G3 Duo - combined external mic / charging cable

Hebs

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Hi folks - a newbie here.

I have a G3 and use the combined external mic / charging cable to feed audio from an intercom which works fine. The cable is also a charging cable and if I connect that to a 12V power source then I get really bad audio interference. Is there anyway to overcome this?

Andrew
 
Welcome to DCT @Hebs :)
First what 12V power source? Power supplies, powerbanks, and even car electrical systems can be rather 'dirty'. If possible try it with a stand-alone 12V battery with only the cam hooked up to it. If that works then your problem is in the power source you were using; if it doesn't solve things then the problem in in the cam or cable.

Phil
 
Welcome to DCT @Hebs :)
First what 12V power source? Power supplies, powerbanks, and even car electrical systems can be rather 'dirty'. If possible try it with a stand-alone 12V battery with only the cam hooked up to it. If that works then your problem is in the power source you were using; if it doesn't solve things then the problem in in the cam or cable.

Phil
Thanks Phil - it's 12v from a vehicle battery in a rally car.
 
Most cars now have computers running even when the car is parked, and that can introduce interference through the entire electrical system. Being a rally car, I'll presume you can test as I mentioned with only the cam hooked up tho the battery and nothing else. That diagnostic step will eliminate any possibility of the car affecting the cam, which will direct you towards where the solution needs to be sought and applied.

My guess at this point is that the intercom and mic input aren't working well together. Could be the intercom signal input level, could be related to signal frequency, could be a specific type of interference. The fix might be as simple as snapping on a ferrite choke (or two), or as complicated as building a filtering or isolating circuit. But we can't know for sure what to try until we know where the problem originates so we need to start there- otherwise it's just guesswork which usually leads to wasted effort and frustration.

Something else which will assist the diagnostics is trying a mic which you know works OK as an input on the cable while you're doing the power isolation testing; that will help us further narrow down the possible source of the problem.

Phil
 
Phil,

Thanks for your help.

I have done some tests; I didn't have another mic, so I used an MP3 player to provide an alternative, standalone, audio feed. The issue seems to be when receiving audio from the intercom AND on power from the vehicle. A summary of tests is:

1. external battery & intercom audio: good
2. external battery & MP3 audio: good
3. no external power & intercom audio: good
4. no external power & MP3 audio: good
5. vehicle power & intercom: bad
6. vehicle power & MP3 audio: good

Does this make any sense?


Andrew
 
Good diagnostics (y) And there's some sense in this because it identifies exactly where the problem is: the intercom when hooked to vehicle power. In that it also shows that the intercom itself does OK, but not with the car also being on the same power source. So what is likely happening is that the power at the car battery is 'dirty/noisy' and it is passing through the intercom to the cable and cam. The fix is to clean up the power to the intercom.

Something like THIS should do the trick. Red to car power 12V+, black to car body or chassis ground, and blue to intercom power input. Probably best to locate this near the intercom rather than at a distance at the battery. A car audio shop should have something similar (or you may have such laying around). Just explain that you want to clean up the input power the same as would be done to a car radio. There shouldn't be any more current than a regular car radio draws- you shouldn't need a huge expensive cap like is wired in for amplifiers.

This is by far the most likely scenario but not the only possibility. It is also cheap and the easiest fix so it's what I'd try first.

Phil
 
In addition, try to keep the power cable physically away from the microphone cable as far as possible, if you run them side by side then it is easy for noise to radiate from one to the other since the microphone signal is tiny.
 
Something like THIS should do the trick. Red to car power 12V+, black to car body or chassis ground, and blue to intercom power input. Probably best to locate this near the intercom rather than at a distance at the battery.

This is by far the most likely scenario but not the only possibility. It is also cheap and the easiest fix so it's what I'd try first.
Great - I will give this a go - thanks very much for your help. (y)

In addition, try to keep the power cable physically away from the microphone cable as far as possible, if you run them side by side then it is easy for noise to radiate from one to the other since the microphone signal is tiny.
Unfortunately power and external mic input are one combined cable, so this is impossible. :(
 
Unfortunately power and external mic input are one combined cable, so this is impossible. :(
Potentially there could be a ground (earthing) issue since you have two pieces of equipment each of which will have its own 0 volts. What does the problem sound like? A clip might help diagnosis.

SawMaster probably knows a lot more about this than me...
 
So a quick update. The...
Something like THIS

...took a while to arrive, so I decided to risk a whole £10 on a ground loop isolator to see if that worked while I was waiting. Great news - it worked a treat. Thanks, Phil and Nigel for taking the time to help - much appreciated.
 
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