Audio Video Battery question

[jeep642]

Hi, I'm new to this forum and after months of searching I figured may be someone with knowledge in electronics might have the answer.

I'm a film maker and I'm putting together a camera system based on the Canon 5D mark II camera.
It's a still camera that shoots high definition video.

The problem is that, by itself, it's far from perfect. The footage is great but sound recording is bad and it's not practical in terms of handling and battery life.
To make it work well, you need a few things:
- a sound preamp to feed a signal strong enough to the camera so as not to use the camera pre-amp (the trick is to bring the recording level in the camera to zero + one click that way the built in preamp doesn't affect the sound)
- an external monitor or viewfinder.
- one main battery to power the whole thing.

The problem comes when I try to power everything from the main battery. I use SWADJ3 25w switching regulators to go from the 14-16 volts of the Anton Bauer main battery to go down to 7.2v for the camera, 12v for the monitor and 9v for the external preamp.

If all the elements are powered separately, everything works fine.
If I use a common battery for everything, it generates a huge amount of noise.

It doesn't sound like a ground loop. I used ground loop isolators, no luck.
The noise fluctuates depending on what the camera does. If it's idle, less noise, if it's computing a lot (recording, using video out), there's more noise.
Someone told me it could be oscillation because my power source is not stable enough, so I built a circuit based on a LM317 (may be more stable than the SWADJ3) no luck.

Obviously the problem comes from the fact that all the elements use the same battery, so I bought a virtual battery (this) to power the preamp, no luck.

I'm still convinced that I need some kind of circuit that would create two isolated completely independent power sources from one battery but I can't find anything like that on the web and my knowledge in electronic is too limited to be able to come up with one.

Any ideas would be greatly appreciated.

Thanks,
JP

[Hero999]

Have you tried filtering the power supply to each of the devices? Try adding ferrite beads and ceramic capacitors.

I still wouldn't rule out a grounding problem. If so using an isolated DC-DC converter for two of the devices should solve the problem.

Have you tried running the preamplifier from 7.2V? If it's designed to work from a 9V battery, it should be able to work all the way down to 6V. If not, crank up the voltage on the 7.2V supply to 8V. The camera will be fine at 8V or even 9V, as it'll be designed to work from a NiCAD/NiMH pack which could be as high as 8.4V to 9v when hot off the charger.

The monitor may also be able to withstand up to 16V, check the manual.

Reducing the number of different voltages as much as possible will simply things, increase the efficiency and make it easier to find an isolated SMPS, if required. I know you can by isolated 12V power SMPSes but I don't know about 8V.