Bose 1401 II Series User Manual

6
TECHNICAL DESCRIPTION
Note: The following description is based on the 1401 II. The 1401 I is very similar with the
exception of the short circuit protection, remote turn-on circuitry, compressor, and any
reference to the use of the 6"x 9" speakers.
The Bose
®
1401™ II Booster/Equalizer incorporates unique circuitry that is different from other
auto amplifier designs. We ask that you take the time to read this technical description before
attempting to service the 1401, and 1401 series II, as it will aid you in the repair process.
The Booster/Equalizer contains a preamplifier, equalizer, short circuit protection circuitry,
remote turn on/off circuitry, Spatial Control™, and two or four power amplifiers, each delivering
25 watts of power into 0.45 ohms.
The 1401, and 1401 II are compatible with all front end radio/tape or tape player auto units
having their own amplifier, or preamplifier outputs. Low level inputs connect to the output of a
front end unit having preamplifier outputs. The booster will produce full output with 250 mVrms
applied to the low level input connections. If the front end has only speaker outputs, the high
level inputs are utilized. The input signal is reduced by the 100k resistors R52, 53, 72, 73 and
then fed to the same differential amplifier as the low level input signal. The high level inputs
produce full output with a 2.75 volt input signal.
A differential amplifier U51 is used at the input to minimize sensitivity to alternator whine and
other electrical noise. The differential amplifier feeds the equalizer. The equalization curve of
the booster has been designed specifically for the drivers supplied with the units.
The first section of the equalizer adjusts the mid frequencies. The signals are then fed to the
network driven by U52, 53, (pins 5 and 10) which provides both high frequency equalization
and the bass slide control. This control provides boost or cut by approximately 8 dB centered
at 170 Hz.
The signal then takes two paths. One is the low frequency path. The signals from the left and
right channels are summed and fed through a lowpass filter. This signal is fed to U53 (pin 12),
the bass equalization circuitry. The output of the U53 (pin 14), becomes a common bass buss,
which feeds the low frequency information to all four power amplifiers.
The second signal path is for the mid and high frequencies, which pass thorough the Spatial
Control™. The slider is a front to back balance control for the mid and high frequencies. This is
not a fader control. The slider maintains constant and total acoustic power for any spatial
setting. The spatial control allows you to shift the mid and high frequency sound image be-
tween the front and rear speakers, with the sum of the power delivered to the front or rear
speakers remaining the same. This allows great flexibility in compensating for the acoustic
properties of various autos, vans, and trucks in which the system may be used. Also a switch-
able lowpass filter, S1 (located on the rear of the unit) is in the second signal path. This control
only affects the signal going to the rear speakers. In position I, the high frequencies going to
the rear speakers are cut 6 dB/octave, starting at 5 kHz. In position II, the filter is disconnected.
This control compensates for different speaker placement. For example: if the rear speakers
were mounted higher than the front speakers, the high frequencies from the rear speakers
might sound too bright relative to the front speakers, thus the lowpass filter attenuating circuit
would than be used.

Bose 1401 II Series Specifications

General

Brand	Bose
Model	1401 II Series
Category	Car Stereo System
Language	English