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. An example of such a panel is our 3U wide master panel which
also contains a handy multiple and power switch. You can also use a 4U high 19” rack blank
panel. These are particularly suitable if you are mounting your modular synth in a 19” rack.
The greater surface area on the 19” blank panel allows you to mount not only the power
supply module but also up to two Dizzy PCBs. And the greater surface area also allows the
power supply's power devices to dissipate more heat safely and that means a greater current
output should you need it.
A standard 4U high 19” panel with an Oakley PSU and single Dizzy. This would be suitable for powering
up to 12 Oakley modules. Note the grounding point just below the main power inlet.
The voltage output of the power supply module is a split rail 15V supply. This means it
generates both +15V and -15V. That is, two power rails, one of a positive voltage, the other a
negative one. These voltages are measured with respect to a common ground which is
normally connected, via your house's wiring, to the earth that you stand on. The voltage
across both rails is 30V, with the common ground sitting exactly in the middle of this at 0V.
The output current capability is the maximum current you can draw out of the power supply.
The current taken from the supply is, for the most part, determined by the amount and type of
modules you are connecting to the power supply. However, the actual patch also has an effect
on the current draw – the more outputs that are connected to inputs increases the current
draw slightly. Also, some LEDs when lit may increase the current draw.
The Oakley PSU features current limiting. This sets the maximum current the power supply
will actually provide. If you try to draw more than the limit the output voltage will fall to
maintain the current at the limit value. The current limit is set by two resistors, R2 and R3, on
the PSU board. It is essential that you make the current limit resistors suit your application.
The next section, and also in the parts list of the Builder's Guide, will give details on what
values to use.
I recommend that you use a Yamaha PA-20 or PA-30 power supply. These are neat tidy
external power supplies that keep the dangerous mains voltage away from your modular. The
PA-20 will allow a maximum current of 520mA (0.52A) to be drawn from each rail. While the
4
