Sound Technology 1700B User manual

SOUND TECHNOLOGY
1400
Dell
Avenue
Campbell,
CA
95008
Tel:
(408)
378-6540
Telex:
357445
SOUND TECHNOLOGY
MODEL 17008
DISTORTION MEASUREMENT
SYSTEM
5-
T
Model
7700
Series
U.
S.
Patents:
3940775,
3978407,
4032857
Manual
Part
Number:
7900-0001
Manual
printed
in
U.S.A.
Copyright
July
1979

WARRANTY
All new Sound Technology products are warranted against defects in materials
and workmanship for two years from the date of delivery. Any instrument or
component that is found to be defective within the warranty period after exami-
nation by Sound Technology or an authorized representative thereof will be
repaired or replaced without charge for labor or material. No other warranty
is expressed or implied. We are not liable for consequential damages.
Before returning a product to Sound Technology for service, authorization
must be obtained from the factory. For products not covered by the warranty,
a purchase order should be forwarded to avoid unnecessary delay. Please
include instrument model number and serial number with all requests for
parts or service to faci I itate the fastest possible response.
All products returned to the factory must be shipped prepaid. For products
under warranty, Sound Technology will pay for shipment back to the customer.

fSl SOUND
L!:J TECHNOLOGY
MANUAL CHANGES
CHANGE SECTION 5 - PARTS LISTS - AS FOLLOWS:
1. Page 5-1, Parts List: AC receptacle (P/N: 3110-0000) replaced by Line Filter
(P/N: 3110-0005).
2. Page 5-2, Parts List, Oscillator: R40 same as R8 (P/N: 1100-0051). R34 now 392K,
1% (P/N: 1016-3392). RS (500 ohm trimpot) now P/N: 1410-0015. R20 (SK trimpot)
now P/N: 1410-0017. R7 (1M trimpot) now P/N: 1410-0020.
3. Pages 5-2/5-3, Parts List, THD Analyzer: U108 same as U106 (P/N: 0100-0001).
U105 now type 2605 grade 6 (P/N: 0100-0014). R213 now 18.2K, 1% (P/N: 1015-2182).
R203 now 120 ohms, 5% {P/N: 1100-0120). R359 now 750 ohms, 5% {P/N: 1100-0750).
R167 and R173 same as R130 {P/N: 1100-3100). R170 same as R149 {P/N: 1100-4100).
R157 etc. and R354 {100 ohm trimpot) now P/N: 1410-0013. R146 etc. {1K trimpot) now
P/N: 1410-0016. R129 etc. (lOOK trimpot) now P/N: 1410-0019. R351 (20K trimpot)
now P/N: 1410-0018. C151 same as C107 {P/N: 2000-0027). C211 now 68 pf, 5%
{P/N: 2000-0068). Entry for P/N: 2040-0000 {.01 uf) should read: C140, 141,219,
220,329,330,335,336.
4. Page 5-3, Parts List, Power Supply: R610 same as R604 {P/N: 1015-1422). R609
same as R602 {P/N: 1015-1464). R606 now 1.5K, 1% {P/N: 1015-1150). R607 now
9.09K, 1% {P/N: 1015-1909). R603 and R614 {500 ohm trimpot) now P/N: 14HY-0015.
5. Page S-3, Parts List, Anal Freq 3rd Digit: R67 now 392K, 1% {P/N: 1016-3392).
R66 now 523K, 1% {P/N: 1016-3523). R65 now 806K, 1% {P/N: 1016-3806). R61
now 1.15M, 1% (P/N:1016-4115). R60now 1.33M, 1% {P/N:1016-4133). R59and
R64 now 1.58M, 1% {P/N: 1016-4158). R58 now 2M, 1% {P/N: 1016-4200). R57 now
2.67M, 1% {P/N: 1016-4267). R56 now 4.02M, 1% {P/N: 1016-4402). R55 now 8.06M,
1% (P/N: 1 016-4806).
6. Page 5-3, Parts List, Osc Freq 3rd Digit: R140, R149 now 392K, 1% {P/N: 1016-
3392). R139, R148 now 523K, 1% {P/N: 1016-3523). R138, R147 now 806K, 1%
(P/N: 1016-3806). R137, R146 now 1.58M, 1% {P/N: 1016-4158).
7. Page S-3, Parts List, Input Switch: R140 same as R103 {P/N: 1005-1698). R119
now 909K, 1% {P/N: 1016-3909).
8. Page 5-3, Parts List, Ratio Switch: C325 now 35 uf (P/N: 2100-0023).

MODEL 1700B MANUAL CHANGE INFORMATION
1. The Sound Technology Model 17008 incorporates two
design refinements not found on the 1700A: a front panel
SIGNAL OFF switch, and an ANALYZER SELECT switch.
The functions of these switches are as follows:
a. SIGNAL OFF: When depressed, this switch replaces
the front panel SIGNAL OUTPUT jack with a floating
short circuit. This enables the user to make signal-to-
noise ratio measurements without the necessity of dis-
connecting cables.
b. ANALYZER SELECT: When depressed, this switch
isolates the INPUT connectors, and allows the 17008 to
monitor the signal appearing at the SIGNAL OUTPUT
jack. The user may then select either VOLTS/POWER to
measure the voltage output, or DISTORTION to measure
the residual distortion of the output signal.
2. Late production versions of the 17008 incorporate two
rear panel connectors to faci I itate interconnections be-
tween the 1700B and the Sound Technology Model 1200A
Stereo Test Panel. These connectors are: EXT Fl LTERS
and SYNC OUT; their use is fully explained in the 1200A
Instruction Manual.
3. With the exception of the added switches and connec-
tors as described above, the balance of this manual is
fully usable with either the 1700A or the 17008.
IMPORTANT
THE PUSHBUTTON SWITCHES ARE
PERMANENTLY LUBRICATED. AP-
PLICATION OF ANY LUBRICANT OR
CONTACT CLEANER WILL SHORTEN
THEIR OPERATIONAL LIFE.

Section
I
II
CONTENTS
OPERATION.
• • . • • • • • • • • • •
1-1.
SCOPE
OF
SECTION
• • . • •
1-2.
INTRODUCTION
••••.••
1-3.
INPUT
POWER
REQUIREMENTS
•
1-4.
POWER
CABLE.
• . • • • • •
1-5.
CONTROLS
AND
INDICATORS
••
1-6.
TEST
SETUP
• • • • •
••.•••
1-10
1-18.
1-7.
Power
Connections.
1-8.
Ground
Connections
1-9. Signal Connections
•••
OPERATING
PROCEDURES
• • • •
1-11. Test Connections
•••••••••.
1-12.
Meter
Zero
Mechanical
Adjustment •
1-13. Distortion
Measurement
•••••..•..•.
1-14. Distortion
Measurement
with External Oscillator
..
1-15.
AC
Voltage/Power
Measurement
••..
1-16.
AC
Voltage
Measurement-Extended
Range
...••
1-17. Voltage Ratio
Measurement
•••••..••.•
AUDIO
MEASUREMENTS
• • • • • • • • • • • • • • • • • . •
1-19.
Maximum
Power
Output
at
Rated
Total
Harmonic
1-20.
1-21.
Distortion
at
1
kHz
••.••.••.
Power
Bandwidth
••••.••••..
Hum
and
Noise/Signal-to-Noise Ratio.
PRINCIPLES
OF
OPERATION.
• • • • • . . •
2-1.
INTRODUCTION
• • • • • • • • • •
2-2.
DISTORTION
ANALYZER
••••••
2-3.
General
Description.
2-4. Buffer Amplifier
•••
2-5. Overload Detector
••
2-6.
Notch
Filter
•••••••••••.
2-7. Distortion Amplifier
and
Attenuator
•••
2-8.
Amplitude
Null
Control
•••
2-9.
Phase
Null
Control
••
2-10.
Sum-Point
Buffer •
2-11.
Tuning
Indicator •
2-12.
Filters
•.••••
2-13. Function Switches.
2-14.
AC
Meter
•••••
2-15.
OSCILLATOR
• • • • • • • •
••
Page
•
1-1
• .
1-1
•
1-1
• •1-1
•
1-1
•
1-1
•
1-3
•
1-3
.1-3
•1-3
• •
1-5
•
1-6
.
1-6
.1-6
.
1-7
.
1-7
.1-8
.1-8
•
1-9
•
.1-9
.
1-9
•1-10
•
••
2-1
.2-1
.2-1
.2-2
.2-2
.2-2
•
.2-2
.2-2
•
.2-2
.2-3
.2-3
.2-3
.2-4
.2-4
•
••
2-4
.2-4
2-16.
General
Description.
• • • •
.2-4
2-17.
Oscillator
Circuit
••
2-18.
Amplitude
Control
••
2-19.
POWER
SUPPLY
•••••••.••
2-20.
General
Description.
2-21. Input
Circuit
••
2-22. +
15
Vdc
Supply
.•••
2-23. -
15
Vdc
Supply. • • •
.2-4
.2-4
.2-6
.
.2-6
.2-6
.2-6
.2-7

Section
III
IV.
v.
CONTENTS, Continued
MAINTENANCE. • • . . • . • .
3-1.
INTRODUCTION •..
3-2. TEST EQUIPMENT • . • • • •
3-3.
PERFORMANCE CHECK ••.•••••••••••
3-17.
3-18.
3-4. General Information
•••••••
3-5. Overall System Check
3-6. Distortion Test .•.•••••
3-7. Circuit Common Isolation Check
3-8. Oscillator Check ••••••
3-9. Frequency Test ••.•••
3-10. Distortion Test .•••••
3-11. Distortion Analyzer Check ••
3-12. dB Volts Test ••.••
3-13. Volts Power Test ••••••
3-14. Filters Test •.•••••
3-15. Residual Noise Test •••••••••••
3-16. Common Mode Rejection Test.
ADJUSTMENT AND CALIBRATION PROCEDURE • • •••••
OSCILLATOR SECTION • • . . • • • • • • • • • • •
Page
••••• 3-1
.3-1
.
3-1
.3-1
•
3-1
• 3-1
. 3-1
• •3-3
.3-3
• .3-4
.3-4
• .3-4
.3-4
.3-5
• .
3-5
.3-6
•
3-6
•3-6
.3-7
3-19.
+15 Volt Adjustment ••••.••••••••••
• .3-7
3-20. Photocell
AC Voltage Adjustments ••••••••
• • 3-7
3-21. Oscillator Integrator Voltage Change Adjustment ••
• • • 3-7
.3-7
.3-8
.3-8
3-22.
Oscillator Integrator Output and Adjustment ••
3-23. Oscillator XlOOO Frequency Range Adjustment •••
3-24.
3-29.
3-30.
3-31.
3-32.
ANALYZER SECTION • • • • • . • • • . • • • • . • •
3-25.
De Zero Adjustment •••.••••.•••
3-26. Null Adjustment •.••••••••.•••
3-26A. Phase Null Integrator Voltage Adjustment •
3-27.
Tuning Indicator Adjustment •••..••
3-28. Calibration at 1 kHz ••••••••••
TROUBLESHOOTING. • • • • . • • • • • • • • • • • • •
SYMPTOM/CAUSE TABLE .•...••••••••••••
COMPONENT REPLACEMENT - CALIBRATION and ADJUSTMENT • •
REPLACEMENT and REPAIR • • • • • • • • • • • • •
• .3-8
.3-8
• • • •
3-9
.3-9a
• .3-10
• •3-10
• •3-11
3-33. Special Precautions. • •••
• •3-11
• 3-12
.3-12
3-34. Contamination. •
•••
3-35.
3-36.
3-37.
WIRir~G • . • • • • • • • . • • • •••••••
3-41.
DIAGRAMS
4-1.
4-2.
4-3.
SOLDERING TECHNIQUES .•••
COMPONENT REPLACEMENT ••..
3-38. Multi-Lead Devices •
3-39. Potentiometers
..
3-40. Power Supply • . .
FREQUENCY MODULE REPAIR. . . •
3-42. General
.•••..•
3-43. Removal/Replacement ••
3-44. Repair Instructions.
INTRODUCTION . . . . . . . .
SCHEMATIC DIAGRAMS . . . . .
COMPONENT LOCATION DIAGRAMS.
SPARE PARTS. • • . . . • • . .
5-l. INTRODUCTION •••.•
5-2. ORDERING INFORMATION ••
5-3 PARTS LIST
.• .
• .3-12
•
3-12
.3-12
•
3-12
• •••• 3-15
• ••.. 3-15
• 3-15
. 3-15
• •• 3-15
• ••.• 3-15
• • 3-17
• .4-1
•. 4-1
.4-1
.4-1
•
•. 5-l
.
5-1
.5-1

1-1.
SCOPE
OF
SECTION
SECTION
I
OPERATION
The
section contains information
and
instructions
necessary for the operation of the
Sound
Technology
Model
1700A
Distortion
Measurement
System. Included are
power
requirements,
cabling information
and
operating
instructions.
1-2.
INTRODUCTION
The
Model
1700A
Distortion
Measurement
System
combines
an
ultra-low
distortion
os-
cillator,
a high-resolution automatic-measuring
distortion
analyzer,
and
an
accurate
ac
voltage/power meter in
one
instrument. Pushbutton operation permits the operator to
quickly
measure
voltage
or
power,
set
level,
and
then
measure
distortion.
The
oscillator
section provides a pure
sine
wave
signal for
testing
from
10
Hz
to
110
kHz.
Amplitude
is
variable
from
3 volts to
less
than 1
mV.
The
analyzer section contains a tracking notch
filter
which
is
always tuned to the os-
cillator
frequency.
The
analyzer measures
total
harmonic
distortion
with a
sensitivity
ran-
ging
from
100%
to
.01%
full
scale,
with automatic nulling
on
all
ranges. Active
filters
may
be
selected
for
low
frequency
and
high frequency noise suppression, enhancing the measure-
ment
resolution.
A
differential
front
end
rejects
common-mode
noise.
The
ac
voltage/power meter inherent in the analyzer measures
ac
voltage,
or
power
ac-
ross
an
8-ohm
external load.
The
measurement
range for
ac
voltage
is
3
mV
to
300
V
full
scale
(30
~V
to 1
mV
in Extended
Range
Para. 1-16)
and
for
power
is
1
~W
to
10
kW
full
scale.
Voltage
ratio
measurements with a
100
dB
or
more
of
dynamic
range
can
also
be
made.
1-3.
INPUT
POWER
REQUIREMENTS
The
Model
1700A
System
may
be
operated
from
either
a 95-125
volt
or
200-250
volt
50
to 60Hz
power
source. A two-position
selector
switch
on
the
rear
panel
selects
the
power
source. Before connecting the instrument to the
power
outlet,
check
that
the
selector
switch
setting
matches the
nominal
line
voltage
of
the source.
The
Model
1700A
System
is
protected
from
ac
power
overloads
by
a fuse (lA, fast-blown)
located in a
cartridge-type
fuse holder
on
the
rear
panel.
1-4.
POWER
CABLE
The
International Electrotechnical
Commission
(IEC)
recommends
that
instrument panels
and
cabinets
be
grounded to
protect
operating
and
servicing personnel.
The
Model
1700A
system
is
equipped with a three-conductor
power
cable assembly which,
when
plugged into the
appropriate
outlet,
grounds the
unit
through the
round
offset
pin.
1-5.
CONTROLS
AND
INDICATORS
The
data sheet
at
the
front
of
the
manual
illustrates
and
describes
briefly
the
Model
1700A
Distortion
Measurement
System's front panel controls
and
indicators.
The
following
provides additional explanatory information:
a.
POWER
ON
switch connects
ac
power
to
Model
1700A
System.
Pilot
lamp
glows
when
instrument
is
turned
ON.
b.
+INPUT
and
-INPUT
terminals
--
Provide connections
for
signal being measured.
c.
GND
(rfJ)
terminal Provides connection
to
chassis ground.
d.
c~
(~)
terminal Provides connection to
circuit
common.
e.
VOLTS/POWER
pushbutton--
Selects Volts
or
Power
measurement
function.
1-1

f. INPUT switch -- Selects full scale meter range for Volts or Power measurement function.
Readings are in
volts rms or watts.
g.
OVERLOAD indicator -- Indicator is lit when input signal overloads input buffer. This
warns operator that Volts or Power measurement is no longer accurate.
h.
i .
j.
k.
l.
m.
n.
o.
p.
q.
r.
s.
t.
SET LEVEL pushbutton -- Selects Set Level function whereby meter displays reference
signal level
for Distortion or Ratio measurement.
SET LEVEL ADJUST -- Adjusts reference signal level for Distortion or Ratio measure-
ment. When control is set to CAL position (max. counterclockwise), RATIO ranges ex-
tend voltage measurement capability to 30 ~V full scale (Paragraph 1-16).
DISTORTION pushbutton -- Selects Distortion measurement function.
dB VOLTS pushbutton -- Selects Ratio measurement function.
RATIO Switch --Selects full scale meter range for Distortion and Ratio measurement
functions.
Readings are in percent or dB.
NOTCH FREQUENCY indicators-- Facilitate tuning when using an external oscillator.
When LOW indicator is lit, Model 1700A System frequency is low with respect to in-
coming signal, when HIGH indicator is lit, Model 1700A System frequency is high with
respect to incoming
signal. System is correctly tuned when both indicators are
extinguished.
(It is normal for one of these indicators to glow when there is no
input to the 1700A.)
SIGNAL COMMON switch -- Switches circuit common from chassis ground, breaking ground
loops. FLOAT position floats (disconnects) circuit common of System from chassis
ground; Chassis
Ground (r,h) position connects circuit common of System to chassis
ground.
FILTERS -- 400Hz pushbutton selects a filter which suppresses low-frequency noise
(such as
60 Hz hum) below 400 Hz. 80 kHz pushbutton selects a filter which suppresses
high-frequency noise
above 80 kHz. The 80 kHz filter also reduces effects of AM
radio station pickup. Both filters affect meter reading only on Distortion and Ratio
measurement functions. They do not affect meter reading on Volts/Power, and Set Level
measurement functions. The 400 Hz filter is usable with fundamental frequencies down
to 400 Hz when making distortion measurements.
METER -- Indicates signal level of measurement selected by Function pushbutton.
DISTORTION OUTPUT BNC connector -- Provides distortion product of signal being analyzed
(suitable for viewing on oscilloscope) on Volts/Power, Set Level, and Distortion
measurement functions. On Ratio measurement function, this output provides a scaled
version
of input signal. Output is 31.6 mV full scale.
FAST RESPONSE/LOW DISTORTION switch --Selects operating mode of oscillator. FAST
RESPONSE causes oscillator amplitude to settle quickly after a frequency change.
This
mode is recommended when ultra-low distortion measurements are not required,
for
ex amp 1e when making frequency response measurements. LOW DISTORTION se1 ects
full ultra-low distortion capability of oscillator. The settling time in this mode
is less than 5 seconds. Actuation of FREQUENCY pushbuttons generally causes oscillator
to go first to FAST RESPONSE mode and then to settle in LOW DISTORTION mode. This
switch controls only the
oscillator and is not connected to the distortion analyzer.
FAST RESPONSE indicator-- Indicates operating mode of oscillator. When lit, oscilla-
tor is in Fast Response mode and does not have ultra-low distortion.
FREQUENCY pushbuttons --Simultaneously select oscillator and distortion analyzer fre-
quency. Four Multiplier switches and 30 Digit switches permit 3-digit resolution
within each range. Frequency range of
Model 1700A System is 10 Hz to 109.9 kHz. One
button in each row must be depressed at all times.
1-2

u.
OSCILLATOR
LEVEL
control
--Adjusts
amplitude of
oscillator.
Level
is
variable
from
3
volts
to
below
1
millivolt.
Control
is
single-turn logarithmic potentiometer.
v.
SIGNAL
OUTPUT
BNC
connector--
Provides
oscillator
output
signal.
Output
impedance
varies with
setting
of
OSCILLATOR
LEVEL
control
and
reaches a
maximum
of
625
ohms
at
mid-range.
w.
BUFFERED
INPUT
SIGNAL
BNC
connector (located
on
rear
panel)
--
Provides replica of
input signal being analyzed. This signal
is
referenced to
ground
and
intended to
be
connected to
an
oscilloscope.
1-6.
TEST
SETUP
In
order to ·take
full
advantage of the unique ultra-low
distortion
measuring cap-
abilities
of
the
Model
1700A
System
it
is
extremely imoortant
that
the cabling
between
the
Model
1700A,
the amplifier under
test,
and
other
test
equipment
be
connected in compliance
with the arrangement
shown
in Figure
1-1
and
described in the following paragraphs.
The
connections
and
controls
numbered
in Figure
1-1
are
similarly
identified
in the
test.
These
connections
have
been
found
to provide the
optimum
test
setup in
most
cases.
1-7.
POWER
CONNECTIONS
a.
Check
that
power
slide
switch
on
rear
panel
of
Model
1700A
is
set
to correct position
for
available
ac
power
(see Paragraph 1-3 for
details).
b.
Do
not
float
the
earth
ground
lead
of
the
power
cord of the
Model
1700A.
(The
dif-
ferential
input
makes
this
step unnecessary for breaking
ground
loops.)
c.
Plug
the
Model
1700A,
amplifier under
test
and
the oscilloscope
(if
used) closely to
each
other
into the
ac
power
bus.
1-8.
GROUND
CONNECTIONS
a.
Connect
Model
1700A
GND
(roh)
terminal (1) to
ground
terminal (chassis
ground)
of
am-
plifier
under
test.
NOTE
This reduces
common
mode
60-Hz
potential differences
and
provides a path to
ground
for
60-Hz
current
that
may
be
injected into the chassis
of
the amplifier
under
test
from
its
own
primary
power
circuits.
b.
Connect
oscilloscope
(if
used) to
BUFFEREDI~PUTSIGNAL
BNC
connector
(2)
on
rear
panel
of
Model
1700A
via cable (3).
NOTE
1. This output
is
from
the
differential
to single-ended converter in the
Model
1700A
which
provides a replica
of
the input
signal.
This signal
is
referenced to
ground.
2.
If
a
BNC
cable
is
not
used
for
this
connection, the oscilloscope
common
(low)
terminal
must
be
returned to the
Model
1700A
System
GND
(r,h)
terminal (1) via
a
direct
connection (4}.
c.
This completes the
ground
connections necessary for proper
Model
1700A
operation.
1-9.
SIGNAL
CONNECTIONS
CAUTION
CONNECTING
OSCILLATOR
OUTPUT
TO
A
HOT
CHASSIS
MAY
BLOW
FUSE,
F2
or
F3.
(Fuses located
on
bottom
of instrument. A
blown
fuse will
make
FLOAT
switch
ineffective
and
cause
hum
problems.)
DO
NOT
EXCEED
THE
INPUT
VOLTAGES
LISTED
BELOW
TO
PREVENT
BLOWING
FlOl
AND
Fl02.
With
Input
Range
Switch
--
3 V
and
Lower.
1.
300V
Below
60Hz
2.
50
V
Above
1
kHz
1-3

• 0
@
• 0
0.
0
0
1-4
c.
::s
+>
Q)
(/')
+>
VI
Q)
1-
c:(
0
0
r--.
..-
r-
Q)
"'0
0
:::E
..-
I
Q)
s...
::s
C'l
u..

a. Connect oscilloscope
(if
used)
to
DISTORTION
OUTPUT
connector (5) via cable
(6).
This
permits monitoring
the
distortion
products
of
the signal being analyzed.
NOTE
The
shell of the
DISTORTION
OUTPUT
BNC
connector
is
returned inside the
Model
1700A
System
to
circuit
common
through a 1
~F
capacitor.
The
shell of the rear-panel
BNC
connector
is
at
chassis ground.
The
above
connections place
this
1
~F
between
the
Model
1700A
System
circuit
common
and
the chassis
when
using
an
oscilloscope.
This permits reasonably
noise-free
viewing
of
the
waveforms
while
still
retaining
a
considerable
amount
of
immunity
to
ground
loop currents flowing
between
the
Model
1700A
SIGNAL
OUTPUT
and
the
input of the
amplifier
under
test.
b.
Turn
OSCILLATOR
LEVEL
control (7)
fully
counterclockwise
(minimum
level).
c. Set gain control
on
amplifier
under
test
to
its
lowest
setting.
d. Connect cable (8)
between
SIGNAL
OUTPUT
BNC
connector (9)
and
input
of
amplifier under
test.
e. Set
SIGNAL
COMMON
switch (10) to
FLOAT.
NOTE
This achieves
the
ultimate
rejection
of
unwanted
power-line
related
noise (es-
pecially
in the leads of the input
of
the
amplifier
under
test).
With
no
other
equipment
such
as
an
oscilloscope connected to the system,
there
is
only a
nominal
.001
~F
of capacitance
between
the
System
circuit
common
and
chassis ground.
The
corresponding reactance,
greater
than 2
megohms
at
60
Hz,
effectively
opens the
ground loops
between
the
Model
1700A
and
the
amplifier under
test.
f.
Connect output of
amplifier
under
test
to a
suitable
8
ohm
load
resistor.
(Load
resistor
should
be
in a location
free
from
any
ac
magnetic
field,
such as caused
by
a
power
transformer, to avoid
hum
pickup).
g.
Connect signal to
be
measured (voltage developed across 8
ohm
load)
between
+INPUT
and
-INPUT
terminals (11).
Use
shielded
twisted-pair
cable
for
this
connection
and
keep
test
leads as
short
as possible to avoid extraneous pick
up
from
stray
ac
fields.
h.
Connect shield (12)
of
input wiring to
COM
(
~)
terminal (13).
Leave
shield
(14)
at
other
end
unconnected.
NOTE
1.
The
input terminals
do
not
have
a
polarity
(as indicated)
for
ac
and
may
be
connected
either
way
with
no
damage
to the
amplifier
under
test.
2.
Each
INPUT
terminal
has
its
own
input
attenuator
and
buffer amplifier. In-
put
impedance
is
100
kilohm
from
each terminal to the
Model
1700A
System
circuit
common.
The
true
differential
input
circuits
of the
Model
1700A
System
help break
the ground loop
that
causes
60-Hz
pickup
on
the input leads of
most
measuring equip-
ment.
3.
Do
not connect
one
channel of
the
oscilloscope
directly
to the output of
the amplifier-under
test
as
this
can
upset the noise
rejection
capability
of the
Model
1700A
System
differential
input
circuitry.
If
it
is
absolutely
essential
to
monitor
this
signal,
leave the
ground
lead of the scope channel disconnected
from
the
amplifier
under
test.
1-lO.OPERATING
PROCEDURES
CAUTION
CONNECTING
OSCILLATOR
OUTPUT
TO
A
HOT
CHASSIS
MAY
BLOW
FUSE,
F2
or
F3.
(Fuses located
on
bottom of instrument. A
blown
fuse will
make
FLOAT
switch
ineffective
and
cause
hum
problems.)
DO
NOT
EXCEED
THE
INPUT
VOLTAGES
BELOW
TO
PREVENT
BLOWING
FUSES
FlOl
AND
Fl02.
1-5

With
Input
Range
Switch
--
3V
and
Lower
1.
300
V
Below
60Hz
2.
50
V
Above
1
kHz
1-11.
TEST
CONNECTIONS
Before
making
measurements
with the
Model
1700A
System,
ensure
that
the
equipment
has
been
connected
as
shown
in Figure
1-1
and
following the instructions given in Paragraphs
1-6
through 1-9.
1-12.
METER
MECHANICAL
ZERO
ADJUSTMENT
The
meter
is
correctly
zero
set
when
the pointer rests over the zero calibration
marks
on
the scale
when
the
Model
1700A
INPUT
switch
is
set
to
300
V,
the
VOLTS
POWER
pushbutton
is
depressed,
and
there
is
no
input signal (input leads disconnected).
To
adjust the zero
set
proceed
as
follows:
a. Rotate zero adjustment
screw
(lbcated
on
front
panel
below
meter) until pointer
is
left
of
zero.
Reverse
rotation until pointer
is
exactly
at
zero.
1-13.
DISTORTION
MEASUREMENT
To
measure
the
total
harmonic
distortion
of a
signal,
proceed
as
follows:
a. Set
FAST
RESPONSE/LOW
DISTORTION
switch to
LOW
DISTORTION
and
select
fundamental
test
frequency in
Hz
by
depressing appropriate
FREQUENCY
pushbuttons.
NOTE
1.
Four
Multiplier pushbuttons (Xl,
XlO,
XlOO,
XlOOO)
and
30
Digit pushbuttons
permit
3-digit
resolution of frequency
selection.
For
example,
453
Hz
would
be
selected
by
depressing the following pushbuttons:
Multiplier
XlO
lst.
Digit
40
2nd.
Digit
5
3rd. Digit
.3
Frequency
40xl0=400
5xl0=
50
•
3xl0=
3
453
Hz
The
11
100
11
Digit pushbutton provides a
10%
overlap
in
range.
For
example,
1010
Hz
can
be
selected in
two
ways:
Multiplier
lst.
Digit
2nd.
Digit 3rd. Digit
Freguencx
XlO
100
lOOxl0-1000
lxlO=
10
0
OxlO=
0
1010
Hz
XlOO
10
lOXlOO=lOOO
0
OxlOO=
0
•
1
.lxlOO=
10
1010
Hz
2.
In
the
Xl
range, operation of the frequency pushbuttons
may
not
always
cause
the
oscillator
to
go
through
its
automatic
stabilization
cycle.
If
the
oscillator
amplitude appears to
be
unstable, momentarily
set
the
FAST
RESPONSE/LOW
DISTORTION
switch to the
FAST
RESPONSE
position
and
then return
it
immediately to the
LOW
DIS-
TORTION
setting.
b.
Depress
VOLTS
POWER
pushbutton
and
set
ADJ.UST
contro1 fully
CCW
to
CAL
position.
c. Set
INPUT
switch to expected
range
setting.
d. Adjust
OSCILLATOR
LEVEL
control and/or gain control
on
amplifier
under
test
for
de-
sired
voltage/power level as indicated
on
Model
1700A
meter.
Up
range
INPUT
switch
when
meter pointer passes
full
scale
and
down
range
when
meter pointer
goes
below
1/3
of
full
scale.
1-6

NOTE
If
OVERLOAD
indicator
lights
and
meter reads
less
than full
scale,
meter reading
is
incorrect
due
to
ADJUST
control being
incorrectly
set.
To
regain accuracy, turn
ADJUST
control
down
(CCW)
until
OVERLOAD
light
is
OFF.
e. Depress
SET
LEVEL
pushbutton
and
rotate
set
level
ADJUST
control until meter pointer
rests
on
SET
LEVEL
mark.
f.
Depress
DISTORTION
pushbutton
and
rotate
RATIO
switch
until
meter
pointer
reaches upper
2/3's
of
scale.
If
desired,
depress 400Hz and/or
80
kHz
FILTER
pushbutton to
filter
noise
from
input
signal.
g. Observe
distortion
either
in percentage or
dB,
as
indicated
by
meter
deflection
and
RATIO
switch
·setting.
For
example,
if
meter reads .67
and
RATIO
setting
is
.1%,
dis-
tortion
measured
is
.067%.
1-14.
DISTORTION
MEASUREMENT
WITH
EXTERNAL
OSCILLATOR
a.
Connect
equipment
as
shown
in Figure 1-1, with the following exceptions:
1. Connect
power
cord of external
oscillator
to
power
source close to source
used
by
Model
1700A,
amplifier
under
test,
and
oscilloscope.
2. Connect output
of
oscillator
to input of amplifier under
test.
The
oscillator
output
may
be
floated
if
this
gives
better
test
results.
3. Connect chassis
of
oscillator
to
GND
(r.h)
terminal
on
Model
1700A.
4. Set
SIGNAL
COMMON
switch
on
Model
1700A
to~(ground)
position.
b. Set external
oscillator
to desired frequency
and
signal
level.
c.
Preset
Model
1700A
FREQUENCY
pushbuttons
to
approximate frequency
of
external
oscil-
lator.
d. Set
ADJUST
control
fully
counterclockwise
(CCW)
to
CAL
position
and
depress
VOLTS
POWER
pushbutton.
e.
Set
INPUT
switch to expected range.
f.
Adjust external
oscillator
amplitude control and/or gain control of amplifier under
test
for
desired voltage/power level as indicated
on
Model
1700A
meter.
g. Depress
SET
LEVEL
pushbutton. Rotate
ADJUST
control
until
Meter
pointer
rests
on
SET
LEVEL
mark.
h. Set
1700A
frequency or external
oscillator
frequency
so
both
NOTCH
FREQUENCY
indicators
are
off
and
that
the tuning
is
approximately centered.
i.
Depress
DISTORTION
pushbutton
and
set
RATIO
switch
so
that
meter pointer
rests
within
upper
2/3's
of
scale.
If
desired,
depress 400Hz and/or
80
kHz
pushbutton to
filter
noise
from
input
signal.
j.
Observe
distortion
in
either
percentage or
dB,
as
indicated
by
meter
deflection
and
RATIO
range
setting.
1-15.
AC
VOLTAGE/POWER
MEASUREMENT
The
Model
1700A
is
an
accurate
ac
voltage/power meter over
its
entire
frequency range.
The
power
scale
is
calibrated
for
an
8-ohm
load,
which
must
be
provided
externally.
Vol-
tage
may
be
measured
directly
from
3
mV
to
300
V
full
scale
and
power
from
1
uV
to
10
kW
full
scale.
To
measure
ac
voltage or
power,
proceed
as
follows:
a. Ensure
that
the
power
and
ground connections are
as
described
in
Paragraphs 1-7
and
1-3
respectively.
1-7

b.
c.
d.
Connect signal to
be measured between + INPUT and - INPUT terminals. Use shielded
twisted-pair cable for low-level inputs. Connect shield to COM (~) terminal.
Set ADJUST control to CAL position and depress VOLTS POWER pushbutton.
Rotate
INPUT switch for an on scale reading (pointer in upper 2/3's of scale).
NOTE
The 400 Hz and 80 kHz FILTERS do not affect readings on the ac Voltage Power
measurement function.
1-16.
AC VOLTAGE MEASUREMENT- EXTENDED RANGE
The sensitivity of the ac voltmeter can be extended to 30 ~V full scale through the
use of
the RATIO switch. To obtain this increased sensitivity carry out the following
steps:
a.
b.
c.
d.
Ensure
that power and ground connections are as described in Paragraphs 1-7 and 1-8
respectively.
Connect signal to be measured between + INPUT and - INPUT terminals. Use shielded
twisted-pair cable for signal connection. Connect shield to COM (~) terminal.
Set Model 1700A controls as follows:
dB VOLTS switch --------------------------------------- depressed
INPUT switch ------------------------------------------ .3 V
ADJUST control ---------------------------------------- CAL
Meter full scale sensitivity is now controlled by RATIO switch as follows:
RATIO switch
-80
dB
-70 dB
-60 dB
-50 dB
NOTE
Full Scale Sensitivity
30 llv
100 llV
300 J.!V
1 mV
The 400Hz and 80kHz FILTERS will affect meter readings in this mode of opera-
tion.
1-17. dB VOLTS MEASUREMENTS
The dB Volts function facilitates the measurement of voltage ratio, signal-to-noise
ratio, and frequency response, in dB or percent. The signal-to-noise ratio measurement
described
below provides an example of the use of this function.
a. Ensure that power and ground connections are as described in Paragraphs 1-7 and 1-8
respectively.
b. Set ADJUST control to CAL position and depress VOLTS POWER pushbutton.
c. Set INPUT switch to expected range and adjust appropriate signal level controls for
desired output signal, as indicated on meter.
d. Depress
SET LEVEL pushbutton and rotate ADJUST control until meter pointer rests on
0 dB mark.
NOTE
For proper 0 dB or 100% set level, reference signal must be at least .1 V and
not exceed 300 V.
e. Remove input signal to amplifier under test and replace with a short circuit across am-
plifier's input terminals. Set SIGNAL COMMON switch to rt
1 (ground)
position.
1-8

NOTE
When
the input signal
to
the
amplifier
under
test
is
removed
and
replaced with a
short,
this
floats
entire
Model
l?OOA
measuring
circuits.
Proper grounding
can
be
restored
by
setting
the
CIRCUIT
COMMON
switch
to
the
r.h
(ground)
position.
f.
Depress
dB
VOLTS
pushbutton.
Select
RATIO
switch range
which
places meter
pointer
in
upper
2/3's
of
scale,
Read
test
result
in
dB.
g.
At
end
of
signal-to-noise
ratio
measurement, return
SIGNAL
COMMON
switch to
FLOAT
position.
1-18.
AUDIO
MEASUREMENTS
Operating
instructions
for
performing
certain
audio measurements as
specified
by
the
Institute
of
High
Fidelity
(1960) are given below.
For
these
tests,
ensure
that
the
fol-
lowing
test
conditions are maintained:
a.
b.
c.
d.
e.
f.
g.
Line:
120
V
~
1%,
60
Hz,
less
than
2%
total
harmonic
distortion.
0
Temperature:
25
~
3
C.
Preconditioning: Unit under
test
should
be
preconditioned
for
1
hour
at
1/10 rated
power.
(FTC
requires 1/3 rated power).
Amplifier
Gain
Controls: Set to
maximum.
Amplifier
Tone
Controls:
Flat.
Amplifier Balance Control: Set to normal.
Test Equipment:
Model
l?OOA
exceeds
all
IHF
requirements
for
test
equipment accuracy.
1-19.
MAXIMUM
POWER
OUTPUT
AT
RATED
TOTAL
HARMONIC
DISTORTION
AT
1
kHz
NOTE
Amplifier
must
be
able to maintain
this
power
for
30
seconds.
a.
Set
Model
1700A
for
frequency output 1
kHz.
b. Connect
SIGNAL
OUTPUT
to
amplifier's
AUX
or
TAPE
INPUT
on
all
channels.
c.
Set
RATIO
SWITCH
so
that
amplifier's
rated
distortion
gives
maximum
on-scale reading,
and
observe
distortion
products
on
oscilloscope.
d. Increase
OSCILLATOR
LEVEL
setting
until
distortion
products
on
oscilloscope
are ex-
cessive while (1) monitoring
power
with
VOLTS
POWER
pushbutton depressed
and
(2)
keeping signal
on
scale
with
INPUT
switch.
e.
When
excessive
distortion
products are
present,
refine
measurement
by
adjusting
OS-
CILLATOR
OUTPUT
while measuring
distortion
until
the
amplifier's
rated
distortion
is
reached.
f.
Switch
Model
l?OOA
to
VOLTS
POWER
function
and
determine
amplifier's
power
eutput
at
rated
distortion.
1-20.
POWER
BANDWIDTH
a.
Maintain
test
setup
as
described in Paragraph
l-19.
b. Adjust
amplifier
level
until
power
is
3
dB
beiow
rated
power
(1/2
power)
at
midband
(full
rated
power
for
FTC).
c. Increase
Model
l?OOA
frequency in steps
from
midband
while measuring
distortion.
Stop
when
distortior'l
is
equal to
amplifier's
specifications.
This
is
upper
power
band-
width
point.
l-9

d. Repeat step
c,
this
time decreasing
Model
1700A
frequency until lower
power
bandwidth
point
is
found.
The
result
may
be
expressed
briefly
(for
example:
Power
Bandwidth
=
15Hz to 37kHz);
or
it
may
be
shown
as
a graph of
distortion
versus frequency, with
power
held constant
at
3
dB
below
rated power.
1-21.
HUM
and
NOISE
or
SIGNAL-to-NOISE
RATIO
Make
this
measurement
following the
instructions
given in Paragraph 1-17 for measuring
voltage
ratios.
Drive the amplifier to
its
rated
power
output with gain controls
set
to
maximum.
Then
remove
the input
and
obtain a
dB
ratio
reading
as
described in 1-17.
1-10

2-1. INTRODUCTION
SECTION II
PRINCIPLES OF OPERATION
The Model 1700A Distortion Measurement System consists of an ultra-low distortion os-
cillator, a total harmonic distortion analyzer, and a de power supply. The system makes
total harmonic distortion measurements by applying a sine-wave of ultra-low distortion
from the oscillator to the input of the amplifier under test while the distortion analyzer
measures the amplifier output. A tunable notch
filter in the analyzer, mechanically ganged
to the oscillator by the front panel frequency select switches, suppresses the fundamental
signal. Automatic nulling circuitry fine tunes the notch filter and ensures that the null
is retained. The signal remaining at the output of the notch filter consists of the dis-
tortion products and noise. This is displayed by an average-reading voltmeter in the
analyzer.
The ratio of the measured distortion components to a previously set fundamental
signal reference level
is defined as the total harmonic distortion and can be read out
directly on the meter in percent or dB. Switchable low-frequency and high-frequency filters
are provided to enhance the readout of the harmonic products.
Other
features of the Model 1700A include separate Voltage and Distortion measurement
range switches, separate Set Level monitoring without range changing, and automatic nul-
ling on all ranges.
The power supply provides regulated de voltages of +15 volts and -15 volts to power
the oscillator and analyzer. Both of these supplies are internally protected against
accidental short
circuit.
2-2. DISTORTION ANALYZER
2-3. GENERAL DESCRIPTION
Refer to Figure 4-2 for a schematic diagram of the distortion analyzer assembly. Note
that the circuit is divided into the following circuit blocks: Buffer amplifier, overlaod
detector, notch filter, distortion amplifier and attenuator, amplitude null filters, fun-
ction switches,
and ac meter. The operation of the assembly is discussed first at a circuit
block level and is then followed by details of each block.
In operation, the signal to be measured is connected to the input of the buffer amp-
lifier. This circuit has two outputs: a fixed output which may be connected to the ac
voltmeter, and a variable output (controlled by the ADJUST control) which is connected to
the notch
filter. The voltmeter is an average reading type which measures the signal level
selected
by the appropriate function switch.
The overload detector monitors the variable output of the buffer amplifier. If an
excessively high output voltage is detected, the detector turns on the front panel OVER-
LOAD indicator.
The notch filter is mechanically ganged to the oscillator frequency select switches
and suppresses the fundamental from the output of the buffer amplifier. The output of
the notch filter is connected to the input of the distortion amplifier through a step
attenuator controlled by the front panel RATIO switch. The attenuator adjusts signal
level
for the distortion amplifier for various percentages of distortion or ratio readings.
The amplitude null control and phase null control circuits supply the notch filter
with its automatic nulling feature. Both circuits monitor the output of the distortion
amplifier and feed control signals back to the notch filter.
The sum-point buffer supplies reference signals to the tuning indicator and to the
amplitude null control
circuit.
The tuning indicator circuit, using frequency information from the notch filter,
provides the operator with a visual indication of the frequency being analyzed versus the
input frequency. This
circuit operates the NOTCH FILTER HIGH and LOW indicators.
The switchable low-frequency and high-frequency filters are connected to the output
of the
distortion amplifier. This permits them to be selected for DISTORTION and dB VOLTS
measurements only.
2-1

The switchable low-frequency and high-frequency filters are connected to the output
of the distortion amplifier. This permits them to be selected for DISTORTION and dB VOLTS
measurements only.
The function switches select the circuit to be measured by the ac voltmeter. When
the VOLTS POWER switch is depressed, the meter monitors the output via a stepped attenuator
from the buffer amplifier. When the SET LEVEL switch is depressed, the meter monitors the
variable output of the buffer amplifier. Operation of the DISTORTION switch routes the
signal
from the distortion amplifier via the low-frequency and high-frequency filters (if
selected) to the meter. When the dB VOLTS switch is depressed, it connects the variable
output from the buffer amplifier directly to the attenuator at the input of the dis-
tortion amplifier and hence to the meter.
2-4.
BUFFER AMPLIFIER
The input of the buffer amplifier contains a pair of step attenuators, one for each
INPUT connector. The attenuators are controlled by Sections SlA, B, C, D of the INPUT
switch. The attenuator outputs are connected to input signal preamplifiers UlOl and Ul02.
The gain of these units is controlled by section SlE of the INPUT switch. Gain is unity
on the 3 Vrange and above, 3.16 on the 1 Vrange, and 10 on the .3 V range and below.
The preamplifier outputs are coupled to Ul03, a bridge amplifier circuit which effectively
acts as a differential to single-ended converter with high common-mode noise rejection.
The gain of the bridge amplifier is controlled by ADJUST potentiometer Rl25 and provides
the
variable signal supplied by the buffer. The range of gain is 10 dB and full scale
voltage is 3.16 volts. The fixed output from the buffer is obtained between the wiper
of Rl25 and ground. This signal remains fixed regardless of the setting of Rl25, except
when the buffer overloads.
2-5.
OVERLOAD DETECTOR
The overload detector signals an overload condition when the variable output of the
buffer
amplifier exceeds approximately 6.5 volts rms sine wave or 9 volts peak. The
circuit consists of comparator Ul07, a half-wave rectifier and filter, a light-emitting
diode driver, and OVERLOAD indicator CR120.
2-6. NOTCH FILTER
The notch filter consists of two 90-degree phase shifters connected in series, making
the output 180 degrees out of phase with the input. By summing the input and output at
summing amplifier U203, the fundamental of the input signal is cancelled out. Feedback
from the output of the summing amplifier to the input of the filter increases the Q of
the circuit and narrows the rejection band of the filter.
Tuning is controlled by changing a set of RC elements for each phase shifter through
operation
of the front panel Multiplier and Digit pushbutton switches. When the reactance
of the capacitance equals the resistance at the incoming frequency, the phase shift is
90 degrees. The RC components are contained in the frequency module (see Figure 4-5 for
schematic diagram).
2-7.
DISTORTION AMPLIFIER AND ATTENUATOR
The output of the notch filter is coupled through a 7-step attenuator to the input
of distortion amplifier U204. The attenuator is controlled by section S2D of the front
panel RATIO switch and reduces the distortion product of the notch filter such that the
full scale voltage input to the amplifier is 1 mV on ranges .03% through 100% and .316 mV
on the .01% range.
Amplifier
U204 is a wide-band high-gain unit with gain controlled by section S2E of
the RATIO switch. The gain is 31.6 for ranges .03% through 100% and 100 for the .01%
range. This gives a full scale output voltage of 31.6 mV on all ranges.
2-8.
AMPLITUDE NULL CONTROL
The amplitude null control circuit controls the amplitude of the signal from the
cascaded phase shifter so that exact balance occurs when it is summed with the input to
the phase
shifters. This ensures the total cancellation of the fundamental signal. The
components which perform this function include phase detector U310, floating integrator
and voltage follower U312, integrating amplifier U311, integrating capacitors, and a
photocoupler
controlling a variable resistor element in the summing network.
2-2

The
reference
input
to
phase
detector
U310
is
a signal
which
is in phase with the fun-
damental
and
the
signal
input to
U310
is
the
distortion
product output
of
the
distortion
amplifier.
With
these
inputs,
the phase
detector
monitors the notch
filter
output
for
an
in-phase
signal.
When
this
occurs the output
of
the phase
detector
supplies drive to the
integrator
causing
the
charge
on
the
integrating
capacitors to change. This in turn causes
the photocoupler to change the value
of
the
variable
resistor
which
in
effect
adjusts
the
summing
current
until
the in-phase
component
is
no
longer
there.
The
integrating
capacitors
are changed
by
the
RATIO
attenuator
S\vitch. This in
effect
maintains the automatic null control loop gain
at
a
relatively
constant
level,
resulting
in
high-speed nulling
on
all
ranges.
The
capacitors
are
precharged to the
integrator
output
voltage level through
resistor
R360.
This avoids switching
transients
and
improves the
speed
of
the
circuit.
2-9.
PHASE
NULL
CONTROL
The
phase null control
circuit
fine
tunes the phase of the second phase
shifter
in the
notch
filter
so
that
the overall phase
shift
is
exactly
180
degrees. This ensures
total
cancellation
of
the fundamental
signal.
The
components
which
perform
this
function include
phase
detector
U307,
floating
integrator
and
voltage follower
U309,
integrating
capacitors,
and
a photocoupler
controlling
a
variable
resistor
in the
resistive
branch
of
the second
phase
shifter.
The
reference
input
to phase
detector
U307
is
the
distortion
product output of the
distortion
amplifier.
With
these inputs the phase
detector
monitors the notch fi
Iter
output
for
an
out-of-phase
signal.
When
this
occurs, the phase
detector
output supplies drive to
the
integrator
causing the charge
on
the
integrating
capacitors to change.
The
integrator
output drives the
variable
gain
amplifier,
U313,
and the voltage to
current
converter,
U314,
which
in turn causes
the
photocoupler to
change
the value of the
variable
resistor
which
in
effect
adjusts
the phase angle
until
the out-of-phase
component
is
no
longer
there.
The
integrating
capacitors are changed
by
the
RATIO
attenuator
switch. This in
effect
maintains the automatic null control loop gain
at
a
relatively
constant
level,
resulting
in
high-speed nulling
on
all
ranges.
The
capacitors are precharged to the
integrator
output
voltage level through
resistor
R344.
This avoids switching
transients
and
improves the
speed
of
the
circuit.
A
set
of
resistors
that
feed signal
from
integrator
U308
to
U313,
which
acts
as a gain
control,is
switched
by
the
front
panel
FREQUENCY
switches. This maintains a
relatively
constant
integrator
voltage
when
frequency
is
changed
and
helps to achieve
perfect
nulling
in
less
than 5 seconds.
2-10.
SUM-POINT
BUFFER
The
sum-point
buffer
supplies a signal
from
the notch
filter
summing
point
to the
tuning
indicator
and
the
amplitude null
control,
each
of
\vhich
uses the signal
as
the
reference input to a phase
detector.
The
buffer
consists
of unity-gain
amplifier
U301
and
high-gain high-speed amplifier
U302.
These
components convert the
sine
wave
at
the
summing
point
into a square
wave
signal.
2-11.
TUNING
INDICATOR
The
tuning
indicator
monitors the phase
relationship
between
the signal input to the
notch
filter's
first
phase
shifter
and
its
output.
The
relationship
is
frequency de-
pendent
and
is
90
degrees
when
the incoming frequency
is
exactly the
same
as
the tuned
fre-
quency
of
the notch
filter.
The
components performing
this
function include phase
detector
U303,
high-speed
amplifier/drivers
U304,
U305
and
HIGH
and
LOW
indicators
CR301,
CR302.
The
reference
input
to phase
detector
U303
is
the signal
at
the input to the phase
shifter
(connected via
the
sum-point buffer)
and
the signal input to
U303
is
the output
of
the phase
shifter.
When
the incoming frequency
is
exactly the
same
as
the tuned
fre-
quency
of
the notch
filter
(90-degree phase
relationship),
there
is
no
output
from
the
phase
detector.
Under
these conditions both
indicators
are
off.
However,
if
the
fre-
quency
of
the notch
filter
is
high
compared
with the input frequency,
U303
produces a
de
output
which
turns
on
the
HIGH
indicator.
Conversely,
if
the frequency of the notch
filter
is
low
compared
1vith
the input frequency, a
de
output
of
the opposite
polarity
from
U303
turns
on
the
LOW
indicator.
2-3

2-12.
FILTERS
Each
filter
is
an
active
3-pole Butterworth having a
flat
response within
its
pass-
band
and
an
attenuation
slope of -18 dB/octave.
The
-3
dB
point
is
80
kHz
for
the
low-
pass
filter
and
400Hz
for
the high-pass
filter.
2-13.
FUNCTION
SWITCHES
The
function switches
select
the
circuit
to
be
measured
by
the
ac
voltmeter.
When
the
VOLTS
POWER
switch
is
depressed the meter monitors the fixed output, via a
step
attenuator,
from
the
buffer
amplifier.
When
the
SET
LEVEL
switch
is
depressed, the meter monitors the
signal
from
a
divider
connected to the
variable
output
of
the buffer
amplifier.
Operation
of
the
DISTORTION
switch routes the signal
from
the
distortion
amplifier via the low-frequency
and
high-frequency
filters
(if
selected) to the meter. This connection
is
not
made
directly
by
the
DISTORTION
switch but
by
the release
of
the
SET
LEVEL
and
VOLTS
POWER
switches
which
occurs automatically
when
the
DISTORTION
switch
is
depressed.
When
the
dB
VOLTS
switch
is
depressed,
it
connects the variable output
from
the buffer amplifier
directly
to the
at-
tenuator
at
the input
of
the
distortion
amplifier
and
hence
to the meter.
2-14.
AC
METER
The
ac
meter
circuit
consists
of
high-gain wide-band amplifier
Ul04,
a full-wave
bridge
rectifier
circuit,
and
de
milliammeter
Ml.
It
indicates the average value of
an
ac
signal.
The
input
sensitivity
is
31.6
mV
full
scale.
The
gain
of
the meter
is
adjusted
by
potentiometer
Rl57.
2-15.
OSCILLATOR
2-16.
GENERAL
DESCRIPTION
Refer to Figure 4-4
for
a schematic diagram of the
oscillator
assembly.
The
oscillator
is
basically
a
Wein
bridge type with a unique ultra-low
distortion
amplitude control
cir-
cu.it. This control
circuit
provides (1) wide frequency range (2)
fast
settling
(3)
flat
frequency response
and
(4) ultra-low
distortion.
No
one
of
these
characteristics
is
sacrificed
in order to achieve
an
improvement
in the
others.
The
oscillator
has
two
operating
modes
-Fast
Response
and
Low
Distortion.
When
Fast
Response
is
selected
the
oscillator
amplitude
settles
quickly
after
a frequency change;
when
Low
Distortion
is
chosen, the
oscillator
settling
time to
.002%
distortion
is
less
than 5 seconds.
Built-in
control
circuitry
automatically guides the
oscillator
through
these
modes
whenever
there's
disturbance to the amplitude,
for
example, a change of
fre-
quency
setting.
2-17.
OSCILLATOR
CIRCUIT
The
basic
Wein
bridge
oscillator
consists
of a reactive
positive
feedback network
and
a
resistive
negative feedback network, both
of
which
are
tied
to the output of
oscillator
amplifier
Ul.
The
positive
feedback network feeds
back
to the
positive
terminal of the
amplifier
and
the negative feedback network
is
coupled to the negative terminal of the
amplifier.
Frequency
of
oscillation
is
determined
in
the
positive
feedback network
by
the
relationship:
f =
---,2::---'-7T--:R::-:::C:--
Where
front
panel
Multiplier
switches change a
set
of capacitors for each frequency
range
and
the Digit switches change the
resistance
value.
These
components
are located
in
the
frequency
module
(see Figure 4-5
for
schematic diagram}.
2-18.
AMPLITUDE
CONTROL
The
ultra-low
distortion
amplitude control
circuit
consists
of
two
control loops:
A high-speed loop
and
a low-speed loop. These
two
loops, acting together,
effectively
vary the negative feedback
ratio
to regulate the
oscillator
amplitude.
2-4