Synthesis Technology MOTM-850 User manual

MOTM-850 Pedal Interface
Assembly Instructions & Owner’s Manual
Synthesis Technology
6625 Quail Ridge Dr.
Fort Worth, TX 76180
[phone]
www.synthtech.com
Oct. 25, 2001

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MOTM-850 PARTS LIST
Please carefully check that all parts are in your kit. If you have a suspected shortage,
please call or email. If you get free extra stuff, keep it for next time.
Capacitor bag, containing the following 10 parts:
4ea 10mfd, 50V Electrolytic C3, C6, C7, C8
6ea 0.1mfd (marked 104) ceramic axial C1, C2, C4, C5, C9, C10
Resistor bag, containing the following 24 parts:
5ea 10K (brown, black, orange) R1, R6, R8, R14, R19
4ea 47K5 1% (yellow, violet, green, red) R12, R13, R20, R23
3ea 820 ohm (gray, red, brown) R3, R7, R22
2ea 332K 1% (orange, orange, red, orange)R2, R24
2ea 68K (blue, gray, orange) R4, R5
2ea 180K (brown, gray, yellow) R9, R10
2ea 715K 1% (violet, brown, green, orange) R15, R21
1ea 620K (blue, red, yellow) R11
1ea 100K 1% (brown, black, black, orange)R16
1ea 82K5 1% (gray, red, green, red) R17
1ea 16K5 1% (brown, blue, green, red) R18
IC bag, containing the following 5 parts:
1ea 2N3904 NPN transistor Q1
1ea LM311N comparator U1
1ea LM78L12 +12V TO-92 regulator U2
1ea LM79L12 –12V TO-92 regulator U3
1ea LT1013 precision dual op amp U4
Misc #1 bag, containing the following 6 parts:
2ea Axial ferrite beads (plain, gray things)L1, L2
1ea MTA-156 power connector JP1
2ea 3-pin header with shunt JP2, JP3
1ea red LED, panel mount D1
 Knobs, 4ea, ALCO PKES90B1/4
 Jacks
1ea Switchcraft 112B stereo jack J1
3ea Switchcraft 112A mono jack J2, J3, J4

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Pots, 4ea containing the following:
4ea 100K cermet Spectrol 149-71104 VR1 – VR4
Front panel
Mounting bracket
Wire bag, containing the following 6 wires:
3ea RG-174 coax, 4 ½ inches
1ea 2-wire set, 22ga. 3 inches (red/black)
1ea 3-wire set, 22ga 2 inches (orange, white, gray)
1ea Power Cable, 20”
Hardware bag, containing:
4ea #8-32 x 3/8 black screws (for mounting module to rack)
4ea #6-32 x 1/2 zinc screws (for attaching pc board to bracket)
4ea 1/4 inch aluminum spacers
6ea #6 KEPS nuts (2 for attaching bracket to front panel, 4 for pc board)
2ea small heat-shrink tubing
4ea small tie-wraps
Organic Solder
No-clean Solder
 PC Board, MOTM-850

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GENERAL INFORMATION
Thank you for purchasing the MOTM-850 Pedal Interface. If you have any issues
concerning the building or use of the kit, please contact us at [phone] or by email:
[email protected]
This kit should take the average builder between 2 to 3 hours. The kit contains many
different resistors and special parts. However, please remember this is NOT a speed
contest; it is an accuracy contest. There is no rule that you have to complete the entire kit
in one day (as long as you wash the flux off!).
Successful kit building relies on having the proper tools. Here is a list of what you will need
to build your MOTM-850:
• Soldering iron, 50W max power
• Needle-nose or chain-nose pliers
• Diagonal cutters
• Allen key set for securing the knobs (1/16” or 1.6mm)
• Magnifying glass: to read the capacitor codes and to inspect solder joints
• Lead bending tool (optional, but makes the job go much faster)
• DVM (Digital Volt Meter) or oscilloscope (to check the output)
• #1 Philips screwdriver
• Fingernail brush for washing off the organic flux
• Old towel for blotting dry pc board
• Heat-shrink gun is highly recommended!
For more information of tools used and suggestions, see the MOTM FAQ and Tutorial pages
at http://www.synthtech.com.
HOW TO FOLLOW THE DIRECTIONS
Please read the entire instruction before proceeding. There may be valuable information at
the end of the instruction. Each instruction has a check box next to it. After you
complete the instruction, check the box. This way you can keep track of where you are in
the process.
VERIFY THE PARTS LIST
Verify that all of the parts are in the kit as shown on the parts list.

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A WORD ON SOLDERING
There are 2 very different types of solder used in the kit. Most of the soldering uses
‘Organic Flux’ solder. This is strictly for use on the pc board, and is NOT to be used
on the front panel wiring!
In order for solder to ‘stick’ to the copper, a chemical called ‘flux’ is embedded in the solder.
The flux leaves a residue on the pc board that should be cleaned with warm water. DO NOT
USE SOAP OR OTHER CLEANSERS. Most of the parts in the kits are ‘waterproof’ and can
be washed in the sink. The flux is OSHA approved for flushing down the drain, so don’t
worry about that! A soft brush is used to gently scrub the board. We recommend a
‘fingernail brush’, which is about 1” x 2” and can be found for about $1.
The other type of solder is called ‘No Clean Flux’; because as the name implies it does not
require washing. This solder is used for wiring the pots, switches, jacks, etc. This solder is
harder to use on the pc board; because even when melted, it is not very fluid (about the
consistency of toothpaste). We will use it VERY SPARINGLY on the pc board.
OK, let’s get started on the board!
PART #1: SOLDERING THE RESISTORS
Since there are more resistors than anything else, we will start here. If you do not know the
resistor color code, refer to the parts list. Resistors are not polarity sensitive, but the board
will be easier to debug (and look nicer) if you point the first color band in the same direction
for all the parts. The color code is also in the README FIRST document that every
customer receives with his or her first order.
You will start by soldering in ALL of the resistors.
Find the RESISTOR bag.
Find the MOTM-850 blank pc board. There is a copy (larger than actual size) of the
silkscreen which shows where the parts go at the end of this document. It will be
useful if you locate the part on the print first, put the part in the board, then
‘check off’ the silkscreen. All parts are inserted from the side of the board with the
white silkscreen (the “top” side).
NOTE: some reference designators are under the resistor! Be careful.
 We will stuff the resistors by value to make things easier. The resistors (and other
long-leaded parts) are inserted on a 0.4 inch spacing. The important thing is to be
sure that the part is sitting all the way down on the board. Push the leads in the
holes, push the part on the board, and then bend the leads on the bottom outwards
to a 45 degree angle (roughly!). This is called ‘cinching the leads’: and keeps the part
from falling out! From the bottom of the board, solder (using the organic flux),
applying heat to the pad for about a half second first, then applying just enough
solder to make a small puddle that looks like a tiny pyramid. Enough solder should

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flow in the hole such that on the top (component) side, a small amount is on the top
pad as well
There are many 1% resistors in this kit. They have light blue body color, and
sometimes the color bands are difficult to read. When in doubt, use a DVM to
measure the value. NO guessing!
The rule of soldering: don’t use too much, you can always add more! Cut the leads
flush with the top of the solder joint with your diagonal cutters.
Locate the 10K resistors (5pcs). Solder the resistors into R1 (by VR3), R6 (left of U3),
R8 (above VR3), R14 (above R8) and R19 (right of C10).
Locate the 47K5 1% resistors (4) and solder into R12 and R13 (left of U4), R20
(above R19), and R23 (top edge of pcb by C5).
Locate the 820 ohm resistors (3) and solder into R3 (left of U1), R7 (between VR2
and VR3), and R22 (by J2).
Locate the 332K 1% resistors (2) and solder R2 (above C1), and R24 (by VR1).
Locate the 68K resistors (2) and solder into R4 and R5 (above VR3).
Locate the 180K resistors (2) and solder into R9 and R10 (beside VR2).
Locate the 715K 1% resistors (2) and solder into R15 (left of U4) and R21 (right of
U4).
Locate the 620K resistor and solder into R11 (between R20/R21).
Locate the 100K 1% resistor and solder into R16 (left of VR3).
Locate the 82K5 1% resistor and solder into R17 (above R16).
Locate the 16K5 1% resistor and solder into R18 (above R17).
PART #2: BOARD WASH #1
Verify all the resistors are in the correct position.
Verify all the resistors are flat on the board. Correct if needed. Check solder joints.
Wash the board in warm water, gently scrubbing both sides. DO NOT USE ANY
SOAP! Just water!

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Shake the board a couple of times, blot dry with an old towel (the leads will frazzle
a good towel). Let dry at least 15 minutes.
 Take a little break! You are about 1/3rd of the way finished.
PART #3: CAPACITORS
Locate the CAPACITOR bag.
 Locate the 0.1mfd axial ceramic caps (6) and solder into C1, C2, C4, C5, C9 and C10.
Note that these are bent on 0.3” centers.
Locate the 10µfd electrolytics (4). Note that there is a stripe on the NEGATIVE
terminal. The pc board has a + on the POSITIVE terminal. Carefully stick the
capacitors into C3, C6, C7 and C8 with the stripe away from the + pad on the board.
All the capacitors will ‘face’ the SAME DIRECTION.
PART #4: MISC and IC STUFF
Almost done with the parts on the pc board! This will finish up the soldering with the
organic flux.
Locate the MISC #1 bag and the IC bag.
Locate the ferrite beads (2). They are axial parts, gray colored with no markings.
These are non-polar, and are soldered into L1 and L2 (by JP1).
Locate the MTA-156 power connector. Solder into JP1. Note that the connector has
a ‘locking tab’ on one side. This side is the “inside” facing relative to the pc board.
Note the silkscreen symbol for JP1 has a line on one side, indicating this is the side
where the locking tab goes.
Locate the MXL1013 op amp. Solder into U4. Note that all ICs are pointing “up”
towards the top edge of the pc board (if you call where the pots are the ‘bottom’
edge). The IC will have a ‘notch’ or indentation in the top by Pin #1.
Locate the LM311 comparator. Solder into U1.
Locate the 2N3904 transistor. DO NOT GET IT CONFUSED WITH THE 2
VOLTAGE REGULATORS!! Solder into Q1.

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Locate the LM78L12 voltage regulator. DO NOT GET IT CONFUSED WITH THE
79L12 REGULATOR!! Solder it into U2.
Locate the LM79L12 voltage regulator. Solder it into U3. Save the LED for later.
 Apply a small bit of solder to the via holes. These are the small pads that allow
traces to “change sides” of the pc board. DO NOT SOLDER PADS FOR THE
REMAINING COMPONENTS!! As an example, if you look at the mounting hole by
J1, you will see 3 via holes around it.
Solder the 2 3-pin header strips into JP2 and JP3. Remove the blue shunts and
DON’T LOSE THEM!
PART #5: FINAL BOARD WASH & INSPECTION
Verify all the parts are in the correct locations. Make sure all of the ICs are pointing
the same direction. Make sure the 3 TO-92 parts (transistor/voltage regulators) are
facing the same direction.
Inspect the solder joints. Any solder shorts? Too much solder? Missing joints?
Wash the board under warm water. Scrub gently. Dry.
THIS IS A GOOD STOPPING PLACE TO REST OR PUT THE KIT AWAY UNTIL
LATER.
You are now finished with the Organic flux solder. All soldering past this point is
using the No-Clean solder. You do not have to wash the board anymore.
PART #6: FINISHING THE PCB
You will now solder in the remaining parts on the pcb in preparation for wiring to the front
panel. USE THE NO-CLEAN SOLDER. BE CAREFUL!
Locate the Spectrol pots. They mount into VR1-VR4. Be sure they are flat and
sticking out perpendicular to the pc board.
Locate the 3 pieces of RG-174 black coax cable. Again, note that one end has
longer wires stripped than the other. The short ends will go in the pc board in
locations J2, J3 and J4. Look at the pc board. Notice that in the coax positions, there
is a large hole pad (lower pad) and a smaller pad (top hole). The braided wire is
soldered into the larger hole. The smaller, inner conductor goes in the top hole. BE
SURE THE SHORTER BRAIDED END GOES INTO THE PC BOARD.

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Solder each coax cable into the holes. Attach a tie-wrap to secure the coax cable
flush to the board. The tie-wrap goes down, into the left hole and up through the
right hole. Secure and trim off any excess.
 Find the red/black twisted wire. It goes into D1. Solder the Red wire into pad #1 and
the Black wire into pad #2.
 Find the orange/white/gray wire. It solders into J1. The White wire goes in pad #1,
the Orange wire into pad #2 and the Gray into pad #3. Carefully cut the ty-wrap off
the bundle first and discard. There is another ty-wrap used to secure the 3 wires in a
bundle to the pcb.
YOU ARE NOW FINISHED WITH THE PC BOARD WORK! BREAK TIME.
PART #7: FRONT PANEL PREPARATION
You will now attach components to the front panel. It is HIGHLY recommended that you
use a set of hollow shaft nut drivers, NOT PLIERS, to tighten the nuts. This prevents
scratching. NOTE: all references to part orientation is from the REAR of the panel.
Locate the 4 Switchcraft jacks. Notice that from the rear, there is a beveled corner.
This corner is ALWAYS CONNECTED TO GROUND, USUALLY WITH A
BRAIDED CONDUCTOR. Each jack has a flat washer, a lockwasher, and a ½” hex
nut. Remove the nuts and washers from each jack. Place aside. Keep the lockwasher
on the jacks. Also, one of the jacks has 3 lugs, but in a different location that the
others. This jack is for the pedal to plug into, and it MUST go into the PEDAL hole.
Insert the 4 jacks/lockwashers, with the beveled corner in the upper right corner,
into the 4 holes. Be sure the jack in the PEDAL hole has the lug in the ‘bottom’
position, when viewed from the rear. Place the flat washer on the jack, then the hex
nut. Hold the jack with one hand on the backside, keeping it ‘square’. Tighten the
hex nut with a nut driver. NOTE: when tight, not much of the exposed threads of the
jack are exposed.
You are now ready to attach the pc board to the bracket and then wire up to the panel.
PART #8: ATTACH PC BOARD TO BRACKET/PANEL
In the HARDWARE bag, locate 4 #6-32 x 1/2 screws, 6 #6 KEPS nuts, and 4
spacers.
Locate the mounting bracket. The pc board attaches to the bracket, with the 4
screws threading from the top of the board, through the spacers, through the
bracket, and then out the bottom of the bracket. The #6 KEPS nut attaches on the
bottom of the bracket. Note the bracket has 2 long mounting flanges with a hole

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in each. These attach to the 2 threaded studs sticking out of the rear of the panel.
The 4 pots each stick in its panel hole when the bracket is screwed down on the 2
threaded posts.
Attach the pc board to the bracket. The flanges will point upwards when the pc
board is sitting on the bracket. Note that the bracket holes for the pc board are
actually oblong. This is to allow adjustment for the pc board to firmly press
up against the back of the panel. As a start, set the 4 screws ALL THE WAY
TO THE LEFT of the oblong holes. Loosely tighten the 4 KEPS nuts on the
bottom.
THIS IS A VERY IMPORTANT STEP, SO PAY ATTENTION AND READ ALL OF
IT BEFORE PROCEEDING!
Note that each of the 4 pots on the pc board have 2 hex nuts and a flat washer.
Remove the first hex nut and the washer. Set aside.
What you will do now is adjust the remaining hex nuts so that when the bracket is
all the way down on the panel’s threaded studs, all the pot hex nuts touch the rear
of the panel.
Screw (by hand) each hex nut on the pots so that it is all the way on (touching
the face of the pot). Now, pick up the pc board/bracket assembly and carefully
slide it over the 2 threaded studs, making sure the pots are aligned in the holes.
Use 2 #6 KEPS nuts and tighten the bracket to the panel.
Loosen the 4 KEPS nuts on the bottom of the bracket. Slide the pcb ALL THE WAY
TO THE RIGHT AS FAR AS IT WILL GO, so that the 4 pot nuts are all pressing
against the panel. By hand, put hex nuts on the outside threads of VR1 and VR4 to
keep the pc board in place. Now, tighten the 4 KEPS nuts on the bracket. The pcb
and bracket should be secure, with no gaps visible between the panel and the pot
nuts. You may need to loosen the nuts on the pots, so that they are touching
the back of the panel. Again, make sure each pot’s nut is touching the back of
the panel (no gaps!). There will be a gap from the edge of the pc board to the panel.
 Remove the hex nuts on VR1 & VR4. For all of the pots, first put on the flat washer,
then the hex nut. Tighten with a ½” nut driver.
PART #9: FINISH WIRING TO THE PANEL
Please read the following instructions carefully. In order to neatly attach the many wires to
the front panel components, the wires are soldered in a specific order.
 Find the red LED assembly. Note that one lead is slightly longer. This is the Anode,
and it is soldered to the Red wire in D1. The other lead is the Cathode, and is
soldered to the Black wire. Insert the LED through the panel, with the longer Anode
lead towards the top panel edge (looking from the rear, this is towards the “left”).