Ignition Noise

[High4Volts]

I need to make a filter. My problem is i am picking up spark plug noise in my radio. I have a few large capacitors. What else would i need to make a filter? i think the capacitors are 9700 mfd. I purchased a filter for this and it did not work for some reason. Thanks for any help.

[russlk]

The noise may be radiated to the antenna, check the grounding strap for the hood. Also, if you have old, leaky spark plug wires, these will make a lot of noise.

[dacflyer]

make sure your also using proper resistor plugs too

[myp71]

Haha good now this will be great for my MECP test coming up soon. <p>It is a spark plug noise,and not ground loop or alt whine? Alt whine goes up or down with the engine like the spark plug noise would.Also ground loops lets noise come in from a different spot. I know all you asked is how to make a filter but just making sure. <p>
Ryan

[High4Volts]

the pitch changes with the rpm's of the engine. It did not make this noise till i replaced an amp and added a passive crossover. I'm pretty sure it's picking up through the crossover but even teh filter i picked up at radio shack did not get rid of it. If it helps, when the lights are on or the air conditioner is on it is alot louder.

[myp71]

Then I would say Ground loop.A ground Loop is where a ground point is shared with your audio system on more than likey in your case would be your blower motor (a/c) and lights.I would make sure that you have your own ground on the body for your audio systems and move power and siginal wires for you audio system as far away from things like your blower motor.<p>Hope that helps
Ryan<p>[ June 08, 2004: Message edited by: My-P71 ]</p>

[haklesup]

It is a ground loop. THe head unit and your amp are grounded at different points of the chassis. tiny differences in the actual potental of ground between the two points is what you are hearing. This would not normally be a problem except that the shield in the line level cable (RCA jacks) is often also at ground potential. When you plug the two amps together it forms a loop in which a current flows that is porportional to the difference in the two ground points. Since this current flows along a signal path coinsiding with the audio amplifier input, it can plainly be heard.<p>Rewiring and filtering are a lot of effort and usually do not work. YOu just can't clean up all the electrical noise in a running automobile<p>A ground loop isolator is all you need, its just a 1:1 transformer. It plugs in between the ouptut of the head unit and the input of the amp. Find one at Radio-hut, wall-store or wherever car audio is sold. Its purpose it to break the DC continuity of signal leads preventing the completion of the ground loop<p>To proove it, unplug the RCA jacks from the Amp but leave it powered up and connected to the speakers. THe sound should stop. Likewise, it is not there when the car is not running.<p>Turning on other accessories like the AC, fan, wipers, signal lamps. all return current to ground at different points on the chassis thereby altering the local ground voltage and causing currents to flow to neutralize it making the ground loop noise worse.

[Edd]

'Mo info pls.
Is it on AM or FM or both ?
Supplementing all of the good info from others:
I think your source is going to be RF input oriented in nature. To answer that, get the noise inteference to its max, and then unplug the ant connection at the radio, if it disappears, the source would then be from the ant's circuitry. A good noise sniffer is a self battery powered pocket AM radio. Place it off station at the hi end of the band and start probing with its ferrite antenna area. That should help pinpoint ur noisiest area/source. Your solution is then giong to be good grounding or most likely shielding. A temporary/impromptu evaluation shielding of plug wires coil wire can be enacted by aluminumyumyum foil wrapping with a wrapped wire connection to a common grounding frame.That route you mentioned of the hi elect cap DC line filtering would be of no use in this situation . In ham work with SENSITIVE receivers, I have had to take mesh from coax cable and make my own mesh shielded looms for the plug HV cktry with associated metal shielded housings for the indiv plugs as well as the dist cover and ignition coil, in order to completely nail it.
That was considering impulse generated RFI. If it is low level audio lines making the pickup and is on both channels: Drop one AF channel at the power amps input, thus leaving the other channel to solely concentrate on and then find the unit that was feeding that input. Next unplug that line at that source and , if typically an RCA plug, then take a wad of aluminum foil and short its end out and evaluate for noise. That way the integrity and quality of the complete shielded line can be evaluated. Next just touch only the ground shell of the RCA plug to the mating jack of the previous device. If still noise free, plug in the cable in its normal manner. Still noise free ? Then work on progressively down the weaker signal chain in the same manner until the inteference pickup is at or approaching the degree that you were initially experiencing.That is the area that you have to make correction on then. Absolutely best that you can interconnect with a linear ground line, electrostatically and electromagnetically spaced away from high current carrying and RFI noisy/generating lines/sources. <p>73's de Edd
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<p>[ June 08, 2004: Message edited by: Edd Whatley ]</p>

[High4Volts]

thanks all. Edd the noise is in AM, FM as well as cd playing. It sounds like it comes from all 4 channels from the amp. I will try a few things you all suggested and see where that leads.

[rshayes]

It sounds more like a ground loop than radiated ignition noise. Ignition noise is very raspy and doesn't have much of a definite pitch. Further, the ignition noise spectrum is usually much lower in the FM band, due to the higher frequency, and FM is more resistant to ignition noise. The CD player should not pick up ignition noise at all.Further, ignition noise should not change when the electrical load changes.<p>A ground loop adds the noise in series with the audio signals, and will appear equally on AM, FM or CD, since these all share the same audio channel. This sounds like your problem. I would try the transformer isolator first.

[Edd]

OhhhTay:
Seems like with the info on the Cd player audio also being affected, that the creeping in of unwanted galvanic gnd loop sig will be in the front lower audio levels. I just covered both bases, as your initial suggested thought was towards it being ignition HV RFI. If you will just shed your low level audio interconnects and start at the pwr amp and work forward re-connecting in using the shorted line test and then opening it up and initially touching only the gnd shell [The source will be more easily discernible due to there being no overriding/masking audio] then a final plug in.
The cheapest 1:1@10Kohm Z audio isolation xformer is probably RS's 270-0054 in the $15 range or for more bucks from Pyramid, RCA and Leon sourcing.
73’s de Edd