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  1. #1
    Approved Vendor ZombieSatty's Avatar
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    Chasing audio noise

    I might be over thinking this, I do it a lot.

    I have an audio noise, a soft, patterned static or pops. Can seem to only hear it on some stations, NPR and lower powered stations specifically; but not convinced it's not constant. I don't THINK it's there with CDs, and the AUX port is blown or something so can't test that (super quiet and static)

    It really sounds like it's in sync with rpm, ie: spark plugs or coils firing. Sound goes away totally when car ign is off (not running).

    Setup:
    >Pioneer head unit - DEH-P8300UB
    >Pioneer amp - GM-D9500F
    >Ion battery in trunk
    >Power wire down drivers side, crosses over to center under driver seat, down center consoles, to pass side trunk, to battery (identical to ION routing).
    >amp and battery grounded to old jack mount location. Engine block grounded to factory battery ground location.
    >twisted RCAs run down center of car straight back to amp.
    >I left the fuseable link in place, if that matters, all other power and ground wire is larger than stock gauge.
    >Head unit case grounded to dash frame, harness ground through factory harness.

    My thoughts:
    RCAs too close to power wire (omg!). I can move them to pass side, but it really seems this is more than that. Plus, this is WAY cleaner.

    I have premptively ran the RCAs for sub line too, and connected to head unit, but not the amp (no sub). They could be a possible interference/antenna for noise?

    Problem with head unit? Pico fuse or something or other?
    Last edited by ZombieSatty; 02-24-2017 at 02:38 PM.
    It's not my fault, blame the radiation.

  2. #2
    siris's Avatar
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    What are your gains set at?
    72 Charger: pissed me off, on jackstands.
    95 SW1m: Dohc swap. DD. I can haz boost?

  3. #3
    Approved Vendor ZombieSatty's Avatar
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    On the amp? All the way up iirc. I did the set headunit volume at 70% fader 100% front or rear, then turn up gains until you hit distortion, then back off a bit. I never got distortion, that I noticed. The eq on the HU is minorly tuned, bass boost and LOUD functions turned off.

    I set the gains in Fontana this year, right before I packed up and headed home. If they were distorting and nobody else noticed.
    Last edited by ZombieSatty; 02-24-2017 at 03:34 PM.
    It's not my fault, blame the radiation.

  4. #4
    siris's Avatar
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    Personally I've noticed with really high gains at the amp, it pics up alot of electrical noise, lower quality amps are really bad with that. Some of the higher quality amps use better MOSFETs and whatnot, so they are more resistant to noise.

    I would try turning the gains down a bit and see if it clears up.
    72 Charger: pissed me off, on jackstands.
    95 SW1m: Dohc swap. DD. I can haz boost?

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  6. #5
    Approved Vendor ZombieSatty's Avatar
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    I'll try.

    Just had a thought. My radio antenna is tucked in my A pillar. Maybe I should put that back?
    It's not my fault, blame the radiation.

  7. #6
    siris's Avatar
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    Maybe? But I wouldn't think it would have any affect on aux input.
    72 Charger: pissed me off, on jackstands.
    95 SW1m: Dohc swap. DD. I can haz boost?

  8. #7
    Approved Vendor ZombieSatty's Avatar
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    True, I am not currently worried about the AUX, figuring that port is blown or bad plug. Maybe it's related however.
    It's not my fault, blame the radiation.

  9. #8
    Approved Vendor ZombieSatty's Avatar
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    Sound is on all radio stations, does not change with volume. Only RPM.

    I'm thinking it might be time to crack the HU open.
    Noisey coils?
    It's not my fault, blame the radiation.

  10. #9
    toka100's Avatar
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    I might be wrong but start at the easiest fix. I would start with the rca cables. The less chance they can receive any noise from the power wire the better. Then I would look at your amp ground. Try a different ground location for the amp itself. Try to keep it under 18" in length also. Then look into other issues.
    Last edited by toka100; 02-27-2017 at 05:41 AM.
    94 sw2. (Boda Fett) . Secret ultimate daily driver build in the works.

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  11. #10
    Approved Vendor ZombieSatty's Avatar
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    Ground is about 2ft or less atm.

    I'll try and rearange the RCAs when warmer weather comes, have to pull interior out.

    I'm not sure at this point if it is present during CD playing/pause.need new batteries for remote (no pause on headunit wtf?)
    It's not my fault, blame the radiation.

  12. #11

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    I deal with this sort of thing a lot where I work (other equipment though, not cars). BTW, I think siris and toka100 both have excellent suggestions on this.

    I think continuing to find out what's affected is a good idea. If you can determine that it's happening with the CD as well, this suggests a common problem for CD, radio and aux, and that would suggest power supply connections to me.

    Your problem is in the area of EMI (electromagnetic interference). This can be generally classed into two kinds: conducted (it is present in the wiring) and radiated (it is being "picked up" by wires acting as antennas). Kind of a simplification, but you get the idea. I deal with this stuff on a daily basis.

    One thing that can happen when you use the chassis as a ground is that it isn't a perfect ground (it has some non-zero resistance) and something that's pushing a lot of current through the ground develops a voltage across it, and sensitive stuff that's sharing the same ground sees this voltage. It's called "ground bounce" in the digital logic community. So, let's say that the primary side of the coils is switching a lot of current each time the coil fires -- this current flows through the block/whatever and chassis ground back to the battery. If your head unit is seeing this as a variation in its supply voltage, you might hear it. Not saying this is what's happening, but it's a possibility.

    One thing people do to overcome this is to provide separate ground returns from each piece of equipment to a central point. This is called a star ground. (worth googling for pictures) Instead of tying each piece of equipment's ground to the chassis nearby, you run a separate wire for each piece of equipment to a junction at or near the battery. Current flowing in another ground conductor is therefore less likely to influence neighbouring circuits (because each has is own separate ground return path). This can be a lot of work to get sorted, and it can happen on the +12 supply as well as ground. I would take all of the audio stuff and give each piece its own power and ground lead back to junctions right at the battery if this seems to be the problem -- it is a brute force approach but it's often effective.

    If you find that this noise is sneaking in through the power supply of the head unit or amp, putting a capacitor across the +12v supply to ground right at the equipment can help. There are many other fixes. If you need to go down that rabbit hole I can be of some help.

    One thing to pay special attention to is any wiring where a low signal level is present, and it's being amplified. So this is your RCA cables. Using good shielded cable is a very good idea here. Good quality connectors will ensure that the shielding continues right up into the connector, and that you have a solid low-resistance connection.

    I just looked around for some online reference to this stuff, and I didn't find any one thing that's really suitable, but you might look for some articles about EMI/RFI and car audio.
    93 SW1, 95 SW2, 98 SW2, 97 SW1 -- all stick. Wagon hoarder.

  13. #12
    Approved Vendor ZombieSatty's Avatar
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    Thanks!
    I'm using Streetwires brand RCA cable. If they are good or bad, i don't know.

    Just going by easiest to PITA, I'll try the cap idea first. Do you have suggestions on what to buy?

    Some research has led me to an issue with many old Pioneer units actually having a fuse on the pcbs between the ground and signal lines of each output on the RCA lines, they call it s PICO fuse or something. The fuses will blow if you ever hot swap (plug/unplug) the RCAs with the unit powered. When they blow, they cause noise in system. Seems I'll check that out as well.
    It's not my fault, blame the radiation.

  14. #13

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    Quote Originally Posted by ZombieSatty View Post
    Thanks!
    I'm using Streetwires brand RCA cable. If they are good or bad, i don't know.
    I have no idea if they are good or bad either, but let's assume for the moment that they have sufficient shielding and make decent contact.

    I'd do the following tests for starters:

    1. See if you can isolate the problem to the head unit: Disconnect the RCA cables to the amp and connect a speaker or two directly to the head unit's speaker terminals and see if the noise is still present. Hearing the noise would suggest that the head unit by itself is where the noise is coming in.
    2. See if you can isolate the problem to the amp: Disconnect the RCA cables at the head unit and, with just the amp operating, see if the noise is present.
    3. If the noise is only present when they are connected in the normal manner, this suggests that the problem may be due to the difference in ground potential between the two units as I described earlier -- no guarantee, but it suggests this may be the case.

    Doing these tests would help identify where the noise is getting into the system and we then have some useful information on how to eliminate it.

    I agree with siris with the idea of not running the amp wide open... if the noise is arising from the connection through the RCA cables, then lowering the amp's sensitivity (and increasing the head unit output for the same volume) will help.

    I'd also see, if possible, if it's happening with the CD player... we need to determine if this problem is present in all cases -- unless you're already confident that it is. The fact that you're hearing it with the aux input suggests that is isn't a radio-only problem.


    Quote Originally Posted by ZombieSatty View Post
    Just going by easiest to PITA, I'll try the cap idea first. Do you have suggestions on what to buy?
    Oh man, I'd be reluctant to see you spend any money on a solution that might not help. If the impulsive noise is originating from the ignition system, and it's showing up via the power wiring, then a film cap of a few microfarads may be all that's needed. For alternator whine, larger caps located (electrically) near the noise source seem to work. Capacitors, BTW, aren't perfect, and a lot of capacitors cease to act like capacitors at high frequencies... so for short impulsive noises with a lot of high frequency content, a smaller value film cap might outperform a big electrolytic. I wouldn't recommend going down this route until more is understood about how the noise is getting into the system. If you need caps (and other noise suppression goodies) I'll just send you some.... tons of that stuff here.

    This guy is spot-on for more to check:

    http://www.termpro.com/asp/pubs.asp?ID=121

    Quote Originally Posted by ZombieSatty View Post
    Some research has led me to an issue with many old Pioneer units actually having a fuse on the pcbs between the ground and signal lines of each output on the RCA lines, they call it s PICO fuse or something. The fuses will blow if you ever hot swap (plug/unplug) the RCAs with the unit powered. When they blow, they cause noise in system. Seems I'll check that out as well.
    Pico fuses are a brand name for small fuses with wire leads that are often soldered directly to circuit boards. It is probably there to prevent the input stage from being damaged by high current in a fault condition. A fuse between ground and signal would act as a short -- maybe it's in series with one of the lines?
    93 SW1, 95 SW2, 98 SW2, 97 SW1 -- all stick. Wagon hoarder.

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