of f
Society 33
33
RCA Vrctor(Old) 45
7B
RCA Victor 33
(H. M. V. ) 45
(New RIAA Curve) 7 B
Rernington 33
Renai s s anc e 33
Stradivari 33
T e chnic ord 7 B
Telefunken 7 B
U rania (Old) 33
Urania (Neu') 33
Vanguard
Vox 33
Westrninster
RIAA, ORTHO, New
NARTB, New AES used
on recordings rnade
since 1955
RIAA
400
LP
RIAA
RIAA
RIAA
LP
LP
RIAA
400
LP
400
LP
RIAA
LP
-rz
LP
-10
-IZ
L,P
-rz
LP
-rz
-5
LP
-IZ
LP
RIAA
- L6-

Record rnanufacturers, during the past two or three years, have rnade a deterrnined effort
to rnake all records reproduce properly by using the RIAA cornpensator setting. Generally,
all new records will perforrn well using RIAA or L.P. settings. However, if a record sounds
better using the compensator at other positions do not hesitate to use it that way.
10. A Stereo Tuner rnay be used with the C-20 by plugging the left and right channels into
Tuner Inputs No. I or No. 2. When the I'INPUT SELECTOR" switch is rotated to the
"TUNERTT positions, the record cornpensator preamplifier is disconnected and the compensator
controls will not need to be adjusted.
The "MODErr selector switch, "BALANCE CONTROL, " I'PHASE'I switch, I'LOUDNESS
CONTROL, r' and the '|BASS" and "TREBLEil controls, the "RUMBLE FILTER,'r "TAPE
JACKil switch, and the "VOLUME and OFF-ON" control all operate in this application and
should be used just the sarne as when listening to records or any other program. Refer to
paragraphs l, Z, 3, 4, 5, 6 and 8 of this section.
A stereo tape rnachine with its own playback preamplifiers should be plugged into the
tTTAFETI inputs. (Not the "TAPE HEAD, inputs.) fhe inforrnation on adjusting the C-20 for
listening to a stereo tuner will also apply when listening to a tape rnachine.
11. The C?0 stereo prearnplifier rnay be used with tape decks which do not have playback
prearnplifiers. Tape heads require a type of playback cornpensation sornewhat the sarne way
that rnagnetic cartri.dges do. Setting the cornpensator controls to the positions rnarked
'rTAF,E' provides correct playback for tape heads and elirninates the need of using playback
preamplifiers with tape decks. (Note, however, that tlae C-20 can not conveniently be used to
record on tape. If you need recording facilities in a tape rnachine, a recording prearnplifier
will be required. In rnany tape machines this preamplifier serves both playback and record
functions. )
IZ. Stereo rnicrophones rnay also be used with the C-20.
If the rnicrophones are low level (1ow output producing only 2 to 10
may be plugged into either an unused pair of phono low (2 to I0 MV) jacks
tape head 1ow (2 to l0MV) jacks.
If the rnicrophones are rnediurn level l0 to 70 rnillivolts, then they
either an unused pair of phono high (10 to 70 MV) jacks or an unused pair
to 70 MV) jacks.
rnillivolts, then they
or an unused pair of
rnay be plugged into
of tape head high (I0
When reproducing microphones in phono or tape head channels set the 'rBASSil record
cornpensator control to rtorr and the TtTREBLE" record cornpensator control to 'rTrAPErr. This
adjustrnent gives a flat response for the rnicrophones. AI1 of the information given in para-
graphs 1, Z, 3, 4, 5, 6, and 8 of this section can apply to the use of rnicrophones as prograrn
sources.
In the event that you should happen to use very high output rnicrophones, 100 millivolts
and up, plug thern into the auxiliary channel. In this channel the record cornpensator controls
do not operate and it will not be necessary to adjust them. All other inforrnation on rnicro-
phones given above does apply.
13. Two tape rnachines can be used with the C-20 stereo prearnplifier. After you have
connected your tape rnachine to the rear panel of the prearnplifier you rnay have someone
bring in a portable rnachine to rnake a copy of one of your tapes or to listen to one of his tapes
on your systern. With the C-20 you no longer have to unplug your permanent rnachine. The
C-20 cornes supplied with two cables havi.ng phone plugs on one en{ to plug into the front pan-
et of the C-20, and pin jacks on the other end to plug into any tape rnachine. (Adapters are
available at anry Hi-Fi retailer to perrnit pin plugs to connect with phone jacks. )
-17-

To listen to the portable or second tape rnachine plug the pin jack end of the two C-20 ca-
bles, rnentioned above, into the tape machine output. Connect the telephone plugs into the
telephone jacks on the C-20 brass panel. The left jack supplies the left channel. The right
jack supplies the right channel. Rotate the input selector switch to'|TAPE". When the tape
jack switch is depressed to the I'INrr position, the perrnanent tape rnachine output is discon-
nected frorn the rear panel. The portable tape rnachine is now connected and any prograrn
originating in this rnachine will be heard through the Q-20, and will also be available frorn the
C-20 I'TAPE OUTPUTTT to drive the perrnanent tape rnachine input. This feature rneans you
can copy a tape frorn the portable machine into your perrnanent rnachine. (Note that this as-
sulnes that your perrnanent rnachine has its own recording prearnplifier. )
To record on the portable rnachine plug the two phono pin plugs of the two C-20 cables into
the input of the portable rnachine. Leave the telephone plugs connected to the C-20 telephone
jacks on the front panel. Operate the tape jack switch to the "OUTil position. The perrnanent
tape machine will be reconnected. Now any program picked up by the input selector switch
will be available to drive the portable rnachine. You can now make a copy on the portable rna-
chine o{ any tape played on the perrnanent rnachine. You can copy any other prograrn source
onto both tape machines at the same tirne.
Whenrecording frorn one tape rnachine to the other the only controls that are effective are
the 'rHF CUTOFF" filter and the "TAPE JACKil switch. (Note that sorne portable tape rna-
chines will drive f}re C-ZO even though the 'TTAPE JACK'! switch is in the trOUT" position.
This is not a normal circuit use and a distorted signal usually results. For low distortion op-
eration follow the recornrnended procedure. )
- r8-

SPECIFICATIONS
Power Requirernents: 11? volts 60 cycles A.C. 35 watts
Input Sensitivity & Auxiliary: 0.25 volts 470,000 ohrns
Input Irnpedance: Tape: 0.25 volts 470,000 ohrns
Tuner l: 0.25 volts 470,000 ohrns
Tuner 2: 0.25 volts 470,000 ohrns
Phono I:2 to I0 rnillivolts 47,000 ohrns for low output car-
tridge
I0 to 70 rnillivolts 47,000 ohrns for hi output car-
tridge
0.1 volt 220 rntnf series with 47,000 ohrns for
Xtal or Cerarnic
Phono 2: Sarne as phono I
Tape Head l: 2 to l0 rnillivolts 4?,000 ohms for low output
head
l0 to 70 rnillivolts 267,O0O ohrns for hi output
head
Tape Head Z: Sarne as tape head I
Tape Cornpare (Monitorl:. 0.25 volts 115,000 ohrns
Frequency Response: +0.5 db ?0 to 20,000 cycles
Distortio:r: Less than O.2% at rated output , 20 t;o 20,0C0 cycles
Hurn and Noise: High leve1 inputs: 85 db below rated outPut
Low level inputs: less than 2microvolts at input terrninals
Main Outprrt; 2 " 5V with rated input
2 output jacks in parallel for each channel
Tape Output: 0'Z5V with rated inPut
I output jack for each channel
Left Plus RightOutput 2.5 volts frorn generator irnpedance of 23,000 ohrns
voltageArnpli{ication: Low level inputs to Main Output: I,000 to I (60db) at 1000
cycle s
Low level inputs to Tape Output: 100 to I (40db) at 1000
cycle s
High 1evel inputs to Main Output: l0 to I (20db)
High Ieve1 inputs to Tape Output: I to I (Odb)
Tape Monitor input to Main Output: l0 to I (20db)
A.C. Ar:x. Outlets: I unswitched for tape rnachine or turntable, colored Red
4 switched, colored Black
Size: Chassis: 12 Il2 inches wide; 4 I/2 inches high; 12 inches
deep
Front Panel: 15 5/8 inches wide; 4 7/8 inches high
Weight: 18 Pounds
Shipping Weight: 28.5 Pounds
_ 1g_