Alesis Midiverb 3 Service manual

ALESIS

MidiVerb 3 (M3)

Service Manual

P/N: 8-31-0014-A

ATTENTION!

THIS DOCUMENT CONTAINS SENSITIVE

PROPRIETARY INFORMATION.

ALL RECIPIENTS MUST HAVE A CURRENT

NON-DISCLOSURE AGREEMENT ON FILE

WITH ALESIS, LLC.

DO NOT MAKE ILLEGAL

COPIES OF THIS DOCUMENT

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 8-31-0014-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 8-31-0014-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 8-31-0014-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 8-31-0014-A

1.0 M3 GENERAL DESCRIPTION

The M3, and other digital effects processors, achieve their results by slicing analog signals
into segments, and then converting them to a numeric value, corresponding to the amplitude of the
signal at that particular instant. These values are then mathematically manipulated, and stored at
various locations in a memory "loop" for eventual playback. By varying the placement and amplitude
of incoming samples, discrete time delays are achieved. When mixed together, and converted back
into analog, these
delays simulate the
reflections associated
with natural reverbs,
and delays, as well
as non natural effects
such as reverse
reverbs, and gated
reverbs. The added
capabilities of an
80C31 micro
controller allow for
user manipulation
and storage of
algorithm parameters,
as well as effects
such as chorus, and
flange, that require
real-time
manipulation of
algorithms. Please
note that there are
several different
board revisions, so
differences will be
noticed from unit to
unit.

2.0 POWER SUPPLY

The power
supply begins with
the 9 Volt, A.C.,

Diagram 1

adapter. Input from J7 is R.F filtered (or bypassed in some units) by the large torroid and C68. From
there it is split for the +12V, -12V, and +5V rails. The +12V rail consists of a voltage doubler (C69,
C73, and 2 diodes), a filter cap (C81) a 7812 regulator (VR1), and filter capacitors (C7, C72, and
C80). The -12V rail is a "mirror" of the +12V rail, consisting of voltage doubler (C70, C74, and 2
diodes), a filter cap (C83), a 7912 regulator (VR2), and filter capacitors (C6, C40, C71, and C82).
The +5V rail consists of a rectifier diode, filter capacitors (C75-C78, and C84), a 7805 regulator
(VR3), filter capacitor (C85), and many 0.1uF bypass capacitors.

3.0 ANALOG SIGNAL PATHS

The inputs (stereo) from J1 and J2 pass through the small toroids for RF suppression
(bypassed in some units), A.C. coupled (C1, C2) and have their impedances fixed at 1M by R2 and
R3. While operating the unit monauraly, the input impedance fixed at 500K (R2, and R3, in parallel).
From there, the inputs are buffered by U1, and passed through the input potentiometers. The stereo
signal is then sent to a X10 gain stage (U1 etc.) and on to the dry side of the mix potentiometer, as
well as summed to mono (Via R21, R22).
The summed stereo signal is sent to the anti-aliasing filter consisting of most of U4, and
associated resistors and capacitors. There are several important features in the filter to be aware of.
The first is the use of the LSTMSB (See section 4.5 for a description) signal from the ASIC. This
signal is injected into the signal path at U4 pin 12. A signal diode at U4 pin 10 limits the incoming
signal to 5V, preventing damage to the analog switch (U6). The output of U4 pin 8 has a tap running
to R46, a 2N4401 transistor, etc., and eventually on to an 8031 input port (U27 pin 13) where it is
used to detect the audio threshold level necessary for triggered flange and gated reverb.
The input sample and hold circuit consists of 1/3 of the 4053 analog switch (U6B), the input
sample cap (C29), a buffer amplifier (U4), and a comparator (U5). Also note the differential amplifier
(R44, R52, R53, 2 signal diodes, 2 NPN transistors) just prior to the comparator. This diff-amp
speeds up the response time of the comparator.
The signal beyond this point is purely digital, until the DAC output cycle of the DASP 8. At the
appropriate time, the DAC will output the processed left, and right signals. This action is coordinated
with the two output sample and hold circuits (U6A&C, 2 op amps of U3, C22, C23), so that each
receives the correct, separate signal for stereo output. After passing through low pass (anti aliasing)
filters (2 op amps of U3, Misc. Resistors & Capacitors), the signals are buffered (2 op amps of U2),
and sent through the output potentiometers. From here, they pass through unity gain amps (2 op
amps of U2), through impedance fixing resistors (R5, R10) and R.F. suppression toroids, to the
output jacks (J3, J4).

3.1 SUCCESSIVE APPROXIMATION

Successive approximation is an empirical approach to the
process of analog to digital conversion. The idea is to divide the
process into short,
manageable sections.
Each significant binary
weight (starting with the
Most Significant Bit) is
taken in turn, thus requiring
only 16 comparisons to
achieve a final value.
The process begins
with the input "sample and
hold" circuit. 1/3 of the
4053 (U6B) is turned on,
allowing the input sample
capacitor (C44) to charge

Diagram 2

[or discharge] to the level

of the current input signal.
When the switch is turned off, the capacitor will hold that level
indefinitely [barring internal leakage ]. At this point, the SAR
(Successive Approximation Register-part of the DASP 8 ASIC)

Diagram 3

will take over. Starting with the MSB, the SAR will set the bit,
and compare the output of the DAC, to the level of the input sample capacitor (via comparator U5).
The results of the comparison are stored in the register, and the next most significant bit is

compared. This process continues until a value is found for all 16 bits, and the data is ready for
further processing by the ASIC. In order to see these signals properly on the scope, it will be
necessary to use an external scope sync (use U6, pin 9 as the sync source). Diagrams 2, and 3,
show the DAC output during a single SAR cycle, with no input, and full input.

4.0 DIGITAL SIGNAL PATHS

The digital portion of the M3 is somewhat complex, incorporating 2 data and address busses,
as well as the control circuitry necessary for intercommunication.

4.1 80C31 MICRO CONTROLLER CIRCUIT

The 80C31 MPU controls all "user interface" functions of the M3. These functions range from
handling the front panel buttons, to continuously updating algorithm information to the DASP 8 ASIC.
Note that the 8031 data buss serves a dual purpose. This buss multiplexes between low order
addresses (1st 8 bits), and data. Latch U26 is used to hold the low order address half, during 8031
read and write cycles. The EPROM (U25) is used to hold both program information, and algorithm
data. The E2PROM (U24) holds system variables, as well as user preset data. MIDI I/O is handled
through the 8031's built in RXD (Read Serial Data), and TXD (Transmit Serial Data) ports. Front
panel keypad decoding is handled through a combination of memory mapped I/O (see section 4.3),
and the 8031's built in I/O ports.

4.2 RESET

The 8031 reset circuit is perhaps the single most important circuit in the M3. When this circuit
is functioning incorrectly, a complete lock-up of the machine, will occur. A thorough knowledge of the
operation of this circuit will greatly facilitate troubleshooting this unit. Note that the first units released
did not incorporate the full reset circuit described below. These units used a simple resistor/capacitor
circuit, and would occasionally fail to reset (particularly if the unit was turned off, and then back on
rapidly). Most of these early units have been retrofitted with an extra board containing the newer
reset circuit. The newest board revisions incorporate the reset on the board.
On power up, the 2N4401 transistor is off (the raw supply hasn't raised up far enough yet to
bias the transistor on, through R202, R203, and the zener divider network). C100 is allowed to
charge to +5V via R201 and the 1N914 signal diode. When the raw supply reaches approximately 7
volts, the transistor will turn on, discharging C100 through R200, and dropping the reset line low.

4.3 MEMORY MAPPED I/O

The M3 utilizes a memory mapped I/O system in order to deal with the wide variety of
functions that the 8031 needs to access. During write cycles of the 8031, data on the 8031 data buss
is made available to a series of latches (U12, U22, and U23). When A15 (address's most significant
bit) is active, the 3 to 8 line demux (U35) is used to decode several other significant address lines,
and send a strobe to the clock input of one of these latches. Consequently, data can be "stored" into
a latch simply by writing a value into a nonexistent memory location. Memory mapped input works
much the same. The address lines are again decoded when A15 is active. This time however,
instead of strobing a clock line, the output enable of the selected latch is strobed, placing it's
information on the data buss. The 8031 can then read the data for use as necessary.

4.4 WRITABLE CONTROL STORE

The writable control store is definitely the most complex circuit in the M3. The purpose of this
circuit is to act as a mutually accessible (8031 and DASP 8) storage area for the DASP 8 "control"
programs. This allows the 8031 to manipulate algorithms in real-time. Because the two devices
operate asychronously a great deal of control logic is necessary to prevent buss conflicts. Timing is