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Thread: Sounds like a ground loop

  1. #1
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    Sounds like a ground loop

    I recently replaced my stock speakers for two reason. The speakers are old, 10 years of use is a pretty good life span but it's time for them to be laid to rest. Prepping for a carputer install, it just didnít make sense for me to go from RCA to speaker level. I've run into problems though which has put the Carputer in a bit of a holding pattern.



    This is what I'm working with:

    Vehicle - 2001 Toyota Sequoia SR5

    Speakers - Front: Infinity Kappa 60.9cs (6 1/2 with crossover and tweeters)
    Rear: Infinity Kappa 52.9i (5 1/4)
    Subwoofer: 2 x Alpine Type R 12"

    Amplifier - Pioneer GM-6400F 60 x 4 for components
    Kenwood 800w Bridged (had it for a LONG time can't remember model number, can check later)

    Capacitor - Stinger 1 Farad

    Wiring - Power: 4 Gauge from battery to Monster Distro Block 8 gauge to equipment running through drivers side
    Grounding: 2 Separate ground points (this was done to avoid having too many components on a single ground and to have the ground wires no more than 12" long)
    Audio: Monster Cable RCA's from line converter to connect to stock HU for Kenwood Amp, 16 gauge from stock HU to speaker level input of Pioneer AMP. Both are running down passenger side.

    Relay: 12V accessory to 30 amp Automotive Relay

    Here's my problem and an overview of some of the troubleshooting/hopeful fixes. I presume I have a ground loop because I am getting alternator whine through my component speakers. I've tested all my ground points and the ohm reading is low, as low as .002 but only as high as .004. I've tested it out from equipment ground connection to other points in the vehicle chassis (as far as my multi-meter cables would let me stretch) and the ohm reading remains low, nothing over .02 ohms. So from my experience the grounds should be good. The thing I'm thinking of doing with the grounds is finding another solid grounding point and getting another distribution block for 2 or 4 gauge from equipment ground and 2 or 0 gauge to a single ground connection. I checked the ground on the Head Unit and it's not as low as I would like it to be but it's still almost insignificant at .03 to .04 ohms. So yesterday I pulled off the speaker level inputs from the pioneer amp and daisy chained from the Kenwood to the pioneer, I would go straight into the Pioneer but the RCA cable is damn near the exact length to get into the Kenwood. The whine dropped significantly but is still present. It got interesting when I hooked up a ground connection from the Kenwood amp chassis (didn't make one, used one that was already on the amp) and the whine got worse. This is why I'm thinking of running grounds to a distro block to a single ground point, is it possible that I have too many grounds and that causing the loop. I'm also thinking about going ahead and grounding the chassis of the head unit. I took the head unit apart this weekend to look inside and see if there was a bad ground somewhere in there but I didn't see anything that seemed off. I want to try and isolate the HU from the system to see if the whine goes away, but I couldn't find my 3.5mm to RCA connector to hook up something else to it. I'm going to look for that again when I got home today.

    Sorry this post is so long and I hope it doesn't drive anyone away from reading it, but I wanted to be as descriptive as possible for a couple reason. First for someone with more knowledge/skill than myself to critique my troubleshooting practices. Second to make sure anyone who has an idea or wants to help can get a solid understanding of my situation. TIA

  2. #2
    Raw Wave
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    800W RMS via 0.02R ~60 x .02 = 1.2 Volts (or 0.6V if W=pk) - so depending where that 0.02 Ohms is....

    I'd common to a single ground point - even jumper leads etc may be enough to tst for improvement.

    Since the HU probably isn't using that much power, it's higher GND resistance shouldn't be that critical...

  3. #3
    MySQL Error soundman98's Avatar
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    while it is a little daunting to see that Huge Wall of text, it is nice to actually have all of the details for once... instead of the normal "my radio buzzes"...

    next time, try breaking it up into smaller, easier to dissolve sections

    while you did try to ground the amp chassis, you could also try to ground the negative rca connection--most amps have the negative rca connected to the chassis, so it will probably have the same effect, but some rca connections are isolated from the amp chassis-- i would recommend trying to ground it on one side at a time, but to try both ends to see if it makes a difference.

    the other thing that i might have missed, or didn't see mentioned is how solid your grounding points are--if you are connected to thin metal for the grounding of either point, or did not sand off the paint, so that you get a metal-to-metal-connection, it is possible that is causing parts of it.

    the other possible issue that could be causing it is your amp gains-- if they are turned up all the way, it could be causing unneccessary problems-- my gains were all the way up to compensate for low input level, and in the process picked up alt noise-- adding a preamp, and turning the amp gains down corrected my gl problem.

    while i have heard in the past to keep ground cables as short as possible, i am starting to find that it is less of a issue than what most think. if you are going to run long grounds, i would consider upgrading to at least a gauge or two larger for the ground wire run.

    also, one of the things that i would check is that the capacitor is wired correctly(should be wired in parallel to the amps), or take it out completely-- you can search for oldsparks posts in the car audio on the true efficiency of caps...

    at the very worst, give a ground loop isolator a try, and if it works, call it a day...

  4. #4
    Raw Wave
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    Thanks Soundman.
    But to clarify for the benefit of others, I have never meant that caps are useless or without merit - I merely contend that a smaller & cheaper battery in its/their place will usually be FAR superior.
    Though I will often attempt to clarify and correct errors - like caps and batteries are an "extra load" to alternators or can make up for alternator under-sizing (see - already there is a contradiction LOL!).

    And if people don't even know the impedance of their amp PSUs and hence inductance with cabling, do they have any idea of the resonant frequency of the tank circuit (ie - the RLC with an input cap)? I assume it's fairly low with big caps....
    But back to this thread....


    It'd be interesting if caps are not wired across the supply.... Do people connect them in series with the +ve? That could account for a lack of output power but with audible noise/hum....
    But I assume "correctly" means as close as possible to the biggest load with the least +ve & gnd resistance possible. (Incorrect as in reversed polarity is usually obvious well before the coroner's report.)


    And the length of grounds shouldn't be any bigger issue than long power cables.
    But unlike the hot power, the inter-ground impedances are a big issue - ie, ground loops.
    Hence why the inter-signal grounds need to be LOW resistance - much lower than the +ve supply (for noise purposes). (If only grounds were separated as in digital and measuring circuits - ie, separate power and signal grounds.)
    If ground cables were exposed to AC as in a domestic audio setup, things might be different. But vehicles usually lack such AC exposure and are well shielded anyway. (That's what had me doubting ground loops in car audios some months back - until I looked a bit harder.... eg ground voltage drops... D'oh!!.)

  5. #5
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    Quote Originally Posted by OldSpark View Post
    Thanks Soundman.
    But to clarify for the benefit of others, I have never meant that caps are useless or without merit - I merely contend that a smaller & cheaper battery in its/their place will usually be FAR superior.
    Though I will often attempt to clarify and correct errors - like caps and batteries are an "extra load" to alternators or can make up for alternator under-sizing (see - already there is a contradiction LOL!).

    And if people don't even know the impedance of their amp PSUs and hence inductance with cabling, do they have any idea of the resonant frequency of the tank circuit (ie - the RLC with an input cap)? I assume it's fairly low with big caps....
    But back to this thread....
    didn't think of that, was just trying to point out that a cap might not be the best option, though, i don't think i pointed very well

    Quote Originally Posted by OldSpark View Post
    It'd be interesting if caps are not wired across the supply.... Do people connect them in series with the +ve? That could account for a lack of output power but with audible noise/hum....
    But I assume "correctly" means as close as possible to the biggest load with the least +ve & gnd resistance possible. (Incorrect as in reversed polarity is usually obvious well before the coroner's report.)
    the OP seems like he knows what he is doing with wiring and all, but it is one of those simple little things-- the first time i ever saw a cap installed, i freaked out that it was installed that way(parallel to the amps), and told the buddy that the installer he had do it was a moron...and then i had to eat crow...

    Quote Originally Posted by OldSpark View Post
    And the length of grounds shouldn't be any bigger issue than long power cables.
    But unlike the hot power, the inter-ground impedances are a big issue - ie, ground loops.
    Hence why the inter-signal grounds need to be LOW resistance - much lower than the +ve supply (for noise purposes). (If only grounds were separated as in digital and measuring circuits - ie, separate power and signal grounds.)
    If ground cables were exposed to AC as in a domestic audio setup, things might be different. But vehicles usually lack such AC exposure and are well shielded anyway. (That's what had me doubting ground loops in car audios some months back - until I looked a bit harder.... eg ground voltage drops... D'oh!!.)

    yup, the biggest reason for short little ground cables is voltage drop across the ground-- in theory, the shorter the wire, the less resistance, the less resistance the amp has to pushing out all that 'used' power(not the best term, but you get the idea), leading to less heat in the amp...

    but, the issue that i have is that ground cables are kind of a double edged sword-- your battery is still somewhere else, and the 'used' power still has to get to the battery to complete the circuit, and there is still going to be voltage drop in the cars frame... i tend to like the theory to use a larger ground wire, and use the correct lenth of cabling, instead of the shortest cable i can make.

    but this leads into a debate of what is best way of transmitting the power to the battery with less voltage drop? i know copper is said to be one of the better conductors (not going to count silver and gold in this--20' of the cable would be well above most sane peoples income/budget!), but is short copper wire/large steel frame, still the best when looking at voltage drop over the average car length of 20ft?

    when i hook up a amp, what wire should i use for ground(copper, copper clad aluminum{more commonly reffered to as CCA}, steel, aluminum)?

  6. #6
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    Thanks for the ideas and info guys gave me some stuff to work with, looks like I won't be able to get to it at all until Sunday, but I'll let ya know how it goes.

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