4)
VTVM
or
DVM
5)
Harmonic
distortion analyzer with built-in 400Hz and 80kHz filters and
residual
THD
below 0.0015%
6)
Low-distortion oscillator
with residual
THD
below 0.0015%
(A
Sound Technology
I700A or
H-P
339 will satisfy
(5)
and
(6))
For the following
tests, a 600 ohm
load must be provided across each
674A
output. 620
ohm
1/2
watt 5% carbon
resistors are suitable.
THE
TEST PROCEDURE BELOW
SHOULD BE FOLLOWED
FROM BEGINNING TO
END FOR CHANNEL
"A", THEN
REPEATED FOR CHANNEL "B".
1)
Signal
Passage
Test
a)
Connect the high
(+)
side of
the
674A
main output to
the input of the
harmonic
distortion analyzer, and
also to the vertical
input of the
oscilloscope.
Connect the
ground
side
of the
674A
to instrument
ground.
b) Ground the (-) input
of the
674A
and connect
the output of the low-
distortion
oscillator to the
(+)
input of the
674A.
c)
Move aM
IN/OUT
switches to
OUT,
and center all
EQ controls.
d)
Adjust the
GAIN control clockwise, and
verify that an undistorted
sinewave
appears at the output.
e)
Continue
to advance the
GAIN control until clipping is
barely visible.
Verify
that this clipping
level exceeds
+l9dBm
for
20Hz, IkHz, and 20kHz input
signals.
f)
Verify
that the
OVERLOAD
lamp
flashes
at, or
slightly below, the
clipping
level at IkHz.
2)
DC offset
a)
Disconnect the oscillator
from the
674A
input.
b) Move all
IN/OUT switches
to
IN. Measure
the
DC voltage appearing at each
output of
the
674A. Either voltage
should not
exceed
30mV DC.
3)
Distortion and
Inverting
Operation
a)
Ground the
(+)
input of
the
674A and
connect
the low-distortion oscillator to
the
(-)
input of the
674A. Adjust the oscillator to
IkHz.
b) Move the
LOWPASS
and
HIGHPASS
FILTER
IN/OUT
switches to
OUT, but
leave the EQ
IN/OUT
switch
IN.
c)
Using the same
procedure as in
the Signal Passage Test
above, verify that
the gain is the same as
previously
measured +0.3dB.
d)
Apply
a
20kHz
signal
and adjust the
output level of
the oscillator and
the
674A's
GAIN
control
until +l8dBm
is observed at
the
674A
main output.
e)
Measure the Total
Harmonic Distortion,
using the 400Hz and
80kHz
filter
on
the distortion meter.
The
THD
should
not exceed 0.08%.
f)
Repeat at
20Hz; +l8dBm output;
400Hz filter
OUT.
The
THD
should
not
exceed 0.05%.
g)
Repeat step (f)
using the lowpass
output of the
674A.
4)
Noise
a)
Adjust the
674A GAIN control to produce unity
input/output gain.
b)
Switch
OUT
the
400Hz
and
80kHz filters in the analyzer.
Connect the
20-20, 000Hz bandpass
filter between the
674A main output and the analyzer
input.
c)
Disconnect the
oscillator from the
674A,
and connect both
(+)
and (-)
674A
inputs to
circuit
ground.
18
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