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