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"? Here are two options you might like to try.

Using Recom DC to DC Converter

This is 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.

LushOne PSU based on Rescom module

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.

Using two 9V "Wall Warts"

If you don't mind having two "wall warts" powering your LushOne then it is easy to build a power supply using common wall warts. A wall wart is one of those DC power supplies built in to a mains plug that are so common as mobile phone chargers etc. This is actually a pretty good solution because it uses easy to obtain parts and you can easily power a lot of modules.

You will need two wall warts with regulated 9V DC outputs and floating grounds. Any wall wart that has a plastic earth pin on the mains plug or no earth pin on the mains plug should have a floating ground. A "floating ground" means that the 0V output of the power supply isn't tied to a particular voltage like mains earth. I have verified that the Maplin part number L67BQ works well. An output of 500mA upwards should be sufficient for a set of three LushOne modules.

Suitable PSUs

Having obtained two wall warts you now need to connect them to the LushOne. There are lots of ways you could do this, but my suggestion is to attach 9V battery connectors to the wall wart outputs so you can connect them in place of the 9V batteries. You will need to get two suitable 9V battery clips like Maplin part number HF28F.

Make sure the wall wart isn't plugged in. Cut the DC connector off your wall wart, separate leads (these are normally "figure of 8" wires so this is an easy job) and strip the insulation from the ends to expose a short length of wire. Without shorting the wires together, plug the wall wart in and using a volt meter measure the voltage between the wires. Label the positive and negative wires. Unplug the wall wart! Now, take your battery clip and connect the red lead to the negative output from the wall wart and the black lead to the positive output. This seems like the wrong way round, but remember that the terminal shapes on the battery are the reversed compared to the connector.
I have illustrated this below. Use short lengths of heat-shrink sleeve to protect the join (as shown).

Connecting PSUs

Now is a good time to check your work. Plug the wall wart back in and measure the voltage at the connector. The circular terminal should be positive and the crimped one negative as shown below.
Connector close-up

Do the same to the second wall wart.

Now, with the LushOne power switch in the "off" position connect the wall wart outputs to the LushOne power inputs using the battery connectors you just added. Plug the wall warts in. I suggest you measure the voltages on the LushOne power inputs before you switch on. Measure between a "GND" connection and the "+9V" input. The voltage should be, you guessed it, +9V. The GND is connected to the 0V power input even when the LushOne is switched off. Measure between the "GND" connection and the "-9V" input. The voltage should be -9V. If all is well, switch your LushOne on and away you go!

Measuring voltages