JVC M-7050 User manual

JVC
Instruction
Book
&
Service
Manual
STEREO POWER AMPLIFIER
M-7050
i se
SSS a ee a a ae ee 1 ee a, Sea a ae eae
i eS
i gl a eS
SIG EL ED ea A a a TI TE a IE
en ee
WARNING: TO PREVENT FIRE
OR SHOCK HAZARD, DO NOT
EXPOSE THIS APPLIANCE TO
RAIN OR MOISTURE.
For Customer Use:
Enter below the Model No. and Serial
No. which is located either on the rear
or bottom of the cabinet. Retain this
information for future reference.
Model No.
Serial No.
Service manual No. 2469
July, 1979
E30580-804A

IMPORTANT (In the United Kingdom)
Mains Supply (AC 240 V~, 50 Hz only)
IMPORTANT
Do
not
make
any
connection
to
the
Larger
Terminal
coded
E
or
Green.
The
wires
in
the
mains
lead
are
coloured
in
accordance
with
following
code:
Blue to N (Neutral) of Black
Brown to L (Live) or Red
\f
these
colours
do
not
correspond
with
the
terminal
identifi-
cations
of
your
plug,
connect
as
follows:
Blue
wire
to
terminal
coded
N
(Neutral)
or
coloured
Black.
Brown
wire
to
terminal
coded
L
(Live)
or
coloured
Red.
If in doubt — consult a competent electrician.
Note
We
recommend
that
you
should
disconnect
the
AC
cord
from
the
outlet.
INTRODUCTION
Thank
you
for
purchasing
the
JVC
M-7050
stereo
Power
Amplifier.
You
are
now
the
owner
of a
truly
sophisti-
cated
system
component
incorporating
many
advanced
features.
“Super-A” high efficient 150W + 150W power output stage (is
equal to class B operation) of extra low distortion (is superior
to class A operation), high slew rate (+300V/ysec), un-
rnesurerable TIM distortion, non magnetic alminium chassis-
base to eliminate the magnetostriction, and high capacitive
power supply are just a few of the host of features which
combine to produce the best possible sound.
JVC also manufactures the EQ—7070 Stereo Phono Equalizer,
a matching preamplifier and the SEA—7070 Stereo Graphic
Equalizer, a matching frequency characteristic controller for
use with the M—7050 Power Amplifier. Before you begin
using, please read the instructions carefully to be sure of
getting the best possible performance from the new unit.
Wishing you memorably enjoyable listening.
WARNING
Dangerous voltage inside
CAUTION (
To prevent electric shock, do not remove
screws, covers or cabinet.
No user-serviceable parts inside. Refer
servicing to qualified service personnel.
CONTENTS
Instruction Manual
page
Front.panel.):.: si. eh a ee FA ee ee g
Important notes 2... ee 5
Troubleshooting... 0.0.0.0... eee tee ee eee 6
Block diagram. 6.2... eee ee 7
Performance graphs... 2... ee ee es 8
Technical description... 0... ee ee 9
Specification ©... 6. ee et ee ees 10
Precautions in servicing
Adjustment procedure of the amplifier
Check after servicing
Exploded views
Parts list of exploded views
Location of circuit boards
Schematic Diagram
(For only qualified service personnel)

cto,
et,
Instruction Manual
FRONT PANEL
PHONES
POWER Switch
Headphones jack (PHONES)
Exclusively for monitoring purposes.
Employ this facility in the following cases, for example:
1. To locate’the beginning of a particular section of tape
when no speaker sound is desirable.
2. To monitor the sound to be transmitted to a remote place
when the amplifier is used as a public address system.
(Note) Plugging in the headphones does not switch off the
speaker sound automatically. When you wish to
listen to sound from the headphones only, set the
SPEAKER switches to OFF.
POWER switch
Press to turn the power on. The red indicator lamp in push
knob will light and the POWER meters will be illuminated. To
turn the power off, press the switch again to release.
Panel IImination:
For a period immediately after the POWER switch is turned
ON, the illumination of the POWER meters is red. Wait for
about 4 - 5 seconds until it changes to white. If it continues to
be red for a longer span, the protection circuit is operating for
some reason. Turn the POWER switch OFF and check the
cause of malfunctioning.
—— Power meter
SPEAKER Switch
POWER meters
The output power is indicated in wattage on the compressed
logarithmic scale in reference to the 8-ohm load impedance.
SPEAKER switches
To listen to the speaker system connected to the rear panel
SYSTEM-1 terminals, press the SYSTEM-1 switch.
To listen to the speaker system connected to the rear panel
SYSTEM-2 terminals, press the SYSTEM-2 switch..
Both speaker systems can be heard by pressing both switches.
When a SPEAKER switch is pressed, the green indicator lamp
on the corresponding switch lights.
(Note) If the load impedance is lower than 4 ohms, the
protection circuit is activated, resulting in inter-
mittent sound.
1.
If
a
single
pair
of
speakers
is
to
be
driven
at
a
time,
the
speaker
impedance
may
be
between
4
and
16 ohms.
2. If two pairs of speakers are to be driven simultaneously,
the speaker impedance should be between 8 and 16 ohms.

CONNECTION DIAGRAM
Refer to item
No. 3 in page 5
Speaker system 4 ~ 1622
Input LEVEL volume
Normally, set to the “MAX”
position. If the preamplifier
produces an excessively large’’
gain, turn the control counter-
clockwise until the proper
adjustment is obtained.
Refer to item
No. 1 in page 5
Refer to item
No. 2 in page 5
Speaker system 4 ~ 1692
SEA-7070
Graphic equalizer
Pre-amplifier
Turn table
Tape Deck
a

IMPORTANT
one,
——
eeen
eoeow
Installation
Select a dry, level place which is neither too hot nor too
cold (between —5° and 40 °C/23°F and 104 °F).
Leave space between the power amplifier and the wall to
provide good ventilation.
Do not allow a curtain, table cloth, etc. to block the
ventilation holes.
Keep the power amplifier away from direct sunlight.
Do not place close to a heater.
Do not place in locations subject to vibrations.
Do not place in locations subject to dust.
Keep as far from a tuner and a preamplifier as possible to
prevent noise.
Power cord
Do not handle the power cord with wet hands.
Do not bend the power cord double.
When unplugging from the wall outlet, always pull the
plug, not the power cord.
Malfunctions
Do not insert any metallic object inside the unit.
Do not allow water to get inside the unit.
Do not employ thinner or benzine to clean the cabinet.
First clean with a neutral cleaner and then wipe with a dry
cloth.
Power switch
Do not plug the power cord into an AC outlet until all
connections are complete.
Switch the power off when connecting other components
to it.
REAR PANEL
1.
Connecting with other components may result in trouble,
such as oscillation or hum. Connect ground terminals of
this set and other components to each other.
SUBSONIC and DIRECT INPUT terminals
Do not connect different kinds of signals simultaneously
to input terminals.
Input cannon connector (for professional use)
(Unbalanced)
AC:
If these terminals are employed, the input signal
passes through a filter having a cut-off frequency of
18 Hz and a slope of 6dB/oct, which results in a
reduction of ultra-low frequency noise, such as that
encountered with warped records, and prevents
speaker intermodulation distortion.
The filter also eliminates the preamplifier DC leak
voltage, thus protecting the speakers.
DIRECT:
These input terminals are directly connected to the
power amplification circuit. Since the M-7050
employes DC amplifier circuitry, there is no
coupling capacitor between the input circuit and the
power amplification stages.
Protective circuit
When the protective circuit has been activated, switch off
the power and determine the cause as follows:
The speaker load impedance
Using speakers with an impedance of less than 4 ohms (or
a short circuit across the speaker terminals) activates the
protective circuit and results in intermittent sound out-
put. When the speaker switch is at the “1 and 2” position,
use a pair of speakers having an impedance of 8 or high-
er, at “1” or “’2” position, use a speaker of 4 or higher.
Input overload
The speaker produces intermittent sounds.
Detecting the offset voltage
The offset voltage of +2 V or more, activates the pro-
tective circuit and results in no sound output.
Caution indicator
When the protective circuit has been activated, meter
illumination changes to red.

TROUBLE
SHOOTING
What
seems
to
be
a
trouble
is
not
always
real
trouble.
{
Make
sure
first.
[ No sound ]
Both channel
Are
indicators
Yes
Does
the
relay
No
Is
the
speaker
switch
Yes
functioning?
operate?
set
to
ON?
One channel
only
No
Reverse
the
L
and
R
Does
the
relay
Check
for
speaker
connections.
operate
connections
Does the channel with
no
sound
shift?
No
Yes
Navsound
Yes
Is
the
input
level
volume
|
Yes
Check
for
trouble
in
the
preamplifier
IfOK......
set to maximum? or connected component.
Both No
channels os
Does the replacement of the preamplifier
or connected component correct distorted
sound?
|
| Distorted sound
only Does the channel with distorted sound shift? No defect in the M—7050
te
No
One channel Reverse the L and R connections.
There may be trouble in the M—7050 it self.
Consult your dealer.

BLOCK DIAGRAM
YBLAW 8Y3MOd
ANddNS
YAMOd
39VLS
YSBAING
dWY
Y3M0d
A1ddNS
YAMOd
3OVLS
LNdLNO
TAA37
(00)
LOaYIa
@-WALSAS
Y3axVadS
(Ho
LINDYID
svia
v-y4adns
(Ov)
SINOSSNS
SANOHd
YOLINOW
Z2HOLIMS
LINDAID
SANILOSLOYd
Yy3ayvV3ads
LINDAID
Ssvig
(Sv)
SINOSSNS
(a4) O
(10
(9q)
LOaYIa
T3A37
dWY
Y3aM0d

PERFORMANCE GRAPHS
Wi THD vs. Output power
oe
|
;
=
&
0.03
=
|
|
ne
=a
{
c
Distortion
of
measurement
system
j
O
0.02
tae
4
1H
=
1KHz
0.0008%
7
6
20Hz
0,0011%
{
-_
20KHz
0.0014%
2
L.
pat
3
0.01
-
|
2
je
:
|
2
0.007
F
a
©
0.005
+
E
Ht
PS
0.003
g
0.002
°
ke
_——
|
KHz
0.001 - +H
0.0007
=
1
rf
2 3 5 ? 10 20 30 50 70 100 200 300 500
Power output (W/8 Q }
@ Spectrum of harmonic distortion
(dB) (dB) (dB)
—70
} 20K 100K 200K } 20K 100K 200K *
10 kHz Fundamental 10 kHz Fundamental
Measurement System Super—A
@
Characteristics
of
TIM
distortion
(Low
pass
filter
fe=100
kHz)
(dB}
3.18K 6.36K 9.54K 12.72K 15K
3.18K 6.36K = 9.54K = 12.72K 15K 19.08K
{He} 15.9K (He) 15.9K
The spectrum of input signal Output signal of M-7050
(Same as input signal)
af. 2 4
| 20K 100K
10 kHz Fundamental
class AB
3.18K 6.36K 9.54K 12,72K 15K
(Hz) 15.9K
An example of TIM distortion
(TIM distortion is sum of
components less than 15 kHz
which showed with arrows.)
1g O8K

TECHNICAL DESCRIPTION
Super A power amplifier
A big problem has remained unsolved in the progress regarding
amplifier technology: how can class-A operation be made
compatible with high power efficiency? The class-A operation
is best in terms of low distortion; its critical drawback is such
that its power loss is greater than the available output power.
Because of this, class-B amplifiers have generally been applied
for power amplification because they offer both acceptable
distortion and power efficiency. However, as long as class-B
amplifiers are employed, the occurrence of crossover distor-
tion and switching distortion is inevitable. Although the
improvements of circuit elements have realized fairly good
class-B amplifiers, when their values of distortion are referred
to, the ‘‘nature” of distortion is still detrimental to the re-
produced sound quality. To solve this problem by improving
circuit technology, JVC has developed its new ‘’Super-A”’
power amplifier.
The Super-A power amplifier consists of a voltage amplifier
stage whose distortion is minimized by compensating for the
non-linearity of semiconductors, and aclass-A power amplifier
stage which includes a bias circuit for raising the power effi-
ciency to such a degree as is comparable to that of a class-B
amplifier. JVC’s Super-A power amplifier offers the following
features:
1) Power efficiency is extremely high despite the class-A
operation, greatly reducing power loss and heat generation
compared with conventional class-A amplifiers.
2) Switching distortion inherent in class-B operation is com-
pletely eliminated; it is perfectly zero.
3) AVecE distortion *1, ACob distortion *2 and A Vpe dis-
tortion “3 are all extremely low because of the unique
non-distortion circuit configuration.
“1 Distortion caused by non-linear variations of current gain
B due to variations of collector-emitter voltage VCE.
*2 Distortion caused by non-linear variations of amplifier
gain which are caused by non-linear variations of feedback
capacity Cob due to variations of collector-emitter voltage
VCE.
*3 Distortion caused by non-linear variations of base-emitter
voltage VBE of power transistor.
Distortion of measurement system
Distortion of ‘“Super—A”
Fig. 1 Output and residual distortion waveforms of measur-
ing instrument
Fig.2 Output and distortion waveforms of Super-A am-
plifier
Fig. 3 Output and distortion waveforms of class-AB ampli-
fier
Voltage amplifier stage utilizing ‘‘Super-A”’
performance to the utmost
Fig. 4 shows operating characteristics of a common-emitter
transistor; 8 varies as VCE varies, resulting in A Vce distortion
as described above.
Fig. 5 shows a variation of the feedback capacity Cop in re-
lation to VCE. This non-linear variation of Cop due to varia-
tions of VCE causes a non-linear variation of the amplifier
gain, leading to the A Cob distortion mentioned above. Fig. 6
shows operating characteristics of a common-base transistor.
What is noteworthy about this type of operation is that,
though its current gain is O dB, its output linearity in constant-
current drive is fairly good since a scarcely varies with varia-
tions of VcE (a= 1) as shown by the equal distance between
adjacent base current curves.
An example of the cascode-connected amplifier circuit is
shown in Fig. 7. The features of this circuit are good frequ-
ency response (because of no mirror effect due to Cob) and
high output impedance. This means that this circuit eliminates
distortion by effectively combining the advantages of
common-emitter and base-emitter configurations. The driver
stage of the Super-A power amplifier employs an applied
circuit of this kind and a drastic reduction in distoriton is the
result.
Fig.4 Output characteristics of common-emitter amplifier
Fig.5 Cop characteristic
Fig.6 Output characteristics of common-base amplifier
Fig. 7 Cascode amplifier
Distortion of ‘‘class AB”
f=10 kHz, THD=0.0008%
Fig. 1.
f=10 kHz, Output power=100W/8 QO,
THD=0.0009%
Fig. 2.
9
f=10 kHz, Output power=100W/8 Q
THD=0.0022%
Fig. 3.

IB1
Vee
Fig. 4.
Emitter Configration
Vcs
Fig. 6.
Base Configration
SPECIFICATIONS
Circuitry.......... Direct-coupled DC circuitry with
F.E.T. cascode connected double
differential input and parallel-push
pull output SUPER-A
Output power....... 150W + 150W 892
Total harmonic
distortion......... 0.0004% (1KHz 150W 8&2)
(Mesured by Y.H.P. HP-1B)
0.003% (20Hz ~ 20KHz, 150W 822)
0.03% (20Hz ~ 100KHz, 150W-822)
Inter moduration
distortion......... 0.003% (60 Hz: 7 kHz= 4: 1,8)
Power bandwidth ....5 ~ 100KHz (0.02%, 892, IHF)
TIM (Transient Intermodulation
distortion) ........ unmeasurable
10
Fig. 5.
Cob characteristic
Slew Rate ........
Switching distortion. .
Hum & Noise......
Frequency charactor .
Subsonic Filter.....
Input sensitibity/
impedance.......
Output ..........
Power suply.......
Power consumption. .
Dimensions .......
Fig. 7.
Cascode amplifier
+300V/p sec.
.0
less than 200 pV (Short circuit)
.DC ~ 100KHz, +0, —0.2dB
18Hz 6dB/oct
.1V (input level volume max) /47KQ
more than 120dB (1.H.F.A)
200(1KHz) 882
speaker-1 4Q.~ 16Q
speaker-2 4Q.~ 160
speaker 142 801~ 162
Monitor phone
Refer to page 30
. Refer to page 30
160 m/m (H), 425 m/m (W),
415 m/m (D)
22.4 kg (49.3 Ibs)