Oakley Filtrex II Builder'S Manual Download

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Oakley Sound Systems

Filtrex II

PCB issue 2

Analogue Filter Rack

Builder's Guide

V2.4

Tony Allgood
Oakley Sound Systems
Carlisle
United Kingdom

Summary of Contents for Filtrex II

Page 1: ...Oakley Sound Systems Filtrex II PCB issue 2 Analogue Filter Rack Builder s Guide V2 4 Tony Allgood Oakley Sound Systems Carlisle United Kingdom ...

Page 2: ... your module please visit the project webpage at http www oakleysound filtrex 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 inte...

Page 3: ...e building a stereo version of this module you will need two Filtrex II boards One of them will be built as a Master and the other as a Slave For the Slave module you should not fit parts marked with a Please see later in this document for a suggested method on how to wire the two modules together Resistors All resistors 5 or better 0 25W types Those items marked with 1 need to be 1 metal film or ...

Page 4: ... polyester C43 C30 C39 68nF 63V polyester C12 C13 C14 C15 100nF 63V polyester C32 C52 C20 C21 C35 C54 C55 C41 C50 C38 470nF 63V polyester C5 C24 680nF 63V polyester C19 C18 C17 C44 1uF 63V polyester C16 2u2 63V electrolytic C51 C33 10uF 35V electrolytic C37 C22 22uF 35V electrolytic C56 C53 C34 C6 C8 C4 C49 C25 C27 C45 C11 C46 C36 C10 100uF 25V electrolytic C42 220uF 10V electrolytic C9 1000uF 35V...

Page 5: ... a bi colour LED in a water clear package Do not fit an ordinary single colour LED in this position Integrated Circuits OPA2134PA U1 U7 NE5534 U8 TL072 U3 U5 U6 U9 U16 TL074 U4 U10 U14 7815 U15 7915 U11 THAT300P U2 4001 U13 4016 U12 Pots All pots 16mm Alpha or Alps types 50K linear dual gang RESONANCE GAIN 1M log UP DOWN 50K linear SMOOTH FREQ FIZZ DRY WET THRESHOLD ENVELOPE 10K linear VOLUME 50K ...

Page 6: ...or both the audio CV and power sockets This will reduce the risk of earth loops Additional parts required for stereo operation on both boards 2 way 0 1 KK Molex header 2 off STV ST A 2 way 0 1 KK Molex housing 2 off STV ST A 4 way 0 156 KK or MTA header 1 off MOTM 4 way 0 156 KK or MTA housing 1 off MOTM You will also need a power source of some kind The recommended supply is a wall wart supplying...

Page 7: ...is would normally defined in dB This pre amplifier will give you a gain from 8dB to 42dB Because the pre amplifier is made from a inverting and non inverting stage the overall behaviour is inverting This means the output is completely out of phase with the input This is not a problem since the inversion is corrected later on the Filtrex Q7 and associating circuitry drive the peak LED This is desig...

Page 8: ...feedback loop as we have seen and the other sets the gain of the input Normally the passband gain of a moog ladder decreases as you turn the resonance up In other words the volume drops as you increase the resonance This can be quite a problem for a post processor like the Filtrex So in the Filtrex the input level is automatically turned up as resonance increases Thus the overall effect is of a co...

Page 9: ...t This block allows the user to select between the output of the filter mixer or pre amplified signal It is easy to see how it works when you consider the action of the wiper moving between one end of its track connected to U7 pin 1 and the other which is connected to the output of the pre amplifier The output of the mixer stage is fed via a DC blocking capacitor to the Volume pot The wiper of thi...

Page 10: ... offset voltage is negligible R50 and R48 may also be removed in this case That completes the description of the audio path Now let us take a look at the processing circuitry of the Filtrex Staying on page two of the schematics the second set of circuits down the page belongs to the full wave rectifier and threshold detector This takes its input from wither the pre amp output or the external side ...

Page 11: ...her words we need our gate to come cleanly on and off with no spurious states as the signal rises and falls U14b pins 5 6 7 is a comparator This is a device based around an op amp that determines whether a signal is higher than a pre selected threshold voltage The threshold voltage is controlled by the user and is set by the Threshold pot The threshold voltage can be set between 12V and 0 7V C44 i...

Page 12: ...ode U12 is switched over to allow the output of the EG logic circuity to control the lag generator The output of this logic circuitry is either high 7 5V or low 0V The logic circuitry can operate in two modes attack decay AD or attack release AR Several sources can initiate the attack phase One is the external gate signal This is a switch type signal that is either at around 0 volts when off or an...

Page 13: ...t the attack phase is over and the decay phase is about to start Pin 10 therefore goes low and C37 is discharged via the down pot R69 and R70 set the 3 8V threshold level R77 with R78 provides a thin slice of positive feedback to force the comparator to switch cleanly it is another Schmitt trigger again The LFO circuit is quite simple It is on page two of the schematics The first TL072 op amp U16a...

Page 14: ...he main audio output and are pretty unpleasant The trigger output is simply generated by a transistor Q12 that turns on when the output of the Schmitt trigger goes high The auto switch switches the function off by shorting the base to the emitter when not required The last thing to describe is the power supply This is a standard three terminal regulator design straight out of the data book R96 and...

Page 15: ...n 1 should thus connect to the socket s sleeve terminal Pin 2 should connect to the tip terminal of the socket For the stereo TRS socket you have three connections to make If you are wanting to use screened cable you will need to use special balanced cable which comes with a single screen that overlaps two identical conductors Like the other connections pin 1 is the ground and should be connected ...

Page 16: ...s However this may cause earth loop problems if you then mount your case into a rack with other pieces of equipment in it Please note that grounding a case is not the same as earthing a case Your case must be additionally earthed if you are fitting an internal mains transformer into your case Please see the next section for some more details on this 16 ...

Page 17: ...nd have a Farnell account you could try their part number 2368009 Some 12V AC output types may also work but this is only because some AC output wallwarts tend to be poorly regulated and have a lot of overhead Do be aware that if they do work some of the time they may not work all of the time If the voltage does fall below the required operating voltage of the Filtrex II the most obvious sign is a...

Page 18: ...d should also be tied to earth using a piece of wire connecting the earth bonding point and the CASE solder pad on the board R126 should be a wire link and not a resistor Powering the Filtrex with the MOTM header The Filtrex may also be powered from the MOTM or Oakley power busses The power socket is 0 156 Molex MTA 4 way header is marked as MOTM on the PCB Friction lock types are recommended The ...

Page 19: ... at all This will prevent you from accidentally damaging your ears your tweeters and upsetting your neighbour s dogs But hey that would be boring Live life in the fast lane Trim it up so that it just oscillates when the resonance it up full BAL Listen to the Smooth output Set the Resonance and Frequency pots to their mid positions Turn the LFO modulation depth pot to its maximum value and select t...

Page 20: ...already present on the Bryant panel I am not sure whether this could be successfully done with the grey painted finish of the Holt panels A Schaeffer FPD file can be found on the Filtrex s project webpage which can be downloaded and edited If printed out at 100 size and in wire mode with reference points you can then use it as a template for drilling your own front panel holes My current favourite...

Page 21: ...erwise is being used then the metal case must be connected securely to earth This is best done with a M4 bolt nut toothed washer and solder tag directly wired with thick wire to the IEC inlet socket s earth tag The Filtrex s circuitry should be then tied to earth as detailed in the power supply section in this document Once again I should stress that building a component level mains transformer in...

Page 22: ...er profile The PCB has been designed so when using MTA connectors the wires move away from the front of the board so can be looped from one board to the other The heatsinks fitted to U11 and U15 must be closely monitored after first building up a stereo unit When being run from a 15V AC wallwart the heatsinks get only slightly warm when driving a single Filtrex II But doubling the power output of ...

Page 23: ... 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 user 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...

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