Power Supply Unit (PSU) for DIY Synthesiser Systems

Constructional difficulty: Moderate if using a low voltage AC output mains adapter.

A completed issue 4 PSU board. The two big resistors on the left set the current limit of the power supply.

The Oakley PSU is a dual output tracking power supply design that is perfectly suited to powering a small to medium sized Oakley modular. Final output current capability is dependant on AC power source, the choice of smoothing capacitors and the heatsink used. However, with a suitable heatsink, capacitors and power source the Oakley PSU has been tested successfully at up to 1.2A per rail.

The PSU module must be fitted to a suitably large metal panel to act as a heatsink for the two power transistors.

It is designed to work with our Dizzy power distribution board. Up to two Dizzy boards may be connected directly to the PCB.

The Oakley PSU features quiet and very well regulated outputs. It is also short circuit protected and current limited. It is garanteed not to latch up on power up.

For safety reasons it is expected that the unit will be used with a external centre-tapped linelump (mains adapter) like the Yamaha PA-20 or PA-30. The PA-20 will allow the PSU module to provide up to 520mA per 15V rail, while the PA-30 will supply up 780mA per 15V rail.

Greater current outputs can be supported when used with an appropriate transformer or line lump, suitably large heatsinks and a change to the value of the current setting resistors on the board. The board will support mains transformers with either twin or tapped secondaries.

A component level mains transformer should only be used if you know how to connect high voltage wiring. On no account should this project be powered by a component level mains transformer if you are not familiar with fusing, earthing and safe connection of high voltage equipment. For safety reasons Oakley Sound can only endorse using this module with a low voltage input, such as the Yamaha PA-20 or PA-30.

The power supply uses standard parts throughout and requires only a simple voltmeter to set up. The circuit board takes less than an hour to build.

Various options are available for different types of switching, earthing and power on indication. The strong glass fibre PCB is silkscreened for easy component identification. It uses generous pad sizes, through plated holes for easy soldering and wide copper double sided tracks for reliable operation. The PCB is 140 x 81 mm.

The newest version of the PSU board is issue 4. Issue 4 is the same size and has the same mounting hole positions as the other issues but has a more robust grounding system and is easier to use with toroidal mains transformers.

The two power devices are chunky TO-247 transistors

Power Supply for 19" Racks

An older issue 2 board fitted to a 4U 19" panel designed to work with an external PA-20 power adapter.

The PSU can be mounted to a 4U high 19" blank faceplate. These are available from various sources and are typically made from 2.5mm aluminium so are easy to drill. The panel would be normally fitted to the rear of your modular's 19" rack case. Because of the generous surface area the panel acts as a very good heatsink. This design is suitable for connection to either the PA-20 or PA-30 power adapters for supplying currents of up to 0.52A or 0.78A per rail respectively.

Up to two Dizzy boards can be fitted to such a panel. The above panel has one Dizzy fitted but you can just see the punch marks for the mounting holes for a second Dizzy board. The small green banana socket is an optional grounding point which can be useful if you have more than one modular and you wish to patch them together.

The rear view of a 6U high 19" flightcase sleeve fitted with the 4U high Oakley PSU and Dizzy assembly. The 2U high ventilated panel mounted above it keeps wandering fingers at bay and finishes off the unit. These perforated panels, like the bigger blank panel, are available from most studio equipment shops.

The Master Module

The power supply board can be fitted to our Master Module design. This module is designed to attach to the front of the modular and sit alongside the other modules in the system. the power inlet would be normally fitted to the rear or side of the case. The 3U Master module design is suitable for use with the PA-20 power supply and as such will supply up to 520mA per rail. We do not recommend that this panel design be used if the power supply draw is expected to exceed 520mA.

This 3U wide panel also includes:

The Builder's Guide gives full details on how to make this very useful module.

The original issue 1 PSU module attached to the rear of the Master panel. The switch, standby LED and sockets are yet to be fitted.

Project Downloads

PSU issue 4 Builder's Guide

PSU issue 3 Builder's Guide

PSU issue 3 User Manual

Construction Guide Our handy guide to building Oakley DIY projects

Parts Guide Our handy guide to buying parts for Oakley DIY projects


A Schaeffer front panel can be made for the MOTM compatible 3U wide 'Master' module. The database for the module can be found be clicking here.

To read these files you will need a copy of 'Frontplatten designer' from Schaeffer. The program also features on-line ordering, so its now even easier to buy your panels from Scheaffer.

The company are based in Berlin in Germany and will send out panels to anywhere in the world. Delivery to the UK normally takes around ten days. For North American users you can also order your Schaeffer panels from Front Panel Express.


Click here for ordering details. 

Power Supply issue 4 PCB ................................... 19GBP

3-pin power socket for external PSU ...................... 2GBP

All of the other parts should be able to be purchased from you usual electronic component supplier. Please see the Builder's Guide for more details.

See the Oakley Sound ordering page for ordering information, shipping charges and payment methods.

All prices include VAT at UK rates. Shipping/postage is additional to these prices. See also the FAQ page.

The three pin power socket for use with external PA-20 and PA-30 power supplies.

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Copyright: Tony Allgood.
Last revised: September 17, 2018.