I was trying to do some noise/distortion measurements on an audio VCA I had made but I was getting 50Hz noise from my power supply. I was looking for around 100/110db of resolution for my measurement system. Even if I moved the wires a little the 50Hz noise would fluctuate, obviously induced pickup. So I went for a simple, cheap solution. Bought 2, 12V/2.4AH gel batteries from Jaycar and some terminals, and voila, a low noise power supply which is portable and completely isolated, so no ground loops.
Testing went very well, unfortunately my VCA had around -80db of signal distortion. But the test setup, a Steinberg UR44 external sound card and my laptop had around 110db S/N ratio with the battery supply. For charging I already had one of those PRO type chargers that do multiple chemistries.
Perhaps others might share any mildly unusual battery supply stories, I'm sure they would be interesting.
