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K6 AUDIO POWER AMPLIFIER ASSEMBLY MANUAL
A and T Labs Inc P.O. Box 4884 Wheaton, IL 60187 Tel: 630-668-7870 Fax: 630-668-7870 Web: www.a-and-t-labs.com Technical Support: [email protected]
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A and T Labs
K6 Audio Power Amplifier
Assembly Manual
Table of Contents
Table of Contents .....................................................................................................................................i 1. INTRODUCTION .................................................................................................................................1 2. HOW IT WORKS - CIRCUIT OVERVIEW ...........................................................................................1 2.1 AMPLIFIERS..................................................................................................................................1 2.2 INVERTER POWER SUPPLY........................................................................................................4 3. CONSTRUCTION................................................................................................................................4 3.1 AMPLIFIER BOARDS ....................................................................................................................6 3.2 INVERTER POWER SUPPLY......................................................................................................10 3.3 HEAT SINKS AND MECHANICAL ASSEMBLY............................................................................12 3.4 POWER SUPPLY FLANGE MOUNTED COMPONENTS.............................................................13 4. TESTING...........................................................................................................................................13 4.1 INVERTER TESTING...................................................................................................................13 4.2 ALTERNATIVE INVERTER TESTING CHECKLIST (If an oscilloscope is available) ....................14 4.3 AMPLIFIER TESTING..................................................................................................................15 5. FINAL ASSEMBLY ............................................................................................................................16 6. OPERATING HINTS..........................................................................................................................17
© 2001 A and T Labs Inc.
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K6 Audio Power Amplifier
Assembly Manual
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1. INTRODUCTION
Congratulations! You are about to experience the satisfaction of building and owning one of the finest pieces of audio equipment around. Please read all of the instruction first, carefully, and then return to the beginning and start construction. We strive to provide complete information, but it is advisable to check the A and T Labs WEB site for any additional notes, changes, or hints that may be helpful. If you find errors or omissions or have suggestions for improving these instructions, please give us your feedback. We begin with an overview of how the design works.
2. HOW IT WORKS - CIRCUIT OVERVIEW
Figure 1 shows a block/connectivity diagram of the amplifier. The unit consists of a pair of linear discrete amplifiers and a full-bridge off-line switching power supply to power them. This design approach has several advantages over the conventional heavy line transformer and filter capacitor alternative. The typical transformer and rectifier/filter power supply needs to employ exceptionally large filter capacitors, since they are charged at the relatively low rate of the power line frequency. While some manufacturers of amplifiers tout this large energy storage as a virtue, it is not in fact a necessity for driving audio loads, and constitutes a destructive threat to the output transistors in the case of abusive loads or short circuits. The K6 switching power supply runs at 75 KHz, allowing the filter capacitors to be much smaller, providing much less stored energy to dissipate in case of a short circuit. At the same time, the supply is capable of providing over 1 KW of continuous power and 2 KW peak to drive the most demanding audio loads. The inverter may be switched between three different rail voltages, to permit operation at different power levels or for low impedance loads. 2.1 AMPLIFIERS The power amplifiers are full discrete designs as shown in Figure 2, (except for the bridging inverter and differential input adapter stage). IC2 provides differential input capability, while IC5 acts as an inverter to drive a second channel for bridging. The normal single ended input is via input blocking capacitor C1 and the R1-R3/C2 input low pass filter network. (This limits the bandwidth to about 160Khz) Complementary differential input stage transistors Q1-Q4 form the first gain stage. Q5 and Q6 along with R15 and R16 provide the next stage of gain, driving the complementary cascode inversion stage, Q10-Q13. Q24 develops the gate bias for the output FETs, and is mounted on the heat sink for thermal tracking. The inverter stage
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operates at unity gain, splitting the approximately 8 volts of bias generated by Q24 and applying it to the output transistor gates referenced to the power supply rails. Q24 is mounted on the heat sink to allow the bias to track the output stage temperature. Q14 and Q15 are emitter followers that drive the output transistors Q16-Q23. Finally, the drains of the output transistors are the amplifier output, via relay K1. The output signal also takes two feedback paths, the first via R36 to R31, 32, and 35, setting the output stage voltage gain at about 30x. The second feedback path, R37 to R14 and the input differential amplifier, set the overall amplifier gain at about 29x, with a closed loop bandwidth of about 350Khz. This completes the primary signal path from input to speakers. In addition to handling the audio signal, several other functions are performed on the amplifier board. The first is automatic servo-nulling of DC input offset voltages, ensuring no DC at the output of the amplifier. This is achieved by IC4, which senses any DC at the output, and injects a compensating current, through R38, into the feedback side of the input differential amplifier. Next, Q7-Q9 detect any clipping of the amplifier by sensing excessive internal drive signals, such as will occur when the feedback loop becomes non-linear under overload conditions. IC3, C19, and R57 capture any clipping occurrences and light LED1 for a minimum of 1 second. IC4a and b detect the presence of any DC offset (due to a fault) at the output of the amplifier, and will release relay K1, protecting the speaker. TC1 is a thermal protector, which can also drop out K1, in case of overheating of the amplifier. Finally, REG1 and REG2 are voltage regulators that keep the supply voltage for the input stages at +/- 30 Volts, while the output stage supply voltage may vary from +/- 41 volts to +/-82 volts, as determined by the switching power supply setting. D11 and D12 regulate the +/- 15 volts for the operational amplifiers IC3 and IC4.
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Bridging Output Direct Input
Bridging Amplifier
Left Channel
Clipping LED Output GND Protection DC/OT LED Output
Level GND
Power Amplifier
Differential Input
+
+15 V
Differential Input Amplifier
+
Fan Fan
GND
-
Protection OC LED ON LED
Switching Power Supply
+
GND
AC Input
+15 V
+
Bridging Output Direct Input GND Level Bridging Amplifier
GND
Clipping LED Output GND Protection DC/OT LED Output
Right Channel
Power Amplifier
Differential Input
+
-
Differential Input Amplifier
Figure 1 Block Diagram
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2.2 INVERTER POWER SUPPLY Figure 3 shows the power supply schematic. The inverter power supply is a basic offline full bridge design, with output current protection and shutdown capability, and three output voltage setting options. The power line input is filtered and rectified by L3, DB1, and C1/C2. With JMP1 in place, DB1, C1 and C2 form a voltage doubler. Q1-Q4 constitute the bridge, with Q1/Q2 and Q3/Q4 conducting alternately in pairs. They are driven via pulse transformer T2 from pulse width modulator/driver IC1. T4 is the main power transformer, driven by Q1-4, with its output rectified by fast recovery rectifiers D1-D4 and filtered by C17-C20. The positive output is divided by R26 and R27. R27 is in parallel with R32, R33, or nothing. The feedback signal is fed to inverting buffer amplifier IC3a, whose output is summed with a similar divider fed from the negative supply rail. IC3b is an inverting summer whose gain of .42 is set by R37/R36. Diodes D12 and D14 ensure that neither power rail supplies more than approximately half of the 11.9 volt summed input necessary to generate the +5 volt sum output. The result, at pin 7 of IC3 is fed back to the pulse width modulator comparator input pin 2 of IC1, where it is compared with the internal voltage reference applied to pin 1. The feedback path includes a compensation network consisting of IC2b, R25, C24, C25, and R39. Current in the bridge inverter is sensed by current transformer T3, whose output is rectified and filtered by D5-8 and C22. T3 puts out 2 volts for every amp of current. The result is compared to a fixed 2.5 volt reference by IC2a, and if excessive currents are detected, a shutdown signal is sent to IC1 pin 10, and LED1 lights. The shutdown condition is latched via the D11 feedback path, until C26 charges, at which point Q5 will reset the shutdown condition. To power the inverter control circuits, a small low voltage supply consisting of T1, rectifier DB2, and regulator REG1 generates + 12 volts. Power for the fans, when used, is generated by a separate winding on T4, rectified by D15 and regulated by REG2.
3. CONSTRUCTION
The amplifier was designed to minimize the need for point-to-point wiring by including many interconnect features on the printed circuit. Several features, such as bridging capability, are also optional. Variable board populations associated with these will be pointed out during construction. The options are summarized in the following table:
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Option Power supply input voltage Bridging
Differential input Amplifier operating voltage
Number of output transistors
Mechanical Assembly
Description/comments For operation in different countries This option allows the two channels to be operated as one amplifier, producing at least twice the power of a single channel. The option is enabled by populating the additional components on the boards. It may then be switched on or off. Equipped or unequipped Provides balanced (section 3.1) differential input capability +/- 41v, +/- 58v, +/-82v +/- 41v is intended for use (section 6) with very low impedance speakers to limit amplifier power dissipation. +/- 58v may be set to limit 8 ohm power output to about 130W/channel, or for typical operation with 4 ohm speakers. +/- 82v provides the maximum output power, 350W/channel into 8 ohms Nominally 8 per channel. Most applications operate Optionally may be with plenty of margin with 8 equipped with 10 per output transistors. For the channel most demanding and (section 4.3) severe environments, an additional two can be installed 5 ¼" high natural The natural convection convection case, configuration may be 3 ½" x 19" forced convection desirable for home case applications where the (section 5) noise of a fan is unacceptable. The 3 ½" unit with fans may be best suited for sound reenforcement or home theatre applications.
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Choices 110v or 240v (section 4.1) Equipped or unequipped (section 3.1)
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Before beginning, refer to and review the soldering techniques and suggestions and static electricity management information sheets. These are very important and must be followed to ensure the highest quality results. Following is a list of tools required to complete this project: · · · · · ·
·
Soldering iron Needle nose pliers Diagonal cutters Small Phillips and flat blade screw drivers Small Allen wrenches Digital voltmeter with milliamp range and ohmmeter capability (0ptional) Oscilloscope and signal generator
3.1 AMPLIFIER BOARDS If you are building a stereo unit, the steps in this section will need to be repeated. You may wish to build the two channels in parallel for efficiency of effort. Begin by installing all resistors, capacitors, and diodes in their appropriate places. (See parts placement Figure 4.) Check values of resistors as you proceed, and take care to orient diodes and electrolytic capacitors properly. Decide if you will want to include the bridging and differential input options. If so, parts required for bridging are marked with a * , parts for differential input are marked with ** , and parts for the extra output transistor option are marked with *** in the checklists. Resistor coding guide - Resistors are identified by color stripes and can be decoded as follows: Code:
First Digit Second Digit Third digit Number of zeroes Percent tolerance 0 Black 1 Brown 2 Red 3 Orange 4 Yellow 5 Green 6 Blue 7 Violet 8 Grey 9 White
Example: 46.5K, 1/4W, 1% - Yellow-Blue-Yellow-Red (space) Brown It's always a good idea to check the value of each resistor with an ohmmeter before installing!
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3.1.1 Resistors: Note: All 1% resistors have a brown last stripe
ü ü Part R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 R28 R29 R30 Value 46.4K 2.05K 2.05K 100 100 10K 10K 100 100 10K 10K 33.2 33.2 162 1K 1K 402 10K pot 5.11K 1K 1K 5.11K 1K 20K 330, 3W 100 330, 3W 100 1K 681 Identity Yel-blu-yel-red Red-blk-grn-brn Red-blk-grn-brn Brn-blk-blk-blk Brn-blk-blk-blk Brn-blk-blk-red Brn-blk-blk-red Brn-blk-blk-blk Brn-blk-blk-blk Brn-blk-blk-red Brn-blk-blk-red Or-or-red-gold Or-or-red-gold Brn-blu-red-blk Brn-blk-blk-brn Brn-blk-blk-brn Yel-blk-red-blk ~ 3/8" rectangle Grn-brn-brn-brn Brn-blk-blk-brn Brn-blk-blk-brn Grn-brn-brn-brn Brn-blk-blk-brn Red-blk-blk-red See Note 1 Brn-blk-blk-blk See note 1 Brn-blk-blk-blk Brn-blk-blk-brn Blu-grey-brn-brn ü ü Part R41** R42** R43 R44 R45 R46 R47 R48 R49 R50 R51 R52 R53 R54 R55 R56 R57 R58 R59 R60 R61 R62 R63 R64 R65 R66 R67 R68 R69 R70 Value 46.4K 402 10K Pot 825K 1K 5.11K 1K 5.11K 1K 1K 825K 1K 510, 1W 510, 1W 10K 1K 825K 15K 15K 2.05K 200 200 200 200 200 200 200 200 1.21K 27.4K Identity Yel-blu-yel-red Yel-blk-red-blk Mount later! Grey-red-grn-or Brn-blk-blk-brn Grn-brn-brn-brn Brn-blk-blk-brn Grn-brn-brn-brn Brn-blk-blk-brn Brn-blk-blk-brn Grey-red-grn-or Brn-blk-blk-brn Grn-brn-blk Grn-brn-blk Brn-blk-blk-red Brn-blk-blk-brn Grey-red-grn-or Brn-grn-blk-red Brn-grn-blk-red Red-blk-grn-brn Red-blk-blk-blk Red-blk-blk-blk Red-blk-blk-blk Red-blk-blk-blk Red-blk-blk-blk Red-blk-blk-blk Red-blk-blk-blk Red-blk-blk-blk Brn-red-brn-brn Red-viol-yel-red AMK6a
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R31 R32 R33 R34 R35 R36 R37 R38 R39 R40
681 1K 2K, 5W 2K, 5W 50 1.5K, 2W 5.1K, 1/2W 10K 825K 825K
Blu-grey-brn-brn Brn-blk-blk-brn See note 1 See note 1 Grn-blk-blk-gold
R71 R72 R73 * R74 * R75** R76**
1.21K 27.4K 46.4K 46.4K 46.4K 46.4K 46.4K 5.11K 200 200
Brn-blk-brn-brn Red-viol-yel-red Yel-blu-yel-red Yel-blu-yel-red Yel-blu-yel-red Yel-blu-yel-red Yel-blu-yel-red Grn-brn-brn-brn Red-blk-blk-blk Red-blk-blk-blk
Grn-brn-brn-brn Brn-blk-blk-red Grey-red-grn-or Grey-red-grn-or
R77** R78 * R79 *** R80 ***
Note 1: Mount R25, 27, 33, and 34 ¼" off the board for better airflow/heat dissipation. * Parts required for bridging option ** Parts required for differential input *** Parts required for extra output transistor option
3.1.2 Capacitors:
ü ü Part Value C1 C2 C3 C4 C5 C6 C7 C8 10uf 50V 150pf 100uf 50v 100uf 50v .1uf, 100v 150pf 82pf .22uf ü ü Part C9 C10 C11 C12 C13 C14 C15 C16 Value .22uf 10uf 35v 10uf 35v .1uf 100v 100uf 100v .1uf 100v 100uf 100v 10uf 35v ü ü Part C17 C18 C19 Value 10uf 35v 1500pf 1uf 35v
C20* 82pf C21* .01UF C22* .01UF C23** 82pf C24** 82pf
* Parts required for bridging option ** Parts required for differential input
3.1.3 Diodes:
ü ü Part D1 D2 D3 D4 D5 Type 1N4148 1N4148 1N4728A 1N4728A 1N4742A ü ü Part D6 D7 D8 D9 D10 Type 1N4742A 1N4744A 1N4744A 1N4740A 1N4742A ü ü Part D11 D12 D13 D14 D15 Type 1N4742A 1N4002 1N4002 1N4002 1N4742A
Next, install small signal transistors and ICs. Adjust R18 to its approximate middle position. Note: Q24 will be installed later, in section 4.3.
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3.1.4 Transistors and ICs
ü ü Part Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Type MPSA06 MPSA06 MPSA56 MPSA56 MPSA56 MPSA06 MPSA56 MPSA06 ü ü Part Q9 Q10 Q11 Q12 Q13 Q14 Q15 Q25 Type MPSA06 MPSA06 MPSA06 MPSA56 MPSA56 MPSA06 MPSA56 VN0610LL ü ü Part IC1 IC2 IC3 IC4 IC5 * Type LM334Z LM334Z LM339AN LF411CN LF357N
IC6 ** LF357N IC7 LM358
* Parts required for bridging option ** Parts required for differential input
Install the fuse clips and terminal blocks. The amplifier boards are designed to mount the input jacks, level set potentiometer, and indicator LEDs on either end of the board, depending on the unit physical configuration. See section 5 and figures 6,7,9, and 10, and determine your planned configuration. Then mount these components accordingly, as follows: 1) Depending on which channel you are building, install the RCA input jack and the level set potentiometer R43 at the appropriate end of the board (back for 3 ½" unit, right end, with the power components at the back of the board, for the 5 ¼" unit). 2) The clipping and protection indicator LEDs go on the opposite end from the input jacks of the board (front for the 3 ½" unit), or on the end of wires to be remoted (about 8") on the front panel for the 5 ¼" unit. If you have populated the bridging option, the board with R73,74 C20,21,22, and IC5 will be the "input" board for the drive signal), with the switch SW1 and LED 3 on the other. The cathodes of all the LEDs (the direction the arrow in the symbol points) is the longer lead. For differential input capability, include the 1/4" jacks on the appropriate ends of the boards, along with the twisted pair shielded cable from the jack to the center of the board. If you do not need differential input, omit coax #2, the twisted pair, IC6 and the components associated with it (R41,42,75,76,77, C23-24). Last, install coax #1 and the relay K1. The temperature sensor, regulators, and thermal sensing FET will be left off until heat sink installation, and the output transistors (Q1623) will be mounted after preliminary testing is completed. 3.1.5 Miscellaneous parts
ü ü Part Fuse clips (4) Term. Blocks (5) © 2001 A and T Labs Inc. ü ü Part LED1 LED2 ü ü Part Twisted pair ** Coax #1 AMK6a
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RCA input jack R43 Level set ¼" input jacks (If used) ** * Parts required for bridging option ** Parts required for differential input
SW1 * LED3 * Coax #2 **
K1 relay Fuse, 6A
3.2 INVERTER POWER SUPPLY Much like the amplifiers, begin by installing resistors, capacitors, and diodes, carefully checking values and orientations. (See parts placement Figure 5.) 3.2.1 Resistors:
ü
Part R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22
Value 316 7.50K 10K
Identity Or-brn-blu-blk Viol-grn-blk-brn Brn-blk-blk-red
ü
Part R23 R24 R25 R26 R27 R28 R29 R30 R31 R32 R33 R34 R35 R36 R37 R38 R39 R40 R41 R42 R43
Value 1K 100K 6.98K 100K 16.9K 36.5K 15K 100K 16.9K 36.5K 15K 100K 100K 100K 46.4K 100K 4.99K 316 1K, .5W 1K 22K 10W
Identity Brn-blk-blk-brn Brn-blk-blk-yel Blu-wht-grey-brn Brn-blk-blk-yel Brn-blu-wht-red Or-blu-grn-red Brn-grn-blk-red Brn-blk-blk-or Brn-blu-wht-red Or-blu-grn-red Brn-grn-blk-red Brn-blk-blk-or Brn-blk-blk-or Brn-blk-blk-or Yel-blu-yel-red Brn-blk-blk-or Yel-wht-wht-brn Or-brn-blu-blk Brn-blk-blk-brn Brn-blk-blk-brn
4.7, 1/2W Yel-viol-gold-gold 75 75 75 75 75 75 75 75 50, 25W Viol-grn-blk-gold Viol-grn-blk-gold Viol-grn-blk-gold Viol-grn-blk-gold Viol-grn-blk-gold Viol-grn-blk-gold Viol-grn-blk-gold Viol-grn-blk-gold See note below Not used Not used 200, .5W 3.48K 1K 2.05K 10K 10K 1K Red-blk-blk-blk Or-yel-grey-brn Brn-blk-blk-brn Red-blk-grn-brn Brn-blk-blk-red Brn-blk-blk-red Brn-blk-blk-brn
Note: R13 is mounted with a pair of short segments of wire soldered to the resistor tabs. © 2001 A and T Labs Inc. AMK6a
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3.2.2 Capacitors:
ü Part Value C1 C2 C3 C4 C5 C6 C7 C8 C9 2200uf 200V 2200uf 200V 1000uf 50V 1000uf 50v .001uf 10uf 50V 100pf .01uf 10uf 50V ü Part Value C10 4700pf C11 4700pf C12 4700pf C13 4700pf C14 560pf 500V C15 Not used C16 Not used C17 470UF 100V C18 470UF 100V ü Part C19 C20 C21 C22 C23 C24 C25 C26 Value 470UF 100V 470UF 100V .01UF .22uf .01UF 3300PF .22UF 1000uf 25v
3.2.3 Diodes, ICs, Q5, and REG1: (Power rectifier diodes, power transistors and REG2 are installed later after heat sink installation)
ü Part D5 D6 D7 D8 D9 Type 1N4002 1N4002 1N4002 1N4002 1N4742A ü Part D10 D11 D12 D13 D14 Type 1N4735A 1N4002 1N4735A 1N4742A 1N4735A ü Part IC1 IC2 IC3 Q5 REG1 Type SG3525 LM358 LM358 VN0610LL 7812
Install the transformers and current transformer, inductors, ZNR1, TR1, LEDs, bridge rectifiers, and the fuse holders. The current transformer T3 is installed with two turns of insulated 16 gage wire wound through the hole in the transformer and soldered into the large holes adjacent to T3. Also wire the voltage select switch at this time. This is the time for determining your power supply jumper configuration: For 120v operation, equip jumpers 1, 2, and 3. For 240 v operation, use jumper 4 only. 3.2.4 Transformers and miscellaneous parts
ü Part T1 T2 T3 T4 ü Part Fuse clips (6) Term. Blocks(10) Voltage select Switch Wire for T3 ü Part L1 L2 L3 ZNR1 F1 Jumpers 1-4 © 2001 A and T Labs Inc. BR1 Description 350uH 350uH 1.8UH x 2 ERZ-V20D431 15 amp fuse Bridge rectifier ü Part TR1 Description KC022L-ND
LED1 Red LED2 Green F2 F3 DB2 .25 amp fuse 8 amp fuse Bridge rectifier AMK6a
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3.3 HEAT SINKS AND MECHANICAL ASSEMBLY Both the amplifiers and the inverter are designed to edge mount their power components on the board, with their attachment to the heat sinks via a linear flange or flat mounting scheme. Figures 6 and 7 show the two basic enclosure designs for the 5 ¼" natural convection and 3 ½" fan cooled units, along with their heat sink flange arrangements. The 3 ½" unit has fans and is the preferred configuration for sound re-enforcement and other heavy duty applications. The 5 ¼" high design is intended for home installations in which the fan noise may be objectionable, and uses natural convection cooling. For this, more heat sink area and vertical fin orientation is necessary, and the unit height is increased to 5 1/4", with the heat sinks across the back. The amplifiers are mounted one above the other, with the power supply at the bottom. For this physical design, it will also be necessary to run wires to the front panel mounted LEDs. The flanges for both amplifiers and the power supply will be prepared at this time and the power components mounted for the power supply. Use the circuit boards or artwork as drilling templates to locate the transistor mounting holes. The flanges also need to be match-drilled with the heat sinks per the drawings. The lateral positioning of the flanges on the boards for the 5 ¼" unit is approximately centered. The mounting of the flanges to the heat sinks can be accomplished with three holes per flanged, drilled to avoid conflict between parts on the board and the screw driver or Allen wrench that will eventually mount the assembly to the heat sink. Drill holes through the flanges such that they are close to vertically centered on the flange, and fall midway between heat sink fins. The easiest approach is to drill and tap the holes in the heat sink. Alternatively, with careful spacing, nuts may be used. Lateral positioning of the amplifier assemblies is such that the input RCA jacks sit just inside the holes on the right side of the enclosure. For the 3 ½" unit, the lateral positioning of the amplifier flanges is centered on the board. Lateral mounting of the assembly on the heat sink is chosen to align the front edge of the board with the front of the heat sink, such that the board mounted LEDs can protrude through their respective front panel holes. Vertical positioning of the holes should be such that the holes fall midway between heat sink fins. Be sure to remove all burs from holes, as they may cut through transistor mounting insulators and cause short circuits, or cause the flanges not to lie perfectly flat against the heat sinks. At this time, prepare the mechanical assembly of heat sink components, drilling the flanges and heat sinks. Mechanical Assembly Prepare mechanical assembly
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3.4 POWER SUPPLY FLANGE MOUNTED COMPONENTS Power supply heat sink mounted components may be mounted at this time. The power transistors and rectifiers mount at the edge of the board, so you will need to align these with your heat sink drilling before soldering to ensure proper alignment. Mount all power components with insulators coated with a liberal layer of heat sink conductive white silicone grease. Tighten well, but do not over tighten ensure insulators do not deform under pressure. Using an ohm meter, ensure that there are no shorts between transistor cases and the heat sink. Solder the components to the board. This should complete the power supply assembly, including the angle flange. 3.4.1 Power Supply Power Components
ü Part Description D1 FR805 D2 D3 FR805 FR805 ü Part D4 Q1 Q2 Description FR805 IRFP450 IRFP450 ü Part Q3 Q4 Description IRFP450 IRFP450
REG2 7812
4. TESTING
4.1 INVERTER TESTING (Without oscilloscope) Begin by once again looking over the inverter board for completeness and correctness of parts values and orientation. Also re-check the quality of all solder connections. Next, install F1 and F2, but leave out F3. Make sure jumpers Jmp1, 2, 3, and 4 are installed properly for the supply voltage of intended use (see section 3.2). Apply input power from a power cord, temporarily connected to the AC input terminals, labeled "N" and "LIVE". From here on, remember to exercise extreme caution in handling and measuring, since the input portions of the inverter are directly connected to the power line. Also note the rectified line filter capacitors will store a substantial charge for some time after the unit is turned off and pose a serious electrocution or damage threat. It is a good idea to discharge them with a low value resistor before handling the supply. Measure at the input to F3 with respect to the ground side of C2 and verify the presence of 320 volts. Also, measure the output of REG1 with respect to board ground, and check for +12 volts (+/- .5v). Double check the orientation of T2. Turn off input power and install F3. For the next test it is advisable to load the output of the inverter lightly, say with a 5K, 10 Watt resistor per rail. Set switch SW2 to the 41 volt position, and apply power. Check for +/- 41 (+/- 2) volts at the inverter output. Switch SW2 to +/- 58 volts and +/82 volts (+/- 2), and check for each voltage at the output.
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K6 Audio Power Amplifier
Assembly Manual
Temporarily connect the shutdown input pin to +12 volts and verify that the output voltages are turned off. 4.2 ALTERNATIVE INVERTER TESTING CHECKLIST (If an oscilloscope is available) After installing all components, except fuses, check component values and orientations again carefully Install fuse F2 only and check for the presence of +/- 12 (+/- .5) volts at the output of regulator IC3 (Reg1) and D13 respectively If an oscilloscope is available, a very useful test that is highly predictive of operational success of the power supply is possible: (Very Important !!: Be sure your scope is operating ungrounded with respect to the AC power line for these tests!) Check the gate drive waveforms at the power transistors (from gate to source) with fuse F2 installed and fuses F1 and F3 left out. This applies +/- 12 volt control voltage without applying rectified line voltage to the power transistors. What you should see is approximately 75Khz, somewhat rounded square waves, with the signals at Q1 and Q2 in phase, and those at Q3 and Q4 in phase, and both pairs 180 degrees out of phase with each other. If the appropriate signals are not found, backtrack to IC1, verifying the square wave output and proper installation of T2. Next, install F1 and verify the presence of 320 (+/- 5%) volts at the input to fuse F3. Install fuse F3 and check for proper output voltage (as set by the S2 switch setting) at the output terminals. This may be a little bit high if no load is applied. Apply a resistive load to the output, (for example 5K, 5 Watt) and check that the voltage stays at the value expected for the particular S2 switch setting. Calculate the load according to V=IR or P=(V*V)/R, and choose loads that are within the power range of the supply, and that can dissipate the power without burning up! That should do it! If you get to this point successfully, then your power supply should have no trouble running the amplifiers! If you have trouble with these last tests, for example if the shutdown LED operates (which will typically be in the form of a pulsating cycle with the LED operating, and
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K6 Audio Power Amplifier
Assembly Manual
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noticeable heavy AC power line load, as evidenced by flickering lights), check for short circuits in the output portions of the power supply. This could include, for example, output capacitors shorted or installed backwards, or rectifiers shorted to the heat sink. 4.3 AMPLIFIER TESTING The amplifiers will first be tested without the output transistors installed. Begin again by carefully checking that all components are present, the correct value or type, and properly oriented. A little bit of patience and scrupulous inspection at this point can go a long way in avoiding smoke, loss of expensive parts, and endless troubleshooting and heartache later! At this time, install the heat sink adapter L-bracket, drilled and prepared previously, with the temperature sensor TC1, (Our kits come with one over temp. cutout per channel. Mount it on the forward end of the board where the LEDs are, opposite the input jacks. See figures 9 and 10). Install temperature sense FET Q24, and regulators REG1 and REG2. Use transistor insulators, heat sink grease, and do not over tighten.
4.3.1 Amplifier Miscellaneous Power Parts
ü ü Part Description ü ü Part TC1 Q24 Description 67F080 IRF510 REG1 LM317T REG2 LM337T
Install 1/2 amp fuses for F1 and F2, and temporarily connect the power supply to an amplifier board, making sure all power polarities are correct. These tests can be accomplished by carefully laying the modules out on the bench. Be sure they are all on insulating surfaces! For these tests you may wish to use the current limiting capabilities of the power supply for extra protection. This can be achieved by placing a jumper on the power supply board between the junction of R17 and R18, and the junction of D5 and D9. Apply power and check for the +/- 15 volt supplies on the board and the +/- 30 volts at the input stages. Do all probing very carefully, as a slip with a probe can easily result in a damaging short circuit! Very carefully measure the voltages across D7 and D8. They should each be in the range of 3 to 5 volts. Adjust R18 until they are each less than or equal to 3.5 volts. If you have a signal generator and oscilloscope, an additional valuable test is to apply a very low level signal, say 5-10 millivolts at 1Khz, and check for drive signals at the emitters of Q14 and Q15. Since the amplifier is open loop at this point, the drive signals will easily overload, and look like square waves, about 12 volts p-p or less, as limited by D7 and D8.
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K6 Audio Power Amplifier
Assembly Manual
If all is well, you may now mount and solder the output transistors. They must be matched, and a circuit for matching them is shown in figure 8. (Transistors supplied in our kits are matched) Mount the transistors on the heat sink angle bracket with mica washers and liberal silicon grease, and check for absence of shorts between transistors and the heat sink, then solder to the amp board. For home use and 8 ohm operation, four output transistors per rail is sufficient. However, if you plan to operate in bridging mode, or at high power with low impedance loads, include the additional transistor per rail, for a total of five per rail. 4.3.2 Amplifier Power Transistors
ü ü Part Description Q16 IRFP9240 Q17 IRFP9240 Q18 IRFP9240 Q19 IRFP9240 ü ü Part Q20 Q21 Q22 Q23 Description IRFP240 IRFP240 IRFP240 IRFP240
Set the power supply in the +/-58 volt mode. Apply power with a 1 amp fuse installed for F1, and a milliameter in place of F2. Adjust R18 for an idle current of about 240 mA. (The bias must be re-set for long term operation at different voltages) Remove the ammeter and install a 1 amp fuse for F2. Check that the output is within a few millivolts of ground. Apply an input signal at a low level, and verify that an amplified output appears. ü ü Description Idle current set ü ü Description Check output DC offset ü ü Description Signal check
If all is well, replace F1 and F2 with 6 amp fuses, and perform similar tests on the second channel. If you used it, remove the current limiting jumper on the power supply board.
5. FINAL ASSEMBLY
Figure 9 shows details of chassis preparation for the packaging shown in Figure 6 for the 5 ¼" unit. Figure 10 shows details of chassis preparation for the packaging shown in Figure 7 for the 3 ½" unit. Following construction of the basic chassis, it's time to mount switches, connectors, and LEDs, and to install wiring. If you are fabricating your own case, you will need to drill holes for LEDs, inputs, outputs, power cord, etc. in the appropriate places. For the 3 ½" unit this includes proper alignment between the front panel LED holes and the LEDs, as mounted on the amplifier boards.
© 2001 A and T Labs Inc.
AMK6a
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K6 Audio Power Amplifier
Assembly Manual
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Following is a checklist for the chassis mounted components: 5.1 Chassis Mounted Components
ü Description 4 output terminals IEC power input connector Power switch ü Description Mount panel LEDs (power supply and 5 ¼" amp clip and overload) Fans (3 ½" unit)
Once all boards have been tested, install them along with their heat sinks in the chassis. Use heat sink grease between the L-bracket and the heat sink. The power supply is installed first in both the 3 ½" and 5 ¼" units. Wiring will need to be installed on the power supply before the amplifier boards are installed. Measure, cut, and strip wires to appropriate lengths to reach the corresponding amplifier terminals. Following is a checklist for inter module and other unit wiring: 5.2 Wiring
ü ü Description IEC AC power connector to power switch Power switch to power supply Fans to 12V power on power supply Power supply voltage select switch (switch installation) 12 volt relay power to each amp +Vcc to each amp -Vcc to each amp ü ü Description Ground to each amp Output from binding post to each amp Output ground from binding post to each amp Power supply power and shutdown LEDs/wires Amp clip and overload LEDs/wires (5 ¼" unit) Bridging coax from input channel to other channel (If used)
Carefully re-check work and perform final testing: Install fuses in power supply and one amplifier. Apply power and check that no DC appears at the amplifier output terminals. Apply a signal and load and check for proper amplifier operation. Test the other channel the same way.
6. OPERATING HINTS
The only special operating instruction pertains to the use of the inverter voltage select switch. In general, lower voltages can be used for two purpose: First, to limit the power available to sensitive loads. Some audiophiles, for example like to limit the available power to near 100 watts into an 8 ohm load. For that kind of operation, choose the 58 volt setting. Second, when driving low impedance speakers, such as 1-4 ohms, the power dissipation in the amplifier may be limited by setting the voltage to 41 volts. In
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K6 Audio Power Amplifier
Assembly Manual
any case, the current detection built into the power supply will protect the amplifier sections, resulting in momentary shutdowns and an LED indication. The supply will reset itself when the overload is removed. Finally, for maximum performance and power output into 8 ohm loads, use the 82 volt power supply setting (Remember that the bias current must be re-set for each voltage for long term operation. See section 4.3) Finally, remember the power levels this amplifier is capable of, and be careful with both your speakers and your ears. Happy listening!
© 2001 A and T Labs Inc.
AMK6a