Microphone and camera using same power sounds like crap

[JohnWin]

Hi,

I'm building a camera shoulder rig and want everything (camera, monitor, light, microphone) to run off of the same battery. So I made a power distribution box with step down voltage regulators.

Everything works great except for the microphone. It's making some weird pulsing sound. I'm assuming it's the power feeding back thru the output. The reason I think that is because if I power the camera with its own battery the mic works fine. the only time the problem occurs is when the mic and the camera are both working off of the same power supply.

I've tried putting a capacitor between the + and - and also tried using a diode different places inline. But those were shots in the dark and didn't work.

Any ideas would be great! Please dumb it way down tho.
Thx!

 

[Harald Kapp]

A capacitor alone will help only so much. You need a filter with a series impedance, e.g. an unductor that blocks higher frequency noise but passes DC. You can buy off the shelf modules e.g. in the car accessory section of your favorite store (e.g. like this one) or roll your own (see e.g. here).

 

[JohnWin]

A capacitor alone will help only so much. You need a filter with a series impedance, e.g. an unductor that blocks higher frequency noise but passes DC. You can buy off the shelf modules e.g. in the car accessory section of your favorite store (e.g. like this one) or roll your own (see e.g. here).

Thank you so much! I'll see if I can get one for the local auto store. Hopefully one with directions in English. Thanks again!

 

[(*steve*)]

Are you using switch mode regulators? They can be very noisy.

Even with this, you can also have problems caused by ground currents.

 

[AnalogKid]

Please post a schematic and photos of your regulator box.

ak

 

[JohnWin]

Are you using switch mode regulators? They can be very noisy.

Even with this, you can also have problems caused by ground currents.

I'm not sure what switching mode regulators are. So idk. I'll attach a photo.

 

[JohnWin]

Please post a schematic and photos of your regulator box.

ak

Ok I uploaded a photo. I'm not sure it worked tho. I don't see it.

I don't have a schematic. There's really nothing to it. Just an input from a battery going to step down voltage regulators then to there connectors. Oh an there's a switch.

 

[Audioguru]

You never said the part number of the voltage regulator, its input and output voltages and the input and output capacitor values.
You say there is more than one voltage regulator. Why?

When posting, there is a button that says, "Upload a file" which is where you browse the schematic on your computer, click on it and click the "open" button.

 

[JohnWin]

You never said the part number of the voltage regulator, its input and output voltages and the input and output capacitor values.
You say there is more than one voltage regulator. Why?

When posting, there is a button that says, "Upload a file" which is where you browse the schematic on your computer, click on it and click the "open" button.

Ok the part # of the voltage regulators is LM2596 DC-DC HW-411 They are the variable type. I get them on ebay and use them all the time. I use one for each voltage I need. On the rig I have a camera which takes 8.4V, monitor 12V, and the microphone at 1.5V. So there are three regulators.

I don't have a schematic or photos of it at their own URL i can use. Honestly there's not that much to it. I think the problem is im powering the camera and the microphone from the same source but thru there own regulators then plugging the mic into the camera which is grounding them together. IDK tho.. I hope the module @Harald Kapp suggested works.

 

[AnalogKid]

Switching regulators are inherently noisy, both through connecting wires and through radiation. The way the regulator inputs and outputs are wired is critical to their noise performance. Photo?

ak

 

[JohnWin]

Switching regulators are inherently noisy, both through connecting wires and through radiation. The way the regulator inputs and outputs are wired is critical to their noise performance. Photo?

ak

That's interesting. Its a big pile of spaghetti too. But the connection are staight foward. the inputs of the three regulators connect to the + and - of the battery. And their outputs go straight to the device via a connector and cable.

I've got to run into town but will be back in a few hours. I'll post the pic when I get back. Do you know a good place to host the pic so it has a URL? Thx!

 

[AnalogKid]

A big pile of spaghetti is the worst possible wiring plan for anything even remotely involving audio.
Use the "Upload a File" button to upload a file.

ak

 

[Alec_t]

Are you using a star ground system? If not, ground currents from the camera and supplies may get superimposed on the microphone signal.

 

[JohnWin]

Hopefully there is a photo attached here

 

[JohnWin]

Are you using a star ground system? If not, ground currents from the camera and supplies may get superimposed on the microphone signal.

No, I don't know anything about a star ground system. But that sounds exactly like whats happening. I'll look it up. Thanks!

 

[Alec_t]

Do you have a spec for the mic? Normally an electret mic rated for 1.5V would get its supply via a load resistor from a higher voltage source and that supply would be decoupled by a capacitor.

 

[JohnWin]

Do you have a spec for the mic? Normally an electret mic rated for 1.5V would get its supply via a load resistor from a higher voltage source and that supply would be decoupled by a capacitor.

Here are the specs for the mic:

• Transducer Principle: Back Electret Condenser
• Directivity Characteristic: Cardioid
• Frequency Response: 50Hz-16KHz
• Sensitivity: -32dB±3dB(0dB=1V/Pa at 1KHz)
• Sensitivity Tone Up: +10dB
• Bass Filter: 60Hz 10dB/octave
• Output Impedance: 2000Ω±30%
• Power Requirement: 1.5V AA battery
• Net Weight: 160g

That load resistor and decoupled by capacitor sounds like the way to go. I just don't know how to do it. But now that you've given me the keywords i can try to figure it out. I'm assuming it would be best to come off the volt reg for the camera which is 8.4v? Or would it be better to come directly off the battery? Thank you so much for your help!

I went to three different stores looking for that Auto Filter Module today. Nobody had them. So i guess I'll order one online. I can try the resistor capacitor thing while I wait for it to arrive.

 

[JohnWin]

A big pile of spaghetti is the worst possible wiring plan for anything even remotely involving audio.
Use the "Upload a File" button to upload a file.

ak

I don't think it's the regulator because when I put its own battery in the camera the mic works great. And its still on its regulator. t really seems to me that it has something to do with them both being on the same power supply.

 

[dave9]

Based on those specs I saw a mic listed the same, claims 100 hours playtime.

http://www.takstar.com/en/product/detail-16-79-15-289

This suggests a couple dozen mA current at most. With that in mind, I'd run a linear regulator (LM317 or whatever, with a small uF cap after it) to the mic from the camera 8.4V and if that wasn't quiet enough, skip the camera step down board and run it straight from the main battery output instead.

Frankly I'd want a linear regulator anyway, would not run a mic off a SMPS.

 

[Audioguru]

You can't hear the 150kHz noise from the switching regulator but it might beat with the frequency of the second or third regulator or any digital encoder or decoder you are using.