BOSE 901 I&II Service Manual
®
®
©1998 Bose Corporation
Service Manual
Contents
Safety Information............................................................................................................................ 3
Specifications................................................................................................................................... 4
Technical Description ...................................................................................................................5-6
Figure 1. Equalizer Controls Response Charts................................................................................ 6
Disassemble/Assembly Procedure ............................................................................................. 7-8
Figure 2. Staple Location ................................................................................................................. 7
Figure 3. Staple Removal Tool ......................................................................................................... 7
Figure 4. Wiring Diagram ................................................................................................................. 7
Figure 5. Top Cover.......................................................................................................................... 9
Figure 6. Front Panel Assembly ....................................................................................................... 9
Figure 7. Indicator Lens Assembly................................................................................................... 9
Test Procedure .......................................................................................................................... 10-11
Figure 8. Test Set-Up ..................................................................................................................... 10
Part List........................................................................................................................................... 12
Part List Notes................................................................................................................................ 12
Figure 9. 901 I Schematic Diagram................................................................................................ 13
Figure 10. 901 II Schematic Diagram............................................................................................. 14
Figure 11. 901 Schematic Diagram (first production run)............................................................... 15
PROPRIETARY INFORMATION
THIS DOCUMENT CONTAINS PROPRIETARY INFORMATION OF
BOSE
THE PURPOSE OF SERVICING THE IDENTIFIED BOSE PRODUCT
BY AN AUTHORIZED BOSE SERVICE CENTER OR OWNER OF THE
BOSE PRODUCT, AND SHALL NOT BE REPRODUCED OR USED
FOR ANY OTHER PURPOSE.
®
CORPORATION WHICH IS BEING FURNISHED ONLY FOR
2
SAFETY INFORMATION
1. Parts that have special safety characteristics are identified by the symbol on
schematics or by special notes on the parts list. Use only replacement parts that
have critical characteristics recommended by the manufacturer.
2. Make leakage current or resistance measurements to determine that exposed
parts are acceptably insulated from the supply circuit before returning the unit
to the customer. Use the following checks to perform these measurements:
A. Leakage Current Hot Check-With the unit completely reassembled, plug
the AC line cord directly into a 120V AC outlet. (Do not use an isolation
transformer during this test.) Use a leakage current tester or a metering
system that complies with American National Standards Institute (ANSI)
C101.1 “Leakage Current for Appliances” and Underwriters Laboratories
(UL) 1492 (71). With the unit AC switch first in the ON position, then in the
OFF position, measure from a known earth ground (metal water pipe,
conduit, etc.) to all exposed metal parts of the unit (antennas, handle bracket,
metal cabinet, screw heads, metallic overlays, control shafts, etc.), especially
any exposed metal parts that offer an electrical return path to the chassis.
Any current measured must not exceed 0.5 milliamp. Reverse the unit power
cord plug in the outlet and repeat test. ANY MEASUREMENTS NOT WITHIN
THE LIMITS SPECIFIED HEREIN INDICATE A POTENTIAL SHOCK HAZ ARD THAT MUST BE ELIMINATED BEFORE RETURNING THE UNIT TO
THE CUSTOMER.
B. Insulation Resistance Test Cold Check-(1) Unplug the power supply and
connect a jumper wire between the two prongs of the plug. (2) Turn on the
power switch of the unit. (3) Measure the resistance with an ohmmeter be-
tween the jumpered AC plug and each exposed metallic cabinet part on the
unit. When the exposed metallic part has a return path to the chassis, the
reading should be between 1 and 5.2 Megohms. When there is no return path
to the chassis, the reading must be “infinite”. If it is not within the limits specified,
there is the possibility of a shock hazard, and the unit must be repaired and re checked before it is returned to the customer.
CAUTION: THE BOSE
PARTS. TO PREVENT WARRANTY INFRACTIONS, REFER SERVICE TO WARRANTY
SERVICE STATIONS OR FACTORY SERVICE.
®
901 I and II EQUALIZERS CONTAIN NO USER-SERVICEABLE
3
SPECIFICATIONS
901 Series I and II Speaker
Dimensions: 20-9/16" W x 12-3/4" H x 12-7/8" D
Weight: 33 lbs
Nominal Impedance: 8 ohms
Percentages of Direct and Reflected Sound Radiation
Power radiated by
reflection: 89%
Power radiated directly: 11%
Power Handling: Continuous sine wave @ any frequency: 50 Watts
Minimum amplifier power: 25 Watts
Peak power (less than 5 seconds): 400 Watts
Maximum amplifier power: 270 Watts rms
@8 ohms
Damping Factor: Any amplifier with a damping factor of 40 or higher
(must follow the speaker wire recommendation in the Owner's Guide)
Driver Complement: Nominal driver diameter: 4-1/2"
Maximum driver excursion: ± 1/4"
Nominal driver impedance: 8 ohms
Weight of each ceramic magnet: 9.6 ounces
901 Active Equalizer
Dimensions: 2-13/16" H x 9-1/4" W x 6-3/4" D
Input Impedance: 150k ohms
Output Impedance: Less than 100 ohms
Minimum Load
Impedance: 5k ohms
Maximum Output
Voltage: 4.0 Volts
Maximum Gain: 18 dB @ 35 Hz
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TECHNICAL DESCRIPTION
The Bose® 901 speakers represent a fundamental advance in realistic home music reproduction. The unique acoustic design of the speakers provide sound distribution in accurate simulation of live sound. The Active Equalizer provides unprecedented accuracy and control of
frequency response characteristics.
Each speaker contains nine high compliance, full range speakers with high energy magnets to
allow large excursions without audible distortion on any program material. The speakers are
acoustically coupled to eliminate audible resonances.
The 901 speakers can be used with any high quality amplifier. Its efficiency enables operation
with moderately powered amplifiers, yet it can be used with the highest powered amplifiers to
reproduce undistorted orchestral peaks at high volume levels.
The Bose 901 Active Equalizer is a highly sophisticated electronic console containing ten
transistors and more than a hundred components to equalize accurately the stereo response
for the effects of radiation impedances, speaker characteristics, enclosure dimensions and
even for the presence of the fashion fabric grille cloth. This equalization to flat power radiation
is achieved with absolutely no audible distortion of any music or speech signals.
Active equalization of the signal before the power amplifier is far superior to passive equalization after the amplifier because it avoids the need to handle high power and does not require
the iron-core inductors that introduce distortion in passive equalizers. In addition, it is feasible
to use many more elements in an active network to provide much greater accuracy in equalization than is practical in the passive network.
The Active Equalizer does much more than just equalize. In addition to providing the flat
acoustic output of the Bose 901, the Active Equalizer offers the choice of nineteen additional
contours that can be selected from the front panel. This gives the listener the flexibility to
exercise his own taste in compensating for recording techniques, listening room characteristics
and the other variables described above. As an example of what is possible through active
equalization, the equalizer panel contains a switch marked "BELOW 40", which reduces
turntable rumble and other low frequency disturbances through a unique filter design that
provides a uniform attenuation below 40 Hz while causing no audible deviations above 50 Hz.
The rumble is removed without removing the life of the bass along with it.
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