Builder`s Guide - Oakley Sound Systems
Contents
1. amp The speed at which the voltage falls is controlled by C8 and the size of the voltage applied to R8 If the applied voltage is negative the op amp s output will rise It is the integrator s output that will be used as the source for the triangle wave output Another quarter of the TL074 op amp pins 9 10 8 is used as a Schmitt trigger It s output is either high at 13V or low at 13V If the output of the Schmitt is initially low it requires 6V at the output of the integrator to make it go high The integrator will need to produce an output of 6V to make the Schmitt go low again To make any oscillator you normally require an output to be fed back into the input Its positive feedback again In a standard LFO like this one the integrator is fed by the output of the schmitt trigger Thus a low at the output of the schmitt causes the integrator to rise When the integrator s output reaches a certain point the schmitt switches state and the integrator s output falls The schmitt trigger changes state once again and the process repeats itself The LFO_RATE pot allows only a controlled proportional of the Schmitt s output voltage to reach the integrator If the proportion is large the voltage on R8 is large and the integrator sweeps fast If the proportion is small the integrator sweeps slowly R6 sets the minimum speed You can change the value of C8 to get different range of sweep speeds Setting C8 at 470nF we can go t2. have a small input signal The input level is expected to be the typical modular signal of 5V peak or 10V peak to peak With the emphasis turned up high it is possible to create large resonant peaks at some frequencies If the through path gain of the Equinoxe was left at 0dB then these peaks would exceed the maximum allowed output level and cause distortion If you are not going to use a SV peak input ie you are connecting your module to a line level input then you can increase the gain of the final stage based around U2a and decrease the padding on the input Lowering R31 will increase the gain of the final stage and increasing R11 will decrease the attenuation on the input pad The OTAs are all controlled from one current source This is clever current source though Based around Q7 and Q10 it is actually a simple exponential convertor In other words a steady increase in base voltage produces a exponential rise in collector current For every 18mV increase in Q7 s base voltage we double the current sourced by Q10 The current source is driven from a simple one op amp inverting summer Its inputs derived from either the FREQUENCY pot the TUNE trimmer and the external CV input The LFO circuit is quite simple and is based around half of one quad op amp U1 One quarter of the TLO74 op amp U1b pins 5 6 7 forms part of the integrator Any positive voltage applied to the right of R8 will cause the voltage to fall at the output of the op
3. of support is the Oakley Sound Forum at Muffwiggler com Paul Darlow and I are on this group as well as many other users and builders of Oakley modules If you can t get your project to work then Oakley Sound Systems are able to offer a get you working service If you wish to take up this service please e mail me Tony Allgood at my contact e mail address found on the website I can service either fully populated PCBs or whole modules You will be charged for all postage costs any parts used and my time at 25GBP per hour Most faults 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 we do not have the time to help everyone individually by e mail Last but not least can I say a big thank you to all of you who helped and inspired me Thanks especially to all those nice people on the Synth diy Oakley Synths and Analogue Heaven mailing lists and those at Muffwiggler com Tony Allgood at Oakley Sound Cumbria UK December 2010 No part of this document may be copied by whatever means without my permission 17
4. schematic location 4 is actually pin 5 and so on Power Location number Schematic Pin number 15V Missing Pin 5V Module GND 15V Not connected 1 NnB WN nA BR WN 5V is not used on this module so location 3 pin 2 is not actually connected to anything on the PCB If fitting the PWR header you will also need to link out pins 2 and 3 of PSU This connects the panel ground with the module ground Simply solder a solid wire hoop made from a resistor lead clipping to join the middle two pads of PSU together 12 Building the Equinoxe module using the Sock4 board This is the simplest way of connecting all the sockets to the main board The Sock4 board should be populated in the way described in our construction guide found on the project webpage There is only one eight way header and it is to be fitted to the bottom side of the board Do not forget to solder in the wire link L2 Link L1 is left open You need to make up only one eight way interconnect It should be made so that it is 100mm long j 819 Eyt 2182 The prototype unit showing the detail of the board to board interconnect Here I have used the Molex KK 0 1 system to connect the Sock4 to the main PCB 13 Hand wiring the sockets If you have bought Switchcraft 112A sockets you will see that they have three connections One is the earth or ground tag One is the signal tag which will be connected to the tip of the jack plug when it is inser
5. 6 56K R40 R13 82K R62 100K R44 R63 R47 R48 R55 R8 R5 R37 R26 R21 270K R65 330K R46 470K R45 R12 R20 Capacitors InF 5mm polyester film 6n8 5mm polypropylene film 100nF 5mm polyester film 470nF 5mm polyester film 2u2 63V electrolytic 22uF 35V electrolytic Discrete Semiconductors BC550 NPN small signal transistor BCS560 PNP small signal transistor Integrated Circuits LM13700 dual OTA TLO72 dual op amp TL074 quad op amp C5 C21 C22 C15 C14 C2 C19 C12 C4 C20 C11 C8 C3 C10 C17 C18 C7 C1 C6 C13 C16 C9 Q1 Q2 Q3 Q5 Q6 Q7 Q8 Q9 Q11 Q12 Q4 Q10 U3 U4 U2 U1 IC sockets are recommended You need two 16 pin one 8 pin and one 14 pin DIL sockets Potentiometers Pots All pots Alpha 16mm PCB mounted types 10K linear 47K linear 100K log Three 16mm pot brackets Trimmer 470K horizontal Miscellaneous Leaded axial ferrite beads MTA156 4 way header MTA100 6 way header Molex MTA 0 1 header 8 way EMPHASIS FREQUENCY MOD DEPTH LFO RATE TUNE L1 L2 PSU Oakley MOTM power supply PWR Synthesizers com power supply I O for connecting to sockets 10 Molex MTA 0 1 housing 8 way I O for connecting to sockets 3 way 0 1 header INV 0 1 jumper For fitting to INV Molex MTA 0 1 housing 2 way LED optional connecting technique for the LED 5mm clear LED lens LED 5mm LED lens securing ring LED if lens is not self securing
6. Oakley Sound Systems SU Oakley Modular Series Equinoxe Voltage Controlled Phaser PCB Issue 5 Builder s Guide V5 0 02 Tony Allgood B Eng PGCE Oakley Sound Systems CARLISLE United Kingdom FREQUENCY EMPHASIS MODULATION DEPTH LFO RATE AUDIO IN AUDIO OUT CV IN LFO OUT OAKLEY amp EQUINOXE ts The 1U wide panel design for the standard Equinoxe for MOTM format systems The fpd file for this panel can be found on the project webpage Introduction This is the Project Builder s Guide for the issue 5 Equinoxe 5U module from Oakley Sound This document contains a basic introduction to the board a description of the schematic a full parts list for the components needed to populate the boards and a list of the various interconnections For the User Manual which contains an overview of the operation of the unit the history of the various board issues and the calibration procedures please visit the main project webpage at http www oakleysound com equinox 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 board population mounting front panel components and making up board interconnects please see our generic Construction Guide at the project webpage or http www oakleysound com construc
7. Switchcraft 112APC 1 4 sockets Four off mounted either on the Sock4 board or on panel Four knobs Around 2m of insulated multistrand hook up wire Components required if using optional Sock4 board Molex MTA 0 1 header 8 way I O Molex MTA 0 1 housing 8 way I O 112APC Switchcraft 1 4 socket SK1 SK2 SK3 SK4 A single wire link is to be fitted to L2 on the Sock4 PCB L1 is left open If using Molex KK you ll also need at least 16 crimp terminals Suitable lengths of wire to make up the single 100mm interconnect and two cable ties 11 Connections Power connections MOTM and Oakley The PSU power socket is 0 156 Molex MTA 4 way header Friction lock types are recommended This system is compatible with MOTM systems Power Pin number 15V 1 Module GND 2 Earth PAN 3 15V 4 Pin 1 on the I O header has been provided to allow the ground tags of the jack sockets to be connected to the powers supply ground without using the module s OV supply Earth loops cannot occur through patch leads this way although screening is maintained Of course this can only work if all your modules follow this principle Power connections Synthesizers com The PWR 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 PSU header The PWR 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
8. aser will create one notch By cascading more stages we can create more notches Four stages like we have in the standard Equinoxe means we have two notches By using an OTA will can vary the frequency of these two notches All the OTAs work together hopefully producing the same phase response Like the swing example no two OTAs will behave identically and there are other things to complicate our simple analysis but that s the wonder of analogue electronics for you Each OTA network is followed by a simple Darlington follower This two transistor circuit behaves as buffer The voltage at the emitter of the second transistor follows the voltage on the base of the first The nice thing is that no current is stolen by the base and the OTA can go about its business with no fear from the outside world pinching its output As we have heard the all pass filters are cascaded together to form a short chain The input signal enters the chain through C11 and leaves it via the SEND pad which is pin 1 on the DEEP header In normal operation the SEND and RETURN pads on the DEEP header are simply linked together R14 and R15 then provide the necessary mixing effect at their junction for the notches to be created U2a pins 1 2 3 acts as a buffer circuit and also amplifies the mixed signal via C10 and R20 up to the high levels associated with modulars If the Deep Equinoxe daughter board is fitted the signal leaves the main board at SEND and re enters t
9. he board at the RETURN The Deep Equinoxe board contains four more stages of OTA based all pass filtering along with some buffers and CV control circuitry The main input signal enters the Equinoxe by means of a resistative attenuator also called a pad This reduces the input level so as not to cause distortion in the input stage and the rest of the circuit R13 and R11 set the gain of the pad QI and Q4 form a discrete input circuit which buffers the padded input signal It also provides the means for some additional mixing from the EMPHASIS pot The emphasis pot provides a resonant type effect to be heard by creating a positive feedback path within the phaser So not only do we get the notches we also now get peaks in the response when the output signal reinforces the input signal The more positive feedback the more peaky the response Too much positive feedback and the system gets carried away and oscillates wildly Getting this right is too complex for me to analyse by mathematics alone so I just let my ears do the talking eh I played around with various feedback paths and listened to the sound created In the end I went for the network of resistors and capacitors you see here A simple solution in the end and very effective It should be noted that the overall gain of the Equinoxe is less than unity or OdB in fact its closer to 6dB This is deliberate although you may find it less than convenient in some situations where you
10. he eight sockets and reduces the chances of mistakes Provision is made for the optional fitting of the forthcoming Deep Equinoxe daughter board This will add a further four all pass filter sections for a choice of 4 6 and 8 stage phasing If you are not fitting this board you simply link pins 1 and 2 on the DEEP header Circuit Description For an excellent starter into phasers and their workings you really should visit R G Keen s excellent site at www geofex com Article_Folders phasers phase html The Oakley Equinoxe phaser is based around phase shift network built from operational transconductance amplifiers or OTAs This type of shifter is not that common compared to the more numerous designs based on FETs and light sensitive devices Other units that use the OTA are the Moog 12 stage phase shifter and the Electro Harmonix Smallstone It is the latter that Jean Michel Jarre used on the Equinoxe album and the reason behind the Oakley device s name Jarre had his unit modified by Michel Geiss and the exact modifications are not known and have become subject to much speculation I wanted to create a phaser that was similar in tone to that used on the Jarre albums but with more compatibility to modern modular synthesisers The Equinoxe uses just four all pass stages to achieve its sound Each all pass stage is identical The core of each stage is half an LM13700 OTA acting as current controlled resistor and inverter in one This resisto
11. hrough the very slow at one cycle per minute to around 10Hz The output of the LFO is then split up to do several duties One branch through R38 goes to drive the phaser core via the NC normally closed lug on the CV input socket Another branch goes to pin of the INV header and its little 2 way jumper so if selected to feed the LFO OUT socket via R39 A third branch of the LFO output goes to a simple inverting amplifier based around U1d pins 12 13 14 This simple circuit creates an oppositely going signal at its output ie when its input is 1V the output is 1V This inverted output goes to pin 3 of the INV header which when the jumper is fitted to short out pins 2 and 3 the inverted output ends up at the LFO OUT socket The fourth branch of the LFO output is sent to the LED driver based around Ula pins 1 2 3 The bi colour LED is in the feedback of this op amp so whatever current is drawn by R18 is also put through the LED If one were to connect the LED and resistor straight across the LFO output and ground the LED would be off when the voltage was less than its turn on voltage This is normally around 2V which is a fair proportion of the 5V output signal The old issue one boards did this and although the LED did give an indication of LED speed it would go out for some time This special driver circuit makes the current through the LED proportional to the input voltage So even at small LFO output levels the LED is s
12. r acts in combination with the 6 8nF capacitor to produce an all pass filter whose amplitude response is flat across the audio spectrum but importantly but one with a uneven phase response At a certain frequency determined by the current driving the OTA the phase shift will be exactly 90 degrees You can think of a phase shift as being like a little time delay but for a specific input frequency only Here s another way of looking at phase Consider a child on a swing and then consider another child next to her on the same length swing He will move at the same frequency as she does but it is unlikely that he will have started at the same time in the swing So as he goes up the other swing may be coming down The two swings are out of phase but moving at the same frequency Only if they started at exactly the same time will they be in phase or if he started his swing at a matching point in both their travels OK its highly unlikely that any two swings will go at the same frequency Even with the same length of rope there are other factors at work to make things more complicated A 90 degree phase shift is equivalent to one swing reaching the top as the other one flies past the middle point Or vice versa And a 180 degree phase shift is when one swing is at the top at one end while the other swing reaches the top at the other end Note that the phase shift remains constant so long as both swings are still moving at the same freq
13. t pdf The issue 5 Equinoxe PCB Siva os7 2 J This is the issue 5 Oakley Equinoxe behind a black finish Schaeffer panel Note the use of the optional Sock4 socket board to facilitate the wiring up of all those sockets I have provided space for the four main control pots on the PCB If you use the specified 16mm Alpha pots and matching brackets the PCB can be held firmly to the panel without any additional mounting procedures The pot spacing is 1 625 and is the same as the vertical spacing on the MOTM modular synthesiser and most of our other modules The design requires plus and minus 15V supplies The power supply should be adequately regulated The current consumption is about 30mA for each rail Power is routed onto the PCB by a four way 0 156 MTA156 type connector or the special five way Synthesizers com MTA100 header You could of course wire up the board by soldering on wires directly The four pins are 15V ground earth panel ground 15V The earth panel connection allows you to connect the metal front panel to the power supply s ground without it sharing the modules ground line More about this later The PCB has four mounting holes for M3 bolts one near each corner These are not required if you are using the three 16mm pot brackets The board size is 143mm high x 72mm deep The board has been laid out to accept connection to our Sock4 socket board This small board speeds up the wiring of t
14. ted The third tag is the normalised tag or NC normally closed tag The NC tag is internally connected to the signal tag when a jack is not connected This connection is automatically broken when you insert a jack Once fitted to the front panel the ground tags of each socket can be all connected together with solid wire I use 0 91mm diameter tinned copper wire for this job It is nice and stiff so retains its shape A single piece of insulated wire can then be used to connect those connected earth tags to pin 1 of I O Pin 1 is the square solder pad All the other connections are connected to the signal or NC lugs of the sockets The tables below show the connections you need to make Pin Pad name Socket Connection Lug Type Pin PANEL GND Connect to all sockets Earth lugs Pin2 LFO OUT Connect to LFO OUT Signal lug Pin3 NC No connection Pin4 AUDIO OUT Connect to AUDIO OUT Signal lug Pin5 NC LFO Connect to CV IN NC lug Pin6 CV_IN Connect to CV IN Signal lug Pin7 GND Connect to AUDIO IN NC lug Pin8 AUDIO IN Connect to AUDIO IN Signal lug 14 Connecting the Bi colour LED Using a two way Molex KK housing to connect the bi colour LED to the circuit board The LED is held onto the panel with a clear Cliplite lens or equivalent You may be able to wire the LED directly to the circuit board if the one you have has long enough leads However most of the ones I have seen won t fit directly so I have to use flying wires to connect the LED
15. till giving out some light A close up of the DEEP header In the standard Equinoxe you need to link out pins I and 2 which connects the output of the all pass filter cascade to the output circuitry Issue 5 Equinoxe Parts List 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 The components are grouped into values the order of the component names is of no particular consequence A quick note on European part descriptions R is shorthand for ohm K is shorthand for kilo ohm R is shorthand for ohm So 22R is 22 ohm 1K5 is 1 500 ohms or 1 5 kilohms For capacitors luF one microfarad 1000nF 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 Wire Link With a resistor lead clipping or short length of thin solid core wire solder a wire loop between pins 1 and 2 of the DEEP header Pin 1 is the square pin Resistors 1 0 25W metal film types are recommended 22R R35 R34 R50 R49 47R R2 100R R7 R6 1K R18 R53 R64 R41 R24 R29 R39 R38 R60 4K7 R19 R9 R17 6K8 R11 7K5 R31 10K R10 R42 R1 R25 R43 R57 R56 R54 R61 R30 R16 15K R3 22K R4 27K R28 R59 R23 R58 R14 R51 R27 R52 30K R22 R15 47K R32 R33 R3
16. to the board Bi colour LEDs have just two legs and each one should go to the solder pad directly beneath it when it is mounted into the panel I normally wire it up so that the LED goes red when the output is positive You can either solder your connecting wires to the LED s legs or use a MTA or Molex connector to make the connection 15 Testing testing 1 2 3 Apply power to the unit making sure you are applying the power correctly The LED should now throb happily If it doesn t turn off and check all the parts again thoroughly If your LED is OK and there is no smoke rising from the board yikes then try the LFO rate It should control the LED s flashing From around one cycle every 30 seconds to around 10 cycles a second Now input an audio signal of some sort any will do but a simple sawtooth wave is quite sufficient Listen to the audio output and play with the controls With all controls to the minimum setting sweep the FREQ pot Do you hear the characteristic phase sweep If not you have got a problem If yes now turn up the EMPHASIS Using the FREQ pot again does the sweep have a more metallic ring to it It ll probably be a bit louder too Now set the FREQ and EMPHASIS pots to their middle position Turn up the MOD DEPTH The LFO should now be modulating the phaser Check that the RATE affects the speed of the modulation 16 Final Comments If you have any problems with the module an excellent source
17. uency Thus the phase shift is still 180 degrees when the swings are at any point in their travels For example when the two swings pass each other in the middle but going different directions So the phase shift doesn t just describe one point in time but the whole relationship between two oscillating bodies Now an all pass filter will create a 90 degree phase shift at one frequency only All other frequencies will be affected but to a lesser or greater extent 90 degrees is important because if we cascade two identical all pass networks together we get 180 phase shift at one frequency And 180 degrees is exactly half a cycle of oscillation Now lets take our two all pass networks and listen to the output Well the output doesn t sound that different But let us now mix the output with the input The overall impact is the signal gets louder However at just one frequency something special happens This is the frequency at which you have 180 degrees of phase difference between the input and the output So as the input wave at that one frequency is going up the output wave is going down When the two are added together they cancel each other out And in theory completely So by mixing the out of phase and the in phase signal we can annihilate the signal So if we were to look at output response over the whole audio range we would find it pretty flat but for a very large notch taken out at just one frequency So a two stage ph
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