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Oakley Sound Systems

Power Supply Unit (PSU)

PCB Issue 4

Project Builder's Guide

V4.4

Tony Allgood
Oakley Sound Systems
CARLISLE
United Kingdom

Summary of Contents for PSU

Page 1: ...Oakley Sound Systems Power Supply Unit PSU PCB Issue 4 Project Builder s Guide V4 4 Tony Allgood Oakley Sound Systems CARLISLE United Kingdom 1...

Page 2: ...t worry in this manual I will try to make it clearer so that you make the right decision about what power source you will need It is designed to be mounted onto a metal panel which is used as a heatsi...

Page 3: ...direct connection to the mains or other high voltage sources further to what is provided in this document Please do not ask me for any additional information pertaining to direct mains connections or...

Page 4: ...you need it The voltage output of the power supply module is a split rail or bipolar 15V supply This means it generates both 15V and 15V That is two power rails one of a positive voltage the other a...

Page 5: ...han 125mA from either the 15V supply and 125mA from the 15V supply Various companies make linelumps with a greater capacity than 500mA If you can get a single phase 1A output one than this will be abl...

Page 6: ...t 15V and one at 15V Both output voltages can be finely adjusted with just one trimmer The 15V will automatically track the output voltage on the 15V The output voltages are available from two screw t...

Page 7: ...o AC outputs with a centre tap or mid point reference voltage So unlike the single phase AC adapter output with two leads this one has three This means you need to use the Oakley PSU in full wave rect...

Page 8: ...PSU with any other types of power pack please do let people know via the Oakley Sound forum at www muffwiggler com The input and switch wiring to suit a PA 20 power supply The power inlet is on the le...

Page 9: ...u need to use an insulating pad This allows the heat to travel through but not any electrical current These will be sold as TO 247 or TO 3P insulating pads You need one pad per transistor but it may b...

Page 10: ...going to be less than 250mA or so The raw AC is fed to a bridge rectifier based around D9 D10 D11 and D12 This is the classic bridge rectifier circuit Although it is drawn somewhat differently in the...

Page 11: ...you were to short out a 7815 to ground it would take around 1 7A from the supply and would heat up until the inbuilt thermal limiter kicked in 1 7A may well be high enough to damage any connected tran...

Page 12: ...puts But by the time the output of the PSU has been rectified and smoothed the DC current taken should not exceed 0 52A on a continuous basis Secondly the amount of current needed to drive the base of...

Page 13: ...but from the output of the 15V regulator This means that the negative output voltage will track the positive one but not vice versa I should add The op amp is wired as a simple inverting amplifier al...

Page 14: ...es On power down any excess current left in the modular will be shunted to the smoothing caps and not damage the now unpowered power supply components Also they also prevent the negative rail from goi...

Page 15: ...is shorthand for mega ohm For capacitors 1uF 1 000nF 1 000 000pF Sometimes the F is not included on the circuit diagram to indicate a capacitor s value ie 100n 100nF To prevent loss of the small as th...

Page 16: ...ts 7805 5V 1A regulator U1 LM723CN 100mA voltage regulator U2 OP177GPZ single precision op amp U3 Good quality DIL sockets are recommended You need one 14 pin and one 8 pin Discrete Semiconductors 1N4...

Page 17: ...2 Suitable power switch Suitable power inlet socket Keystone 8191 PCB terminal screw 0V fitted between OP1 OP2 4mm banana socket Optional fitted on panel 4mm ring terminals crimp solder For connection...

Page 18: ...m spacers 4 off M3 star washers 10 off M3 plain washers 6 off For PCB and power devices M3 hex nuts 2 off For power devices M4 16mm pan head screw 1 off For 0V Earth bond point M4 washer 2 off For 0V...

Page 19: ...spacers but don t fit the PCB in just yet Now you need to prepare the leads on the two TO 247 power transistors The three legs need to be bent upwards so that the PCB can be fitted over them Note tha...

Page 20: ...hey should not be touching the metal panel Place a star washer on a 6mm screw and a plain washer over that Place into one of the PCB s mounting holes and screw into the hex spacer but do not tighten D...

Page 21: ...together when switched on You can replace the switch with a simple wire link but I do recommend that a switch be fitted so the socket doesn t have to take the full surge current when you insert it wit...

Page 22: ...er and S1R and S1S together when switched on You can replace the switch with two wire links but I do recommend that a switch be fitted so the socket doesn t have to take the full surge current when yo...

Page 23: ...more complex system will have perhaps more than one modular more than one mixing desk and perhaps a heap of other outboard equipment This is when it makes sense to look at grounding your modular case...

Page 24: ...ed first to a bonding point which grounds the panel The bonding point then connects to a 4mm banana socket on the left Thus both the metal panel and the banana socket have a good connection to the PSU...

Page 25: ...s better performance and is simpler An M4 ring terminal crimped to 24 0 2 insulated wire This sort of connector is suitable for both the panel ground bonding point and attaching to the dedicated 0V sc...

Page 26: ...trical ground is mains earth and historically it was solely referred to as that but usage incorrect or not has meant a shift in the meaning Ideally we should call our common reference connection withi...

Page 27: ...er to have to experience It has been purely luck that has saved me in several of those cases So I will say again do not attempt to build a mains transformer into your modular case or any other project...

Page 28: ...can also be tolerated although you need to consider three things 1 You may need a physically larger transformer for the same output power 2 The power supply s components including the smoothing capaci...

Page 29: ...e useful to make a two bonding points on the panel One solely for the mains earth which can be located near the mains IEC inlet socket And another located next to the PSU for the PSU 0V and optional 4...

Page 30: ...Mains wiring diagram For experienced builders only 30...

Page 31: ...r In an Oakley modular one of the grounds pin 2 is solely used for the electronics in the module I call this module ground or module 0V it s the reference point for all the circuitry used in a module...

Page 32: ...d 0V screw terminal on the PSU board Now connect all the signal lugs marked as T on the body of the socket on the first four of the right hand column of sockets Then do the same on the left hand row Y...

Page 33: ...2A or 10A setting Now put your probes across the 15V and 0V terminals The meter should read approximately 630mA for current limit resistors of 1R or approximately 780mA for current limit resistors of...

Page 34: ...mment about this builder s guide or have a found a mistake in it then please do let me know But please do not contact me directly with questions about sourcing components or general fault finding Hone...

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