Direct Reflecting® Car Stereo Speaker System
Bose 1401 four channels: 100 Watts continuous into 0.45 Ohms
Bose 1201 two channels: 50 Watts continuous into 0.45 Ohms
Individual Amplifiers: 25 Watts continuous into 0.45 Ohms resistive loads from 40 Hz to 17 kHz with less than .09% THD with 14.4 Volts DC.
Power Supply Tolerance: Will operate without noticeable performance defects between 10.5 and 16.5 Volts DC.
Speakers:
4 1/2" Driver, 6" x 9" Driver
2 or 4 full range drivers 1201 or 1401 II
Impedance: 0.45 Ohms
Maximum Power: 25 Watts (1201 and 1401 II has short circuit protection)
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, and 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 low pass 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 between 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 switchable low pass 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 low pass filter attenuating circuit would then be used.
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 amplifiers. 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 capacitor 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.
The over-current protection network is Q54 and Q55. If the unit draws substantial current across either or both R137 or R139 the voltage approaches .6 volts, creating the same chain of events as previously mentioned in the turn off section. The over-current protection circuit will attempt to recycle a turn on approximately every three seconds. If the over-current conditions are still present, the unit will not turn on.
The 1401™ series I has a compressor circuit. This circuit contains two sections. IC U53, (pins 5, 6, and 7) is the clipping detector, and Z50, is used as a variable attenuator. The compressor affects only the common bass buss signal. Pin 6 of each of the differential amplifiers is tied to an overload signal buss, which is fed to Pin 5 of IC U53. Pins 5, 6, and 7 of IC U53 comprise a voltage comparator network. The voltage at Pin 6 of U53 is the threshold voltage of the comparator. When the voltage at Pin 5 goes negative with respect to Pin 6, due to any amplifier being over driven, the voltage of pin 7 will go negative, with respect to speaker reference (SR). When the voltage of pin 7 goes negative, it turns on the LED, which is inside Z50, its resistance goes down, which attenuates the bass signal. In effect, if any amplifier begins to be over driven, the compressor circuitry is activated and will reduce the amount of common bass signal to the power amplifiers, thereby reducing the bass gain, preventing the amplifier from clipping, reducing potential distortion.
1201 Technical Description
The Bose® 1201 Booster/Equalizer is a two speaker system similar to the 1401™ II. In general, the same troubleshooting rules apply to both units. The RCA and high level inputs are the same, as well as the connectors for the power and speakers. The 1201 also has mute and short circuit protection circuits.
The 1201 has two amplifiers instead of four. The system has switchable equalization for the 4.5" driver or the new 6"x 9" speakers. The equalizer attenuates frequencies above 1kHz in the 4.5" position and turns off the bass equalization in the 6"x 9" position. The 1201 does not have Spatial Control™ or frequency controls.
A new feature for the 1201 is an input level control that provides the ability to interface with a variety of front ends. The input level control adjusts the amp gain for a power sensitivity of approximately 100-1000 mV (low level) and 1-10 Volts (high level) to produce 25 Watts of power per channel at full output at 1 kHz.
Also new in the 1201 amplifier is a compressor circuit. The compressor monitors the power amplifiers and reduces the input gain when the power amplifier begins to clip. Comprised of 1/2 of U1 and U3, U3 acts as a current controlled resistor across R109/209 whose equivalent resistance is inversely proportional to the current into pins 3/6. With no control current, U3 looks like an open circuit. As the current into pins 3/6 increases, the net resistance of R109/209 goes down and reduces the compressor amp gain. Control current is provided by detector/driver circuit of Q601-603. The outputs of the power amps (U4, U5, pin 6) pulses when the amp begins to clip. These pulses are detected by Q602, 603 and is filtered. The DC voltage is converted to control currents by R302, 402.
The mute circuit is different than in the 1401 II. It contains two comparators that serve as voltage and time delay sensors. U6, pins 1-3, senses the ANT SW control voltage and goes low if the ANT SW input or supply falls below 9-10 Volts. When U6, pin 1, goes high, C510 charges through R516. When C510's voltage exceeds that of U6, pin 6, (after approximately 2.5 seconds) pin 7 goes high and unmutes the amplifier. If U6, pin 1 goes low, C510 discharges immediately through D501 and mutes the amplifier. During short-circuit conditions, Q503 turns on and pulls U6, pin 2, high causing pin 1 to go low, starting the mute cycle.
Bose 1401, Bose 1401II block diagram for reference
TEST PROCEDURES
[Before connecting the Booster/Equalizer to the power supply, test the zener diode for a possible short by checking the resistance between the power and ground wires. Set your Ohmmeter to the x1 scale. Connect the leads of the meter to the red and black wires. In one direction (red to red, black to black) you should get a reading of infinity. In the other direction (red to black and black to red) you should get about .6 ohms for a reading.]
[The Booster/Equalizer has four separate amplifiers, two of which are 180º out of phase with the remaining two amplifiers. Also, the outputs are returned through the Booster/Equalizer's Speaker Reference. It is important to connect the unit as directed to prevent damage to the 1401 series I, or activation of the current protection circuits in the 1401 series II, and 1201. DO NOT connect speaker returns to ground.]
1401 II/1201 Power Wire Connection
Red wire is B+, Black wire is ground, Purple wire is Switched B+, and the Brown wire is Audio ground.
1401 I Speaker Wire Connection
Left Front
1. Output: White/Yellow
2. Return: White/Blue
Right Front
1. Output: White/Green
2. Return: White/Orange
Left Rear
1. Output: Gray/Blue
2. Return: Gray/Yellow
Right Rear
1. Output: Gray/Orange
2. Return: Gray/Green
1401 II/1201 Speaker Wire Connection
Left Front
1. Output: Yellow
2. Return: White
Right Front
1. Output: Green
2. Return: Orange
Left Rear
1. Output: Blue
2. Return: Yellow
Right Rear
1. Output: Orange
2. Return: Gray
Connection diagram
Test procedure
The Booster/Equalizer should be operated and tested using a 100 Ohm load for each of the speaker outputs until the unit functions properly. Center the bass control and Spatial Control.
Initial Turn-On Test
Connect the speaker to 100 Ohm loads and connect the power harness to a power supply at 13.8 Vdc.
Turn on the power supply and check the current draw. If the unit is drawing more than 250 mV shut off the power supply and check the outputs for shorts.
Note: On the 1401 II and the 1201 if the unit shuts off and then tries to turn on approximately every 3 seconds the outputs could be shorted.
Apply a 125 mV 1 kHz signal to the low level inputs and adjust the Spatial Control to electronically center (the front and rear output should be the same amplitude).
Low Frequency Response Test
Apply a 35 mV 1 kHz signal to the low level inputs.
Reference a dB meter to the output of the Booster/Equalizer.
Apply a 35 mV 100 Hz signal and slide the low frequency control to the minus (-) side. There should be a -6.5 dB ±1 dB decrease in output.
Center the control. Reference a dB meter to the output of the Booster/Equalizer.
Slide the control to the plus (+) side. There should be a +6.5 dB ±1 dB increase in output.
Spatial Control, High Frequency, and Rear Switch Control Test
Apply a 35 mV 15 kHz signal to the low level inputs.
Reference a dB meter to the output of the Booster/Equalizer.
Slide the spatial control to maximum right (front speakers). There should be a +1 dB ±1 dB increase in output and a -30 dB cut to the rear speakers.
Slide the spatial control to maximum left (rear speakers). There should be a +1 dB ±1 dB increase in output and a -30 dB cut to the front speakers.
Center the spatial control and switch the rear high frequency switch to position I. The rear output should be -10.5 dB ±1 dB from the front output.
Return the rear high frequency switch to position II.
Power and Distortion Test
Connect the speaker outputs to 0 .45 Ohm loads.
Apply a 1 kHz signal to the low level inputs and increase the input until the output signal just begins to clip. The output reading should be approximately 3.36 Volts.
Decrease the applied signal until the output reads 3.20 Volts. The distortion should be .09% for all four channels.
Note: The length and size of the wiring and the connection to the load is very important. Make sure the connections are as tight as possible to achieve correct distortion readings.
High Level Input Test
Apply a 1 kHz signal to the high level inputs. Increase the input level until the output just begins to clip. The signal input reading should be approximately 2.75 Volts.
Protection Circuit Test
Note: This test is for the 1401 II and the 1201 only. Signal is applied to the low level input.
Apply a 1 kHz signal so the output of the unit is approximately 1.50 Volts.
Short anyone of the outputs to ground. The unit should immediately shut down and then try to turn on every three seconds.
Remove the short. The unit should turn on and operate properly without damage to the channel that had been shorted.
PCB identification
