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GT-108 STEREO

AUDIO POWER AMPLIFIER

ASSEMBLY MANUAL

Revision 1p05

December 23, 2022

Summary of Contents for GT-108

Page 2: ...Board 12 Power Supply Final Assembly 12 Section 3 Assembling the Amplifier Circuit Boards 15 Install the Resistors 16 The following are 0 1 resistors 18 Install the Diodes 18 Small Capacitors 19 Power...

Page 3: ...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 51 Pass Transistor 51 R...

Page 4: ...unting screw and insulator 27 Figure 26 first amplifier channel completed and installed 28 Figure 27 from left to right 6 lug 10 lug RCA connector ground lug 29 Figure 28 power supply with attached gr...

Page 5: ...ections It helps if you 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 few helpful videos about the assembly process Tools You ll N...

Page 6: ...esign and or component changes at any time without prior notification Recommended Solder The kit must be assembled with 63 37 tin lead Rosin Core solder1 The recommended diameter is 0 031 inches Keste...

Page 7: ...3 Install the capacitors 4 Install the integrated circuits 5 Install the transistors 6 Install the pass transistor Q5 as you mount the PCB to the heat sink Component Order You ll notice that the compo...

Page 8: ...and the second marked GT102 108 PSU Delta Rev 1 The parts marked with an asterisk come from the Delta parts bag Watt 1 resistors if you use a lead bending jig use the 0 45 width Designation Value Colo...

Page 9: ...glass 1N4148 D8 D11 has the number 48 visible BZX55B33B D1 and D14 has the number 33 visible BZX79 B10 D2 has the number 10 visible Also typically when these diodes are packed you can preliminarily i...

Page 10: ...0 PIV rectifier diode Warning Don t cut the leads of D4 D7 until after the leads have been formed and the diodes have been soldered into the PCB Form the leads of D4 D7 as shown in Figure 3 Solder one...

Page 11: ...shaped marked 10nk400 Install the Integrated Circuits Install the integrated circuits Orient U1 so that pin 1 on the chip matches pin 1 the square pin on the PCB Orient U2 to match the silk screen out...

Page 12: ...over your completed circuit board one more time Looking on the component side double check 1 polarity banded end of diodes matching the banded end on the silk screen 2 polarity of C1 C2 C6 C7 and C7 m...

Page 13: ...to fasten the PCB to the mounting brackets and heat sink see Figure 9 Don t tighten the screws yet 3 Place a thin film of thermal compound on the metal tab surface of Q5 as shown in Figure 6 Inset Q5...

Page 14: ...s of Q5 on the solder side of the board and clip the leads Inspect your work from both the top and the bottom of the board to make sure there are no solder bridges between the leads Once the power sup...

Page 15: ...g this as the 108 is a delta built upon the 102 In general you ll start with the components that lay closest to the board working your way toward the taller components You will 1 Install the resistors...

Page 16: ...ll progress to the larger 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 ch...

Page 17: ...39 15K Brown Green Black Red Brown R41 15K Brown Green Black Red Brown R43 15K Brown Green Black Red Brown R44 15K Brown Green Black Red Brown R23 20K Red Black Black Red Brown R60 20K Red Black Black...

Page 18: ...iode D2 BZX79 10 B10 10 V Zener diode D6 BZX79 10 B10 10 V Zener diode D7 BZX79 10 B10 10 V Zener diode D8 BZX79 10 B10 10 V Zener diode D11 BZX79 10 B10 10 V Zener diode D4 BZX79 C15 C15 15 V Zener d...

Page 19: ...F 100V 1J100 small blue box shape film C12 0 1 F 100V 1J100 small blue box shape film C6 0 1 F 100V 1J100 small blue box shape film C1 220pF COG 221 radial COG typically brown4 C11 100p COG 101 radial...

Page 20: ...easier to insert them into the board Double check their marking before you install them Orient the transistor so its body shape matches the silk screen outline Leave the top of the transistor about of...

Page 21: ...1 will be installed a few steps from now Designation Value Marking Done 1 Done 2 C13 10000 F 63V 10000 F 63 WVDC The speaker coupling capacitor will either snap or push into place Verify once more tha...

Page 22: ...through the L1B hole and solder it on the back of the board 6 Solder the L1A side of the inductor to the PCB 7 There will be about 5 of wire that you won t use at this step Save it as we ll use some...

Page 23: ...insulation taken from the spare wire used to wind the inductor Figure 19 273 style mounting left side and plain mounting right side If you have a plain heatsink then orient the transistor as shown on...

Page 24: ...22 F 50 V and minus sign for polarity C22 10 F 50 V 10 F 50 V and minus sign for polarity Install Relay K1 It s important to get K1 installed flat onto the PCB To do this 1 Insert K1 through the PCB...

Page 25: ...or no operation at all 2 There are no solder bridges between pads which should be isolated Solder bridges may stop the amplifier from working correctly Install the Power MOSFETS and Mount the Amplifi...

Page 26: ...eads clean This step uses just a small amount of the thermal compound in the squeeze tube Put the squeeze tube in a safe place as you may choose to use the rest of its contents when you fasten the amp...

Page 27: ...ridges between the leads of Q4 8 Locate Q5 an IRFP140 the insulator and the 6 32x1 2 sems screw used to mount Q5 to the heat sink a Insert the screw through Q5 s mounting hole from the front side Use...

Page 28: ...Tighten the mounting screw that holds Q19 and Q5 to the heatsink Solder Q19 s leads to the PCB You have just completed the first of two amplifier modules Return to the beginning of Section 3 Assembli...

Page 29: ...side by side it will become quickly apparent which is which Figure 27 from left to right 6 lug 10 lug RCA connector ground lug Attach the Power Supply Ground Wire 1 Cut a 7 length of black 18 AWG str...

Page 30: ...let entering from the solder side Solder the wire on the component side Attaching RIGHT Module Power Wires 1 For the module designated as RIGHT see Figure 29 cut an 11 overall length of Red Black 18 A...

Page 31: ...the wires at one end of the cable Leave the other end tightly twisted but un tinned Build the Ground Harnesses Figure 31 Channel Grounding Harness The left and right channel ground harnesses are the...

Page 32: ...e 32 Install the feet here Build the Ground Lifter There s one more small circuit board to build the ground lifter circuit board It supplies a robust diode bridged connection between the AC mains grou...

Page 33: ...th ends Insert one end into the CHGND eyelet on the ground lifter PCB Insert it from the side with the bridge rectifier and solder it on the silk screen side of the PCB 3 Twist and tin the other end o...

Page 34: ...5 Connect the green wire from the ground lifter assembly to the ground terminal of the power entrance connector It will be the top most terminal and the last open terminal on the connector 6 Dress the...

Page 35: ...black ring Install it from the outside of the chassis into the left channel marked RCA jack hole The mounting hardware arrangement is shown in Figure 39 Use the left channel shielded cable and ground...

Page 36: ...ed to fasten a solder lug to the terminal The black plastic insulators have shoulders that fit inside the mounting holes Make sure that the shoulders are centered in the mounting holes They keep the b...

Page 37: ...dy there from a previous step Don t install a nut yet 3 Cut an 11 length of white 18AWG stranded wire Strip about 3 8 of insulation from both ends Tin one end Insert the tinned end into the small open...

Page 38: ...nt side Installing Amplifier Modules into the Chassis Be careful not to flex the chassis It s a bit squishy with the top off but becomes quite stout once the top is installed and screwed in place You...

Page 39: ...lue Transformer wire iv VioletTransformer wire v Gray Transformer wire vi Brown Transformer wire 5 Twist together the stripped ends of the brown and gray transformer wires 6 Twist together the strippe...

Page 40: ...ires of the transformer Twist and tin each wire preparing them for installation into the power supply in a later step Transformer Installation 1 Set the transformer into the chassis wire side up over...

Page 41: ...er of the chassis connects to the GWGND eyelet of the ground lifter PCB Make sure that the wire from the CHGND eyelet of the ground lifter PCB connects to the grounding stud located between it and the...

Page 42: ...ifier modules to the power supply A quick look at the cover illustration will clarify anything not made clear by the following instructions Wiring Amplifier Power 1 Identify the red black zip cord tha...

Page 43: ...ug in place Make sure the nut is tight b Above that nut place these three 6 ground lugs i From the ground eyelet of the power supply PCB ii From the ground black binding post of the left amplifier iii...

Page 44: ...power entrance connector through the front hole in the wall 3 Make sure neither will be pinched when the wall is tightened in place But first we ll complete installation of the toroidal transformer 4...

Page 45: ...etween 900 and 1100 Ohms The nominal value is 1000 Ohms 2 Connect an ohmmeter to the right channel red and black binding posts The resistance should read between 900 and 1100 Ohms The nominal value is...

Page 46: ...livolt meter to the wires that come out of the tops of R32 and R33 for the LEFT channel 4 Disconnect inputs and speakers from the amplifier 5 Power On Wait 1 minute for the amp to stabilize The DC vol...

Page 47: ...ce connected or with the input shorted you will hear almost nothing from your speakers The amplifier may have a tiny pop thump at turn off determined by where in the cycle the musical signal was befor...

Page 48: ...Page 48 of 56 Figure 50 Power Supply Schematic...

Page 49: ...Page 49 of 56 Figure 51 Amplifier Module Schematic...

Page 50: ...Page 50 of 56 Figure 52 Overall Wiring power transformer is wired for 120 VAC...

Page 51: ...but then we wouldn t be able to directly connect the drain to a grounded heatsink That direct connection makes for the most effective heatsinking Regulator Control Circuits and their Power Supply R26...

Page 52: ...or amplifier which changes the power supply from constant current to constant voltage operation From 37 volts to 60 volts the output would rise quickly were it not for the effect of C1 which continues...

Page 53: ...dB point of 2 Hz when driving an 8 Ohm speaker 4 Hz when driving a 4 Ohm speaker Relay Control Circuit K1 mutes the output of the amplifier during power up and power down That avoids any pops or clic...

Page 54: ...bers Color Number Black 0 Brown 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Gray 8 White 9 The color band positions have the following meaning Position Meaning 1 Left most Digit e g most signifi...

Page 55: ...e end Hold the blade perpendicular to the cable and draw it across the cable lightly as you rotate the cable along its long dimension This creates a scored line through the plastic jacket With a sharp...

Page 56: ...wire exposed It works best if you twist the insulation in the same direction as the drain strands are twisted If it s difficult to get it started then cut off a little bit of the end of the drain wire...

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