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TECHNICAL DESCRIPTION
The 1401™II has four separate power amplifiers. Each power amplifier receives a summed
signal from the common bass buss, and the mid and high frequency information from the
Spatial Control™ slider. Using all four speakers to reproduce the bass frequencies provides full
rich bass response while directing the other frequencies to the appropriate, left/right/front/back
speakers, to maintain proper spatial characteristics.
Each power amplifier uses a high slew rate operational amplifier (U11 left front, U21 left rear,
U31 right front, U41 right rear). These ICs are the low level stage for each of the power amplifi-
ers. Pins 4 and 7 of the ICs provide out-of-phase signals to the driver transistors. The voltage
across the 47 Ohm resistor attached to pin 6 of each IC is proportional to the current flowing
into the driver transistors.
The bias current of the driver transistors is device dependent. The emitter resistor voltage
(R11, 12, 21, 22, 31, 32, 41, 42) divided by .47 Ohms will give you the bias current of that
transistor. The bias current should typically be 20-60 mA, with a maximum of 140 mA.
The output transistors are unbiased. Therefore, the output waveform will show crossover
distortion. "Glitches" will be visible at higher frequencies when driving a load. The distortion
from these "glitches" is well above the range of human hearing.
Power is supplied to the 1401 from the vehicle's fuse block. This is fed directly to the output
transistors. A network composed of R111 and C91 filters the 14.4 Vdc for all of the ICs in the
unit. An 18V zener diode (D55) provides over voltage switching transient and load dump
protection. U53, C92, R112, and R113 create a stable voltage that is 1/2 Vcc which is used as
a "0" Volt reference for the audio signal.
The turn on/off transient eliminator circuit works in conjunction with the remote turn on and
over current protection circuit. When power is applied to the 1401, the output of U52 goes high,
which turns on Q63. This turns on Q15, 16, 25, 26 for the left amplifiers and Q35, 36, 45, 46
for the right amplifiers which prevents the driver and power transistors of each amplifier from
turning on. This eliminates a turn on "thump" as the amplifiers stabilize during power up. U52's
output will go low after approximately three seconds, turning off Q63, which turns off Q15, 16,
25, 26, 35, 36, 45, 46 which, in turn enables the driver and output transistors in the circuit to
operate.
The turn off detector is Q51 and Q52. When the 1401 is turned off, Q51 turns off, turning on
Q52. This makes the gate of SCR Q62 go high, turning on the SCR. This pulls the voltage of
pin 6, U52 low, causing U52 to go high, turning on the transistors Q15, 16, 25, 26, 35, 36, 45,
46, which shuts off the driver and output transistors, eliminating any transients. In addition,
whenQ52 goes high, it turns on Q61 And Q80 which discharges C53, the signal return capaci-
tor through R142.
The remote turn on detector is Q53. When voltage is applied to the remote sense line, Q53
shuts off. This makes the gate of SCR Q62 go low, turning off the SCR. This allows C52 to
charge, which brings the voltage of pin 6, U52 up, causing U52 to go low, turning on the driver
and output transistors. Also, when Q53 shuts off, Q61 and Q80 shuts off, allowing C53 to
charge.
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