AkitikA DYNACO STEREO 120 User manual

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UPDATING THE
DYNACO STEREO 120
SOLID STATE
POWER AMPLIFIER
REV B
© 2013 AkitikA, LLC
All rights reserved
Revision 1.17
Jul 27, 2013

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Table of Contents
Table of Contents................................................................................................................ 2
Table of Figures .................................................................................................................. 3
Section 1: About this Manual ............................................................................................. 4
Who Should Attempt this Project? ................................................................................. 4
Tools You’ll Need........................................................................................................... 4
Project Overview ............................................................................................................ 5
Important Safet Notes ................................................................................................... 5
About Components ......................................................................................................... 5
Recommended Solder ..................................................................................................... 5
Section 2: Saving the Stuff that Should Be Saved.............................................................. 6
Opening the Amplifier .................................................................................................... 6
Cutting the wires on the old amplifier modules.............................................................. 6
Removing the LEFT channel module......................................................................... 6
Removing the RIGHT channel module ...................................................................... 7
Removing C7 RIGHT ............................................................................................... 10
Removing C7 LEFT.................................................................................................. 10
Removing the Output Zobel Networks ..................................................................... 10
Salvaging the Heat Sinks from the Amplifier Modules................................................ 12
Section 3: Checking the Stereo 120 Power Suppl .......................................................... 12
Prepare and Connect the Test Load .............................................................................. 12
Test the Power Suppl .................................................................................................. 13
The Voltage is Much More than 75.6 volts .................................................................. 13
The Voltage is Much Less than 68.4 volts.................................................................... 13
There’s No Voltage at All............................................................................................. 14
Section 4: Assembling the Amplifier Circuit Boards ....................................................... 14
Install the Resistors ....................................................................................................... 15
Install the Small Capacitors and the Diodes ................................................................. 17
Last Capacitors and the Transistors .............................................................................. 18
Winding the Output Inductor ........................................................................................ 19
Solder the LM3886 into the Board ............................................................................... 20
Final Inspection of the Circuit Board............................................................................ 22
Mounting the Updated Amplifier Board to the Heat Sink............................................ 23
Section 5: Wiring In the Updated Amplifier Modules...................................................... 24
Revise the Grounding S stem....................................................................................... 24
Revise the Power S stem.............................................................................................. 25
Complete the Ground S stem ....................................................................................... 26
Wiring the Inputs .......................................................................................................... 26
Wiring the Outputs........................................................................................................ 27
Connecting the Left Channel Amplifier Module .......................................................... 27
Connecting the Right Channel Amplifier Module........................................................ 28
Making the Speaker Binding Posts User Friendl ........................................................ 29
Section 6: Testing the Completed Amplifier .................................................................... 29
Test #1........................................................................................................................... 29
Test #2........................................................................................................................... 30

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Test #3........................................................................................................................... 30
Test #4........................................................................................................................... 30
Resistor Color Code...................................................................................................... 32
Table of Figures
Figure 1-Location of the four screws that hold the cover to the base................................. 6
Figure 2-Location diagram for cutting wires ...................................................................... 8
Figure 3-After the Amplifier Modules have been removed................................................ 9
Figure 4- Removal of components is completed .............................................................. 11
Figure 5- Separating heat sinks and circuit boards ........................................................... 12
Figure 6-Connecting a test load to the power suppl ....................................................... 13
Figure 7-Empt the amplifier components into a soup bowl............................................ 14
Figure 8-Closeup of Completed Amplifier board ( our big cap ma look a bit different)
........................................................................................................................................... 15
Figure 9-First four resistors are installed, leads bent on the back side, soldered, then
clipped............................................................................................................................... 15
Figure 10-Zero Ohm R22 installation detail..................................................................... 17
Figure 11-showing LED cathode orientation.................................................................... 18
Figure 12-Starting to wind the output inductor................................................................. 20
Figure 13-finishing step for the output inductor ............................................................... 20
Figure 14-Showing method of attaching brackets to the PCB.......................................... 21
Figure 15-Template for checking mounting height of LM3886....................................... 21
Figure 16-LM3886 installation step three, just the corner pins are soldered.................... 22
Figure 17-The LM3886 sits up off the board to avoid shorts between the front and back
rows of pins. The bod should be at right angles to the circuit board .............................. 22
Figure 18-Mounting assembled PCB to heat sink ............................................................ 23
Figure 19-a completed amplifier module.......................................................................... 24
Figure 20-Rewiring the Power and Half the Grounds ...................................................... 26
Figure 21-completed wiring.............................................................................................. 27
Figure 22-Schematic of amplifier module ........................................................................ 31
Figure 23-demonstrating the resistor color code .............................................................. 32

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Section 1: About this Manual
This manual gives ou all the information ou need to bring our Solid State D naco
Stereo 120 Power Amplifier up to date using UpdateM D naco replacement modules.
This manual covers the Rev B design. It’s ver similar to the original design, but includes
most (but not all of) the improvements made in the Akitika GT-101 design:
• Added components give quiet turn-off even when paired with C12 Upgrade kits
(the original design required the quiet turn-off mod to be retro-fit into the board)
• Value changes slightl increase the maximum output power prior to clipping.
• The PCB has a different grounding arrangement which allows the LED’s to run
more brightl .
• The GT-101 uses 0.1% tolerance gain setting resistors. The modules described
herein use standard 1% tolerance gain setting resistors.
The onl part of our Stereo 120 that reall needs to work is the power suppl . With this
kit, ou’ll build good sounding, highl reliable amplifiers to replace the original amplifier
modules.
Check www.updatemydynaco.com for “Hints for Kit Builders” before you begin
assembly
Who Should Attempt this Project?
You can build this kit and update our D naco Stereo 120 if ou 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 ou:
1. know a bit about electronics, or
2. have a friend who knows a bit about electronics
3. can get to YouTube to watch a video about the assembl process
Tools You’ll Need
You’ll need the following tools to update our Stereo 120:
1. flat blade screwdriver for #6 screws
2. Phillips screwdriver (#2)
3. pliers or nut drivers suitable for #6 hardware (5/16” nut driver or hex wrench)
4. needle nose pliers (helpful, but not strictl necessar )
5. pencil t pe soldering iron of 25 to 50 Watts (no huge honking soldering guns or
blowtorches)
6. wire cutters and strippers
7. multi-meter (helpful, but not strictl necessar )
8. magnif ing glass, to verif identification codes on the 3 COG capacitors

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Project Overview
The project consists of the following steps:
1. Removing the old amplifier modules, saving some parts for re-use.
2. Checking out the old D naco Stereo 120 power suppl .
3. Assembling the updated amplifier module PC Boards.
4. Mounting the updated amplifier modules to the heat sinks.
5. Wiring in the updated amplifier modules.
Important Safet Notes
B purchasing this kit, ou have agreed to hold AkitikA, LLC harmless for an injuries
ou ma receive in its assembl and/or use. To prevent injuries:
• Wear safet glasses when soldering to prevent e e injuries.
• Alwa s unplug the power before working on the amplifier.
• Large capacitors hold lots of energ for a long time. Before ou put our hands
into the amplifier:
o Pull the AC plug!
o Wait 1 full minute for the capacitors to discharge!
• Remove jewelr and rings from our hands and wrists, or an thing that might
dangle into the amplifier.
• If working in the amplifier, keep one hand in our pocket, especiall if ou’re
near the power suppl or power suppl wires. This can prevent serious shocks.
• Build with a budd nearb . If ou’ve ignored all the previous advice, the can
dial 911 or get ou to the hospital.
About Components
We reserve the right to make design/or component changes at an time without prior
notification.
Recommended Solder
The kit must be assembled with 60/40 Rosin Core solder. The recommended diameter is
0.032 inches. Among man such sources of solder, I have used Radio Shack part number
64-009. It contains 8 oz. of solder, which is much more than ou’ll need to assemble the
kit.

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Section 2: Saving the Stuff that Should Be Saved
Opening the Amplifier
1. Make sure the amplifier is unplugged. f 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 bottom 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 both the top and bottom of the amplifier, flip it over.
4. Lift the perforated metal top off of the amplifier.
Cutting the wires on the old amplifier modules
Refer to Figure 2. It shows where the wires must be cut to remove the old amplifier
modules. Those cuts are detailed in the text below. Each cut is marked b an X.
Removing the L FT channel module
1. To remove the LEFT channel module, cut the following wires close to the end
that connects to the LEFT channel PC-14 module. Make onl one cut per wire,
leaving the wire attached at the end farthest from the LEFT PC-14 module.
a. E elets 8, 9, 10, 11, 12, and 13
2. Cut the wire that attaches to E elet 5 of the PC-15 power suppl circuit board
close to the PC-15 circuit board.
3. Loosen the two screws that hold the left channel heat sink in place (note that one
of the screws holds a mounting foot
1
). Save the hardware for later re-use.
4. Cut the red wire that connects to Q5’s collector, close to the lug. Although there
are multiple wires on the collector, onl cut the wire that connects to C12.
1
If our mounting feet are falling apart, ou can order a replacement set from updatem d naco.com.

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5. Cut the black wire that connects to Q6’s emitter, near the emitter. There are two
wires on the emitter... ou need onl cut the wire that runs to the black left speaker
binding post.
Save the LEFT module and mounting hardware. We will re-use the heat-sink and some
other bits as described in “Salvaging the heat sinks from the amplifier modules”.
Removing the RIGHT channel module
6. To remove the RIGHT channel module, cut the following wires close to the end
that connects to the RIGHT channel PC-14 module. Make onl one cut per wire,
leaving the wire attached at the end farthest from the RIGHT PC-14 module.
a. E elets 8, 9, 10, 11, 12, and 13
7. Loosen the two screws that hold the RIGHT channel heat sink in place (note that
one of the screws holds a mounting foot
2
). Save the hardware for later re-use.
8. Cut the red wire that connects to Q5’s collector, close to the lug. Although there
are multiple wires on the collector, onl cut the wire that connects to C12.
9. Cut the black wire that connects to Q6’s emitter, near the emitter. There are two
wires on the emitter... ou need onl cut the wire that runs to the black RIGHT
speaker binding post.
Save the RIGHT module and mounting hardware. We will re-use the heat-sink and some
of the other bits as described in “Salvaging the heat sinks from the amplifier modules”.
2
If our mounting feet are falling apart, ou can order a replacement set from updatem d naco.com.

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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 the 3 sets of #6 hardware that hold C7 RIGHT to the bottom 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 about 1 foot of wire remains connected to
the RIGHT RED Binding post.
Removing C7 L FT
4. Remove the 3 sets of #6 hardware that hold C7 LEFT to the bottom 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 about 1 foot of wire remains connected to the
LEFT RED Binding post.
Removing the Output Zobel Networks
1. Clip the lead of the 0.1 uF capacitor that connects to the RIGHT RED binding
post, near the RIGHT RED Binding post.
2. Clip the lead of the 4.7 Ohm resistor that connects to the RIGHT BLACK binding
post, near the RIGHT BLACK binding post.
3. Clip the lead of the 0.1 uF capacitor that connects to the LEFT RED binding post,
near the LEFT RED Binding post.
4. Clip the lead of the 4.7 Ohm resistor that connects to the LEFT BLACK binding
post, near the LEFT BLACK binding post.
5. Remove the terminal strip and the two attached resistors and capacitors.
Figure 4 shows what the amplifier should look like when ou’ve completed this step.