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S
E
R
V
IC
E
M
A
N
U
A
L
S
2
5
0
S250
FIVE CHANNEL
POWER AMPLIFIER
F
IV
E
C
H
A
N
N
E
L
P
O
W
E
R
A
M
P
L
IF
IE
R


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CONTENTS
FRONT PANEL / REAR PANEL VIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
ALIGNMENT PROCEDURE / ALIGNMENT POINTS . . . . . . . . . . . . . . . . . . . . . . . . 5
WIRING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
PCB LAYOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8
SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11
ELECTRICAL PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1
4
EXPLODED VIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
5
EXPLODED VIEW PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
6
PACKING DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
7
SERVICE SAFETY PRECAUTIONS
1. Replacing the Fuses
CAUTION: FOR CONTINUED PROTECTION AGAINST THE RISK OF FIRE REPLACE ONLY
WITH SAME TYPE OF FUSE.
REFERENCE NO.
PART NUMBER
DESCRIPTION
PSU Board
F1*AH
5120-0506-0
12.5A 250V Time Lag 6.3x32mm UR
F1*C
5120-0025-0
6.3A 250V HBC Time Lag 5x20mm SEMKO/VDE
Amp Board
F1-F2*AH
5120-0040-0
6.3A 250V Time Lag 5x20mm UL
F1-F2*C
5120-0025-0
6.3A 250V HBC Time Lag 5x20mm SEMKO/VDE
NOTE:
*AH : North American version only
*C : European version only
2. Safety-check out (North American model only)
Before returning the product to the customer, make leakage current or resistance measurements
to determine that exposed parts are acceptably insulated from the supply circuit.
Parts marked with the symbol
are critical with regard to the risk of fire and electric shock.
Replace only with parts recommended by the manufacturer.
!
!
!
!
!


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1. LEVEL CONTROL
5. 12V TRIGGER INPUT
2. INPUT JACK
6. SPEAKER TERMINALS
3. SOFT CLIPPING SWITCH
7. AC INLET
4. AUTO TRIGGER SWITCH
Five Channel Power Amplifier S250
3
4
1
2
NAD
SOFT CLIPPING
PROTECTION
1. POWER SWITCH
3. PROTECTION INDICATOR
2. POWER INDICATOR
4. SOFT CLIPPING INDICATOR
FRONT PANEL / REAR PANEL VIEW
FRONT PANEL CONTROLS
The graphic symbol of a lightning flash with an arrow point
within a triangle signifies that there is dangerous voltage
within the unit and it posses a hazard to anyone removing
the cover to gain access to the interior of the unit. Only
qualified service personnel should make such attempt.
The graphic symbol of an exclamation point within
an equilateral triangle warns a user of the device
that it is necessary to refer to the instruction
manual and its warnings for proper operation of
the unit.
REAR PANEL CONNECTIONS
AC MAINS INPUT
120V
TRIGGER IN
+12V
AUTO TRIGGER
2
1
3 4 5
6
7
1
RETURN TO CONTENTS


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SPECIFICATIONS
Specifications
are
measured
in
accordance
with
IHF
standard
IHF-A-202,
1978.
NOMINAL
LIMIT
1. THD
#0.02%
#0.03%
2. Continuous Power Output
8 ohms
$125W
$100W
20kHz, 5 ch. for 8 ohms, 4 ch. for 4 ohms)
4 ohms
$125W
$100W
3. Clipping Power
$135W
$110W
4. S/N Ratio
A-wtd
$96dB
$93dB
maximum)
Audio BPF
$89dB
$86dB
5. Frequency Response
0 ~ -0.1dB
0 ~ -0.25dB
6. Input Sensitivity
100 ± 2 mV
100 ± 3 mV
maximum)
7. Channel Separation
1kHz
$77dB
$70dB
20kHz
$67dB
$50dB
8. Soft Clipping
Output Reduction
0.4 ~ 0.6 dB 0.3 ~ 1.0 dB
THD
5 ~ 6.5%
4 ~ 10%
RETURN TO CONTENTS


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R44
R40
R41
TP1
TP2
RELAY
R27
J1
R45
IDLE CURRENT ALIGNMENT FOR EVERY POWER AMPLIFIER MODULE
1. Remove the load and the input signal.
2. Connect a digital voltmeter between TP1 and TP2.
3. Switch the amplifier on and, after one minute, adjust R27 to obtain a reading of
5mV ±0.5mV.
4. Leave power on for 3 minutes to allow the idle currents to stabilize. Re-adjust R27
as necessary to obtain a reading of 4.4mV ±0.5mV.
ALIGNMENT PROCEDURE
ADJUSTMENT POINTS
RETURN TO CONTENTS