I am building a mobile sound system powered by a car battery. I have a small mixing table that runs on 12V but it needs AC power (50Hz) and won't work with DC (I tried that, with very weird results.)
Currently I am using a 12V to 230V inverter and the provided power supply to convert it back to 12V alternating current. This seems wasteful and I do not want to introduce another voltage level into my design just to power the mixing board.
How could one build a simple circuit that does this? I have basic electronics skills (soldering, know about resistance, voltage, current) but never built a circuit board. I would prefer to avoid opening the device, except it is very easy to do the modifications.
The mixing board is a Renkforce MX260 USB DJ Mixer. Th manual can be found here.
Best Answer
The solution you already have is the best trade-off in the given conditions and let me explain:
It's a bad idea to have a switched mode power supply near an audio device. They're noisy.
But a home made switched mode power supply is worse. You won't get the low level EMI that can be reached (and imposed by regulations) on a commercial product.
In the same time I guess that form the same battery you will supply other devices to. Most likely with the signal ground tied to 12V ground.
But without looking inside the mixer box you don't know how is the AC power input related with the signal ground so your AC supply must be insulated from 12V battery/signal ground otherwise you might short or overload some internal circuits inside the mixer. Just think what happens if you have a half-wave rectifier inside and you connect the ground to the "hot" wire.
A pure analog solution like a 50Hz generator followed by an amplifier and then a 50Hz transformer to raise the voltage from 12V peak to peak (bridge configuration) to 17V peak to peak has a very low efficiency and requires a hard to find 12v to 17V 1A transformer.
Modifying an inverter from 230VAC to 12VAC is almost impossible and certainly will alter the EMI compliance.
What you can do is to find the smallest inverter, the smallest I could find was 50W so you won't have cooling issues, and use-it with a 12V transformer which you already did.
It's the best option from the size, noise ,time spent and cost.
The next best is to disassemble the mixer and see the internal power supply schematic, this can save some money and space with much simple solutions.