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Oakley Sound Systems

3U Oakley Modular Series

Overdrive

Soft and hard clipping module

User Manual and Builder's Guide

V1.1.3

Tony Allgood 

B.Eng

Oakley Sound Systems
CARLISLE
United Kingdom

Summary of Contents for Overdrive 3U

Page 1: ...Oakley Sound Systems 3U Oakley Modular Series Overdrive Soft and hard clipping module User Manual and Builder s Guide V1 1 3 Tony Allgood B Eng Oakley Sound Systems CARLISLE United Kingdom ...

Page 2: ...nd some basic testing methods 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 Construction Guide at the p...

Page 3: ...he frequency response of the effected output The mix out or balance pot is essentially a wet dry mix control that allows you to add only as much of the effect as you want Voltage control is determined not within this unit but as part of the signal chain placed before this module Using a VCA to control the signal level that is fed into this unit will determine the strength of the overdrive or disto...

Page 4: ...th my SH 101 and SH 1 and it s pretty much the plaintive solo sound on my own music albums The Oakley Overdrive module uses very similar circuitry to this prototype pedal The basic circuit topology remained the same but I changed the design to allow it to run from a split power supply I was careful to recreate the same voltage limits as in the 9V design as I was keen to replicate the op amp s satu...

Page 5: ...ure synthesiser this is generally the only way you can do it But I find that using it between the VCF and the final VCA gives me right sounds for solo work The VCF will naturally vary the signal level as the cut off changes and having the VCA last will ensure that any additional hiss produced by the high gain amplifier in the overdrive module will be only heard along with the signal and therefore ...

Page 6: ... design requires plus and minus 12V or 15V supplies The power supply should be adequately regulated The current consumption is about 15mA for each rail Power is routed onto the PCB by a four way 0 156 Molex MTA type connector or 2 x 5 way 0 1 header The former is normally used by Frac based systems as well as our own 5U MOTM compatibles The latter is found on most Euro modular systems The four pin...

Page 7: ...positions D1 and D3 This makes for asymmetrical distortion but I have not found the results to be especially different in synthesiser use You could also use two diodes in series for one of the places eg D1 could be replaced by one 1N4148 and a 1N34A in series U3 and U4 are three terminal regulators They are listed as 100mA devices and are 5V and 5V respectively They are very common devices but be ...

Page 8: ...K7 is a 4700 ohm resistor 6n8 is a 6 8 nF capacitor Resistors 5 0 25W or better 47R R15 R16 220R R5 1K R14 R2 R9 1K5 R4 10K R1 15K R10 27K R7 33K R3 R6 R11 100K R8 R13 360K R12 Capacitors 10pF low K ceramic C6 C17 47pF low K ceramic C5 47nF polyester C15 150nF polyester C14 220nF polyester C1 C2 470nF polyester C9 C3 C4 100nF multilayer ceramic C7 C8 C11 C12 2u2 63V electrolytic C16 C10 C19 C20 C1...

Page 9: ...ll hoop of uninsulated wire resistor lead clipping into the two holes of LK This joins the two ground pins of the 4 way 0 156 header Miscellaneous Leaded Ferrite beads L1 L2 Double pole changeover switch SW1 2 4 way 0 1 Molex MTA header SKT And one of the following 4 way 0 156 Molex MTA header PWR For 15V systems 2x5 way 0 1 header PSU For 12V systems 3 5mm sockets Two off mounted off board You ll...

Page 10: ...t one side going to the balance pot which will provide the dry signal and the other side going into the overdrive s core circuitry The core of the overdrive module is based around the same circuit as used in many guitar overdrive foot pedals To my knowledge this type of design first appeared in the Ibanez Tubescreamer TS 808 pedal but it also appears in other commercial pedals including the Boss O...

Page 11: ...eat part of the overdrive sound is also due to frequency shaping C2 rolls off the gain at lower frequencies C5 and the slew rate of the op amp act to curtail high frequency components It is these that set the width of passband that area in which the op amp acts as an amplifier In addition C9 will effectively block any DC signals to the amplifier The Oakley Overdrive has a major difference that the...

Page 12: ...This boosts high frequencies and produces a much sharper sound This is particularly apparent in the distortion mode since this part of the circuit produces much more higher harmonics due to the more severe clipping affect The output of the tone control stage is fed to the other end of the balance pot called mix out on the front panel This is a simple arrangement that lets the user apportion the mi...

Page 13: ... LK This connects the module ground and earth together and will make the module behave the same way as your other modules For assembly into Oakley 5U and 3U complete systems you can omit the wire link All audio connections are via a four way 0 1 header on the PCB called SKT This may be different to other Oakley PCBs you may have built Doing it like this allows you to remove the board from the fron...

Page 14: ... I tend to use one colour because I m a minimalist There is absolutely no need to use screened cable for such short runs The connections of the lugs of the sockets that go directly to the PCB are summarised in the table below Socket Name Tag type Header SKT Pin number INPUT Signal 1 the square one INPUT Earth 2 OUTPUT Signal 3 OUTPUT Earth 4 Once that is done your module is ready for testing 14 ...

Page 15: ... if it were coming straight out of the VCO Be careful to check your listening levels as the output signal will get louder in the next section Now rotate the BALANCE pot and you should hear the sound becoming brighter Now turn up the GAIN and listen as the sound gets both louder and brighter still Change the switch to DISTORTION and the sound gets louder still and more harsh There will a small clic...

Page 16: ...n 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 no...

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