4. RIAA frequency response
Instruments: Sinewave oscillator, AC millivoltmeter.
Conditions: Switch suppressor out.
Check: Gain at 20Hz to be +16.406 ± LödB.
Gain at 20kHz to be -19.608 ± i.ödB.
Both with reference to gain at 1kHz.
Test both channels.
5. Maximum delay line dynamic range and gain balance
Instruments: Sinewave oscillator, oscilloscope, AC
millivoltmeter.
Conditions: Switch suppressor in. Apply 1kHz sinewave
(1) signal to inputterminals in turn. Adjust preset
potentiometers
(VR1,
VR2) for minimum
visible clipping at 2V rms output. This will
have a limited effect on the nominal 7V DC
test voltage shown at the delay line output
(IC4,
pins 8 and 12).
Check: Distortion at 2V rms at
1
kHz must be less than
1
%. Channel balance at 0.3V rms output must
be ±2dB.
Switch suppressor out and recheck.
Conditions: Switch suppressor in. Apply 50mV rms at
(2) 20kHz sinewave to input terminals in turn.
Adjust preset potentiometers
(VR1,
VR2) for
minimum distortion and 'fuzz' on output
signal.
6. Detector operation (part of)
Conditions: Switch suppressor in, set suppressor
sensitivity control to maximum.
Check: With no input, the suppressor activity
indicator must not light.
7. Delay length
Instrument: Counter/timer.
Conditions: Switch suppressor in.
Check: Clock frequency must be 80kHz to 92kHz.
8. Detector operation (part of)
Instrument: Toneburst or pulse generator.
Conditions: Switch suppressor in. Apply a single cycle
toneburst or doublet pulse at 10Hz repetition
rate,
1.6kHzfundamental or 600μs
duration,
of
5mV peak-to-peak
amplitude,
to one input
channel.
Short-circuit
the other
input.
Set
suppressor
sensitivity
control
to maximum.
Check:
The suppressor indicator must flash.
Reverse channels and recheck.
9.
Blanking
operation
(part
of)
Instrument:
Toneburst or pulse generator.
Conditions:
As for Test
8,
but
with
amplitude
increased
to
lOOmV peak-to-peak.
Check:
The attenuation of the
toneburst,
between
suppressor
switched out and in must be
greater
than
50:1.
10.
Blanking
operation
(part
of)
Instruments:
Toneburst or pulse
generator,
oscillator and
oscilloscope.
Conditions:
Switch
suppressor
in.
Apply
a
signal
source
as
for
Test 8, but with amplitude
increased
to
100mV
peak-to-peak,
to one
channel.
Apply a
1kHz sinewave signal, 5mV rms amplitude to
the
other
channel.
Trigger the oscilloscope
with
the pulse
input
and
observe
the
sinewave
output.
Check:
From the start of the input ('scope
trigger)
pulse,
the waveform must reach 100% ± 25%
of
the prior level within 5ms. It must stay at
100%
± 25% until it reaches 100% ± 10% of
the
final value after a total of 35ms.
Reverse channel inputs and recheck.
See
oscilloscope
waveform,
diagram 14.
11.
Delay line gain
Instruments:
Sinewave
oscillator,
AC millivoltmeter.
Conditions:
Switch suppressor in. Apply 1kHz sinewave
to
both input channels to obtain 200mV rms
nominal
output.
Check:
Channel balance to be better than 2dB.
Difference
in output between suppressor
switched
out or in must
be
within
2dB
on both
channels.
12.
Delay and
processing
frequency
response
instruments:
Sinewave
oscillator,
AC millivoltmeter.
Conditions:
Switch suppressor
in.
Apply
a
1
kHz sinewave
input
to
both
channels to
obtain
a
200mV rms
nominal
output.
Check:
Gain at 20Hz must be 16.4dB ± LödB.
Gain at 20kHz must be -^.ödB ± 1.5dB
with reference to arbitrary OdB at 1kHz at
approximately 200mV rms output.
Test both channels.
13.
Preamplifier ('straight through') noise
Instrument:. AC microvoltmeter.
Conditions: Switch suppressor out. Short-circuit both
input channels.
Check: Output hum and noise, 20Hzto 20kHz, must be
less than 80μV rms.
15.
Preamplifier
output
Instruments:
Sinewave
oscillator,
AC millivoltmeter.
Conditions:
Switch suppressor out. Apply 1kHz sinewave
input
to both channels.
Check:
Output
before
visible
clipping
must
begreater
than
7V rms.
16.
Preamplifier
distortion
Instruments:
Sinewave
oscillator,
distortion
factor meter,
AC millivoltmeter.
Conditions:
Switch
suppressor
out.
Apply
a
1
kHz sinewave
inputto
both
channels,
to give
approximately
200mV
rms
output.
Check:
Distortion must be less than
0.01%.
17.
Delay line distortion
Instruments:
Sinewave
oscillator,
distortion
factor meter,
AC miilivoltmeter.
Conditions:
Switch suppressor
in.
Apply a 1kHz sinewave
input
to both
channels,
to give approximately
200mV
rms
output.
Check:
Distortion must be less than 0.10%.
18.
Delay line noise
Instrument:
AC microvoltmeter.
Conditions:
Switch
suppressor
in.
Short
circuit
both
input
channels.
Check:
Output hum and
noise,
20Hz-20kHz, must be
less
than
200MV
rms.
14
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