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Oakley Sound Systems

5U Oakley Modular Series

One of Three
Voltage Controlled Oscillator

PCB Issue 5

Builder’s Guide

V5.0.7

Tony Allgood

B.Eng PGCE

Oakley Sound Systems
CARLISLE
United Kingdom

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Summary of Contents for VCO 5U

Page 1: ...Oakley Sound Systems 5U Oakley Modular Series One of Three Voltage Controlled Oscillator PCB Issue 5 Builder s Guide V5 0 7 Tony Allgood B Eng PGCE Oakley Sound Systems CARLISLE United Kingdom 1 ...

Page 2: ...2 ...

Page 3: ...e unit the history of the various board issues and all the calibration procedures please visit the main project webpage at http www oakleysound com vco htm For general information regarding where to get parts and suggested part numbers please see our useful Parts Guide at the project webpage or http www oakleysound com parts pdf For general information on how to build our modules including circuit...

Page 4: ...itches and extra pots wired to the board by individual wires This module allows all the socket wiring to be done via the socket PCB and two MTA solderless or Molex connections If you are building this module in the standard Oakley format this new system will reduce assembly time and possible wiring errors Some people will wish to use this Oakley design in a non standard format such as fitting it t...

Page 5: ...r leaving the unit by the power supply lines A LM723 voltage regulator IC is used to provide the 10V This is an old IC design some 30 years but it is a superb device and has very low noise The only problem is that you have to set the output manually PSU is a trimmer to set the voltage to be exactly 10 00V The PCB has been laid out for a 6mm cermet trimmer for long term stability Additional power s...

Page 6: ...by the second transistor that controls the frequency of the VCO The op amp method also has another bonus it allows an additional current to be injected into the inverting pin of U3 This current will directly control the output current of the exponential convertor R15 allows an input CV to control this current We now have a linear frequency modulation input whose sensitivity is set by R15 Connectin...

Page 7: ...oise from accidental triggering of the VCO The buffered signal is then passed to a simple differentiator based around C9 back on page one again This part in conjunction with D1 and R24 only allow only fast moving rising edges of the input waveform to reset the VCO core In theory this should allow any pulse wave to be used as sync waveforms but the best sync sounds can be obtained when a falling sa...

Page 8: ...ed emitter resistor R17 can be used to effectively measure the emitter current since the voltage on its bottom end will fall as collector current rises Previously we took this voltage passed it through a diode to compensate for the base emitter voltage drop Vbe of the matched pair and then fed a small proportion of the resultant voltage back to the base of the left hand transistor This works well ...

Page 9: ...ection of this is the CV summer and is based around U9 pins 1 2 3 This circuit simply sums together the PWM pulse width modulation CV input and the voltage from the wiper of the Width pot The output of the CV summer will go from around 5V to 5V when being controlled by the Width pot alone The pulse wave generator itself is based around the second half of the comparator U7 pins 5 6 7 This compares ...

Page 10: ...ro This is because the offset added compensates for the altering amounts of time the waveform spends in the high or low states The summing circuit also inverts the waveform so once again we create the wrong phase A simple op amp inverter circuit U9 pins 9 10 11 turns the pulse wave the right way round again If you do not want this dynamically varying output signal then all you need to do is omit R...

Page 11: ...e that is a very good part However the actual theoretical value of compensation should be closer to around 3500ppm K when used in the circuit that I have chosen The Meggitt part thus falls slightly short of this and may cause the VCO to lose V oct tracking over the full keyboard range unless the ambient temperature is pretty stable It is therefore preferable to get something closer to the ideal va...

Page 12: ...00nF one thousand nanofarad To prevent loss of the small as the decimal point a convention of inserting the unit in its place is used eg 4R7 is a 4 7 ohm 4K7 is a 4700 ohm resistor 6n8 is a 6 8 nF capacitor Resistors All 5 carbon 1 4W or better Components designated as 1 should be 0 25W 1 metal film or better 22R R50 42 41 60 7 75 100R R11 390R R19 23 470R 1 R37 1K R55 62 24 56 39 67 1K 3500ppm K ...

Page 13: ...c C18 10uF 25V electrolytic C3 22uF 25V electrolytic C15 5 7 17 6 19 24 26 1 Discrete Semiconductors 1N4148 signal diode D2 BAT42 Schottky diode D1 BC550 NPN transistor Q1 2 4 5 J112 J FET Q3 Integrated Circuits LM1458 dual bi polar op amp U6 LM13700 transconductance amp U8 LM2903 dual comparator U7 LM723 voltage regulator U1 LT1013CP low drift dual op amp U2 U3 THAT300P matched NPN quad array U4 ...

Page 14: ...nd socket PCB 2 off 4 way 0 1 MTA Molex housing MAIN 2 cable 2 off 5 way 0 1 MTA Molex header POTS Pot PCB and socket PCB 2 off 5 way 0 1 MTA Molex housing NSE cable 2 off 6 way 0 1 MTA Molex header MAIN 1 Main PCB and socket PCB 2 off 6 way 0 1 MTA Molex housing MAIN 1 cable 2 off 55mm 8 way jumper lead LINK interconnect 1 off MTA156 4 way header PWR Oakley MOTM power supply MTA100 6 way header P...

Page 15: ...so that all the nut is in place on the bush of the switch Now use the inner nut to tighten the switch to the panel This way you won t scratch the front of the panel Use a 5 16 open ended spanner to do this but don t tighten it too much it s only a little switch It doesn t matter which way the switch goes in so long as the toggle moves up and down Note you do not have to use the tagged washer that ...

Page 16: ...sizers com The PWR2 power socket is to be fitted if you are using the module with a Synthesizers com system In this case you should not fit the PWR header The PWR2 header is a six way 0 1 MTA but with the pin that is in location 2 removed In this way location 3 is actually pin 2 on my schematic location 4 is actually pin 5 and so on Power Location number Schematic Pin number 15V 1 1 Missing Pin 2 ...

Page 17: ...and the pot board All the remaining interconnects will be made using either the MTA system or the slower but cheaper Molex system Make up the 4 way interconnect first This should be made from wires 100 mm long Make sure you get pin 1 going to pin 1 on the other housing pin 2 to pin 2 etc This cable will connect to the headers called MAIN 2 on each board The second lead is a 5 way interconnect This...

Page 18: ... can be found and fixed within one hour and I normally return modules within a week The minimum charge is 25GBP plus return postage costs If you have a comment 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 or Paul Darlow directly with questions about sourcing components or general fault finding Honestly we would love to help but ...

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