Power On/Off Circuit
The power on/off circuit is designed to turn the amplifier on slowly and off quickly. When AC power is initially applied to the subwoofer, AC signals on the secondary of the power transformer are negatively rectified through CR2 and CR7 into peak holding capacitor C31, and divided by R19 and R20. When the resulting DC voltage at pin 2 of U15A is lower than the reference voltage of
Signal Sensing Turn-On Circuit
The amplifier will not turn on until an input signal is detected. The first stage of the detection circuit amplifies the WOOFER signal by 40dB - to insure that even the smallest input signal is detected - and high pass filters it to eliminate DC offset errors. This amplified signal is negatively rectified by CR9 and held by C85. When the voltage at pin 6 of U16B goes lower than the
Thermal Protection
The thermal protection turns off the amplifier when the heatsink reaches an excessively high temperature. This condition is detected by the NTC (Negative Temperature Coefficient) thermistor TS2. At higher temperatures, TS2 has a lower resistance - causing a higher voltage at pin 6 of U15B. When this voltage exceeds the reference voltage at pin 5, the output of U15B goes low to
! Qualified Service Personnel Only | |
POWER ON / OFF |
|
REFERENCE |
|
CR15 |
|
R18 |
|
COMPARATOR | ON / OFF |
U15A | CR5 |
AC POWER |
|
RECTIFIER |
|
CR2,CR7 |
|
R12, C31 |
|
R19, R20 |
|
SIGNAL SENSING |
|
|
| |
| SIGNAL | REFERENCE |
| |
| R103, R84 |
| ||
SIGNAL AMPLIFIER | RECTIFIER |
| ||
COMP | ON / OFF | |||
U16A | AND HOLD | |||
U16B | CR3 | |||
R57, R75 | CR9, R145 | |||
|
| |||
C28, C84 | C85 |
|
|
THERMAL PROTECTION |
|
| COMPARATOR |
TEMP | ON / OFF |
| U15B |
TS2, R147 | CR6 |
| R22, R23 |
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