Alesis Microverb User manual

Confidential Alesis Service Manual 8-31-0160-A
ALESIS
MicroVerb/
Microverb II
(C1/C2)
Service Manual
P/N: 8-31-0160-A
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Confidential Alesis Service Manual 8-31-0160-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 8-31-0160-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 8-31-0160-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. 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.

MicroVerb/MicroVerb II Service Manual 1.00 1 3/7/2003
1.0 General Description
The MicroVerb and MicroVerb II digital reverbs 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 reverb, as well as non
natural effects such as reverse reverb, and gated reverbs. This service manual covers both the
Alesis MicroVerb and MicroVerb II, since both units are virtually the same. The differences between
these units are the algorithms programmed into the EPROM (U1), the digital clock rate, and the
input filter values.
2.0 Power Supply
The power supply begins with the 9 Volt A.C., adapter (Alesis P2 type). Input from J6 is R.F.
filtered by C1. From there it is split for the +12V, -12V, and +5V rails. The +12V rail consists of a
voltage doubler (C5, C6, and D2, D4), a 7812 regulator (VR2), and filter capacitors (C10, C21). The
-12V rail is a "mirror" of the +12V rail, consisting of voltage doubler (C4, C7, and D3, D5), a 7912
regulator (VR3), and filter capacitors (C11, and C22). The +5V rail consists of a rectifier diode (D1),
filter capacitors (C2, C3, C9), a 7805 regulator (VR1), and a multitude of 0.1uF bypass capacitors.
3.0 Analog Signal Paths
The inputs (stereo) from J1 and J2 pass through the A.C. coupling capacitors (C35, C36) and
have their impedances fixed at 1M by R5 and R7. While operating the unit monauraly (right input
only), the input impedance is fixed at 500K (R5, and R7, in parallel). From there, the inputs are
buffered by U16, and passed through the input potentiometers. The stereo signal is then sent to a
low pass filter/buffer (U16 etc.) and on to the dry side of the mix potentiometer, as well as summed
to mono (Via R12, R13, and defeat jack J5).
The summed stereo signal is sent to the anti-aliasing filter consisting of most of U15, 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 4.1 for a description) signal from the ASIC. This
signal is injected into the signal path at U15 pin 5. A signal diode/capacitor combination (D8, C32)
at U10 pin 12 shunts any incoming signal exceeding 5V to the power supply of U9, preventing
damage to the analog switch.
The input sample and hold circuit consists of 1/3 of the 4053 analog switch (U9B), the input
sample capacitor (C20), a buffer amplifier (U10), and a comparator (U8).
The signal beyond this point is purely digital, until the DAC output cycle of the DASP 16. 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 (U9 A&C, 2 op amps of U10, C18, C19),
so that each receives the correct, separate signal for stereo output. After passing through low pass
(anti aliasing) filters and buffering (2 op amps of U15, Misc. Resistors & Capacitors), the signals are
sent through the wet side of the mix potentiometer. From here, they pass through R13, R14 to the
output potentiometer, and finally on to the output jacks (J3, J4).

MicroVerb/MicroVerb II Service Manual 1.00 2 3/7/2003
4.0 Digital Signal Paths
4.1 The DASP 16 ASIC
Below is a description of the most important DASP-16 pins.
Pin #(s) Name Function
61-68, 2-11 BDRAM0-15 DRAM Data buss.
10-17, 19-26 DAC0-15 DAC Data outputs.
27 SNHINH
Controls sample and hold circuit timing.
28 ADCDATA
A/D comparison input.
30 CLOCK ASIC Clock input (6MHz for MicroVerb or 8Mhz for MicroVerb II)
31 ERROR
This signal indicates a math overflow condition, and consequently turns on the clip LED circuit.
32 LSTMSB
This signal indicates the last state of the MSB (the sign bit in two's complement math). This signal, in conjunction
with R27, R29, R44, and C17, is used to bias the incoming analog signal slightly positive, or negative, depending
on the result of the last DAC cycle (i.e. if the last DAC cycle started off with a negative value, LSTMSB will be 1,
causing the input to the sample and hold circuit to pull slightly positive. On the next cycle, the reverse will occur).
This reduces any audio pop during the attack portion of the input signal, and allows for a faster response to small
signals.
33-34, 36-41 EPRMDATA0-7 EPROM Data buss.
42-49 EPRMADR0-7 EPROM Address buss.
50 WRN Write ENable line to DRAMs.
51 CAS Column Address Strobe to DRAM.
53-60 DRAMADR0-7 DRAM Address buss.
Diagram 1
Diagram 2

MicroVerb/MicroVerb II Service Manual 1.00 3 3/7/2003
4.2 The Shaft Encoder
At first the shaft encoder
circuitry may appear more
complex than is necessary to just
switch programs. The reason for
the extra circuitry is to ensure that
noise isn't generated when
switching programs. Diagram 3
shows the important signals
present during preset switching
(only 1 bit is shown for the
encoder and latch, however, the
principal applies to all 4 bits).
Output from the shaft encoder is
latched by U13 (note that the 4
outputs of latch that correspond
to the outputs of the encoder are
fed back to the other 4 data
inputs of the latch). Any time that
the shaft encoder changes, the
upper 4 bits of the latch will be different from the lower 4 bits for exactly 1 clock cycle (on the next
clock pulse, the lower 4 bits will change to the new value). 4 bit magnitude comparator U12 is used
to detect these changes. Normally the A=B line of U12 (pin 6) stays high (the upper and lower 4 bits
from U13 are equal) until the shaft encoder changes position. At this point, U12 A=B drops low,
discharging C23. One U13 clock cycle later A=B again raises high allowing C23 to charge slowly
through R39 (D7 provides protection for A=B during those times when A=B is high and C23 still has
very little charge on it yet). Now note the line that travels from the junction of C23 and R39, via U11,
to the A12 line of the EPROM U1. This has the affect of temporarily forcing all use of the EPROM
address buss to be limited to the lower half of the address space. The algorithms in this half of
memory were written simply to clear the DRAMs of existing data during program changes, thus no
data - no noise!
4.3 Overflow Indicator
Due to the necessity of trying to convey several possible states with a single tricolor LED
requires a small amount of logic (U14). The 3 states that need to be covered are:
♦No signal input-LED is orange
♦Signal is present-LED is green
♦The ASIC is experiencing a math overflow-LED is red
Whether or not a signal is present, it is input to the logic via Q1. Overflow conditions are sent
to the logic from the ASIC. When no signal is present, the EPRMADR7 line of the ASIC is used to
switch between the red and green LED portions to simulate the appearance of orange.
5.0 Successive Approximation
Successive approximation is a "divide and conquer" approach to the process of analog to
digital conversion. The idea here, is to divide the task into short, manageable sections. Each
significant binary weight (starting with the Most Significant Bit) is taken in turn, thus requiring
only 12 comparisons to achieve a final value.
The process begins with the input "sample and hold circuit". 1 switch of U9 (4053) is
turned on, allowing the input sample capacitor (C20) to charge (or discharge) to the level of the
current input signal. When the switch is turned off, the capacitor will hold that level indefinitely
Diagram 3

MicroVerb/MicroVerb II Service Manual 1.00 4 3/7/2003
(barring internal leakage ). At this point, the SAR (Successive Approximation Register) in the
ASIC 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 U8). The
results of the
comparison are stored,
and the next most
significant bit is tested.
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 this
signal properly on the
scope, it will be
necessary to use an
external scope sync
(Use U13 pin 11).
Diagrams 4 and 5 show
typical DAC output
during successive
approximation with no and high input levels respectively.
6.0 Updates and Corrections
6.1 C13
If a blue monoblock capacitor is found in this position, it must be replaced with a 0.1µF
CerDisk or Film capacitor. The reason this is necessary is due to the fact that these capacitors were
found to leak excessively for the circuit (these capacitors are fine for power supply filtering, but
when used as a component in a voltage divider, the excess leakage will cause a significant enough
of a voltage drop to trigger TTL logic). A faulty C13 will cause the LED to indicate an input signal is
present (always green) regardless of input conditions.
6.2 C16
See Section 6.1 for details. A faulty C16 will cause the LED to indicate an overflow (always
red) regardless of input conditions.
6.3 C20
Large Mylar capacitors in this position should be replaced with film capacitors. (again
because of excessive leakage). A failure of this capacitor will cause distorted effects (wet signal).
Diagram 4
Diagram 5

MicroVerb/MicroVerb II Service Manual 1.00 5 3/7/2003
6.4 C23
See Section 6.1 for details. If C23 is faulty, the unit will not have any effects out (no wet
signal).
6.5 C32
See Section 6.1 for details. If C32 is faulty the +5V rail will not be solid at the 4053 (U9). This
will manifest itself as a distorted wet signal.
6.6 Input/Mix/Output Potentiometers
Note that when replacing any of the 3 potentiometers due to "scratchiness", it's a good idea
to replace all 3 if possible. This is due to the fact that disassembly and subsequent reassembly can
cause the other potentiometers to fail in the same fashion. Also note that when replacing
potentiometers, it's a good idea to reattach the front panel before soldering any new potentiometers
in. This prevents damage to the potentiometers due to misalignment.
6.7 Goldstar 4053s (U9)
These devices have been found to be somewhat unreliable, and should be replaced. We are
currently using Phillips CD4053s as replacements. The failure of this device usually causes extreme
D.C. offset in the SAR output of the DAC.
6.8 Goldstar 7404s (U11)
These devices have been found to be somewhat unreliable, and should be replaced with TI
74HC14s. If this component fails it will cause small "Pops" to be heard when switching programs.
6.9 Beige Power Supply Jacks
These are older jacks and should be replaced with the newer black jacks (the older beige
types have a tendency to break the center pin).
7.0 Test Procedures
Testing the MC or C2 is extremely simple.
Use a clean audio source (CDs preferred) and set up the unit according to the user's manual.
Listen to the wet (effects) output for any distortion.
Be sure to move all of the potentiometers through the full range of their movement.
Listen for any dropouts which would indicate a scratchy potentiometer.
To ensure that the shaft encoders are functioning properly all programs should be listened to
briefly.
Turn the input level all the way down, and the output level all the up.
Listen for excessive noise in the noise floor.
As a final check it's a good idea to physically shake the unit so that no loose parts remain inside
the unit.

MicroVerb/MicroVerb II Service Manual 1.00 6 3/7/2003
8.0 Troubleshooting and Repair
Described Symptom Possible Causes Solution
Unit is completely dead. (No lights, no effects). Faulty Power supply. Replace supply and retest.
Faulty P.S. jack. Replace and retest.
Faulty +5 volts. Troubleshoot and repair as necessary.
Unit turns on, but no effects. C23 is leaking. Replace and retest.
Faulty ASIC. Troubleshoot and repair as necessary.
Faulty DAC. Troubleshoot and repair as necessary.
Faulty 4053. Troubleshoot and repair as necessary. (See
also section 6.7).
LED stays green no matter what. C13 is leaking. Replace and retest.
LED stays red no matter what. C16 is leaking. Replace and retest.
Faulty ASIC Troubleshoot and repair as necessary.
Problem with LSTMSB line. (This will usually be
noticed as a DC offset in the signal at U14 pin
7).
Troubleshoot and repair as necessary. (See
also section 4.1).
Distorted effects. Failure in power supply section (+ or - 12V rail
is bad).
Troubleshoot and repair as necessary.
Faulty or wrong type 4053 (This can cause a
DC offset at the input to the comparator [U8 pin
3]).
Troubleshoot and repair as necessary. (See
also section 6.7).
Faulty ASIC. Troubleshoot and repair as necessary.
Faulty DRAM(s). Troubleshoot and repair as necessary.
Faulty DAC Troubleshoot and repair as necessary.
Input sample capacitor is leaky. Troubleshoot and repair as necessary.
Noise when switching effects. Goldstar 7404s. See section 6.8.
Faulty shaft encoder. Replace and retest.
Intermittent effects. C23 leaking somewhat. Replace and retest.
Faulty shaft encoder Replace and retest.
Bypass jack normaling contact is dirty. Troubleshoot and replace if necessary.
All trademarks are property of their respective companies.

Confidential Alesis Service Manual 8-31-0160-A
ALESIS
MicroVerb/
Microverb II
(C1/C2)
ECN
HISTORY

Confidential Alesis Service Manual 8-31-0160-A
ALESIS
MicroVerb/
Microverb II
(C1/C2)
BOM

MicroVerb/MicroVerb II Service Manual 1.00 7 3/7/2003
9.0 Service Parts List
Note: This list reflects resistor and capacitor values for the MicroVerb II. Care should be taken when repairing the original MicroVerb
to replace these components with the original value (not the one listed here for the MicroVerb II).
GROUP DESCRIPTION ALPARTNO QTY FROM POSITION PCB MANUFACT NOTES
CAP 0.01 MFD CERDISC 1-02-0103 3 C24,27,31 Main C1/C2
CAP 0.01 MFD CERDISC 100V 1-02-0103 1 C1 Main
CAP 0.033 MFD FILM 100V 5% 1-20-0333 2 C39,40 Main
CAP 0.047 MFD 100V 5% 1-21-0473 1 C33 Main
CAP 0.1 MFD 50V 5% 1-21-0104 3 C13,16,23 Main
CAP 0.1 MFD 100V 5% 1-05-0104 5 C8,12,32,35,36 Main
CAP 1000 PFD CERDISC 1-02-0105 3 C18-20 Main
CAP 220 PF 100V 5% 1-21-0221 1 C34 Main
CAP 30 PFD CERDISC 100V 1-02-0300 2 C14,15 Main
CAP 330 MFD ELEC 1-09-0337 6 C2-7 Main
CAP 330 PF 100V 5% 1-21-0331 1 C29 Main
CAP 4.7 MFD ELEC 1-11-0475 8 C9-11,17,21,22,37,38 Main
CAP 4700 PFD FILM 100V 5% 1-20-0472 4 C25,26,28,30 Main
HDW 6-32x1/2 PF BLK 5-00-0001 2 FRONT PANEL SCREWS
HDW 6-32x1/2 PP BLK 5-00-0002 2 REAR PANEL SCREWS
IC 27C64 EPROM 2-19-0064 1 U1 Main
IC 74HC00 2-14-7400 1 U14 Main
IC 74HC04 2-14-7404 1 U11 Main
IC 74HC374 2-14-0374 1 U13 Main
IC 74HC85 2-14-7485 1 U12 Main
IC CD4053 2-23-4053 1 U9 Main
IC DASP-16 ASIC 2-27-0001 1 U2 Main
IC LM311 2-22-0311 1 U8 Main
IC PCM54HP 2-25-0054 1 U7 Main
IC TLO84 (LF347) 2-21-0084 3 U10,15,16 Main
IC TMS4416 2-16-4416 4 U3-6 Main
JAC 1/4 CLIFF (MONO) 4-02-0001 5 J1-5 Main
JAC 3.5mm JACK (P2) 4-16-0001 1 J6 Main
ME 1N4002 POWER DIODE 2-01-4002 6 D1-6 Main
ME 1N914 2-00-0914 1 D7,8 Main
ME 2N4401 2-03-4401 1 Main
ME 7805 +5V REG 2-11-7805 1 VR1 Main
ME 7812 +12V REG 2-11-7812 1 VR2 Main
ME 7912 -12V REG 2-11-7912 1 VR3 Main
ME 8 MHz CER RES 7-01-0002 1 Z1 Main
ME LED (BI-COLOR) 3-03-0001 1 L1 Main
ME SHAFT ENCODER SWTCH 6-00-1001 1 S1 Main
ME XFORMER P2 7-40-0902 1
POT 1 KB DUAL 0-09-1002 1 R2 Main
POT 10 KB DUAL 0-09-1004 2 R1,3 Main
RES 1.6K 1/4W 5% 0-03-0162 6 R16-19,21,22 Main
RES 100 1/4W 5% 0-03-0101 1 R34 Main
RES 10K 1/4W 5% 0-03-0103 1 R30 Main
RES 11K 1/4W 5% 0-03-0114 2 R23,24 Main
RES 150K 1/4W 5% 0-03-0154 1 R31 Main
RES 1K 1/4W 5% 0-03-0102 8 R4,5,14,15,20,28,41,43 Main
RES 1M 1/4W 5% 0-03-0105 5 R5,7,32,33,39 Main
RES 220 1/4W 5% 0-03-0221 1 R42 Main
RES 22K 1/4W 5% 0-03-0223 4 R35-38 Main
RES 3K 1/4W 5% 0-03-0302 2 R25,26 Main
RES 4.7K 1/4W 5% 0-03-0472 2 R9,11 Main
RES 47K 1/4W 5% 0-03-0473 2 R8,10 Main
RES 5.1M 1/4W 5% 0-03-0515 1 R44 Main
RES 510K 1/4W 5% 0-03-0514 3 R27,29,40 Main
RES 680 1/4W 5% 0-03-0681 4 R12,13,45,46 Main
SOC 28 PIN DIP .6 4-06-0028 2 U1,7 Main
SOC 68 PIN ASIC SOCKET 4-12-0068 1 U2 Main
CASE 9-02-1001 1
FRONT PANEL 9-01-1011 1
REAR PANEL 9-03-1013 1
RUBBER STRIP 5 9-23-1006 2
STANDARD KNOB 9-11-1001 4