Yamaha MS400 Service Manual page 17

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6) Output noise level
Ground the input terminals LINE INPUT (XLR) and
MIC INPUT (XLR) with a 600 ohm resistance
connected to each terminal and measure the noise
level at the output terminals LF and HF. The
measured value should be as specified below. Use
a DIN audio filter for the noise meter.
LF -62dBu
HF -65dBu
7) Frequency response characteristics
Input -20dBu signals of 50Hz, 1kHz, 2kHz and 15kHz
to the input terminal LINE INPUT (XLR). Using the
output voltage measured at the output terminal LF
when a 1kHz, -20dBu signal is input as standard
(0dB), check that the output voltages measured at
LF and HF are as specified below.
Frequency (Hz)
50
1k
2k
15k
8) Tone control high change characteristics
TE
Input a 5kHz, -20dBu signal to the input terminal
L 13942296513
LINE INPUT (XLR), move the tone control high VR
and check that the output voltage measured at the
output terminal HF then is as follows, using the
output voltage when the VR is at the center click
position as standard (0dB).
MAX(+3): +2.5dB ± 1dB
MIN(-3):
9) Tone control low change characteristic
Input a 50kHz, -20dBu signal to the input terminal
LINE INPUT (XLR), move the tone control low VR
and check that the output voltage measured at the
output terminal LF then is as follows, using the output
voltage when the VR is at the MAX position as
standard (0dB).
the MAX position as standard (0dB)
MIN(-10): -9dB ± 1dB
10) MIC input
Input a 500Hz, -55dBu signal to the input terminal
MIC INPUT (XLR), set the MIC level to MAX (10)
and check that the output voltage measured then is
28 ± 1dBu.
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11) Protection circuit
Apply DC+5V (power supply output resistance = 10
kohm) between Pins 1 and 2 of the connector CN208
.
and check that the relay turns off within 1 second.
Also, check that it returns automatically within 10
seconds when the input signal is shut off.
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LF HF
+8.5±2.0dB --
0dB -16.5±2.0dB
-9±2.0dB -4.5±2.0dB
-- +6.5±2.0dB
-3.5dB ± 1dB
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