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Summary of Contents for AkitikA GT-108
- Page 1 GT-108 STEREO AUDIO POWER AMPLIFIER ASSEMBLY MANUAL © 2022 AkitikA LLC All rights reserved Revision 1p05 December 23, 2022 Page 1 of 56...
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Page 2: Table Of Contents
Table of Contents Table of Contents ........................ 2 Table of Figures ........................3 Section 1: About This Manual .................... 5 Who Should Attempt this Project? ................. 5 Tools You’ll Need......................5 Project Overview ......................5 Important Safety Notes ....................6 About Components ...................... -
Page 3: Table Of Figures
Power-On Tests ......................45 Set the Bias Current ....................46 Install the Top ......................47 Section 6: Using the GT-108 .................... 47 Section 7: Specifications and Schematics ................. 47 Section 8: Theory of Operation ..................51 Power Supply ........................ 51 Bulk DC Supply ...................... - Page 4 Figure 7-Installing Q5 on the heatsink and to the PCB ............ 13 Figure 8-Remember to solder Q5's leads ................14 Figure 9-Assembled Power supply mounted on heat sink ..........14 Figure 10-Empty the amplifier components into a soup bowl .......... 15 Figure 11-Close-up of bare Amplifier PCB ..............
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Page 5: Section 1: About This Manual
Section 1: About This Manual This manual gives the information you need to build Akitika LLC’s GT-108 Stereo Power Amplifier. The GT-108 delivers a total of 120 Watts in the form of 60 Watts per channel into 8-Ohm loudspeakers. Who Should Attempt this Project? You can build this kit if you can: 1. -
Page 6: Important Safety Notes
63/37 Rosin Core solder. Akitika LLC’s liability shall in no event exceed the cost paid to Akitika LLC for the kit. https://en.wikibooks.org/wiki/Practical_Electronics/Soldering has entries for both 60/40 and 63/37 solder blends. -
Page 7: Section 2: Building The Power Supply Pcb
Section 2: Building the Power Supply PCB This section details the process of building the power supply circuit board. We start with an overview on this page. The specifics you need to start building begin on the next page. The bare power supply PCB is shown in Figure 1. Figure 1-Component side of power supply PCB before loading Begin by carefully emptying the contents of the envelope marked “GT-102 PSU Module”... -
Page 8: Figure 2-Installing Resistors
Color Code column and the resistor from left to right. The GT-108 is based on parts from the GT-102, with the addition of a number of parts that are unique to the GT-108. You will therefore see that there are two power supply envelopes. -
Page 9: Install The Diodes
Install the Diodes Now install the diodes. Be careful to observe the polarity markings on the diodes. You’ll notice that one end of the diodes has a band. That band indicates the cathode of the diode. Match the banded end of the diode with the banded end of the silk screen. The following information should help you identify the diodes. -
Page 10: Figure 3-Form The Cathodes Of D4-D7 As Shown (Banded End Denotes Cathode)
Designation Type, Package Description Done? () BZX55B33, DO-35 33 Volt 2% zener diode BZX55B33, DO-35 33 Volt 2% zener diode BZX79-B10, DO-35 10 Volt 2% zener diode 1N4148, DO-35 0.2 A, 100 PIV, switching diode 1N4148, DO-35 0.2 A, 100 PIV, switching diode 1N4148, DO-35 0.2 A, 100 PIV, switching... -
Page 11: Install The Last Resistor
Install the Last Resistor R12 should be air-mounted, with the bottom of its body about 1/8” above the PCB. 2 Watt, 5% resistor Designation Value Marking Done? () Install the Small Capacitors Now install the small capacitors: C1, C2, and C3 are polarized, showing a minus sign (-) on the negative end of the capacitor. -
Page 12: Install The Big Capacitors
Designation Type Description Done? () 2N3904, TO-92 60 V NPN bipolar transistor 2N3904, TO-92 60 V NPN bipolar transistor 2N3904, TO-92 60 V NPN bipolar transistor 2N5401, TO-92 150 V PNP bipolar transistor 2N5401, TO-92 150 V PNP bipolar transistor Don’t use too much solder on the transistor leads. -
Page 13: Figure 5-Note The Rounded Brackets Used For The Power Supply Heatsink And Pcb
Figure 5-Note the rounded brackets used for the power supply heatsink and PCB 1. Use two 6-32x3/8” screws to fasten a pair of mounting brackets to the heat sink, placing the screw through the 9/64” clearance hole in the bracket. Note that one hole in the mounting bracket is a 9/64”... -
Page 14: Figure 8-Remember To Solder Q5'S Leads
Figure 8-Remember to solder Q5's leads 5. Line up the PCB, brackets, and Q5 so everything is square and fits comfortably, then tighten the 5 screws: a. 2 that hold the brackets to the PCB b. 2 that hold the brackets to the heatsink c. -
Page 15: Section 3: Assembling The Amplifier Circuit Boards
Section 3: Assembling the Amplifier Circuit Boards This section details the process of building the amplifier module circuit boards. We start with an overview on this page. Begin by carefully emptying the contents of one of the envelopes marked “GT-102-108 Amp Delta Kit” and one “GT-102 Amplifier Module” into a broad soup bowl, as shown in Figure 10. -
Page 16: Install The Resistors
(higher wattage) resistors. Important Notes: 1. The GT-108 is a dual channel amplifier. You will build two identical channels. We’ve provided two Done columns, Done1 for the first channel you build, and Done2 for the second channel. We recommend that you build the channels one at a time, completing the first channel, then returning to this point to build the second channel. - Page 17 Brown, Black, Black, Brown, Brown Brown, Black, Black, Brown, Brown Brown, Black, Black, Brown, Brown Brown, Black, Black, Brown, Brown Brown, Black, Black, Brown, Brown Brown, Black, Black, Brown, Brown Brown, Black, Black, Brown, Brown Brown, Green, Black, Brown, Brown Brown, Green, Black, Brown, Brown 8K06 Gray, Black, Blue, Brown, Brown...
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Page 18: The Following Are 0.1% Resistors
The following are 0.1% resistors Designation Value Color Code Done 1 Done2 Brown, Black, Black, Brown, Violet; 0.1% In some kits, the resistor may have numbers: 1K 0.1% on a brown body 20K, Red, Black, Black, Red, Violet 0.1% In some kits, the resistor may have numbers: 20K 0.1% on a brown body. -
Page 19: Small Capacitors
Designation Value Package Done1 Done2 LED1 LED, green T1 LED package LED2 LED, green T1 LED package Figure 12-Note flat side of LED package sits under number 1 and 2 in LED1 and LED2 Small Capacitors Designation Value Marking, Type Done 1 Done 2 0.1µF@100V... -
Page 20: Power Resistors
Power Resistors The following resistors are power resistors, having a larger body than the ¼ Watt resistors installed in the previous section. These resistors are all mounted vertically as in the examples shown in Figure 14. Figure 14-Vertical resistor mounting 0.1@2W, 5% Written on body 0.1@2W, 5%... -
Page 21: Install The Voltage Regulators
2N5551 NPN, 150 volts J176 176, P channel JFET ZVN2110A or 2110, N Channel MOSFET 100 Volt ZVN3310A or 3310 Install the Voltage Regulators Now install the voltage regulators. The two regulators have similar, but different part numbers. Make sure to get the right one in the right place. They are not interchangeable. Orient the regulators so their body shape matches the silk-screen outline. -
Page 22: Install T8 And T9
3. From the component side, place one stripped end of the wire into the L1A terminal. Bend it on the solder side to retain it, but don’t solder it yet. Route it around the output capacitor as shown in Figure 15. 4. -
Page 23: Figure 17-Spreading Thermal Compound On Driver Transistors
Figure 17-Spreading thermal compound on driver transistors Two slightly different types of heatsinks have been supplied, see Figure 18. Either: 273 Heatsink, or Plain Heatsink Figure 18-Do you have a 273 or a plain heatsink? If you have a 273 heatsink, orient the transistor as shown on the left side of Figure 19. Add 3/8”... -
Page 24: Install The Polarized Capacitors
Figure 20-Installing T8 and T9 on the circuit board Leave about 0.1-0.2” between the bottom of the heatsink and the tops of the ¼ Watt metal film resistors. Hint: Start by soldering only the center leg. This makes it easy to adjust the transistor’s height. -
Page 25: Final Inspection Of The Circuit Board
Final Inspection of the Circuit Board After you’ve taken a break, look over your completed circuit board(s) one more time. Looking on the component side, double check: 1. polarity of diodes matching the banded end on the silk screen. 2. polarity (flat side of LEDs). 3. -
Page 26: Figure 22-Mounting The Pcb To The Heat Sink
Figure 22-mounting the PCB to the heat sink 3. Place a dab of thermal compound on the back of the Q4, which is a IRFP9140 power MOSFET and spread it into a thin film, being careful to keep the leads clean. -
Page 27: Figure 24-Threading The Screwdriver To Q4'S Mounting Screw
4. Insert Q4 into the circuit board. Fasten Q4 to the heatsink using a 6-32x1/2” screw. You can thread a Phillips driver from the front to the back of the board to tighten this screw. Tighten all 5 mounting screws as you make sure that Q4 is perpendicular to the plane of the board. -
Page 28: Figure 26-First Amplifier Channel Completed And Installed
10. Remove Q5’s mounting screw carefully in order to keep its insulator in place. Place Q19’s mounting leads into their PCB holes. Re-insert Q5’s mounting screw thru Q19’s tab, the body of Q5, and into the heatsink. Slowly tighten the screw as you push Q19’s body to lay flat on Q5. -
Page 29: Section 4: Wiring It All Together
Note: The X1, X2, VCC, PGND1 and PGND2 eyelets will remain open until a later assembly step. The overall mechanical parts of the GT-102 and GT-108 are quite similar, so the wiring kit may say either GT-102 or GT-108. Page 29 of 56... -
Page 30: Attach The Amplifier Module Power Wires
Attach the Amplifier Module Power Wires Figure 29-Right and Left Channel Designations Attaching LEFT Module Power Wires 1. For the module designated as LEFT (see Figure 29), cut a 9” overall length of Red/Black 18 AWG zip cord. 2. Separate the Red and Black wires about 1 inch at each end. 3. -
Page 31: Prepare Input Shielded Cables
Prepare Input Shielded Cables 1. Prepare a 5 1/2” length of shielded cable for the LEFT channel input per the directions that begin on Page 55. Prepare both ends per those directions. Twist and tin the wires at one end of the cable. Leave the other end tightly twisted, but un-tinned. -
Page 32: Install The Feet
You’ll get the best results if you’ve tinned the stripped ends of the wires before you crimp them into the solder lugs. Once all the connections are crimped in place on a given lug, solder the lugs using enough heat to make the solder flow. When you do this, the wires should be straight, as the heat will encourage the insulation to back off a bent wire. -
Page 33: Ac Power Wiring
Designation Value Marking Done 24.9 Red, Yellow, White, Gold, Brown 10 nF 10nJ100 GBPC3506W 1. Locate the green 18 AWG stranded wire with a FASTON terminal installed on one end. Cut it to an overall length of 14”, measured from the far-end of the FASTON. -
Page 34: Figure 37-Power Wiring With Iec Connector Installed Into Chassis
3. Starting outside the chassis, insert the black and white wires (already connected to the IEC power connector) into the hole in the back-right corner of the chassis as shown in Figure 37. Make sure that the writing on the power connector is right side up! Push until it clicks in place. -
Page 35: Install The Rca Jacks And Speaker Binding Posts
9. Starting with the switch outside the chassis, push the FASTONs on the bottom switch terminals as indicated in Figure 38. The black or white wire may be on either side of the switch, so long as they both attach to the bottom row of contacts. Figure 38-Installing power wires on the switch 10. -
Page 36: Install The Speaker Binding Posts
in Figure 39. Use the right channel shielded cable and ground harness that you previously built. 1. Insert the RCA jack and the two insulating washers and ground lug as shown in Figure 39. The ground lug already has two black wires attached. Tighten the mounting nut. -
Page 37: Amplifier Channels Final Wiring
binding post nuts and tighten it with a 5/16” nut-driver. The free end of the white wire will be connected to the left channel amplifier OUT in a later step. Right Speaker Binding Post 1. Slip the #10 lug from the right channel ground harness (black 18 AWG wire) over the black binding post stud. -
Page 38: Installing Amplifier Modules Into The Chassis
1. Identify the 18 AWG white wire that connects to the LEFT channel red binding post. Twist the conductor strands tightly, and insert the wire into the LEFT Channel OUT eyelet from the solder side of the board. Solder it on the component side of the board. -
Page 39: Figure 42-Wiring Toroidal Transformer For 120 Volt Operation
Figure 42-Wiring toroidal transformer for 120 Volt operation 1. Cut a 2.5” length of 3/16” diameter heat-shrink tubing. Slide it over the blue and violet leads of the power transformer. Slide it as far from the cut ends of the wire as possible. -
Page 40: Transformer Installation
Figure 43-Western Union splice has diameter less than the insulated wires and no sharp points 9. Cut the red and orange transformer wires to a length of about 2”. 10. Remove 3/8” of insulation from the red and orange transformer wires. 11. -
Page 41: Testing The Power Supply
4. Dress the black-white twisted pair that goes from the switch to the power entrance connector into the crease along the right side of the chassis. 5. Dress the transformer primary leads as shown on the front cover of this manual. 6. -
Page 42: Final Amplifier Wiring
5. Locate the supplied IEC power cord. Make sure it is NOT connected to the AC wall socket yet. Connect one end to the IEC power connector on the chassis. 6. Standing well away from the amplifier, connect the plug into the AC wall socket. Keeping one hand in your pocket, use the other hand to turn on the power switch. -
Page 43: Install The Wall And Fasten The Transformer Down
2. This step is optional, but it is recommended if you listen for long periods at high levels. Spread a thin film of thermal compound on the 3/8” wide ridge of the heatsink (the side with two 6/32 mounting holes). Note: the transformer is not yet fastened in place. -
Page 44: Figure 47-Routing The Wires Thru The Slots In The Wall
Figure 47-Routing the wires thru the slots in the wall Refer to Figure 47 to see how the power and ground wires route through the slots in the wall: 1. Route the power supply ground wire through the back hole in the wall. 2. -
Page 45: Visual Inspection
5. Fasten the wall to the bottom of the chassis using two 6-32x3/8” black screws installed from the bottom of the chassis and into the fasteners on the wall. Make sure that the wires pass easily through the slots in the wall, and aren’t being pinched. -
Page 46: Set The Bias Current
resistor on the output. The voltage will typically decline with time. When a speaker is present, the DC voltage will be less than 10 millivolts. 2. Turn the power off. Set the Bias Current At this step, you will set the bias pots for the correct bias current. You’ll repeat this for both the left and the right channels. -
Page 47: Install The Top
(they will be slightly staggered in time). 4. Please note that with inputs disconnected, the speakers should be quite quiet. Section 6: Using the GT-108 Don’t block the ventilation holes on the sides or the top of the amplifier. - Page 48 Figure 50-Power Supply Schematic Page 48 of 56...
- Page 49 Figure 51-Amplifier Module Schematic Page 49 of 56...
- Page 50 Figure 52-Overall Wiring (power transformer is wired for 120 VAC) Page 50 of 56...
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Page 51: Section 8: Theory Of Operation
Section 8: Theory of Operation Power Supply Please refer to Figure 50. Bulk DC Supply We begin at the left side of the schematic. The toroidal power transformer steps the 120V or 240 V AC mains (selected as a wiring) option to about 73 Volts RMS . -
Page 52: Start-Up Circuits
Q15-Q18 form a Darlington differential input pair that keeps the input impedance high, making the GT-108 a friendly load for most tube preamps. C2 blocks the input stage bias voltage from appearing on the input RCA jack. -
Page 53: Reference Voltage Generator
Reference Voltage Generator R1, R2, R5, D11, and U2 establish a 38-volt reference at node VMIDLOWZ. D11 assures that 20 volts appears across U2, keeping it well within its 36-volt rating. R9 isolates VMIDLOWZ. D12 helps charge C1 more quickly during turn-on, establishing the output voltage relatively quickly. -
Page 54: Appendix 1 - Resistor Color Code
Appendix 1 - Resistor Color Code Figure 53-demonstrating the resistor color code Here’s an extreme close-up of a ¼ W metal film 20K (20,000) Ohm resistor, designated by the standard resistor color code. The colors map to numbers: Color Number Black Brown Orange... -
Page 55: Appendix 2 - Preparing A Shielded Cable End
Appendix 2 - Preparing a Shielded Cable End This section tells how to prepare the ends of the shielded cable. This process will be repeated four times, at both ends of both input cables (although the cables will have different overall lengths). 1. - Page 56 6. Peel back and remove the foil. Remove the plastic wrap from the red and black wires. The drain (bare wire), red, and black wires are exposed now that gray insulating jacket, foil shield, and plastic over-wrap have been removed. 7.
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