BOSE 1600VI SM Schematic
Model 1600VI and 1800VI Professional
Stereo Power Amplifiers
®
®
©
1998 Bose Corporation
Service Manual
Part Number 199747 Rev. 00
CONTENTS
Safety Information............................................................................................................................ 4
Electrostatic Discharge Sensitive (ESDS) Device Handling ........................................................ 4
1800VI Specifications................................................................................................................... 5-6
1600VI Specifications................................................................................................................... 7-8
Figure 1. 1600VI and 1800VI Block Diagram .................................................................................. 9
Theory of Operation.................................................................................................................. 10-18
Disassembly/Assembly Procedures ....................................................................................... 19-30
Figure 2. Cover Removal Screw Location Side View..................................................................... 19
Figure 3. Cover Attaching Hardware.............................................................................................. 20
Figure 4. Rear View - Attaching Hardware..................................................................................... 20
Figure 5. 240V Configuration ......................................................................................................... 21
Figure 6. 1600VI and 1800VI Amplifier Assembly ......................................................................... 21
Figure 7. Bottom Mounted Components ........................................................................................ 22
Figure 8. Side View - Bottom Mounted Components ..................................................................... 27
Figure 9. Heatsink Bridge............................................................................................................... 27
Figure 10. Input Module Screw Location........................................................................................ 29
Test Procedures ........................................................................................................................ 31-33
Figure 11. EQ Card Placement ...................................................................................................... 31
Frequency Response Test Table .................................................................................................. 32
Part List Notes................................................................................................................................ 34
Main Part List............................................................................................................................. 35-37
Figure 12. Amplifier Test Setup Diagram ....................................................................................... 31
Figure 13. Front Panel Views, 100V and 120V Variation, 240V Variation...................................... 37
Figure 14. Back Panel View ........................................................................................................... 37
Figure 15. Cross Section View....................................................................................................... 38
Figure 16. 1600VI and 1800VI Amplifier T op View ........................................................................ 39
Figure 17. 1600VI and 1800VI, Amplifier Assembly Removed View ............................................. 40
Electrical Part List..................................................................................................................... 41-54
Packing List .................................................................................................................................... 55
Figure 18. 1600VI and 1800VI Amplifiers Packing Diagram ......................................................... 55
Wiring Diagrams........................................................................................................................ 56-57
Figure 19. 1600VI and 1800VI Wiring Diagram............................................................................. 56
Figure 20. 1600VI and 1800VI 240V Wiring Diagram ................................................................... 57
IC Pinout Diagrams ................................................................................................................... 58-59
2
CAUTION: The Bose® 1600VI and 1800VI Professional
Stereo Power Amplifiers contain no user-serviceable
parts. To prevent warranty infractions, refer servicing
to warranty service centers or factory service.
PROPRIETARY INFORMATION
THIS DOCUMENT CONTAINS PROPRIETARY INFORMATION OF
BOSE® CORPORATION WHICH IS BEING FURNISHED ONLY FOR
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.
3
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 and then in OFF position, measure
from a known earth ground (metal waterpipe, conduit, etc.) to all exposed metal parts of the
unit (antennas, handle bracket, metal cabinet, screwheads, 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 HAZARD 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 between 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 rechecked before it is returned
to the customer.
ELECTROSTATIC DISCHARGE SENSITIVE (ESDS)
DEVICE HANDLING
This unit contains ESDS devices. We recommend the following precautions when repairing,
replacing or transporting ESDS devices:
• Perform work at an electrically grounded work station.
• Wear wrist straps that connect to the station or heel straps that connect to conductive floor
mats.
• Avoid touching the leads or contacts of ESDS devices or PC boards even if properly
grounded. Handle boards by the edges only.
• Transport or store ESDS devices in ESD protective bags, bins, or totes. Do not insert unprotected devices into materials such as plastic, polystyrene foam, clear plastic bags, bubble wrap
or plastic trays.
4
1800VI SPECIFICATIONS
Size: 3.5"H (2U) x 19"W x 13.25"D
89mm x 483mm x 337mm
Weight: Net: 33 lbs. (15 kg)
Shipping weight: 39 lbs. (17.7 kg)
Display: 7 LED indicators per channel
1 green - READY, 5 yellow - SIGNAL,
1 red - CLIP/PROTECT
Operating Temperature: 0° to 50° C, up to 85% RH
Performance Specifications
Continuous Average Output Power,
both channels driven: 450 Watts per channel into 8 Ohms from
20 Hz to 20 kHz, with no more than 0.2% THD
600 Watts per channel into 4 Ohms from
20 Hz to 20 kHz, with no more than 0.2% THD
Bridged Mono Operation: 1400 Watts into 8 Ohms from 20 Hz to 20 kHz,
with no more than 0.2% THD
Voltage Output: 60 V line voltage per channel into 8 Ohms
49 V line voltage per channel into 4 Ohms
Dynamic Headroom: 1.0 dB nominal
Power Bandwidth: 5 Hz to 40 kHz (+0, -3 dB)
Frequency Response: 20 Hz to 20 kHz (±0.75 dB)
Channel Separation: > 65 dB @ 1 kHz; > 55 dB @ 10 kHz
Damping Factor: > 170
Input Impedance: 25k Ohms unbalanced, each leg to ground,
50k Ohms balanced
*Sensitivity: High: .775 Vrms for rated power into 4 Ohms @
1 kHz, 57 mVrms for 1W into 4 Ohms @ 1 kHz
Low: 1.5 Vrms for rated power into 4 Ohms @ 1 kHz,
116 mVrms for 1W into 4 Ohms @ 1 kHz
*Gain: High: 36.0 dB (±0.5 dB)
Low: 30.3 dB (±0.5 dB)
*The amplifier sensitivity is set to 0.775V rms for rated output. To reduce the sensitivity by 6 dB to
1.5V rms, remove JP100 (CH1) and JP200 (CH2), located on the main amplifier board.
5
1800VI SPECIFICATIONS
Input Overload: +18 dBu
IM Distortion: < 0.1%
THD: @ 0.775 V Sensitivity, < 0.2%
@ 1.5 V Sensitivity, < 0.1%
Signal-to-Noise Ratio: > 100 dB, A-weighted, referenced to rated
power into 4 Ohms (high gain)
> 78 dBW, A-weighted, referenced to 1 W into
4 Ohms (high gain)
Slew Rate: 10 V/µS (bandwidth limited)
40 V/µS (RFI filtering removed)
®
CMRR: > 80 dB @ 1 kHz (without Bose
> 60 dB from 20 Hz - 20 kHz (without Bose
input module)
input module)
Power Consumption: 55 W at idle
800 W with musical program
1500 W at full power into 8 Ohms (continuous)
2400 W at full power into 4 Ohms (continuous)
Power Requirements: 120 VAC/50-60 Hz (USA and Canada)
230 VAC/50-60 Hz (Europe/UK)
240 VAC/50-60 Hz (Australia)
100 VAC/50-60 Hz (Japan)
Fusing: 15 Amp Slo-Blo (125 V/60 Hz)
8 Amp Slo-Blo (230 V/50 Hz)
6
1600VI SPECIFICATIONS
Size: 3.5"H (2U) x 19"W x 13.25"D
89mm x 483mm x 337mm
Weight: Net: 30 lbs. (13.6 kg)
Shipping weight: 36 lbs. (16.3 kg)
Display: 7 LED indicators per channel
1 green - READY, 5 yellow - SIGNAL,
1 red - CLIP/PROTECT
Operating Temperature: 0° to 50° C, up to 85% RH
Performance Specifications
Continuous Average Output Power,
both channels driven: 240 Watts per channel into 8 Ohms from
20 Hz to 20 kHz, with no more than 0.2% THD
325 Watts per channel into 4 Ohms from
20 Hz to 20 kHz, with no more than 0.2% THD
Bridged Mono Operation: 700 Watts into 8 Ohms at 1 kHz, with no
more than 0.2% THD
Voltage Output: 43.8 V line voltage per channel into 8 Ohms
36.0 V line voltage per channel into 4 Ohms
Dynamic Headroom: 2.0 dB nominal
Power Bandwidth: 5 Hz to 40 kHz (+0, -3 dB)
Frequency Response: 20 Hz to 20 kHz (±0.75 dB)
Channel Separation: > 65 dB @ 1 kHz; > 55 dB @ 10 kHz
Input Impedance: 25k Ohms unbalanced, each leg to ground,
50k Ohms balanced
*Sensitivity: High: 0.775 Vrms for rated power into 4 Ohms,
83 mVrms for 1 W into 4 Ohms
Low: 1.5 Vrms for rated power into 4 Ohms,
160 mVrms for 1 W into 4 Ohms @ 1 kHz
*Gain: High: 33.3 dB (±0.5 dB)
Low: 27.6 dB (±0.5 dB)
*The amplifier sensitivity is set to 0.775V rms for rated output. To reduce the sensitivity by 6 dB to
1.5V rms, remove JP100 (CH1) and JP200 (CH2), located on the main amplifier board.
7
1600VI SPECIFICATIONS
Input Overload: +18 dBu
IM Distortion: < 0.1%
THD: @ 0.775 V Sensitivity, < 0.2%
@ 1.5 V Sensitivity, < 0.1%
Signal-to-Noise Ratio: > 100 dB, A-weighted, referenced to rated
power into 4 Ohms (high gain)
> 78 dBW, A-weighted, referenced to 1 W into
4 Ohms (high gain)
Slew Rate: 40 V/µS (bandwidth limited)
®
CMRR: > 80 dB @ 1 kHz (without Bose
> 60 dB from 20 Hz - 20 kHz (without Bose
input module)
Power Consumption: 45 W at idle
500 W with musical program
1000 W at full power into 8 Ohms (continuous)
1550 W at full power into 4 Ohms (continuous)
input module)
Power Requirements: 120 VAC/50-60 Hz (USA and Canada)
230 VAC/50-60 Hz (Europe/UK)
240 VAC/50-60 Hz (Australia)
100 VAC/50-60 Hz (Japan)
Fusing: 10 Amp Slo-Blo (125V/60Hz)
7 Amp Slo-Blo (230V/50Hz)
8
H
Figure 1. 1600VI and 1800VI Block Diagram
AC
N
Sequence
Send
Rcv
Line
Filter
Fuse
Sequence
(230V)
Only
On/Off
Standby
Regulation (not used
with 1600VI)
Phase Control
Power Supplies
Commutation
Control
(Class H)
Amplifier
CH 2
CH 1
CH 1
9
CH 2
Sequence
CH 1
Input
CH 2
CH 1 CH 2
Control
Input
Module
Level
Control
Lowpass
Filter
Display
Temperature
Sense
CH 1 CH 2
OUT OUT
Output
Relays
CH 1
OUT
Protection
®
Bose
EQ Card(s)
Display
Drive
Fan Drive
CH 2
OUT
THEORY OF OPERATION
1. General
The Bose® Model 1600VI and 1800VI Professional Stereo Power Amplifiers are two-channel,
installed/portable amplifiers made for professional sound applications. The 1600VI is rated at
240 Watts into 8 Ohms and 325 Watts into 4 Ohms. In the bridged-mono setting it can deliver
700 Watts. The 1800VI is rated at 450 Watts into 8 Ohms and 600 Watts into 4 Ohms. In the
bridged-mono setting it can deliver 1400 Watts.
The protection circuits designed into the amplifiers will protect them from unexpected faults,
excessive temperature, continuous current limiting and shorted outputs.
The balanced inputs use high quality, high common-mode rejection differential amplifiers for
exceptional hum and noise rejection.
Through the use of equalization cards the amplifier can provide active equalization for Bose
402™, 502®A, 502B, 802®, Model 25/32, Model 8, Model 1B and FreeSpace® 360 professional
loudspeakers. These cards fit into the J6, Channel 1 and J7, Channel 2 connectors located on
the Input Module motherboard or the Bose ACM-1 Amplifier Control Module.
Additional Features are as follows:
• Two input connectors per channel allow 1/4" TRS, XLR, or quick connect terminal block
connection
• Two input connectors for each channel are wired in parallel
• Accepts balanced or unbalanced lines
• Independent CH 1 and CH 2 Level Controls with 11 detented positions
• Level Control Defeat Switch
• Dual Mono Mode for combining the power of both channels into a single higher powered
channel
• Sequencer connection for sequentially powering-up multiple amplifiers to limit instantaneous
in-rush current
• Bi-Amp/Full Range configurable
• Internally configurable for Parallel Mono mode for single channel low impedance operation
• Internally configurable for 0.775V or 1.5V rms input sensitivity
• Internally configurable input polarity of XLR connectors
• Class H dual-rail power supply
• Additional protection circuitry includes Clipping Eliminator, AC Lines Fuse
• Power Connected/Standby Indicator
• 7 LED display per channel, including power ready and Clip/Protect indicators
• Two-speed fan cooled
2. Circuit Descriptions
This section discusses the theory of operation of the 1600VI and 1800VI Amplifiers.
For a better understanding of the circuitry involved, refer to the schematics included with this
manual. Component pin designation is notated as follows: U1-7 means U1 at pin 7.
Unless otherwise noted, this discussion centers around the CH 1 circuitry.
The CH 2 circuitry is essentially identical.
10
THEORY OF OPERATION
2.1 Input Module
Note: Some amplifiers will be equipped with the Bose® ACM-1 Amplifier Control Module in
place of the Bose Input Module. This module retains all of the capabilities of the Bose Input
Module, except sequence (see section 2.8), and includes the ability to control and monitor the
amplifier over a control network. Refer to the ACM-1 Amplifier Control Module service manual,
part number 199746 for more information.
The Input Module consists of signal input connections, mode switching, optional equalization,
and power sequencing circuitry. The module operates from +15V and -15V, supplied by the
host amplifier through J2-2 and J2-1 respectively.
The signal inputs are designed for balanced connection, though unbalanced inputs can be
configured by proper input wiring. Channel 1 (CH1) line-level inputs are made via P4 and J4,
Channel 2 (CH2) input connections are made via P1 and J5. P4 and P1 allow for the insertion
of either male XLR or phone plugs. The phone plug terminations are: tip positive (+), ring
negative (-), and sleeve ground. The XLR connections pins 2 and 3 are user configurable. As
shipped, jumper blocks JB2 and JB1 have jumpers between pins 2 to 3 and 5 to 6. This jumper
configuration assigns XLR pin 2 to positive (+) and pin 3 to negative (-), pin 1 is ground in all
configurations. If the jumpers are placed across JB1/JB2 pins 1 to 2 and 4 to 5 the XLR pin
assignment becomes pin 2 negative (-), and pin 3 positive (+). The Euro-block terminal block
connectors J4 and J5 assignments are: pin 1 positive (+), pin 2 negative (-), and pin 3 ground.
The CH1 input signal is applied to ICs U1, and the CH2 signal to U2. U1 and U2 are unity gain
(0 dB) differential amplifiers (SSM2141). These inputs are protected against RFI (Radio
Frequency Interference) and ESD (Electro-Static Discharge). The signals are then routed to
the A inputs of op-amp/switch ICs (BA3128) U4 (CH1) and U3 (CH2) and to EQ card
connectors J6-4 and J7-4 respectively. The switch’s B inputs are driven by the output of the EQ
cards via J6-5 and J7-5.
The input module detects the presence of EQ cards via J7-6 and J6-6. Without the card
installed these pins are pulled high (+15V) which keeps both CH1 and CH2 sections of dual
LED D23 extinguished. This logic high signal is also applied to the control pins of the switch
ICs which selects the A (unequalized) input. When an EQ is plugged into J7 and/or J6 pin 6 the
EQ is detected and pulls the control pin low (+7.5V), turning on the corresponding LED(s) and
switching the IC to the B input which selects the output of the EQ card.
On some EQ cards the equalization can be modified for either full range “FULL BANDWIDTH”
or bi-amplified “HF ONLY” operation. The equalization mode switch SW2 selects either FULL
BANDWIDTH or HF ONLY modes of the EQ cards installed. These control signals are sent to
the EQ cards via J6-7, 8 and J7-7, 8.
The selected signals from U4 and U3 are buffered by U7B and U7A which are wired to P2 and
P3. These phone connectors provide balanced, buffered, equalized outputs (if an EQ card is
installed) to drive additional amplifiers or other equipment. This allows external equipment to
provide equalized signals without the need for additional equalization. The pin assignment for
these connectors are the same as for the input phone connectors P1B and P4B. The output
circuitry is also protected from RFI and EMI.
The amplifier can be operated in four different output modes: normal (two independent channels) dual mono (one input channel, two separate channels), bridged mono, or parallel mono.
These modes are selected via SW1 and control the operation of op-amp/switching ICs U6 and
U5. Parallel mono operation requires internal modifications to the amplifier, contact the local
Bose Pro Product dealer for information on parallel mono operation.
11
THEORY OF OPERATION
When SW1 is set to the NORMAL mode, CH1 and CH2 operate independently. In this mode a
logic high is applied to the control pins of U6 and U5. This routes the outputs of U4 and U3 to
their respective channels in the amplifier via J1-20 and J1-16.
In DUAL MONO mode both amplifier channels are driven by the signal applied to the CH2
input. U6-1 is driven high (+15V) and U5-1 is driven low (+7.5V), selecting CH2 to drive both
channels of the amplifier.
In BRIDGED MONO operation the CH2 signal is routed directly from the equalizer switch U3 to
the amplifier inputs. U5 control pin 1 is driven low (+7.5V) selecting the inverting input of the
op-amp switching IC signal. This inverting signal is then sent to the B input of U6 whose
control signal at pin 1 is driven low selecting the B input. This routes the inverted signal to the
CH1 input of the amplifier.
For information on sequence operation see Section 2.8, Sequence Send/Receive.
2.2 Power Amplifier Circuitry
The 1600VI and 1800VI amplifiers use a conventional class AB push-pull power amplifier
circuit, with a commutated two-stage (dual-rail, class H) power supply. U100A-1 is the input
stage, providing differential inputs for input and feedback connections as well as most of the
open-loop voltage gain of the circuit. Local and global negative feedback from the output stage
via R109, R113, R111/ R112 and R129 sets the closed-loop gain at 33.3 dB for the 1600VI and
36.0 dB for the 1800VI. Removing jumper JP100 disconnects R111 from the circuit and sets
the closed-loop gain at 27.6 dB for the 1600VI and 30.3 dB for the 1800VI. The factory default
settings are 33.3 dB for the 1600VI gain and 36.0 dB for the 1800VI gain. The output of
U100A-1 drives Q100 and Q101, operating as common emitters that level-shift the drive signal
and couple it to the pre-driver amplifiers Q102 and Q103. Q102 and Q103 provide additional
voltage gain, and when combined with the voltage gain of the input op-amp is sufficient to
swing the input signal between the +90V/1600VI and +106V/1800VI power supply rails. Q104
and Q122 are connected as an NPN-PNP conjugate pair and used as a VBE multiplier for bias
control. Q104 is thermally connected to the output transistors and together with Q122 provides
bias stabilization over a wide temperature range. R124 allows the bias current to be adjusted
to its optimum value.
The predrivers Q102 and Q103 provide the base current to the drivers Q108 and Q109.
These drive the output transistors; Q110, Q112, Q114, Q116, Q118 and Q120 for the positive
half-cycle, and Q111, Q113, Q115, Q117, Q119 and Q121 for the negative half-cycle.
Note: Output transistors Q112, 118, 212 and 218, along with the corresponding channel 2
output transistors Q113, 119, 213, 219, are not used in the 1600VI amplifier.
Q105 operates as a V-I limiter, sensing the voltage drop across emitter resistor R148 (Q106
across R149 for the negative side), and reducing the drive signal to the output stage under
overload conditions (see Section 3.1 Over-Current Protection for more information). From the
Amplifier Board, the signal passes to the Output Board via E100 (E200 for CH 2). R100, L100,
R110 and C100 on the Output PCB comprise the output pole circuit for amplifier stabilization.
12
THEORY OF OPERATION
2.3 Output Relays
Note: Refer to the Output PCB schematic for the following.
Relay K100 is used to connect the output signal to the Speaker Output Binding Posts through
J1. The CH1 and CH2 (K100 and K200) output relays are energized independantly of each
other. In CH1, immediately after the power switch is turned on, +6 Vdc is applied to terminal 2
of D105 (ready LED) on the display board via the voltage divider formed by R112/R113. Terminal 1 of D105 is connected to pin 6 of K100 via J3-8 and J6-5 on the I/O board. A small amount
of current is drawn through R102 and the relay coil, which is enough to illuminate the red LED
portion of D105 but not enough to activate the relay. In the meantime, C13 begins to charge
through R26 on the I/O board, which delays turning on Q2 and Q3 by a few seconds.
When Q3 turns on, VLF+ is applied to pin 6 of K100 which activates the relay. VLF+ is also
applied to terminal 1 of D105, which reverse biases the red LED and D107, and forward biases
the green LED, drawing current from ground through R112.
2.4 Magnetic Field Power Supply
When the power switch is OFF (S1 across E1 and E2) and the linecord is connected to an AC
voltage, D1 illuminates (Standby LED). When the power switch is turned ON (S1 across E2
and E3), the LED goes off and gate voltage is applied to triac Q1, which turns it on and energizes the transformer primary winding.
The secondary winding of the power transformer has two taps that supply the two pairs of DC
supply voltages, ±90 Vdc and ±45 Vdc for the 1600VI and ±106 Vdc and ±53 Vdc for the
1800VI, each having its own bridge rectifier and filter capacitors. The ±15 Vdc is tapped from
the ±53 Vdc for the 1800VI and the ±45 Vdc for the 1600VI through R6 and R8, and regulated
by Q2, Q3 and zener diodes D3 and D6. The ±15 Vdc supply powers the op-amps and smallsignal transistors.
Note: Refer to the Regulator Board schematic diagram for the following.
The Regulator Board is not used on the 1600VI.
In the 1800VI, the triac Q1 drives the primary of the magnetic field power transformer by
operating as a phase controlled switch; its gate signal depends on the signal supplied to
opto-isolator U3 located on the regulator board. U4B provides steering for the photodiac in U3,
allowing the triac to fire on both alternations of the power line. U2 on the Regulator Board
provides AC to DC conversion, with the AC line voltage providing the input to the converter
through limit resistors R3 and R4, and the 12.5 Vdc output determined by feedback resistor
R6. This voltage provides the positive supply for U4, DC reference for comparators U4C and
U4D, and the current through opto-isolator U1 which sets the voltage for the voltage-to-current
converter U4A. Note that U4 (MC3405) is a dual op-amp and dual-voltage comparator in a
singe package (U4A/U4B are op-amps and U4C/U4D are open collector comparators).
2.5 Start-up Sequence (1800VI only)
When the power switch is OFF (S1 across E1 and E2) and the linecord is connected to an AC
voltage, D1 illuminates (STANDBY LED). When the power switch is turned ON (S1 across E2
and E3), the LED goes off and AC HI is supplied to the Regulator Board.
13
THEORY OF OPERATION
D2 and D3 on the Regulator Board provide overvoltage protection to U4. U4B-14 is a full-wave
rectifier that outputs positive pulses to comparator U4C. The reference voltage is set at 0.7Vdc
by R10 at pin 3. Where pin 2 crosses the threshold, the output of U4C-1 goes open and C6
begins to charge through R21 and U4A-8.
U4A is a voltage-to-current converter (Howland current pump), whose output current is
determined by the voltage at the junction of R12 and R13. As the voltage increases, the
charging current to C6 increases.
The voltage on C6 is connected to comparator U4D-6. The reference voltage is set at 0.7Vdc
by R22 at pin 5. When pin 6 crosses the threshold, the output of U4D-7 goes open and base
current is supplied to Q1 through R14. Q1 turns on, and current flows through the LED portion
of U3, illuminating it and turning on the diac. This applies voltage to the gate of triac Q1 on the
Power Supply Board which fires it and allows it to conduct current through the primary side of
the power transformer.
When the output of U4B-14 drops below the threshold voltage of U4C-3, U4C-1 goes low and
C6 discharges rapidly through it. When the voltage on C6 drops below the threshold voltage of
U4D-5, U4D-7 goes low and Q1 and U3 turn off, removing the gate voltage to the triac
momentarily interrupting the current through the primary side of the transformer.
The triac is switched on and off every half-cycle of the 60Hz AC line. Thus, the triac switches
the AC line current off at a rate twice the line frequency, at the instant the line current crosses
the zero axis. The triac will then remain off for a number of degrees of the sinusoid, before
switching on again. The phase angle at which the triac switches on is the “firing angle” of the
triac. This produces enough voltage to the primary of the power transformer to allow the
secondary regulator stage to begin to operate.
2.6 Power Supply Regulation (1800VI only)
The firing angle of the triac controls the voltage on the primary of the transformer, and is
determined by the conduction of the optocoupler U3 on the Regulator Board.
As the conduction of the optocoupler increases, so does the conduction angle of the triac. The
photodiac conduction of the optocoupler is controlled by the current through the LED portion of
the optocoupler, the amount of current through the LED is equal to the amount of current
through transistor Q1. When the LED in U3 is fully ON, the triac conducts earliest in the AC
cycle: the power supply is operating at maximum output. The LED current is supplied by
voltage regulator U2 on the Regulator PCB. U5A differential amplifier senses the secondary
supply voltages through R37 and R38. The output voltage at U5A-1 increases at the rate
determined by R30 and C8 (slow start-up). The idle secondary voltages are set by R36 on the
Regulator Board .
2.7 Load Regulation (1800VI only)
When the amplifier is driven at high power into a load, the high DC supplies (rail voltages) will
begin to “sag”. Differential amplifier U5A-1 senses this and increases the LED current to
optocoupler U1. This action increases the phototransistor conduction, which increases the
output current of U4-8, increasing the charging rate on C6. This ultimately increases the triac
conduction which increases the primary voltage, which increases the secondary voltages, thus
providing steady, regulated DC supplies for the amplifier stage.
14
THEORY OF OPERATION
The -15Vdc supplied to U5A-4 is backed up with a voltage divider off the -106Vdc supply (R26/
R27). Without this, if the -15Vdc supply should fail for some reason, the output of U5A-1 would
go high, drawing maximum current through the LED in U1 and latching the triac into full conduction. To prevent this, D8 will become forward biased and supply negative DC to U5A-4,
keeping it operating normally. Note that if the +15Vdc supply should fail, the output of U5A-1
would go negative, turning off the triac.
2.8 Sequence Send/Receive
The amplifier can be powered up while the power switch is in the OFF position by applying a
DC control voltage of +7V to +15V to the Sequence RCV terminal. Q3 on the Input Module
Board will turn on and carry the control voltage through to the SND terminal, which is connected to the next amplifier in the sequential chain. Q1 also turns on which turns on Q2,
providing enough current to pass through the LED portion of optocoupler U1 on the Power
Supply Board to illuminate it and turn on the diac. This provides a gate voltage to fire triac Q1,
which powers up the primary circuit. Once the secondary voltages are up, the +15Vdc supply
keeps the Receive circuit operating.
2.9 Commutators
Under idle or small-signal conditions, the low-rail voltage is applied to the collectors of the
output transistors through D13 and D19 on the Power Supply Board. The output of the amplifier is connected to the Power Supply Board via J1-10/J2-10. The signal is half-wave rectified
by D7 and D14, sending the positive half of the signal to comparator U2A-1 and the negative
half to comparator U2B-7. When the signal level exceeds the threshold of the comparator, Q4
(positive) or Q10 (negative) turns on. Current can now flow from ground through Q8 which acts
as a current source for Q6. Q6 or Q11 turn on providing gate drive to the power FET Q9 (positive) or Q14 (negative). When the FETs turn on, the high-rail voltage is connected to the collectors of the output transistors. D13 and D19 become reversed biased and switch off the low-rail
voltage from the circuit. Zener diodes D11 and D18 provide gate protection to the FETs.
Q7 and Q12 speed up the turn off time of the FETs.
This two-stage approach minimizes the voltage across each of the output devices which also
minimizes the power dissipation required. Without this approach, the output transistors would
be required to support the entire power supply voltage under small-signal conditions and the
“unused” portion of the power supply voltage would be turned into heat.
2.10 Display Circuit
In addition to the READY LEDs discussed in section 2.3 (Output Relays), the Display Board
contains five SIGNAL LEDs and one CLIP/PROTECT LED per channel.
The clipping indicators are driven by transistors Q100 (CH1), and Q200 (CH2) located on the
Display Board. The signal for the clipping indicators initially comes from U100A-1 and U100B-7
on the Amplifier Board. This is the same signal that operates the anti-clipping opto-isolator on
the I/O Board. D30 on the I/O Board half-wave rectifies the positive-going portion of the signal
and drives comparator U9B which is a switch. C9 and R62 establish the time constant of the
clipping indicator. D23 rectifies the negative-going portion and also drives comparator U9B.
When clipping occurs, U9B-7 changes from positive to negative, which forward biases D100
on the Display Board and turns on Q100. Q100 supplies current for clipping LED D104,
causing it to illuminate.
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THEORY OF OPERATION
The output signal is sensed at the speaker output via the I/O Board (J2-3 Output Board to J6-3
I/O Board to J3-6 I/O Board to J1-6 Display Board). D22 half-wave rectifies the signal and
provides a DC voltage proportional to the amplifier’s output to drive the signal display circuit.
C2 and R19 determine the response characteristics of the display.
The signal driver circuit comprised of U1-U4 is basically a ladder comparator driving LEDs,
with a twist. Assume that the signal at U2A-3 is zero volts (ignore R24 and D23 for now). R13
and R14 are a voltage divider that establishes a reference voltage for the comparators (four
per channel). The comparators compare this reference voltage against the voltages established by the tapped voltage divider made up of R22, R20, R15 and R25. The CH1 LEDs are in
the following sequence (lowest to highest): D105 (red/ green), D13 (amber), D15 (amber), D14
(amber), D12 (amber), D11 (amber), and D104 (red).
With the input at zero volts, all of the comparator outputs are at -12V, except for U2B-7 which
is high. None of the signal LEDs have any voltage across them, all are extinguished. As the
input signal rises, it crosses in sequence at the thresholds established at each of the four
comparators. First U2A-1 fires; its output goes high and D13 illuminates. Next U1B-7 fires, its
output goes high, D13 extinguishes (no net voltage across it) and D15 illuminates. Finally U1A1 fires, D15 extinguishes, and (this is the twist) D23/R24 supply current to the bottom of the
R15, R20, R22 and R25 voltage divider, which inverts the relationship of the comparators to
each other.
When U1A-1 fires, the current through R24 reverses the sequence of the voltages that establish the thresholds for the three comparators. This allows the same comparators to perform
double-duty. The new thresholds leave U1A-1 high, U2B-7 low, U2A-1 and U1B-7 low and D14
on. D11 and D12 are off. As the input signal rises further, U1B-7 fires, extinguishing D14 and
illuminating D12. Next U2A-1 fires, extinguishing D12 and illuminating D11. Finally U2B-7 fires,
extinguishing D11. The last LED is the clipping indicator, D104.
3.0 Protection Circuitry
Protection functions are provided that will deactivate the output relays. Protection is provided
for the following fault conditions:
3.1 Over-Current Protection
The amplifiers are protected from short-term excess current through the output stage by
electronic current limiters. When the current through the output transistors becomes excessive,
the voltage drop across the emitter resistors R148 and R149 bias the current limiter transistors
Q105 and Q106 on, which shunt the drive current via D106 and D107. R139, D102, R140 and
D103 determine the V-I limits.
When the current-limiters turn on, the voltage at voltage divider R127/R128 becomes less
positive, providing base current for Q1 on the I/O Board through R38. When Q1 turns on two
things happen; current flows through U3 (LED/LDR module) via D31 which attenuates the
input signal, removing the high current condition as well as providing base current to Q5
through D1 which turns off Q2 and Q3, causing the relay to disengage. C13 provides a time
delay to prevent the relay from disengaging during momentary program peaks. When the relay
disengages, it causes the red LED in D105 (READY LED) to illuminate and also turns on Q100
and D104 (CLIP/PROTECT LED).
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THEORY OF OPERATION
3.2 Clipping Eliminator Circuit
This circuit is controlled by the LED/LDR opto-isolator U3, located on the I/O Board. The LED
portion of this component is driven from a bridge rectifier (D4) that gets its input signal from
U100A-1 on the Amplifier Board. Under normal conditions (undistorted amplifier output) there
is almost no signal at this point. If the amplifier is driven into clipping, the signal level at
U100A-1 rises rapidly because the feedback signal no longer represents the input signal.
Once this occurs, the LED in U3 illuminates, reducing the resistance of the LDR portion which
in turn reduces the input signal. The clipping-eliminator circuit is activated by switch S2B on
the I/O Board. When the switch is off, the signal driving the bridge rectifier is shorted to ground.
3.3 DC Offset
DC offset is sensed by the comparator amplifier U2A on the I/O Board. If a DC component
should appear at the output, it is sensed through either D6 or D7, depending on its polarity.
The output of U2A-1 will switch from -14Vdc to +14Vdc, which turns on Q5 via D8. This deactivates the relay, turns the READY LED red, and turns on the CLIP/PROTECT LED.
In addition, the output of U2A-1 is conveyed to the Regulator Board via D15, J100-10 to
Regulator Board J1-12 and D9. The positive voltage on U5A-2 causes the output of U5A-1 to
become less positive, shutting off the conduction current through optocoupler U1, which shuts
off the triac and primary current.
Note: The Regulator PCB is not used in the 1600VI amplifier.
3.4 Overheated Output Transistors
A thermistor (RT100) is positioned near the amplifier PCB's heatsink. As the negative coefficient thermistor heats up, the voltage on comparator U2B-6 located on the I/O PCB drops.
When it crosses the reference voltage set up by voltage divider R42/R43, U2B-7 goes positive.
This forward biases D17, turning on Q5, which deactivates relay K100. As the heatsink temperature cools, the thermistor will cool until the voltage at U2B-6 once again crosses the
reference voltage at U2B-5, allowing the relay to reactivate.
3.4 Fan Speed Control
The fan operates at low speed when the amplifier is first turned on. The voltage at the
thermistor is connected to the Fan Drive circuit on the Output Board via D16 (on the I/O Board)
and J6-4/J2-4. As the heatsink temperature increases, the voltage at U1A-3 on the Output
Board decreases until it crosses the threshold set by voltage divider R4 and R6. When this
occurs, the output of U1A-1 toggles low, which turns on Q1. Q1 shorts across R1 and applies
the full VF+ voltage to the fan, kicking it into high speed.
3.5 Major Faults
The slo-blo line fuse protects the unit from further damage when a major fault such as a
shorted output transistor or a secondary power supply fault occurs. If the unit is run at or near
its rated power, the fuse will eventually blow. The rated line fuse allows the unit to be operated
without interruption for all musical applications.
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THEORY OF OPERATION
4.0 Operating Modes
The Bose® 1600VI and 1800VI amplifiers are capable of being configured to operate in several
different modes in order to allow greater flexibility in use.
4.1 Bridged Mono/Dual Mono Switching
The Stereo/Mono Switch (S1) on the Input Board is a three-position switch used to select
Normal Stereo, Bridged Mono or Dual Mono operation. In the Bridged Mono position, it connects CH 1 in parallel with the CH 2 input, but inverts the signal to CH 1. The CH 1 input
connection becomes disabled. The speaker output signals are identical except CH 1 is 180
degrees out of phase. In this way, a single speaker can be connected between the two “+”
speaker terminals and receive twice the voltage as a single channel. When connected in this
way, each channel “sees” one-half the impedance of the speaker that is connected between
them. If an 8 ohm speaker is used, each channel will see a 4 ohm load. The result is twice the
rated power (per channel) into twice the rated impedance.
Note: Each channel can still be independently controlled with its own level control so it is
important that both level controls be set to the same position for a balanced output.
When S1 is switched to the Dual Mono position, CH 1 is connected in parallel with the CH 2
input, but in phase. The CH 1 input connection becomes disabled. This allows both channels
to be driven with the same signal without the use of special patch cords. Each channel can still
be independently controlled with its own level control.
4.2 Parallel Mono
To operate in Parallel Mono mode, leave S1 in the Normal Stereo position. Removing jumpers
JP201 and JP203 will disconnect the CH 2 predrivers from the output stage. Installing jumpers
JP102, JP104, JP202 and JP204 will connect the CH 1 predrivers to the CH 2 output stage. In
this way, both channels will operate at exactly the same level, and will be controlled by the
CH 1 level control.
In addition, removing JP1 will prevent the CH 2 clip LED from activating, and installing a 16 ga.
jumper wire between WL100 and WL200 on the Output Board will tie both amplifier outputs
together before the relays.
When operating in parallel mono, either of the speaker output terminals (CH 1 or CH 2) can be
used since they both have exactly the same signal present. When a speaker is connected to
the output terminals it can be driven with twice the current capacity of a single channel. The
result is twice the rated power (per channel) into half the rated impedance.
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