Oakley Sound Systems Power Supply Unit (PSU) PCB Issue 2 and 3 User Manual V3.
Introduction This is the User Manual for issue 2 and issue 3 of the PSU circuit board from Oakley Sound. The Oakley PSU is a power supply unit designed to be used in conjunction with the Oakley Dizzy power distribution system. When built onto the 3U master panel the maximum peak current output is 520mA per rail using the recommended Yamaha PA-20 power supply. When built onto the larger 4U 19” rack panel and using the Yamaha PA-30 power supply the maximum current draw is 780mA per rail.
Safety Warning This supply has been designed to work with isolated low voltage AC inputs only. Connection to any other supply is done at your own risk. Low voltage is classified as being less than 25V with respect to the ground potential. Voltages above this level can, and often are, lethal to living creatures. Oakley Sound Systems will not advise on building or modifying this board to allow for direct connection to the mains, or other high voltage sources, further to what is provided in this document.
The Oakley PSU module The power supply board will allow the conversion of a suitable low voltage alternating current (AC) to be rectified, smoothed and regulated for operation with the Oakley Modular. The module is designed to be fitted to a suitably large metal panel which functions as a heatsink for the series pass devices connected to the PSU circuit board. This metal panel should have adequate airflow around it.
PA-30 will allow up to 780mA (0.78A). Remember though you can't use a PA-30 with the 3U master panel and expect to draw 0.78A out of it without the panel getting too hot. If you are using the 3U master panel then you should draw no more than 0.52A per rail. If you are using a 500mA (or 0.5A) AC wallwart* then the most current you can take from this power supply module is 125mA from each rail. That is, take no more than 125mA from either the +15V supply or the -15V supply.
As we have seen the standard circuit provides two outputs, one at +15V and one at -15V. Both output voltages can be finely adjusted with just one trimmer. The -15V will automatically track the output voltage on the +15V. The output voltages are available from two screw terminal blocks. It is expected that each terminal block will be connected to one Dizzy board. However, you can with care connect more than one Dizzy board to each output block.
The Power Supply to the Power Supply The inlet, switch and LED wiring on a 19” panel assembly. The top connector is the power supply inlet coming from a PA-20. The middle bunch of wires is for the two pole DPST rocker switch. At the bottom is a red 5mm LED in a low profile clip connected to the board via my usual Molex KK method. The standard method of powering the unit is from a low voltage tapped AC source. The safest available option is to use a ready made 'wallwart' or ‘line lump’ supply.
your own. Maplin in the UK sell a suitable three way connector to fit the Yamaha one perfectly. Their part number is FM51F. In the UK the line lump’s part number is V9812300 and the total cost is around £30 including VAT and postage. We do have permission from Yamaha-Kemble in the UK to use this particular part for the Oakley system, but in other countries this may be not so clear cut. The liability issue once again rears its ugly head and they may not want to sell power items for third party use.
The following supplies may also be used but have not yet been tested: Maplin N58AT This is a 1A single phase unit. It has the potential to deliver up to 250mA per rail when the Oakley PSU is used in half wave rectification mode. Make R2 and R3 both 1R5 resistors. If you have successfully used the Oakley PSU with any other types of power pack please do let me know either directly or via the Oakley Sound forum at www.muffwiggler.
Linelumps and Wallwarts: Wiring Diagrams Input wiring will depend on the type of wallwart or linelump you will be using. Standard AC output wallwart Single phase, two wire, wallwarts or linelumps need to use half wave rectification so the Oakley PSU can generate both positive and negative supplies simultaneously. They only need the terminal's AC1 and 0V2 wired to the power socket. AC2 and 0V1 are left unused. Wallwart with single phase AC output, eg.
Recommended Option: Centre tapped wallwarts and linelumps Centre tapped linelumps like the Yamaha PA-20 will have three wires coming from their connector. It will have two AC outputs and one 0V. Take one of the AC outputs to terminal AC1 and the other AC output to terminal AC2. It should not matter which AC output goes to AC1 or AC2. The 0V should go to the 0V2 terminal. The 0V1 terminal is left unused. Figure 2. Linelump wiring with centre tapped output, eg.
Linelumps and Wallwarts: Fitting a Grounding Point Using double insulated wallwarts and linelumps mean that you do not have to have a mains safety earth fitted to your modular. However, if your modular is to talk to the rest of the studio you need to make sure that the modular's ground is tied to earth somewhere in your system. The most usual way of doing this is via the connecting cable's shield or screen connection.
If both power supplies have a banana socket then it is a simple matter of patching the two power supplies together with a banana patch lead. The nice thing about bananas is that they are stackable so it's easy even if you have more than two PSUs to connect up. I recommend that you use thick multistrand cable to make your grounding leads and that you use good quality 4mm banana sockets and plugs.
Using an Internal Mains transformer Be afraid, be very afraid... Some of you old hands will laugh about the level of hysteria that surrounds direct mains connection to DIY projects. However, this fear is more to do with our litigious society than the real danger to the builder. Even so, I have had more than my fair share of high voltage shocks over the years and it is not something I would want any builder to have to experience. It has been purely luck that has saved me in several of those cases.
2. The power supply's components, including the smoothing capacitors, should be rated at a high enough working voltage to handle the increased voltage across them. 3. The heatsink will need to dissipate even more energy because of the greater voltage drop across the regulators. In the wiring diagram shown on page 17 I have included a suggested wiring method for connecting up a mains transformer. Not all mains transformers are the same, some have additional windings, others have tapped windings.
However, this alone may not be sufficient for a solid safety earth bond. All panels should be earthed directly, either with their own direct connection to the earth tag on the power inlet, or via the modular's earthed metal mounting rails and suitable toothed washer and screw. If you have a wooden case with wooden mounting rails and you are toying with the idea of using a mains transformer in your DIY power supply project then you may want to rethink your plans.
Mains wiring diagram.
The Oakley Power Bus In an ideal world I wanted the Oakley power bus to be based on a five way 0.156” MTA or Molex connector. This would contain +15V, -15V and three grounds. One ground would be the safety ground; this would be connected to the front panels and then directly onto the main’s supply earth. The second would be a clean ground for all the analogue modules to take their supply reference, the zero volt line, ie. 0V. The third would be a dirty ground.
Final Comments I hope you that the Oakley PSU lives up to your expectations and provides you with a reliable source of power for your modular system. If you have any questions about the module, an excellent source 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 have a comment about this user manual, or have a found a mistake in it, then please do let me know.
