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

 

[davenn]

ok have you got any schematics of the PSU's you built up ?
At this stage it would probably be very helpful to us so that we could see if you have missed out on adequate capacitor bypassing etc on the regulators.

cheers
Dave

 

[(*steve*)]

I am not convinced that you would want to record your main sound track using the 5D. It is useful perhaps as a guide to synchronisation of the sound and image. See here for discussion of that topic. (But this is beside the point)

Here is a group of people doing what you're doing (I think). Maybe they have some experience with this problem (worth a try).

You say there is no noise when used singly, but there is when all 3 are used. What about when pairs are used? Is, for example, powering the 5D and the monitor OK, but powering the 5D and the pre-amp not? Do you get the noise if you have everything powered by this device, but you do not connect the pre-amp and monitor to the camera (i.e. you use the internal microphone)?

 

[jeep642]

ok have you got any schematics of the PSU's you built up ?
At this stage it would probably be very helpful to us so that we could see if you have missed out on adequate capacitor bypassing etc on the regulators.

cheers
Dave

I will draw a schematic asap and post it here.

Thing is I'm not sure it will help becaus ethere's not much to draw. All I'm using is those SWADJ3 25w switching regulators. There's 3 of them, I feed them the 14-16v of the battery and set each one of them to deliver 7.2v, 9v and 12v out. Pretty basic. Which is probably why I'm having issues.

 

[jeep642]

I am not convinced that you would want to record your main sound track using the 5D. It is useful perhaps as a guide to synchronisation of the sound and image. See here for discussion of that topic. (But this is beside the point)

Here is a group of people doing what you're doing (I think). Maybe they have some experience with this problem (worth a try).

You say there is no noise when used singly, but there is when all 3 are used. What about when pairs are used? Is, for example, powering the 5D and the monitor OK, but powering the 5D and the pre-amp not? Do you get the noise if you have everything powered by this device, but you do not connect the pre-amp and monitor to the camera (i.e. you use the internal microphone)?

Actually, once set up the proper way (and bypassing the camera preamp is key) you can get a VERY decent sound (to not say good) with this set up. Namely the 5D and a Juicedlink 454. Now back to the point.

Thanks for the link, I will check it out.

To clarify what I was trying to explain,
-If I power the 5D, the monitor and the external preamp each with their own battery, everything is fine.
-If I power the 5D and the monitor with the same battery, everything is fine, mainly because there's no sound involved.
-If I power the 5D and the monitor with the same battery and use the external preamp powered by it's own 9v battery, everything is fine.
-If I power the 5Dm, the monitor AND the external preamp with the same battery I get the noise (a lot).



Also, the preamp feeds a high level to the camera and you can either monitor the sound from the preamp or from the camera (to do it from the camera a firmware hack is required).
The interesting thing is that it's logical that you might here some noise monitoring the sound from the camera because the audio might have picked up interferences along the way but when you monitor it from the preamp, what you're listening to is the sound taken directly from the mic even before it gets to the camera; it seems that this noise makes its way back to the preamp headphones through the cable used to feed audio to the camera. Or it gets there through the power supply cable... which could it be?.. after month of searching, I still can't put my finger on it.

 

[jeep642]

Here is a group of people doing what you're doing (I think). Maybe they have some experience with this problem (worth a try).

Funny you sent me this link, the link they mention on the first post directs to where I got the original design from...

Problem is, none of these guys ever tried to power the preamp with it. They just use it for the 5D, a monitor, lights etc... Only things that don't involve sound. I actually have a thread there about it. No one could ever find the solution to the problem... (yet)

 

[(*steve*)]

OK, at least we know we're not duplicating effort

My first try beyond checking filtering/decoupling would be to get some toroidal ferrite cores and wrap *all* the cables through them as many times as possible. See if this reduces the noise. If you're really keen you could do it one at a time and see where you get improvement.

Something like this:

Unless you can beg, borrow, or steal some, wait until we've looked at your circuit diagram. There may be other things to try as well (or even before you try this).

 

[(*steve*)]

Oh, and did we ask you what the noise sounds like? And whether or not you can hear it whilst recording or if it is only present on the recorded signal.

 

[(*steve*)]

-If I power the 5D, the monitor and the external preamp each with their own battery, everything is fine.

Try powering the 5D and the preamp from your power supply and leave the monitor on its own power supply or totally disconnected.

This was a combination I didn't see. It's the one most likely to cause problems if it is power supply noise related.

 

[jeep642]

OK, at least we know we're not duplicating effort

My first try beyond checking filtering/decoupling would be to get some toroidal ferrite cores and wrap *all* the cables through them as many times as possible. See if this reduces the noise. If you're really keen you could do it one at a time and see where you get improvement.

Something like this:

Unless you can beg, borrow, or steal some, wait until we've looked at your circuit diagram. There may be other things to try as well (or even before you try this).

Thanks, I will try that.

 

[(*steve*)]

Thanks, I will try that.

This may come to naught if your problem is filtering/decoupling related.

 

[jeep642]

Here's the schematic for the PSU with the SWADJs. As you can tell, pretty basic, which is probably why I have issues.

12v is for the monitor.
9v is for the preamp
7.2v is for the camera.

Also, the diagram to show where the sound comes from and where it goes.

and a zip file of a recording of the noise: (the limit to upload is 97.7k so I had to make it an audio .mov files to be small enough)
@0s: all off
@2s: preamp on
@8s: 5D on
@13s: video out on
@18s: monitor on
@24s: 5D recording

The sound has been recorded from the headphones out of the preamp. It would be exactly the same to record it out of the camera.

 

[davenn]

hi jeep,

you board layout shows you supplying 12V from a 5V regulator, that aint gonna work is there a typo in there ?
its very incomplete with much missing.

You have no filter capacitors around any of the regulators there's gonna be lots and lots of noise (hum etc) on the power rails

what are the regulators ? ie what chip ? I suspect the 7.2V rail regulator isnt capable of supplying the current needed for the camera specially if it isnt heatsunk, its going to need to be a regulator of at least 2A capability.

You need to do an actual schematic of what you need, that way it will be clearer what components and values thereof are needed. And what components you havent put in the cct that are needed to make it work correctly.
for example ...
if they are adjustable regulators say like a LM317.... there should be resistors shown to set the required output voltages

cheers
Dave

 

[(*steve*)]

Depending on the current drawn from each of these devices, and the gauge of wire used, it is possible that variations in power drawn could affect the ground level between various pieces of equipment and thus introduce noise.

The grounding arrangement on that board is almost certainly contributing to your problems.

But let's wait until we know what regulator modules you're using.

 

[jeep642]

But let's wait until we know what regulator modules you're using.

This is what I used.

I got that from a thread on a 5D forum. Someone was powering a bunch of devices, viewfinder, monitor, camera, etc... with these.

If I had known what kind of trouble it would be to incorporate a preamp in this set up I might have though twice about it!!!

 

[jeep642]

Actually, someone noted that on the SWADJ regulator web page it says "typical ripple is 25mV and under ideal circumstances". May be these regulators were not stable enough.
It made sense so I went and built this. They say it's "low ripple". (Whatever that means, may be 25mv is already low ripple.)


I just finished testing it and...no luck,

I did 2 things:

First I powered the camera with the SWADJ, and the preamp with the new circuit = noise.
Then I powered the preamp with the SWADJ, and the camera with the new circuit = noise.

So either this circuit is not stable enough or it's another problem.

 

[jeep642]

Here's an idea. You guys tell me what's the better option.

Instead of trying to fix something that obviously needs a whole lot of fixing how 'bout I start from scratch with better insight from more knowledgeable people.

All I'm trying to do (and I'm not attached to the original design in any way) is to go from a main battery power supply (14-16v, 90A/h) to 12v, 9v, 7.2v.

I'm pretty sure none of the devices I use draw more than 1 amp so I don't think it needs to be heavy duty in terms of current handling. Apparently, the only difficult thing is that it needs to be VERY stable because of the use of a sound preamp (on the 9v).

 

[jeep642]

hi jeep,

you board layout shows you supplying 12V from a 5V regulator, that aint gonna work is there a typo in there ?
its very incomplete with much missing.

Sorry. Yes it's a typo. the regulator is set at 12v to (obviously ) supply 12v out.

I'm sure there's much missing, given the catastrophic results but I'm sorry to say, it is not incomplete. That's all there's to it. Power goes in, 3 SWADJ set up at 3 different voltages, the 3 different voltages go out.
Simple (on paper... or as long as you don't use any sound devices with it!)

 

[davenn]

ok thanks for the additional info that helps lots

next question is where is the power coming from that is supplying these 3 regulators ?
I think you said it is a battery. Reading the data sheet, I suspect they are step down regulators so for a constant 12V out you are going to need a minimum of 13-14V input
else it isnt going to produce a good 12V out. No prob with the 5V and 7.5V rails there tho.

I will post more when I get home from work gotta go ....

Dave

 

[jeep642]

next question is where is the power coming from that is supplying these 3 regulators ?
I think you said it is a battery. Reading the data sheet, I suspect they are step down regulators so for a constant 12V out you are going to need a minimum of 13-14V input
else it isnt going to produce a good 12V out. No prob with the 5V and 7.5V rails there tho.

I have two main batteries:

a Anton Bauer Dionic 160
and a Anton Bauer Dionic 90

All Anton Bauer batteries for ENG cameras are 14.4v but when I test them fully charge they're above 15v.