DYNACO Stereo 120 Use and care manual

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UPDATING THE
DYNACO STEREO 120
SOLID STATE
POWER AMPLIFIER:
SUPER HEATSINK
VERSION
© 2011 AkitikA, LLC
All rights reserved
Revision 1.12: Octo er 20, 2011

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Ta le of Figures .................................................................................................................. 3
Section 1: A out This Manual ............................................................................................ 4
Section 1: A out This Manual ............................................................................................ 4
Who Should Attempt this Project? ................................................................................. 4
Tools You’ll Need........................................................................................................... 4
Project Overview ............................................................................................................ 5
Important Safety Notes ................................................................................................... 5
Section 2: Checking the Stereo 120 Power Supply ............................................................ 6
Opening the Amplifier .................................................................................................... 6
Check the Power Supply Voltages.................................................................................. 6
Section 3: Saving the Stuff that Should Be Saved.............................................................. 7
Cutting the wires on the old amplifier modules.............................................................. 7
Removing the LEFT channel module......................................................................... 7
Removing the RIGHT channel module ...................................................................... 8
Removing C7 RIGHT ............................................................................................... 11
Removing C7 LEFT.................................................................................................. 11
Removing the Output Zo el Networks ..................................................................... 11
Section 4: Trou leshooting the Stereo 120 Power Supply ............................................... 13
Prepare and Connect the Test Load .............................................................................. 13
Test the Power Supply .................................................................................................. 13
Just In Case – Trou le Shooting ................................................................................... 14
The Voltage is Much More than 78 volts ..................................................................... 14
The Voltage is Much Less than 66 volts....................................................................... 14
There’s No Voltage at All............................................................................................. 14
Section 5: Building the Updated Circuit Boards............................................................... 15
Install the Resistors ....................................................................................................... 15
Install the Small Capacitors and the Diodes ................................................................. 17
Last Capacitors and the Transistors .............................................................................. 18
Winding the Output Inductor ........................................................................................ 18
Solder the LM3886 into the Board ............................................................................... 19
Final Inspection of the Circuit Board............................................................................ 22
Mounting the Updated Amplifier Board to the Super Heat Sink.................................. 23
Section 6: Wiring In the Updated Amplifier Modules...................................................... 25
Building and Installing the Power Wiring Harness ...................................................... 25
Building and Installing the Ground Wiring Harness .................................................... 26
Wiring the Inputs .......................................................................................................... 27
Wiring the Outputs........................................................................................................ 27
Connecting the Left Channel Amplifier Module .......................................................... 27
Connecting the Right Channel Amplifier Module........................................................ 28
Making the Speaker Binding Posts User Friendly........................................................ 29
Section 7: Testing the Completed Amplifier .................................................................... 29
Test #1........................................................................................................................... 29
Test #2........................................................................................................................... 30
Test #3........................................................................................................................... 30
Test #4........................................................................................................................... 30
Resistor Color Code...................................................................................................... 32

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Table of Figures
Figure 1-Location of the four screws that hold the cover to the ase................................. 6
Figure 2-Location diagram for cutting wires ...................................................................... 9
Figure 3-After the Amplifier Modules have een removed.............................................. 10
Figure 4- Removal of components is completed .............................................................. 12
Figure 5-Connecting a test load to the power supply ....................................................... 13
Figure 6-The first four resistors are installed with leads ent on the ack side, ut not yet
soldered. ............................................................................................................................ 15
Figure 7-leads soldered and clipped ................................................................................. 16
Figure 8-showing LED cathode orientation...................................................................... 17
Figure 9-Starting to wind the output inductor................................................................... 19
Figure 10-finishing step for the output inductor ............................................................... 19
Figure 11-Showing method of attaching rackets to the PCB.......................................... 20
Figure 12-Template for checking mounting height of LM3886....................................... 21
Figure 13-LM3886 installation step three, just the corner pins are soldered.................... 21
Figure 14-The LM3886 sits up off the oard to avoid shorts etween the front and ack
rows of pins. The ody should e at right angles to the circuit oard .............................. 22
Figure 15-Mounting assem led PCB to super heat sink................................................... 23
Figure 16-a completed amplifier module.......................................................................... 24
Figure 17-Showing Detail of attaching power wiring harness to C12.............................. 24
Figure 18-Showing the Final Wiring (shown with original, rather than super heatsinks) 24
Figure 19-Final wiring viewed from the other side of the amplifier (shown with original,
rather than super heat sinks) ............................................................................................. 25
Figure 20-wiring harness .................................................................................................. 26
Figure 21-Ground wiring harness ..................................................................................... 27
Figure 22-Schematic of amplifer module ......................................................................... 31
Figure 23-demonstrating the resistor color code .............................................................. 32

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Section 1: About This Manual
This manual gives you all the information you need to ring your Solid State Dynaco
Stereo 120 Power Amplifier up to date using UpdateMyDynaco replacement modules
and UpdateMyDynaco Super Heat Sinks. These heat sinks offer these advantages
compared to recycling the original Dynaco heat sinks:
1. The Super Heat Sinks let you deliver 60 Watts Per Channel into 8 Ohms with
much less temperature rise than the original heat sinks. It even allows the delivery
of significant 4 Ohm power, limited mainly y the power supply regulator’s
designed-in fold- ack.
2. The amount of disassem ly and reassem ly is much less when you use the Super
Heat Sinks. You preserve the old Dynaco amplifier modules, and the jo of
updating your Dynaco will pro a ly take a out an hour less time.
3. A secondary market for original Dynaco Stereo 120 amplifier modules might
develop on EBay. Perhaps you could offset the cost of the UpdateMyDynaco kit
y selling the original modules.
The only part of your Stereo 120 that really needs to work is the power supply. With this
kit, you’ll uild good sounding, highly relia le amplifiers to replace the original amplifier
modules.
Who Should Attempt this Project?
You can uild this kit and update your Dynaco Stereo 120 if you can:
1. solder (using normal rosin core solder and a soldering iron).
2. use simple hand tools like screwdrivers, wire cutters, and pliers.
3. read and follow directions.
It helps if you:
1. know a it a out electronics, or
2. have a friend who knows a it a out electronics
3. can get to YouTu e to watch a few helpful videos a out the assem ly process
Tools You’ll Need
You’ll need the following tools to update your Stereo 120:
1. flat lade screwdriver for #6 screws
2. Phillips screwdriver (#2)
3. pliers or nut drivers suita le for #6 hardware (5/16” nut driver or hex wrench)
4. needle nose pliers (helpful, ut not strictly necessary)
5. pencil type soldering iron of 25 to 50 Watts (no huge honking soldering guns or
lowtorches)
6. wire cutters and strippers
7. multi-meter (helpful, ut not strictly necessary)
8. magnifying glass, to verify identification codes on the 3 COG capacitors

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Project Overview
The project consists of the following steps:
1. Checking out the old Dynaco Stereo 120 power supply.
2. Removing the old amplifier modules, output capacitors, and a few associated its,
while saving some parts for re-use.
3. Assem ling the updated amplifier module PC Boards.
4. Mounting the updated amplifier modules to the super heat sinks.
5. Mechanical installation and wiring in the updated amplifier modules.
Important Safet Notes
By purchasing, using, or assem ling this kit, you have agreed to hold AkitikA, LLC
harmless for any injuries you may receive in its assem ly and/or use. To prevent injuries:
• Wear safety glasses when soldering to prevent eye injuries.
• Always unplug the power efore working on the amplifier.
• Large capacitors hold lots of energy for a long time. Before you put your hands
into the amplifier:
o Pull the AC plug!
o Wait 1 full minute for the capacitors to discharge!
• Remove jewelry and rings from your hands and wrists, or anything that might
dangle into the amplifier.
• If working in the amplifier, keep one hand in your pocket, especially if you’re
near the power supply or power supply wires. This can prevent serious shocks.
• Build with a uddy near y. If you’ve ignored all the previous advice, they can
dial 911 or get you to the hospital.

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Section 2: Checking the Stereo 120 Power Supply
The only part of your old Stereo 120 that really needs to work is the power supply. In this
section, we show how to check your power supply. If your amplifier modules haven’t
een adly damaged, this is the simplest method of assuring your power supply is ok. If
the amplifier modules have een damaged, then you’ll have to use the procedure in
Section 4: Trou leshooting the Stereo 120 Power Supply to trou leshoot, separating
amplifier module pro lems from power supply pro lems.
Make sure that the power cord is out, and has been out for at least 1 minute before
starting this section.
Opening the Amplifier
1. Make sure the amplifier is unplugged. If it was recently powered, allow the amp
to sit for one full minute before proceeding.
2. Remove the four screws along the outside edge of the ottom that hold the cover
in place (see Figure 1).
Figure 1-Location of the four screws that hold the cover to the base
3. Holding oth the top and ottom of the amplifier, flip it over.
4. Lift the perforated metal top off of the amplifier.
Check the Power Suppl Voltages
At this point:
1. The perforated metal top is off the amplifier.
2. AC power, inputs, and outputs, are disconnected.
3. You can see into the amplifier, as shown in Figure 2.
4. You have a voltmeter ready, set to a scale that allows measuring the nominal
output voltage, 72 Volts DC.
Now:
1. Make sure that the power switch is off.

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2. Plug the amplifier into the AC wall socket.
3. Standing off to one side, turn the power switch on. O serve the amp for a out a
minute to make sure no smoke is curling out of any of the modules.
4. If all seems calm, measure the voltage on C12 (see Figure 2). Write down the
num er here:
The voltage on C12 was ____________Volts DC.
• If this num er is etween 66 and 78 Volts, then your power supply is good.
• If this num er is outside this range, your power supply has a pro lem.
Section : Saving the Stuff that Should Be Saved
Cutting the wires on the old amplifier modules
Make your life easier y following this advice:
1. Print out a ig copy of the pictorial diagram (Figure 2).
2. Set the print out near the amp.
3. Align the picture and the amp in the same orientation.
4. Verify twice efore cutting once!
Removing the LEFT channel module
To remove the LEFT channel module, cut the following wires in the following places:
Step Which Wire Where to Cut Done
1 The wire from PC-15 eyelet 5 to LEFT
PC-14 eyelet 10
Close to PC-15 eyelet 5
2 The wire from C12 + terminal to C of
LEFT Q5.
Close to C of LEFT Q5
3 The wire from LEFT PC-14 eyelet 9 to
RIGHT PC-14 eyelet 9.
Close to LEFT PC-14
eyelet 9.
4 The wire from C7 LEFT + terminal to
LEFT PC-14 eyelet 8.
Close to LEFT PC-14
eyelet 8
5 The wire from C7 LEFT - terminal to
LEFT PC-14 eyelet 11.
Close to LEFT PC-14
eyelet 11
6 The wire from the LEFT input socket to
LEFT PC-14 pin 12 (typically a green
wire).
Close to LEFT PC-14
eyelet 12
7 The wire from the LEFT input socket
ground to LEFT PC-14 pin 13 (this is
typically a lack wire).
Close to LEFT PC-14
eyelet 13
8 The wire from LEFT Q6 E terminal to
LEFT Speaker ground terminal.
Close to the LEFT Q6 E
terminal. This may e
difficult. If so, don’t worry
and read on!
You may not e a le to reach your cutters to LEFT Q6 E terminal. Don’t worry. We’ll
make it easier now, while we check your work to this point. With the exception of this

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one wire, the LEFT power amplifier module is free to lift out as soon as you remove the
two #6 screws that hold the LEFT heat sink to the chassis. Unscrew the screws, lift out
the module, and cut the wire that you couldn’t reach in the previous step.
Save the LEFT module and mounting hardware. Perhaps you can sell it on E- ay. The
Super Heat Sink version of the kit doesn’t use the old module or heat sink, ut you should
save the 2 6-32x1/2” screws and the ru er foot as they will e re-used to mount the left
channel super heat sink module amplifier.
Removing the RIGHT channel module
To remove the RIGHT channel module, cut the following wires in the following places:
Step Which Wire Where to Cut Done
1 The wire from C12 + terminal
to C of RIGHT Q5.
Close to C of RIGHT Q5
2 The wire from C11 + terminal
to RIGHT PC-14 eyelet 10.
One inch from C11 + terminal
3 The wire from C7 RIGHT +
terminal to RIGHT PC-14
eyelet 8.
Close to RIGHT PC-14 eyelet 8
4 The wire from C7 RIGHT -
terminal to RIGHT PC-14
eyelet 11.
Close to RIGHT PC-14 eyelet 11
5 The wire from the RIGHT input
socket to RIGHT PC-14 pin 12
(typically a lack wire).
Close to RIGHT PC-14 eyelet 12
6 The wire from the RIGHT input
socket ground to RIGHT PC-14
pin 13 (this is typically a green
wire).
Close to RIGHT PC-14 eyelet 13
7 The wire from RIGHT Q6 E
terminal to RIGHT Speaker
ground terminal.
Close to the RIGHT Q6 E
terminal. This may e difficult. If
so, don’t worry and read on!
Similar to efore, you may not e a le to reach your cutters to RIGHT Q6 E terminal.
Don’t worry. We’ll make it easier now, while we check your work to this point. With the
exception of this one wire, the RIGHT power amplifier module is free to lift out as soon
as you remove the two #6 screws that hold the RIGHT heat sink to the chassis. Unscrew
the screws, lift out the module, and cut the wire that you couldn’t reach in the previous
step.
Save the RIGHT module and mounting hardware. Perhaps you can sell it on E- ay. The
Super Heat Sink version of the kit doesn’t use the old module or heat sink, ut you should
save the 2 6-32x1/2” screws and the ru er foot as they will e re-used to mount the right
channel super heat sink module amplifier.

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Figure 2-Location diagram for cutting wires

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Figure 3-After the Amplifier Modules have been removed

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Removing C7 RIGHT
1. Remove and save the 3 sets of #6 hardware that hold C7 RIGHT to the ottom of
the chassis.
2. Unroll one foot of the wire that’s wrapped around C7 RIGHT and connects to the
RIGHT RED Binding post.
3. Cut this wire near C7 RIGHT so that a out 1 foot of wire remains connected to
the RIGHT RED Binding post. The rest of the wire wrapped around the capacitor
will e used to make the new inductor on the UpdateMyDynaco modules.
Removing C7 LEFT
4. Remove and save the 3 sets of #6 hardware that hold C7 LEFT to the ottom of
the chassis.
5. Unroll one foot of the wire that’s wrapped around C7 LEFT and connects to the
LEFT RED Binding post.
6. Cut this wire near C7 LEFT so that a out 1 foot of wire remains connected to the
LEFT RED Binding post. The rest of the wire wrapped around the capacitor will
e used to make the new inductor on the UpdateMyDynaco modules.
Removing the Output Zobel Networks
1. Clip the lead of the 0.1 uF capacitor that connects to the RIGHT RED inding
post, near the RIGHT RED Binding post.
2. Clip the lead of the 4.7 Ohm resistor that connects to the RIGHT BLACK inding
post, near the RIGHT BLACK inding post.
3. Clip the lead of the 0.1 uF capacitor that connects to the LEFT RED inding post,
near the LEFT RED Binding post.
4. Clip the lead of the 4.7 Ohm resistor that connects to the LEFT BLACK inding
post, near the LEFT BLACK inding post.
5. Remove the terminal strip and the two attached resistors and capacitors.
Note that the new circuit oards include a Zo el network that takes the place of the
components on the terminal strips. Figure 4 shows what the amplifier should look like
when you’ve completed this step.

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Figure 4- Removal of components is completed

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Section 4: Troubleshooting the Stereo 120 Power Supply
This section only applies if your power supply didn’t pass the test outlined in Section 2:
Checking the Stereo 120 Power Supply. If your power supply did pass that test, move on
to . This section descri es how to verify proper operation of the power supply, separating
power supply trou les from amplifier module trou les.
Make sure that the power cord is out, and has been out for at least 1 minute before
starting this section.
Prepare and Connect the Test Load
We’ll recycle parts of the amplifier oards to make a test load resistor for the power
supply. If you know that your power supply and regulator are working correctly, you may
skip ahead to Section 5: Building the Updated Circuit Boards.
1. Keeping the leads as long as possi le, remove two 300 Ohm power resistors from
one of the PC-14 circuit oards. If you have any dou ts a out the resistors, check
them with an ohm-meter.
2. Connect the two resistors in series, twisting and soldering.
3. Connect the series resistors across C12. Figure 5 shows how the test circuit will
look. The ground side connection is a it round-a out, ut it’s there none the less.
Figure -Connecting a test load to the power supply
Test the Power Suppl
1. Make sure that neither the resistors nor their connections rest on the chassis. This
is important.

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2. Make sure that none of the other dangling wires is making contact with anything
else.
3. When everyone is clear of the amplifier, plug it in, and turn it on.
4. Measure the DC voltage on the terminals of C12.
5. The voltage should e etween 68 and 76 Volts, with a nominal voltage of 72
Volts. If it falls in this range, your power supply checks out. Remove the load
resistors and move onto Section 5: Building the Updated Circuit Boards.
Just In Case – Trouble Shooting
The Voltage is Much More than 78 volts
Most likely the pass transistor (Q9 on the power supply heat sink) is shorted. However,
repairing the power supply module is eyond the scope of this manual. You can complete
Section 5: Building the Updated Circuit Boards, ut don’t move on to Section 6: Wiring
In the Updated Amplifier Modules until you have repaired the power supply module.
Check www.updatemydynaco.com , the Power Supply Circuit Description, for more
information.
The Voltage is Much Less than 66 volts
Most likely the pass transistor is open. However, repairing the power supply pass module
is eyond the scope of this manual. Don’t continue until you have repaired the module.
Check www.updatemydynaco.com , the Power Supply Circuit Description, for more
information.
There’s No Voltage at All
Check:
1. Is the AC socket powered?
2. Is the amp plugged in?
3. Is the power turned on?
Remove the power, check and replace the fuse with a properly rated fuse. Sometimes,
fuses just get tired. Sometimes they low to prevent a disaster. At this point, we’re not
sure what the case is here.
Maintaining a respectful distance, power the amp again, and o serve if the fuse lows. If
it lows quickly, unplug the amp, and go to www.updatemydynaco.com , the Power
Supply Circuit Description, for more information. The FAQs at the end of the document
may e especially helpful.
At this point, if you’re scared, confused, or nervous, find someone who knows what
they’re doing to help you. A ove all, e safe!

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Section 5: Building the Updated Circuit Boards
This section details the process of uilding the circuit oards. We start with an overview
on this page. The specifics you need to start uilding egin on the next page.
In general, you’ll start with the components that lay closest to the oard, working your
way toward the taller components. You will:
1. Install the resistors
2. Install the small capacitors
3. Install the diodes
4. Install the LEDs
5. Install the medium size capacitors
6. Install the transistors
7. Install the ig capacitor
8. Wind and install the output inductor.
9. Install the LM3886.
Install the Resistors
In general, you install the resistors y placing the ody on silk screen side of the oard,
and the leads through the indicated holes. Bend the leads over on the ack of the oard to
keep the resistors from falling out until your solder them in place. Try to end the leads in
a direction that won’t lead to solder ridges etween traces that should remain
disconnected.
We recommend the following procedure:
1. Insert all the resistors of the same value, e.g. R14, R19, R20, and R21.
2. Bend the leads as descri ed a ove.
3. Solder the leads on the ack of the oard.
4. clip the leads.
Figure 6-The first four resistors are installed with leads bent on the back side, but not yet soldered.
Turn the page for specific directions a out each resistor.

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Figure 7-leads soldered and clipped
When you’re done this section, there will only be one empty resistor slot, R16, a no-load,
which will remain empty.
Track your progress y placing a check-mark in the done column as you install each
resistor. Check resistor values with a meter, or y reading the color code
1
. Orient the
resistor with the fat rown and on the right, then you can read oth the Color Code
column and the resistor from left to right.
Designation Value Color Code Done?
R14 10 Brown, Black, Black, Gold, Brown
R19 10 Brown, Black, Black, Gold, Brown
R20 10 Brown, Black, Black, Gold, Brown
R21 10 Brown, Black, Black, Gold, Brown
R13 100 Brown, Black, Black, Black, Brown
R1 100K Brown, Black, Black, Orange, Brown
R2 100K Brown, Black, Black, Orange, Brown
R3 100K Brown, Black, Black, Orange, Brown
R5 100K Brown, Black, Black, Orange, Brown
R7 100K Brown, Black, Black, Orange, Brown
R8 100K Brown, Black, Black, Orange, Brown
R4 1K Brown, Black, Black, Brown, Brown
R6 1K Brown, Black, Black, Brown, Brown
R9 1K Brown, Black, Black, Brown, Brown
R10 1K Brown, Black, Black, Brown, Brown
R18 1K Brown, Black, Black, Brown, Brown
R11 20K Red, Black, Black, Red, Brown
R12 20K Red, Black, Black, Red, Brown
R17 2K87 Red, Gray, Violet, Brown, Brown
R15 10 (1 Watt) Brown, Black, Black, Gold, Brown. This
resistor ody is larger than the others.
R16 This Location Remains Empty
Note: R8 and R18 are near each other on the oard. Be careful...don’t mix them up!
1
See “Resistor Color Code” on page 32 to see how to read resistor color codes.

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Install the Small Capacitors and the Diodes
Now we’ll install the following small capacitors:
Designation Value Marking Done?
C3 220 pF 221
C4 220 pF 221
C9 47 pF 470
Here’s what these three caps look like (not to scale):
Next we install diodes D1 and D4.
Be careful! Diodes ha e a polarity. Make sure the band on the diode aligns with
the banded end of the silk screen!
Designation Value Marking Done?
D1 1N4004 4004
D4 1N4004 4004
Here’s what the diodes look like (not to scale):
Next we install LEDs D2 and D3 (Light Emitting Diodes – note that in normal operation,
these diodes will e dark. However, in a fully darkened room, you’ll see a dull green
glow from the powered LEDs.)
Be careful! Light Emitting Diodes ha e a polarity, also! Read carefully to make
sure you’re putting the diodes in the right way! The cathode of the LED is
indicated by a bar (negati e sign) molded into the package. On some packages,
there is no bar, but seen from the top, the circular outline with ha e a flat side.
That flat side is the cathode. Finally, if the leads are uncut, the shorter of the two
leads will be the cathode.
Designation Value Marking Done?
D2 T1 style none
D3 T1 style none
Figure 8-showing LED cathode orientation

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Last Capacitors and the Transistors
Now, the medium tall polarized electrolytic capacitors:
C1 and C6 are polarized. Make sure the negati e sign on the capacitors faces
away from the positi e sign on the silk screen!
Designation Value Marking Done?
C1 47 µF, 63 V 47 µF, 63 V, and minus sign for polarity
C6 47 µF, 100 V 47 µF, 100 V, and minus sign for polarity
And the non-polarized capacitors:
Designation Value Marking Done?
C2 1 µF, 63 V or
100V
1 uF, 63 V or 100V ( ox shaped mylar
capacitor)
C5 0.1 µF, 100V 104
C8 0.1 µF, 100V 104
C10 0.1 µF, 100V 104
Install the transistors. Spread the outside leads a it to make it easier to insert them into
the oard.
Orient the transistor so its body shape matches the silk-screen outline. Lea e the
top of the transistor about ½” off the board! The lead length pre ents stress on the
body and keeps the transistor safe from too much heat during the soldering
operation.
Designation Value Marking Done?
Q1 2N5551, NPN 2N5551
Q2 2N5551, NPN 2N5551
Q3 2N5551, NPN 2N5551
Now install the speaker coupling capacitor:
Watch the polarity! Make sure the minus sign faces away from the plus sign on the
silk screen. That puts the minus side of the cap along the outer edge of the circuit
board.
Designation Value Marking Done?
C11 3300 uF 63V 3300 uF, 63 WVDC
The speaker coupling capacitor will either snap or push into place. Verify once more that
you have polarity correct, and then solder oth speaker terminals to the circuit oard.
This will pro a ly take more heat, time, and solder than anything you have soldered up to
now.
Winding the Output Inductor
This step takes just a it of finesse, ut if you’ve come this far, you have nothing to worry
a out. If you’re a it frazzled, take a reak efore proceeding.

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There...feel etter? OK, let’s go. Just follow these steps, measuring the wire length
carefully if you want to succeed the on first shot.
1. Cut a 21 1/2” length of 16 AWG solid wire from the output inductors wound
around the old Dynaco output capacitors.
2. Strip ack 3/8” of insulation from oth ends of the wire. Be careful not to nick the
conductors.
3. From the component side, place one stripped end of the wire into the L1A
terminal. Route it around the output capacitor as shown in (see Figure 9) Solder
the wire into the L1A hole.
4. Wind 5 turns of wire, closely spaced, so it looks like Figure 10. When you get to
the end of the coil, fold the end across the existing turns, toward the L1B hole.
5. Pull the end of the wire through the L1B hole, and solder it on the ack of the
oard.
Figure 9-Starting to wind the output inductor
Figure 10-finishing step for the output inductor
Solder the LM3886 into the Board
This is the last step in stuffing the circuit oard. By now, you are pretty good at soldering.
Your skill will help you with this step. Just follow the instructions calmly and carefully,
and you’ll do just fine.
1. You’ll start with one small it of mechanical assem ly as shown in Figure 11.
Use two #6-3/8” Phillips head screws (they have captive lock-washers) to fasten
two rackets to the solder side of the amplifier PC oard. Watch the racket
orientation, and don’t install any more fasteners at this time!
2. With the rackets attached to the PC oard, use the template in Figure 12 to check
the LM3886 mounting height. If your printer has printed to the correct scale, the

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square in the figure should e very nearly 1” y 1”. Print this page, and set the
oard and rackets against the page to check the LM3886’s height a ove the
oard.
3. Match the outline of the LM3886 and the PC oard to the drawing. When the
match is pretty good, solder one corner pin of the LM3886. Recheck the match,
and solder an opposite corner pin (see Figure 13). If something has moved, just
reheat the corner pins and pull the LM3886 in or out as needed. If you miss a right
angle y a little, don’t worry. Since you’ve only soldered two pins down, it’s easy
enough to reheat those two pins, and move the LM3886 up and down a it until it
sits at the right height.
4. Check your work:
a. The LM3886 ody should sit up off the oard to avoid short circuits
etween the rows of pins (See Figure 14).
. The LM3886 ody should sit at right angles to the plane of the oard. If
the result comes up a it away from a right angle, don’t worry. The
mounting system is compliant enough that this won’t e a pro lem.
5. Solder all the remaining pins of the LM3886 to the PCB.
Figure 11-Showing method of attaching brackets to the PCB