Mains power for the LushOne

Once you start using the LushOne seriously you'll find it does tend to chew through the batteries fairly quickly. A frequently asked question is "is there an option for a mains power supply"? Unfortunately +/- 9V is not a common power requirement these days and off the shelf options are limited. One day I would like to do a proper kit for a power supply but at the moment I don't have time. However I have found an option that I think is  effective and should be suitable for a moderately experienced builder to put together on stripboard or similar.

In the interests of safety I required a design that didn't require the builder to build their own mains equipment. This meant that a design that could be powered from a common "wall wart" power supply was needed. Music From Outer Space have a nice design for a linear power supply that runs from a 12V AC wall wart and could be adapted for +/-9V operation. I played about with this design but AC wall warts aren't very common these days and the voltage drop on the regulators is quite high getting to 9V so it runs rather hot.

I really wanted something that would run from a single 12V DC wall wart as are common and compatible with most of my other equipment. To get positive and negative voltages from a DC source means using some kind of switching power supply. There are lots of ICs that could be suitable but they are all surface mount and I know lots of people are not comfortable (perhaps unreasonably) working with surface mount parts. Anyway I don't have any real experience designing switch-mode systems and I am not too excited about learning.

Finally I found a nice module that does everything I need in one block. The snappily named RECOM REC7.5-1209DRW/H3/A/M/CTRL takes a 12V DC input and provides +9V/-9V outputs at up to 417mA each. Even better it is a stocked item at Mouser so it is easy to buy. The Mouser part number is "919-7.5-1209DRWH3AMC". The outputs should be enough to drive between 3 and 5 LushOne modules. If you want to drive two modules than a 250mA 12V DC wall wart should be ample.


Using the Recom module is dead simple. Just connect an input to the input pins and take the output from the output pins (as shown below). I haven't checked the behaviour of the device for reverse polarity input (and the documentation doesn't tell me) so make sure you wire the input round the right way. To be safe it might be an idea to put a chunky (with sufficient continuous ratings) rectifier diode to protect the input. The module does have output short circuit protection which is a good feature.

In use the Recom module is quite efficient but does still get fairly hot (operating temperature specification is up to 71C). I would try and place it somewhere which has good air circulation. The Recom module fully isolates the output voltages from the input so it won't provide a path for ground loops. The isolation does mean that if you are connecting the LushOne to other equipment you should make sure there is a ground connection made because there won't be one through the power supply.