Ignition noise suppressing

Discussion in 'Automotive Electronics' started by R!f@@, Jul 11, 2015.

  1. R!f@@

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    Apr 2, 2009
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    I was able to suppress the ignition noise in a car audio installation that was done by the know it all individuals.
    The owner want an equalizer to be installed. This is where problems lies, The equalizer is generating ignition wine. Since without it, there is no noise that can be heard.
    So I believe the noise is there but inaudible and the equalizer is boosting the noise level to the audible range.
    I checked the equalizer, removed the power amp and converted it to a signal level one ( before it was speaker level). I did notice there was no power inductor filter as I have seen on car audio players. A laminated core inductor placed at the 12V line.
    I have yet to figure out if the power line is injecting the noise or it is from the signal lines.
    The signals are all fully shielded RCA cables. Before it was just plain wires and wired from speaker level signals.
    Now the Audio is much cleaner than before .
    I will post some scope pictures of the noise and need to figure out a filter that can be placed in the power line to filter out the noise.
    Before that does anybody have any idea on a filter design that I could use ?
     
  2. Bill G

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    Jul 14, 2014
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    I'm not doubting your expertise or methods here but are you sure it is ignition noise. I have seen many times were alternator whine is mistaken for ignition noise. You could scope the alternator output and see what it looks like or if you have some larger clip on ferrite cores just as a test. If it is the alternator it will only get worse and you could be a hero to the owner. Sure beats a dead battery some morning.
     
  3. R!f@@

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    Now you have said it I wonder.
    The noise is wining kinda .
    When engine is started I get low frequency wine and increase in tone when engine revs up.
    So it is either ignition or alternator.
    Best part is the noise is amplified when the equ settings are increased. And the frequency setting that effects or amplifiers the noise it 4KHz and up.
     
    Last edited: Jul 11, 2015
  4. Bill G

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    I think what you are hearing is definitely alternator whine. Ignition noise usually comes across as pops and crackles.
     
  5. R!f@@

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    OK. So how to get rid of it.
     
  6. Bill G

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    Scope the alternator output, it should be a clean and fairly even ripple display. If it is not and has a lot of hash and strange looking parts to it you have an alternator problem and it needs to be repaired or replaced. It's not unusual to have a failing component and still work fine as far as normal automotive demands are concerned.
     
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  7. R!f@@

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    I will do that and get back with scope image
     
  8. Bill G

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  9. R!f@@

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    Tht was a good info. Thanks

    One question though. Before I attended the works there was noise without equalizer. Now after proper wiring with ground shields I cannot hear any noise. With Eq it is coming back
     
  10. nsaspook

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    The noise is usually from a current loop in the signal path. The easiest way is to break the loop with a isolation device but moving the signal/power/grounding of all units to common connection points might help .
     
  11. R!f@@

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    That is how I removed the noise in the first place. Proper ground techniques and shielding
     
  12. nsaspook

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    I had to use ground loop audio transformers in my car for a remote headphone amp to stop engine noise.
     
  13. MikeML

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    I made a second career fixing this problem, primarily in aircraft audio systems. The cause is always the same: a ground loop, caused by more than one item (in the audio path) being locally grounded to the car body. Unrelated current flows along the car body create a voltage drop (in the mV range) between disjoint audio grounds, and that introduces common-mode signal, usually alternator whine, into the audio.
    Filtering does nothing, because the offending signal is in the audible range...

    The fix is not simple; frequently requiring mounting all of the audio devices in close proximity to one another (so that they can share a single point ground), rewiring, sometimes adding ground-loop isolators (audio transformers).

    The goal is simple. Imagine building the entire audio suite on a wooden kitchen table. There is no car body ground. Every interconnection must carry ground through the wiring harness. Every power feed (negative side) is brought to a single point. When the audio system is installed in the vehicle, there is only one place that can touch the frame! If things like the head end are intrinsically grounded by their mounting screws, then that must become the de-facto single-point ground for the entire system.

    It is really hard to fix a screwed-up install without revisiting every single connection, and possibly redoing the entire install.
     
    Last edited: Jul 11, 2015
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  14. MaxHeadRoom

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    Old Style alternator regulators both mechanical and the later electronic version, used to be variable switching so the frequency would change in pitch as the Alt output went up, now they are practically all hi freq switching PWM in order to be out of the audio range, and switch at a known frequency, this was to make suppresion easier to predict, so if it is the Alt on a modern car, the whine should be be a constant freq if heard at all.
    Max.
     
  15. MikeML

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    Max, that is not correct. I have scoped lots of modern alternator controllers (regulators) and their typical field-switching on-off rate is still 50 to 250Hz. The pulley-belt system drives the multi-pole alternator such that the ripple frequency (the offending whine) is directly proportional to engine rpm and is typically between 500Hz and 8kHz, right in the audio passband. It cannot be filtered in the audio; the only solution is getting rid of ground loops, usually by using single-point grounding. The ripple is not at all effected by the frequency that the field is pwmed.
     
    Last edited: Jul 11, 2015
  16. ian field

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    Whine is usually the alternator, not the ignition.
     
  17. ian field

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    Most people start by adding points capacitors to the leads coming from the alternator, attached as close to source as possible.

    For more persistent cases you can get feed-through or co-axial type suppression capacitors that have a tab for bolting to the frame and the lead feeds through the component.
     
  18. MikeML

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    Which is a sure indication that they do not know what they are doing.

    Which does nothing to cure the problem because the noise is not getting into the audio devices via the +12V power line. Any well-designed headend, equalizer, or amplifer has a power supply rejection ratio of >100db.

    The vehicle's battery is equivalent to a several Farad bypass capacitor wired right across the alternator's output. What do you think adding another 100nF in parallel with the battery (your proposed filter cap) is going to do???

    Been there, done that, got the t-shirt! Power line filters do nothing to cure this problem.
     
    Last edited: Jul 11, 2015
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  19. ian field

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    Shunts the start of the wire antenna whose other end terminates at the battery.

    And points capacitors are usually around 220 - 250nf - not 100nf. The units sold for suppression are probably bigger still - but I don't do much car electrics these days.
     
  20. MikeML

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    This presumes that the problem is RFI; alternator whine isn't. It is at audio frequencies.
    I have tried "filtering" power going to audio and two-way radio devices with simple bypasses (nF to 10,000uF), and LC filters. Never resulted in an improvement, except in a couple of cases.

    The improvement came from a series L (ferrite or iron core, mH to H). The reason that it improved things was for a perverse reason. The audio device contained a (too big) capacitor shunting +12V to Gnd. That capacitor caused a large ripple current to flow along its own power leads, effectively creating a (local) ground loop. Putting a series L in the +12V lead effectively limits the ripple current flowing into the device, and breaks-up the ground loop. In effect, the audio device was trying to smooth the alternator output and thereby attracted alternator ripple current into itself. Naive design...
     
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