Alesis RA-100 User manual

ALESIS
RA100 Amplifier
(PA)
Service Manual
P/N: 8-31-0020-A

Preface
This document is intended to assist the service technician in the operation,
maintenance and repair of the Alesis device. Together with the User Reference
Manual, this document provides a complete description of the functionality and
serviceability of the Device. Any comments or suggestions you may have
pertaining to the document are welcome and encouraged.
READ THIS!
In addition to any purchase price that Alesis may charge as consideration for Alesis selling or
otherwise transferring this service manual (“Manual”) to you, if you are not a service and repair
facility (“Service Center”) authorized by Alesis in writing to be an authorized Service Center,
Alesis sells or transfers the Manual to you on the following terms and conditions:
Only Service Centers authorized by Alesis in writing are authorized to perform service and repairs
covered by an Alesis warranty (if any), and transfer of the Manual to you does not authorize you
to be an authorized Service Center. Therefore, if you perform, or if the Manual is used to
perform, any service or repairs on any Alesis product or part thereof, any and all
warranties of Alesis as to that product and any service contract with Alesis for that
product shall be voided and shall no longer apply for such product, even if your services
or repairs were done in accordance with the Manual.
All service or repairs done by you or with reference to the Manual shall be solely your
responsibility, and Alesis shall have no liability for any such repairs or service work. All such
service or repairs are performed at the sole risk of the person performing the service or
repairs. You agree that all such work will be performed in a competent, professional and safe
manner at all times and to indemnify and fully hold Alesis and its successors and assigns
harmless in the event of any failure to so perform.
Your purchase of the Manual shall be for your own ultimate use and shall not be for purposes of
resale or other transfer.
As the owner of the copyright to the Manual, Alesis does not give you the right to copy the
Manual, and you agree not to copy the Manual without the written authorization of Alesis. Alesis
has no obligation to provide to you any correction of, or supplement to, the Manual, or any new or
superseding version thereof.
Alesis shall have the right to refuse to sell or otherwise transfer repair parts or materials to you in
its sole discretion. You shall not use, sell or otherwise transfer spare or replacement parts
supplied by Alesis to you (i) to repair or be used in products manufactured for or by third parties
or (ii) to any third parties for any purpose.
You shall not make any warranties or guarantees with respect to the products of Alesis or the use
thereof on behalf of Alesis or in your own name.
The foregoing describes the entire understanding related to sale or transfer of the Manual to you,
and no other terms shall apply unless in a writing signed by an authorized representative of
Alesis.
All Trademarks are property of their respective companies.

Warnings
TO REDUCE THE RISK OF ELECTRIC SHOCK OR FIRE, DO NOT EXPOSE
THIS PRODUCT TO WATER OR MOISTURE.
The arrowhead symbol on a lightning flash inside a triangle is
intended to alert the user to the presence of un-insulated
"dangerous voltage" within the enclosed product which may be of
sufficient magnitude to constitute a risk of electric shock to persons.
The exclamation point inside a triangle is intended to alert the user
to the presence of important operating, maintenance and servicing
instructions in the literature which accompanies the product.
REPAIR BY ANY PERSON OR ENTITY OTHER THAN AN AUTHORIZED
ALESIS SERVICE CENTER WILL VOID THE ALESIS WARRANTY.
PROVISION OF THIS MANUAL DOES NOT AUTHORIZE THE RECIPIENT TO
COMPETE WITH ANY ALESIS DISTRIBUTOR OR AUTHORIZED REPAIR
SERVICE CENTER IN THE PROVISION OF REPAIR SERVICES OR TO BE
OR MAKE REPAIRS AS AN AUTHORIZED SERVICE CENTER.
ALL REPAIRS DONE BY ANY ENTITY OTHER THAN AN AUTHORIZED
ALESIS SERVICE CENTER SHALL BE SOLELY THE RESPONSIBILITY OF
THAT ENTITY, AND ALESIS SHALL HAVE NO LIABILITY TO THAT ENTITY
OR TO ANY OTHER PARTY FOR ANY REPAIRS BY THAT ENTITY.
Regarding the Power Supply Fuse
CAUTION: The product under service may employ the use of a
replaceable fuse. Danger of fire or electrocution if fuse is
incorrectly replaced. Replace with only the same type or
equivalent type recommended by the equipment manufacturer.
Regarding the Internal Battery
CAUTION: The product under service may employ the use of a
internal battery. Danger of explosion if battery is incorrectly
replaced. Replace only with the same or equivalent type
recommended by the manufacturer. Dispose of used batteries
according to the manufacturer's instruction.

Safety Instructions
Carefully read the applicable items of the operating instructions and these safety
suggestions before using this product. Use extra care to follow the warnings
written on the product itself and in the operating instructions. Keep the operating
instructions and safety suggestions for reference in the future.
1. Power Source. The product should only be connected to a power supply which is described
either in the operating instructions or in markings on the product.
2. Power Cord Protection. AC power supply cords should be placed such that no one is likely to
step on the cords and such that nothing will be placed on or against them.
3. Periods of Non-use. If the product is not used for any significant period of time, the product's
AC power supply cord should be unplugged from the AC outlet.
4. Foreign Objects and Liquids. Take care not to allow liquids to spill or objects to fall into any
openings of the product.
5. Water or Moisture. The product should not be used near any water or in moisture.
6. Heat. Do not place the product near heat sources such as stoves, heat registers, radiators or
other heat producing equipment.
7. Ventilation. When installing the product, make sure that the product has adequate
ventilation. Improperly ventilating the product may cause overheating, which may damage the
product.
8. Mounting. The product should only be used with a rack which the manufacturer
recommends. The combination of the product and rack should be moved carefully. Quick
movements, excessive force or uneven surfaces may overturn the combination which may
damage the product and rack combination.
9. Cleaning. The product should only be cleaned as the manufacturer recommends.
10. Service. The user should only attempt the limited service or upkeep specifically described in
the operating instructions for the user. For any other service required, the product should be
taken to an authorized service center as described in the operating instructions.
11. Damage to the Product. Qualified service personnel should service the unit in certain
situations including without limitation when:
a. Liquid has spilled or objects have fallen into the product,
b. The product is exposed to water or excessive moisture,
c. The AC power supply plug or cord is damaged,
d. The product shows an inappropriate change in performance or does not operate
normally, or
e. The enclosure of the product has been damaged.

The input signal drives QX15 (one half of a diff amp pair; consisting of
transistors QX15 and QX16). QX16 is driven by a feedback signal from the
output section through a 39K resistor (RX30). This 39K resistor is used to match
the impedance seen at the base of QX15 so that the voltage at the base of both
transistors is approximately 0.1V. This insures consistent operation of the input
diff amp.
The output of the first diff amp is used to drive a second diff amp pair
(QX12 and QX13) where the actual gain of the amplifier is set up. this is done
with a Vbe multiplier (QX04) connected to the second diff amp pair that can be
used to adjust the amount of current that the output section will deliver to the load
(more about this in section XX).
The output of the second diff amp pair drives the output stage that
consists of two pairs of driver and power transistors (QX05/QX07 and
QX01/QX03). This stage of the circuit is where the current to the output is
amplified.
The input diff amp (QX15 and QX16) is protected from high input voltages
with a limiter made up of two diodes (DX08 and DX09) connected in parallel (with
reverse polarities) directly across the bases of both transistors. This limiter is
used to keep the input voltages at or below 0.7V.
`The mute fast supply circuit is also connected into the input stage to
eliminate any voltage surges that could be caused during power up or power
down that could damage circuit components or speakers. This circuit consists of
a JFET (QX11) connected across the supply storage capacitor (CX08) for the
input diff amp and an RC time constant that charges the gate of the JFET. As the
unit is powered up, the JFET acts like a 30:resistor short to ground around the
supply storage cap until a -10V supply from the units power supply is applied to
the gate of the JFET through the RC time constant (RX43 and CX09). Once
CX09 is charged and applied to the gate, the JFET turns off and allows CX08 to
charge and supply voltage for the input stage. As the unit is powered down,
CX09 quickly discharges through DX13 and C4 turning the JFET back on and
shorting any leftover supply voltage to ground immediately.
The thermal shutdown circuit is also connected into the input stage. This
circuit is similar to the mute fast supply in that a transistor (QX10) is connected
across the supply storage capacitor top the input stage and, when turned on,
shorts the supply voltage to ground. The biasing voltage for QX10 is determined
by a transistor (QX09 -placed in the heat sink) in parallel with a voltage divider at
the base of QX10. The base of QX09 is left open so that it acts like a zener diode
and can drop about 7.7V across it. This voltage is applied to RX39 and RX40 and
keeps about 0.48V at the base of QX10. As temperature increases in the heat
sink, the voltage across QX09 begins to increase, causing a larger voltage to be
seen at the base of QX10. As this voltage increases, QX10 begins to turn on
and short some of the supply voltage to the input stage to ground. This causes a
reduction in output current and allows the unit to cool down.

The first stage drives a second diff amp pair that is used to drive the
output stage. This is where the clip indicator is connected.
As QX12 and QX13 are being turned on and off, there is a constant
current being delivered through RX27. This current sets up a voltage drop of
about 0.45V that is seen at the base of QX14. Any sharp increase in current
through QX12 or QX13 will cause a voltage peak at the base of QX14 and turn it
on. When QX14 is turned on, DX11 becomes forward biased and allows CX16 to
discharge through RX42 and turns off QX18. The LED is no longer forward
biased and turns off.
The outputs of QX12 and QX13 are connected to a Vbe multiplier
where the current gain of the output stage can be adjusted. This output is used to
drive the output stage.
The base current of QX04 is set up by a current mirror and can be
adjusted with RX08. Since the voltage across RX08 and RX09 remains constant
at 0.7V, adjusting RX08 will determine the amount of current that flows through
RX10 which in turn determines the output voltage of the Vbe multiplier (VR20 +
0.7V) that drives the output section. This Vbe voltage drop is what determines
the amount of current that can flow through QX01 and QX07 by setting the base
currents to QX03 and QX05. This adjustment should be made with the amp
powered up at room temperature and the outputs unloaded. With these
conditions satisfied, RX08 should be adjusted until the voltage drop across RX18
and RX02 together is about 2.5mV.
As QX13 turns on, the emitter of QX17 gets pulled down to -0.7V which
turns it on and allows more current to flow through RX33. This decreases the
voltage at the base of QX08 which turns it on faster and decreases the voltage
drop across it. This in turn pulls the output voltage drop across the Vbe multiplier
up towards the positive rail and turns on QX05.
When QX12 is turned on, the same thing in that the Vbe multiplier output
is pulled down toward the negative rail and turns on QX03.
QX05/QX07 and QX01/QX03 make up the output sections of the amplifier.
They are set up as current amplifiers that deliver large amounts of current to the
load.
When QX05 is turned on, 7mA of current flows through RX19 and QX05.
This brings the voltage at the base of QX07 to 0.7V below the positive rail and
turns it on. This allows a large amount of current to flow through RX18 and RX44
to the load (approximately 5.3 amps for a 4:load) and the voltage drop across
RX02 decreases.
When QX01 and QX03 are turned on, current is pulled back through RX44
and RX02 which increases the voltage drop across RX02.
This whole process is seen as large voltage swings at the output that
follow the input signal.
L1 is placed in parallel with RX44 so that when the unit is first powered up,
any large current transients are forced through RX44. The decreases power to
the speakers until the unit reaches steady state operation, at which point the

inductor then acts like a short around RX44. This protects the speakers from
being damaged if the unit is on with the volume controls turned up.

ALESIS
RA100 Amplifier
(PA)
SCHEMATIC
AND
PCB
FILES

ALESIS
RA100 Amplifier
(PA)
BOM

GROUP DESCRIPTION ALPARTNO QTYPER POSITION PCB MANUFACT NOTES
ASS AMP MODULE W \ HEATSINK 8-20-0028 REPLACEMENT ASSEMBLY
CAP 100 MF ELEC 6.3V 6x11mm 1-07-0100 4 C101,105,201,205 AMP 6x11mm/0.1
CAP 47 MF ELEC 25V 6x11mm 1-09-0476 4 C108,113,208,213 AMP 6x11mm/0.1
CAP 1.0 MF ELEC 50V 5x11mm 1-11-0105 4 C103,115,203,215 AMP 5x11mm/0.1
CAP 2.2 MF ELEC 50V 5x11mm 1-11-0225 2 C109,209 AMP 5x11mm/0.1
CAP 4.7 MF ELEC 50V 6x11mm 1-11-0475 4 C107,110,207,210 AMP 6x11mm/0.1
CAP 10,000MF ELEC 63V 35x50 1-12-0103 2 C2,3 PWR 35x36/0.4
CAP 10 MF ELEC 63V 6x11mm 1-12-0106 5 C04,106,111,206,211 AMP 6x11mm/0.1
CAP 0.1 MF MONOBLOCK 250V 1-21-0105 1 C1 PWR 0.4 SPC
CAP 0.047 MF POLY 100V 5SP 1-22-0473 4 C116,117,216,217 AMP 0.2 SPC
CER 220 PF CERDISC 1-02-0221 4 C102,104,202,204 AMP 0.2 SPC
CER 330 PF CERDISC 1-02-0371 2 C114,214 AMP 0.2 SPC
CER 68 PF CERDISC 1-02-0680 2 C112,212 AMP 0.2 SPC
CON SPADE CONN (PCB MOUNT) 4-11-0002 13 PWR 0.2 SPC
CON 9-PIN FEM SIL CONN 4-15-0015 2 HARNESS 0.15 SPC
CON 9-PIN MALE SIL CONN 4-15-0014 2 J1,2 AMP 0.15 SPC
HDW 4-40x3/8 PPB 5-00-0022 12 POWER TRANS
HDW 6-32x1/4 PPB 5-00-0003 4 P/S PCB
HDW 10-24x1/2 BLK HEX CAP 5-00-0024 22 EXTERNAL
HDW 4-24x5/16 PPB PLAST 5-00-1002 2 PUSH CLIP CONN
HDW #6 INT STAR BENT LUG 5-01-0011 2 GND (PART OF HARNESS)
HDW 1/4" FEM SPADE LUG 5-01-0012 22 HARNESS PWR
HDW 10-24 KEPS NUT 5-02-1024 5 TRANS/RECT
HDW 6-32 KEPS NUT 5-02-4401 1 GND
HDW FUSE CLIP 5-05-1001 2 AMP
HDW HEAT SINK 9-02-1004 2
JAC 1/4 MONO CLIFF JACK 4-02-0001 4 J3,4,6,7 INOUT

JAC PUSH CLP CONN 2 CTR BLK 4-08-0001 1 J5 INOUT
JAC IEC320 CONN/FUSE HLDR 4-09-0001 1
ME 1N4148 100V DIODE 2-00-4148 26 D101-113,201-213 AMP 0.4 SPC
ME 1N4002 200V DIODE 2-01-4002 1 D1 PWR 0.5 SPC
ME TRANS, MPSA42 2-03-1042 6 Q112,113,117,212,213,217 AMP MOT TO92/0.1
ME TRANS, 2SC4382 2-03-4382 2 Q105,205 AMP SANKEN TO220/0.1
ME TRANS, MPS8099 2-03-8099 8 Q104,106,110,114,204,206,210,214 AMP MOT TO92/0.1
ME TRANS, MPSA92 2-04-1092 2 Q108,208 AMP MOT TO92/0.1
ME TRANS, 2SA1668 2-04-1306 2 Q103,203 AMP MOT TO220/0.1
ME TRANS, MPS8599 2-04-8599 10 Q102,109,115,116,118,202,209,215,216,218 AMP MOT TO92/0.1
ME TRANS, J112 FET 2-05-0112 2 Q111,211 AMP MOT/NAT TO92/0.1
ME TRANS, 2SC3858 W/MICA 2-07-3858 2 Q101,201 AMP SANKEN 0.2 SPC
ME TRANS, 2SA1494 W/MICA 2-08-1494 2 Q107,207 AMP SANKEN 0.2 SPC
ME 2x5mm RECT LED (GRN) 3-00-0002 1 POWER LED 0.1 SPC
ME 2x5mm RECT LED (RED) 3-02-0003 2 CLIP LED 0.1 SPC
ME DPST 16A PWR SWITCH 6-03-0001 1
ME BRDGE RECT 10A/200V/300 7-03-0001 1
ME XFORMR 120/240 (71.9VC) 7-40-2500 1
ME 3uH COIL 9-09-0001 2 L1,2 AMP
MIS THERM GREASE .01-.02 OZ 7-11-0001 0 Q101,102,103,104,105,106,107,201,202,203,204,205,206,207 AMP FYI ONLY
MIS FOAM STRIP 9-23-1016 2 CASE TOP EDGES/FRONT PANEL
ML TOP COVER 9-03-1043 1
ML BRACKET 9-03-1044 4 AMP PCB-HEATSINK
ML FRONT PANEL 9-15-0042 1
MTL CASE CHASSIS 9-03-1045 1
PCB PCB, PANEL REV C 9-40-1056 1 PWR,POT A/B,AMP A/B,IN/OUT,LED A/B/C
PLS KNOB 35mm 9-15-0040 2
POT 1K TRIMPOT CERMET 0-08-0102 2 R108,208 AMP

POT 10KA SINGLE 0-09-1005 2 R145,245 POT
RES 0 OHM 1/4W 5% 0-03-0000 24 AMP 0.4 SPC
RES 100 OHM 1/4W 5% 0-03-0101 14 R101,119,121,122,127,133,134,201,219,221,222,227,233,234 AMP 0.4 SPC
RES 1K OHM 1/4W 5% 0-03-0102 2 R129,229 AMP 0.4 SPC
RES 10K OHM 1/4W 5% 0-03-0103 12 R104,116,135,136,138,141,204,216,235,236,238,241 AMP 0.4 SPC
RES 100K OHM 1/4W 5% 0-03-0104 2 R142,242 AMP 0.4 SPC
RES 1.1K OHM 1/4W 5% 0-03-0112 2 R140,240 AMP 0.4 SPC
RES 1.5K OHM 1/4W 5% 0-03-0152 8 R124-126,128,224-226,228 AMP 0.4 SPC
RES 15K OHM 1/4W 5% 0-03-0153 2 R139,239 AMP 0.4 SPC
RES 2.2K OHM 1/4W 5% 0-03-0222 6 R106,109,114,206,209,214 AMP 0.4 SPC
RES 220K OHM 1/4W 5% 0-03-0224 4 R103,117,203,217 AMP 0.4 SPC
RES 2.2M OHM 1/4W 5% 0-03-0225 2 R143,243 AMP 0.4 SPC
RES 2.7K OHM 1/4W 5% 0-03-0272 4 R1,2,110,210 AP/PR 0.4 SPC
RES 27K OHM 1/4W 5% 0-03-0273 2 R137,237 AMP 0.4 SPC
RES 33K OHM 1/4W 5% 0-03-0333 10 R105,115,120,123,132,205,215,220,223,232 AMP 0.4 SPC
RES 39K OHM 1/4W 5% 0-03-0393 2 R130,230 AMP 0.4 SPC
RES 47 OHM 1/4W 5% 0-03-0470 4 R107,112,207,212 AMP 0.4 SPC
RES 47K OHM 1/4W 5% 0-03-0473 2 R113,213 AMP 0.4 SPC
RES 5.6K OHM 1/4W 5% 0-03-0562 2 R131,231 AMP 0.4 SPC
RES 68 OHM 1/4W 5% 0-03-0680 2 R111,211 AMP 0.4 SPC
RES 0.22 OHM 5W 0-05-0022 4 R102,118,202,218 AMP 1.1 SPC
RES 3.3K 1W CARBON FILM 0-05-0332 2 R246,247 PWR FUTABA
RES 4.7 OHM 2W METAL OXIDE 0-05-0470 2 R144,244 AMP 0.8 SPC
RUB RUBBER FEET 9-23-1024 4 NOT ATTACHED
WIR WIRE, 9 PIN ASSY L/R 9-89-0004 2 9 PIN CONN-TERM PIN (2 WIRES PER) 20 GA
WIR WIRE, BRIDGE RECT 9-89-0005 4 FEM SPADE-TERM PIN 20 GA
WIR WIRE, I/P ASSY L/R 9-89-0006 2 TERM PIN-TERM PIN (2 WIRES PER) 20 GA
WIR WIRE, POWER CONN SPADE 9-89-0007 2 FEM SPADE-FEM SPADE 20 GA

WIR WIRE, POWER CONN TERM 9-89-0008 2 FEM SPADE-TERM 20 GA
WIR WIRE, POWER CONN RING 9-89-0009 1 FEM SPADE-RING 20 GA
WIR WIRE, POWER SWITCH 9-89-0010 2 FEM SPADE-FEM SPADE 20 GA
WIR WIRE, LED RIGHT 9-89-0011 1 TERM PIN-TERM PIN 20 GA
WIR WIRE, LED LEFT 9-89-0012 1 TERM PIN-TERM PIN 20 GA