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Summary of Contents for Oakley midiDAC
- Page 1 Oakley Sound Systems midiDAC Issue 3 Single Channel midi-CV Convertor User Manual and Builders Guide V3.5.1 Tony Allgood B.Eng PGCE Oakley Sound Systems Carlisle United Kingdom...
- Page 2 This is the issue 3 midiDAC in a natural finish Schaeffer panel. Note the new rounded corners. The toggle switches are APEM flat blade toggle switches available from Farnell. The round LED holders come from Maplin, whilst the knobs are the Rapid's 'matt black control knobs' for 1/4” fitting.
- Page 3 Construction Guide at the project webpage or http://www.oakleysound.com/construct.pdf. The issue 3 midiDAC is a single channel midi to analogue convertor. This project is a joint development between Oakley Sound and Trevor Page. Trevor wrote the firmware for the processor used in this project.
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Page 4: Other Features
If you have a complete Oakley Modular System, it is recommended that you do not directly connect the midiDAC’s power supply to the same power bus as the modules. That means don’t connect it to the Dizzy board. This is because pin 3 of the power inlet on the midiDAC... -
Page 5: The Printed Circuit Board
Oakley modules. Connection to the Dizzy distribution system will not damage the midiDAC module, but it may introduce unwanted noise on the power lines. Therefore please connect the midiDAC directly to the power supply output pins. -
Page 6: Circuit Description
The PCB has four mounting holes, one in each corner. However, using the midiDAC with the recommended pots and brackets, will give you sufficient support without the need for additional mounting hardware. The pots are Spectrol 248 series or BI TT equivalents, supplied by Farnell, CPC and Rapid Electronics here in the UK. - Page 7 Firstly, you need a very accurate reference voltage. This will set the maximum output voltage that the DAC circuit will supply. For the midiDAC the reference comes from a reference voltage chip, U3. This generates a stable 5.00V at its output.
- Page 8 Note that not all of the eight outputs from the demultiplexor are connected to S/H circuits. The PIC only processes six midi controllers so the other two outputs are unused. The pitch and pitch bend CV are processed further by the midiDAC. This circuitry is seen on page two of the schematics.
- Page 9 CV, and thus aid centralising the TUNE pot’s range. In this version of the midiDAC, the pot and trimmer take their end voltages from the +5V and -5V reference voltages. This should lead to greater stability of the CV output even if the power supplies change slightly.
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Page 10: Midi Channel Selection
A third logic output is also available that can drive a midi active LED which is unused in the midiDAC-3. This output goes low for 500mS if any valid midi data is present on the midi port. Midi Channel selection Midi channel is selected by four lines which must be either floating or be grounded. - Page 11 Gate Trigger Modes The midiDAC allows the selection of two gate trigger modes via the ‘Legato mode’ switch. This is marked on the new PCB as ‘RE-TRIG’. You can connect a simple SPST switch to this or a simple jumper. The setting of this switch/jumper determines how the gate signal responds to overlapping notes.
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Page 12: Note Priority
Note Priority The midiDAC firmware uses last note priority. That is, it will assign the pitch CV to the last note to be held. However, all 'overlapped' notes are still retained in memory and are reactivated in order should the most recent notes to be held be released. - Page 13 The HEF4104BP is a four channel low to high level shifter. Its available from Farnell and also from Oakley Modular. The REF02 is a 5V reference. Get the cheapest one in DIL form on offer. All but one of the ICs are dual in line (DIL or DIP) packages. These are generally, but not always, suffixed with a CP or a CN in their part numbers.
- Page 14 One of the ICs is a three pin TO92 style package. This is the 78L05 which is a 5V 100mA regulator chip. The multiturn trimmers are the ones that have the adjustment on the top of the box. Spectrol and Bourns make these. Some types are 22 turns, while others are 25 turns. Either will do. They should have three pins that are in a line at 0.1”...
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Page 15: Parts List
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. - Page 16 BC550 small signal NPN transistor Q2, Q1 5mm LED of any colour GATE, LEG D1 is not fitted. Integrated Circuits 16F628-04 midiDAC PIC CD4051B 1-8 mpx CD4066B analogue switch HEF4104BP level shifter 6N137 optocoupler 74HC04 Hex invertor 78L05 +5V regulator...
- Page 17 Connectors 4-way Molex 0.156” header 1off (PSU) 4-way 0.1” header and socket 2 off (CN1, CN2) 3-way 0.1” header and socket 2 off (midi thru and Dizzy Bus) 2-way 0.1” header and socket 1 off (midi in) Miscellaneous 4MHz Crystal (parallel resonant) FERRITE L1, L2, L3, L4 LED clips...
- Page 18 How you connect your midiDAC very much depends on where you are going to use the midiDAC. You may already have an idea of how you are going to connect your midiDAC to your chosen system. For those building the standard Oakley midiDAC modular panel I will give the wiring instructions in detail.
- Page 19 MOTM system, I have stuck with just two grounds. If you are fitting your midiDAC into a single box with some other analogue synth circuitry, the connect the two midiDAC grounds to the central power supply star point. You do not need any further connections to ground from or to the midiDAC.
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Page 20: The Front Panel
The rear view of a recently made midiDAC-3. This one has been built onto a natural finish Schaeffer front panel. The sockets are Switchcraft 112APC with a small amount of heatshrink acting as a strain relief for the connected wire. No wired ground connection is made to the output sockets. - Page 21 Calibration There are two trimmers on the midiDAC PCB. Both of them are designed to allow you to make the midiDAC respond correctly to the rest of the modular system. If you already have a perfectly tuned and calibrated system, it is best to trim the midiDAC to suit your system rather than the other way around.
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Page 22: Final Comments
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.
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