Wiring Interference Maybe...?

[f0xy]

Ive had the bullet camera wired into the car for a while (spliced into cigg lighter wiring), and its worked great! So i thought it would be time to get a microphone to go with it, as the camera was just a camera. Picked one up on ebay, little small microphone....Has a 9v DC input and an audio jack. It came with a mains adaptor, so you could plug it into a wall socket, and it would be reduced into 9v, then you could plug it in.

I got hold of a reducer for cars, that can be changed from between 1.5v and 12v, with one being 9v, just what i required. I spliced this into the exact same point as the bullet camera. Ran the audio into the AV lead thats for the camcorder (white and red), along with the video lead from the bullet camera (yellow), so everything was going through one cable into the video camera....Before i just had the video(yellow) plugged into this lead that goes to the camcorder, as there was no audio.

Anyway, when i plug the lead into the camcorder, and set it to record, I can hear the noise, and see the video fine, but over the top i get a high pitch whistle/whine. This happens with the car on AND off, so im guessing it cant be alternator whine or anything?!?

I found out something about ground loops can cause this? But ive tried things that ive read and there seems to be nothing wrong with the wiring side....The polarity of the voltage reducer is fine, ive checked it...

Wierd thing is, if i unplug the power from the car, and run the microphone off the mains using the adaptor that came with it using an extension lead to the car, it records fine, no high pitch whisle, all the video and audio is fine. So im guessing its definately something to do with the power side of things on the car......Everythings been checked and it powers MP3 player + portable CD player fine, with no whine....?

Has anyone ever had anything like this?

 

[bmh.01]

I'd guess its the voltage reducer. When i've recorded in bay with the Clio i've always had a lot of alt whine but if its doing it whilst not running then its got to be the reducer.

 

[f0xy]

hmmm

do you know what a ground loop is? i dont really fully understand from reading on the net...

 

[bmh.01]

Where you have two seperate circuits using the same ground should be 0v so theres no potential difference between them. A ground loop is when there is a potential difference between the two grounds of the circuits (ie 0v for one and 0.001v for the other) so you get interferance, i'd guess the problem will be to do with the ground the voltage converter is providing compared to the one whatever else is using which is giving you interferance through the mic and they're very sensitive to it.

 

[KDF]

hmmm

do you know what a ground loop is? i dont really fully understand from reading on the net...

Attach the ground cable from the mic to the chassis of the car, had the same problem but with the video from a mains invertor in my car.

 

[f0xy]

tried that^ still didnt make a diff



seems the mic is s**te........clipping all the time......

but i got rid of the reducer, and ran the mic straight to 12v dc power. now i get a wierd whine....gotta be alternator? due to change in pitch with revs?

http://www.vimeo.com/1298046

 

[bmh.01]

Thats alt whine for sure, thats the noise I always used to get. Where have you routed the cable?

 

[KDF]

sorry you need to ground the earth on the audio cable to the earth of the car, not the earth of the power cable.

Just get a cable and strip the ends then touch an earth on the car and touch the earth of the mic and see if the whine goes away.

 

[Andi-B]

if that doesn't work, get a suppressor for the car, best bet would be an stereo suppressor like this - http://www.halfords.com/webapp/wcs/...oreId=10001&catalogId=10151&langId=-1&x=0&y=0
should Go in line on your power feed and should eliminate audio interference.

 

[bmh.01]

Doubt a suppressor will get rid of the alt whine though. As thats interferance acting on the cable to the mic, you'd need a grounded screened cable to eliminate it. The knock sensor uses screened cable if you look at it as it is just a microphone sensitive to specific vibrations.