Alesis MATICA 500/900 (A4/A8) Service Manual

ALESIS

MATICA 500/900

(A4/A8)

Service Manual

P/N: 8-31-0030-A

The information in this document contains privileged and confidential information.
It is intended only for the use of those authorized by Alesis. If you are not the
authorized, intended recipient, you are hereby notified that any review,
dissemination, distribution or duplication of this document is strictly prohibited. If
you are not authorized, please contact Alesis and destroy all copies of this
document. You may contact Alesis at [e-mail] or at
[e-mail].

Copyright Alesis, LLC
Confidential Alesis Service Manual 8-31-0030-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.

Confidential Alesis Service Manual 8-31-0030-A

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.

Confidential Alesis Service Manual 8-31-0030-A

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
step on the cords and such that nothing will be placed on or against them.

3. Periods of Non-use
AC power supply cord should be unplugged from the AC outlet.

4. Foreign Objects and Liquids
openings of the product.

5. Water or Moisture

6. Heat

7. Ventilation

8. Mounting

9. Cleaning

10. Service

. Do not place the product near heat sources such as stoves, heat registers, radiators or

other heat producing equipment.

. When installing the product, make sure that the product has adequate
ventilation. Improperly ventilating the product may cause overheating, which may damage the
product.

. 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.

. The product should only be cleaned as the manufacturer recommends.

. 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.

. AC power supply cords should be placed such that no one is likely to

. If the product is not used for any significant period of time, the product's

. Take care not to allow liquids to spill or objects to fall into any

. The product should not be used near any water or in moisture.

11. Damage to the Product
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.

. Qualified service personnel should service the unit in certain

Confidential Alesis Service Manual 8-31-0030-A

General Troubleshooting

While this manual assumes that the reader has a fundamental understanding of electronics and
basic troubleshooting techniques, a review of some of the techniques used by our staff may help.

1. Visual Inspection - A short visual inspection of the unit under test will often yield results without the
need of complex signal analysis (burnt, or loose components are a dead giveaway).

2. Self Test - Alesis products that utilize microprocessor control contain built in test software which
exercises many of the units' primary circuit functions. Self test should always be done following any
repair to ensure basic functionality.

3. Environmental Testing - Applying heat and cold (heat gun/freeze spray) will often reveal thermally
intermittent components (Clock crystals, I.C.s, and capacitors are particularly prone to this type of
failure).

4. Burn in Testing - Leaving a unit running overnight often reveals intermittent failures such as
capacitors that begin to leak excess current after a significant amount of time.

5. Cable Checks - Wiggling cables can reveal intermittent failures such as loose cables or poorly
soldered headers. Remember to check power supply cables as well.

6. Flexing the PC Board - Poor solder joints and broken traces can often be found by pressing the PC
Board in various places.

7. Tapping Components - Sometimes tapping on a component (particularly crystals) will cause it to fail.

8. Power Down/up - Turning the unit off and back on rapidly several times may reveal odd reset and/or
power supply failures.

9. Reset Threshold - A Variac (variable transformer) can be used to check reset threshold levels. This
can be particularly useful in helping customers with low line problems.

10. Compressors - Using a compressor/limiter is often helpful when attempting to solve low level noise
problems, as well as assisting with DAC adjustments.

11. Sweep Tests - Sweep generators are very useful in checking the frequency response envelopes of anti­aliasing filters.

12. Piggybacking - Piggybacking I.C.s is particularly useful when troubleshooting large sections of logic.
This is especially true when working with older units.

Alesis A4/A8 Service Manual------ iv 03/07/03

Table of Contents

PREFACE ......................................................................................................... ii

WARNINGS ...................................................................................................... ii

SAFETY SUGGESTIONS .................................................................................iii

General Troubleshooting ...................................................................................iv

1.00 Theory of Operation .................................................................................. 1

1.10 Input Section................................................................................... 1

1.20 Pre-Amp Section ............................................................................ 2

1.30 Main Amplifier Section .................................................................... 2

1.40 Output Device Protection................................................................ 3

1.50 Bias Circuit ..................................................................................... 3

1.60 Speaker Protection ......................................................................... 4

1.70 Fan Speed Control.......................................................................... 4

1.80 Thermal Management System........................................................ 5

2.00 Updates and Corrections........................................................................... 5

2.10 Stripped Heat Sinks........................................................................ 5

2.20 New Case Bracket Insulator(s) ....................................................... 7

2.30 Transformer Insulators.................................................................... 8

3.00 Troubleshooting......................................................................................... 9

4.00 A4 Service Parts List ................................................................................. 10

4.10 A8 Service Parts List ...................................................................... 13

5.00 Service Manual History ............................................................................. 16

INDEX ............................................................................................................... 17

Alesis A4/A8 Service Manual------ v 03/07/03

1.00 Theory of Operation

The A4/A8 amplifiers are basic stereo amplifiers. They have 0dBm input sensitivities for
rated output at 4:, with the ability to drive any load impedance from 2: to an open circuit. They
have balanced inputs via Neutrik combination connectors providing XLR and 1/4" TRS
connections and also a barrier strip. The output of the amplifier is obtained by way of four five
way binding posts. Reference designations in the text refer specifically to the A4 amplifier except
where otherwise noted. Though reference designations between the two units are different, the
designs are virtually identical. The only significant differences occur in the output section (since
the A8 is required to handle much more power than the A4).
Here are some of the major features and building blocks of the Matica:

à An input balanced to unbalanced converter.
à A second stage pre-amp and an amplifier gain stage utilizing a monolithic front end with

discrete complimentary transconductance stage and a complimentary output stage in a
common collector configuration.

à Output device protection is accomplished with a conventional volt-amp current limiter circuit.

The output devices use a new perforated emitter technology unique to MOTOROLA. The
output devices are driven by similar technology devices, but they have been optimized for
extremely linear current gain with a unity gain bandwidth (Ft) of 50 MHz.

à The speakers are protected by output relays. They are activated during the first 3 to 5

seconds the amplifier is turned on. Also, if a DC condition exists at the output of the amplifier
or the amplifier is driven to full output below 5Hz the relays will be activated.

à Thermal management and protection are accomplished with a large heavy aluminum

extruded heat sink the is fan cooled. If the sink gets warmer than 55 deg. C, the fan is
automatically stepped up in speed and if the heat sink gets warmer than 80 deg. C the fan is
run at high speed and the output relays are activated to disconnect the load until the unit has
cooled to 65 deg. C. There is also a unique feature of the amplifier fan circuit in that when the
amplifier is providing an output signal of a little more that a watt the fan speed is modulated
or increased by the signal. This will help get longer run times with the amplifier under
extreme load conditions.

1.10 Input Section

The input stage is made up of a dual Signetics 5532A op amp. This is a low noise
selected version of the 5532. One half of the dual is used for each channel. The circuit is a basic
balanced to unbalanced converter. It can be driven unbalanced but 6dB differences in gain may
result for various hookups. If the (+) input is driven with the (-) input grounded the gain will be
unity. If the (+) input is driven with the (-) input left open there will be a gain reduction of 6dB.
This is not recommended as a noisier condition may result. If the (-) input is driven, gain will be
unity and will not change with the grounding or ungrounding the (+) input The maximum input
level before clipping in about +21dBm. Since there is no level control in front of the converter this
is the maximum input level for the amplifier. Connections to the Alink connector are between R1,
R2 and R3, R4. These are provided so an outboard impedance may be connected to modify the
gain and overload characteristics as well as its frequency response. Following the amplifier is a
passive low pass (R7, C1) filter that begins to limit the high frequency gain of the amplifier.

Alesis A4/A8 Amplifiers Service Manual------ 1 03/07/03

1.20 Pre-Amp Section

The pre-amp section also uses the Signetics 5532A op amp. The circuits of the pre-amp
are of opposing signal polarity to provide push pull characteristics and are connected via the
stereo/bridge switch. Each of the two pre-amp channels has 15.7 dB of gain but channel A is
inverting and channel B is not.
Since the main amplifier is inverting, channel A will not invert the signal and channel B
will. Doing this facilitates two things. When the stereo/bridge switch is in the bridge mode
channel B will already be out of phase with A so no signal inversion will have to be done to
achieve bridge operation. Also by operating B out of phase all the time, (even in stereo
operation) getting the phase of the signal flipped back at the speaker terminals, the amplifiers
low frequency power bandwidth will be increased. This allows the power supply to be utilized
more efficiently.
This section also shapes the bandwidth of the amplifier further via another low pass pole
being added to each stage. First and second stage high pass filtering occurs via the 100uf
coupling capacitors preceding the volume pots and after the pre-amp stages. The pre-amp
stages drive the main amplifier directly.
ALINK connections at the junction between R8, C2 and R13, C5 are for sending the
output signal of the input stage at a low impedance for use with auxiliary equipment. The
connection between R9, R10 and R14, R17 are to be used to for defeating the level controls by
supplying an input signal from a very low source impedance to swamp out the signal from the
pots.

1.30 Main Amplifier Section

The main amplifier is composed of four sections:

à The monolithic front end.
à A complimentary voltage gain stage or transconductance stage
à The output driver
à The output stage

The amplifier is configured in the inverting mode. This allows for the inputs of the op amp
to remain at a 0 voltage potential and ease operation on a +/- 15 volt supply. The large voltage
swing is accomplished with a discrete, complimentary darlington connected transconductance
stage Q1, Q2, Q3, and Q4. The current in the transconductance stage is set by the voltage
divider network made up of R19, R20, R21, and R22. The first transistor in the darlington is a
TO-92 packaged device with the current set by R27, and R28. The collector of this transistor is
not tied to the second collector in the darlington connection but rather to the +/-15 volt supply to
help increase the bandwidth of the stage and reduce the dissipation in the TO-92 devices. The
closed loop gain of the amplifier has been set for 10X or 20dB. The DC output offset is a
function of the input offset voltage error of the op amp times the gain of the system. With the
offset error of the op amp at about +/- 1mv the amplifier will have less than +/- 10mv of output
offset. The feedback network is composed of R25, R18, and C11. C11 reduces the bandwidth of
the amplifier. The large low frequency gain of the op amp helps to reduce the supply ripple that
is introduced into the system by the lack of supply rejection in the voltage gain stage. Under
driven conditions at mild loads of 4 or 8: at mid and high frequencies, the output of the op amp
will appear not to have any signal or very little signal on it. When the amplifier is clipped, or
driven to its rail, the output of the op amp will be driven to its rail, or about +/- 14 volts. It is trying
to correct the loop error or non linearity of clipping in the amplifier. The only other time the output
of the op amp will become a large signal is at a 2: condition at lower frequencies. This is due to
the loss of loop gain when the transconductance stage is required to deliver large amounts of
current to the output stage drivers. CR1 and CR2 are connected as clamps to the discrete

Alesis A4/A8 Amplifiers Service Manual------ 2 03/07/03