F I G . 27 SINGLE T R A C E SWEEP
cycle appears stationary on the screen, it is a 20 Hz tone.
If 10 cycles appear on the screen at the same settings, the
tone is 200 Hz.
To examine audio tones in the mid-range, press the 200-
2,000 button. Further adjustment of the SWEEP control
should lock the waveform on the screen. Again, an esti-
mate of frequency may be made. If the SWEEP is set fully
counterclockwise, the trace is sweeping at the rate of
200 Hz. Count the number of cycles on the screen, multiply
by 200, and the result is the audio frequency.
Tones in the highest range are observed with the SWEEP
FREQUENCY button in the 2,000-20,000 band. If the
SWEEP control is set fully counterclockwise, (a 2000 Hz
sweep), two cycles on the screen represent a 4000 Hz
tone; three cycles are a 6000 Hz tone, etc.
The screen can simultaneously display left and right
stereo channels as a dual trace, as shown in Fig. 28. To
view both signals, depress L and R pushbuttons of the
DUAL TRACE MODE SELECTOR.
FIG. 28 DUAL TRACE DISPLAY
It is possible to magnify the display for closer viewing by
adjusting the SWEEP EXPANSION control on the top panel
as desired.
PHONO PICKUP COMPLIANCE AND TRACKING CHECK
With the aid of a test record, compliance and tracking of
a pickup may be checked. Follow the instructions on the
test record jacket and make certain the spot on the MPI 4
is properly centered, then:
1. Depress the STEREO button.
2. Start the phono turntable and set the pickup on the
appropriate test band.
3. Ad|ust the GAIN control to obtain approximately a
2-inch display. Figure 29 shows good compliance and
tracking, while Figure 30 shows distortion due to
improper tracking.
FIG. 29 GOOD T R A C K I N G
FIG. 30 I M P R O P E R T R A C K I N G
FREQUENCY RESPONSE CHECK
Check the frequency response of your system with the aid
of a test record. The graph in Fig. 31 shows an ideal RIAA
curve using the CBS STR 100 test record. Make this test
and all single frequency tests at low acoustic levels to
prevent potential loudspeaker damage. To perform a
frequency response check:
1. Play the 1000 Hz test tone on the phonograph.
2. Adjust the preamplifier volume control for an ade-
quate sound level. Be cautious. The use of loud single
frequency program material can overload loudspeaker
systems.
3. Set the POWER LEVEL selector to a setting which pro-
vides column heights closest to the 0 dB mark on the
level scale.
4. Adjust your preamplifier volume controls to obtain
precise 0 dB readings for both columns using the
15