Dreaded Alternator Whine in car stereo - Page 1
Forum section: electronics / projects

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 07:33:14 pm
content: Hi All, I don't know where else to turn to. I've been trying to hunt down an alternator whine in my car stereo for a very long timeand I thought, why not just try to filter the 3 phase AC ripple from the alternator as a last resort. I came across this capacitor made specifically for the purpose but it is not available in the US.http://www.audiotec-fischer.de/lng/en/helix/products/accessory/cap-33.htmlLooks to be 33,000uF 105ºC rated low ESR with screw terminalsIt is probably no different than a low ESR cap I can get from digikey. Does anyone have any suggestions or comments on the type of cap, rating and value for the purpose?

author: 8086
author_rank: Super Contributor
timestamp: May 20, 2013, 07:38:12 pm
content: 30V? I would have thought a much higher voltage would be necessary for the possible transients you get in automotive electrics.Unless someone knows why this might not be an issue?

author: Paul Price
author_rank: Super Contributor
timestamp: May 20, 2013, 07:40:11 pm
content: Don't bother hunting after that capacitor. What you really just need is an inductor in series with the power lead to your car stereo bypassed by a 3300/15V capacitor at the radio.http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0&_nkw=power+filter+for+car+radio&_sacat=0&_from=R40http://www.ebay.com/itm/PAC-CSS-12-High-Power-Noise-Filter-in-Car-Radio-CB-EQ-/200921028390?pt=US_Wire_Harnesses&hash=item2ec7d39726http://www.ebay.com/itm/American-International-Audiovox-S-15A-Car-Audio-Stereo-CB-Radio-Noise-Filter-/140976391316?pt=LH_DefaultDomain_0&hash=item20d2d90494The inductor need not be wound with 2-gage wire, you only need to use one of the filters above (directly above link) to filter the power lead to your radio or CD player, and not to your kick-ass poweramp power.One of the LC low-pass filter methods above are exactly what is best suited to solve your noise problem.If when you gun the engine from idle with your headlights on and the brightness of your headlights do not noticeably change, then your battery and alternator wiring is ok. If you see a large change, check your car battery connections, one or both might not be making a good connection to the cables or to the chassis of the car. In rare occasions, rust damage to the chassis of the car cause problems like this, but this applies to old rust wagons.There is nothing wrong with your car battery, but make sure your radio has a good heavy wire connecting the case of thestereo the chassis of the car, and where you will also connect the ground lead of the filters above that I recommend.The link directly above is cheap and good for what you need.http://www.ebay.com/itm/10piece-Toroid-Core-Inductor-Wire-Wind-Wound-for-DIY-220uH-3A-mah-/290901739833?pt=LH_DefaultDomain_0&hash=item43bb184939You can roll your own by buying the toroid above and inserting it in series with the +12 to your car stereo and a 3000uf/15V capacitor connected at the radio +12V to ground. You can build this circuit if you have a soldering iron or hand wire these two components in place.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 07:41:14 pm
content: 33 millifarad? You can get a nice, big "capacitor" somewhere in the 10-50kF range with ESR well under 10 milliohm, it's called a "battery", and shoving an inferior capacitor in parallel isn't going to do you much good.

author: jahonen
author_rank: Super Contributor
timestamp: May 20, 2013, 07:45:24 pm
content: Take a look at previous thread about this subject, do you have a similar problem?https://www.eevblog.com/forum/beginners/car-engine-signal-interference-with-cell-phone/Regards,Janne

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 20, 2013, 07:45:51 pm
content: Your battery could be a heap of shit with the esr so high that it doesn't swallow up the transients. A capacitor could do the job, but it would almost be a waste of money. A LC low pass could also work but it would also not really be suited. A battery upgrade should work for you.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 07:53:26 pm
content: Quote from: smashedProton on May 20, 2013, 07:45:51 pmIf you put something in parallel with the battery that has a high capacitance and a lower ESR than the battery itself, you'd better be prepared for the resulting ripple current.

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 20, 2013, 08:00:03 pm
content: Yes,but the fact that the ripple is not being filtered correctly by the battery means that either the battery is bad, or the car stereo has very poor input tolerances. Car grounding could also be an issue.

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 08:09:46 pm
content: I replaced the battery once with no effect on the noise. I've replaced the alternator and had it bench tested before installing it once with little effect on the noise.I've moved the ground around on the head unit and amplifier too many times to count. I've re-run the RCA cables interconnecting the two a few times and tried different cables too. They are not run parallel to any power. I've connected a pair of bookshelf speakers in the trunk with no change in the noise so it is not being induced into the system through the speaker or speaker wires.If I remove the serpentine belt and run the engine (very briefly as this cuts the water pump too) the whine completely goes away.I've sanded down all applicable grounds and power connections. Swapped different amplifiers and head units with usually worse results.Building an inductor is not practical since it would have to be wound with 2 gauge wire (for the amplifier).The electrical system in this car (mid 90's BMW) is a nightmare and it doesn't help (I'm sure) that the battery is under the rear seat bench (i.e. long power cable run).

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 08:15:34 pm
content: Quote from: HooRide on May 20, 2013, 08:09:46 pm"Amplifier"? You seem to have misspelled "starter"! Have you considered a quieter car?

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 08:23:24 pm
content: Quote from: c4757p on May 20, 2013, 08:15:34 pmHaha, I think the starter cable is only 4 gauge. My car stereo system consists of the head unit and an amplifier and I believe the noise is entering the system through the power or ground on both the head unit and car amplifier. The amplifier has a 2 gauge cable from the battery positive terminal.I have considered a quieter car, sadly.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 08:26:18 pm
content: Quote from: HooRide on May 20, 2013, 08:23:24 pmWhy? How the hell much current does it draw? (Bear in mind that I have no car audio experience - I'm pleased if I can hear the sound at all over the road noise - but I'm having a hard time imagining upwards of 80A!) Keep in mind that some cable resistance may add to the low-pass filtering effect of any local capacitors, both inside the amplifier and any you might add.

author: G7PSK
author_rank: Super Contributor
timestamp: May 20, 2013, 08:30:09 pm
content: Check the engines earth strap for dirt and corrosion, also the alternator mounts if it does not have an earth lead of its own, the usual thing is corrosion between dissimilar metals, aluminium, steel and copper junctions are very common and cause a lot of problems from noise on radios etc to starting and battery failures.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 08:32:16 pm
content: I had a small amplifier (supposedly rated 300W, but it used two monolithic amplifier ICs rated 80W each, so a complete lie...), and it ran its power through a pi filter using two 2.2mF capacitors and a 1mH choke about the size of a small line transformer. That was more than enough. Even if your special little starter/amplifier/toaster combo unit truly does draw 960W, an equivalent filter will be probably just about the size of a small brick, which is nothing compared to whatever it must use for a heatsink (pieces of bread?).

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 08:37:23 pm
content: Quote from: c4757p on May 20, 2013, 08:26:18 pmIt is rated at 70A continuous a full output (4 x 100 watts @ 4ohm load) and internally fused for 80A. McIntosh amplifiers (car or home) are not known for being efficient, or small.I have replaced the engine ground strap and cleaned the alternator mounts with a steel brush when installing the new alternator.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 08:40:24 pm
content: I cannot imagine what four speakers each drawing 100W must sound like. All I know is I don't want to be anywhere near it.Quote from: HooRide on May 20, 2013, 08:37:23 pmI'll say! 100W into 4 ohms is 5A! This thing draws 70A to deliver 20?

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 08:44:44 pm
content: Quote from: c4757p on May 20, 2013, 08:32:16 pmA toasted english muffin would be great after my 20 minute commute to school every morning! I'll work on that if I ever solve this stupid noise issue.I incorrectly assumed it would be much bigger than a small brick, maybe I'll try that this weekend then. Any build suggestions?

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 09:08:00 pm
content: Quote from: HooRide on May 20, 2013, 08:44:44 pmRedacted: I need more coffee. No way that suggestion will handle the current.

author: Paul Price
author_rank: Super Contributor
timestamp: May 20, 2013, 09:15:22 pm
content: If you disconnect the super power amp inputs from the other stereo components, do you still hear the whine? Do you hear the whine at low volumes only?

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 09:17:49 pm
content: Quote from: c4757p on May 20, 2013, 09:08:00 pmPerfect, I have plenty of those laying around and several caps. I'll try that out.As for the isolated DC:DC converter that someone used in the other thread, I tried one of those for my head unit and it didn't help as the noise is also coming into the amplifier and the converter I got is only rated 10A.Quote from: Paul Price on May 20, 2013, 09:15:22 pmWith out anything connected to the amplifier inputs, there is still a whine. With shorting caps (RCA plug with the center pin and ground soldered together the noise becomes more faint but still there. Volume on the head unit does not affect the whine except, obviously, with moderate volume it can no longer be heard. I don't remember for certain but I believe changing the gain on the amplifier affects the level of the whine. I'll have to double check when I get home.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 09:18:43 pm
content: Quote from: HooRide on May 20, 2013, 09:17:49 pmNote my second edit. You're not getting 70A through that. I'm having a stupid day, apparently.

author: Paul Price
author_rank: Super Contributor
timestamp: May 20, 2013, 09:21:17 pm
content: Are both wires of each speaker connected directly through wires back to the power amp or are using the chassis for a speaker return?

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 09:24:58 pm
content: Quote from: c4757p on May 20, 2013, 09:18:43 pmI've got a 120V to 12V @ 20A step down transformer that I can use (the secondary). The amplifier "only" uses 7A idle power and at idle is all I need to test the results.

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 09:27:02 pm
content: Quote from: Paul Price on May 20, 2013, 09:21:17 pmGood question, everything is independently wired and there are no accidental shorts to ground or otherwise.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 09:28:46 pm
content: Quote from: HooRide on May 20, 2013, 09:24:58 pmYou might be disappointed by the inductance of the secondary, depending on the transformer. (Jesus m.f.ing Christ, 7A quiescent?) It sounds like you're in good hands here with Paul, but one thing I would suggest if you want to investigate filtering like that is to crack it open, and separate the low-current input side power from the high-current output side power. Then you can add all the filtering you want to the former. The feedback loop ought to have more than enough bandwidth to counter the noise (well, since it's audible noise and an audio amp, it had better...), so there's a good chance that it's originating in the input side.

author: Paul Price
author_rank: Super Contributor
timestamp: May 20, 2013, 09:34:35 pm
content: Do you connect the power amp ground return to the chassis at the amplifier or with a separate wire to the battery ground from the battery on the chassis?Did you try connecting the ground in this fashion...directly or very near to the ground connection where the battery connects itself to the car chassis?Have you tried any large capacitor on the +12V power connection, say a 3000 to 30,000uF/15V cap with heavy leads directly across the amp's + and ground leads?

author: HooRide
author_rank: Regular Contributor
timestamp: May 20, 2013, 09:53:35 pm
content: Quote from: Paul Price on May 20, 2013, 09:34:35 pmI've tried several ground points, directly to battery, where the battery connects to the chassis, a very large seatbelt bolt (read that those generally are a bad place due to difference in the alloys used for heavy duty (grade 8+) bolts) and right now is it ground to where the stock amplifier was once grounded.I have not tried a large cap at the amplifier input leads, I will try that in the next few days. What would be the difference between that and connecting it as close as possible to the alternator?Quote from: c4757p on May 20, 2013, 09:28:46 pmI never thought I'd get to modifying the equipment! Sounds like fun, good thing this weekend is 3 days long.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 10:00:54 pm
content: Quote from: HooRide on May 20, 2013, 09:53:35 pmAs I said, it's much more likely to be a ground issue and you won't have to.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 10:02:21 pm
content: Quote from: HooRide on May 20, 2013, 09:53:35 pmIt serves its purpose at the input leads. It just chews on a bit of ripple that the battery should be handling at the alternator.

author: Paul Price
author_rank: Super Contributor
timestamp: May 20, 2013, 10:11:13 pm
content: Connecting the capacitor right at the amplifier + and ground leads gives and additional inductive effect due to the length of the lead running from the battery connection, which helps the filtering effect. How are you connecting the +lead of the poweramp to the battery...are you attaching directly to the connector or perhaps on top of the large wire coming from the alternator? Do you have an alternator filter?You could also try taking apart an old discarded PC power supply. Inside you will usually might find a large toroidial inductor about 2-in in diameter. Take all the thick enameled wire off it and wind as many turns of #10 to #8 AVG insulated wire on it as you can and insert this at the power point after adding an added bypass capacitor, connect the inductor directly at the + power input wire at the power amp.If that doesn't work, you've have exhausted everything but prayer/voodoo to solve the problem...except......You can, in utter desperation try connecting a 5 to 10 amp 12V sealed Sealed Lead Acid Battery directly across the power connections on the power amp. The SLA battery acts like a super-duper capacitor. Use thick wire #6 or better to connect to the SLA battery.If all else fails, realize that the car battery itself could be considered as a very very large capacitor that filters the alternator noise right at the source, and a larger or a new fresh battery would have a higher effective capacitance, that is, in another way of looking at it, having a lower internal resistance, and thus it has more filtering effectFinally, try another power amp, there must be something wrong with it. It should have good power supply noise rejection and it appears it does not.You say you still hear the noise after you have disconnected the poweramp input cables, so you know the trouble is in your poweramp.

author: lemmegraphdat
author_rank: Frequent Contributor
timestamp: May 20, 2013, 10:43:36 pm
content: Is this noise in the stereo all the time no matter where the car is when it is running? No matter if you are listening to the radio or a CD?

author: MacAttak
author_rank: Unknown
timestamp: May 20, 2013, 10:50:58 pm
content: I used to do a lot of very high-end car audio installs. 100w of power is very low... I've worked on systems with thousands of watts of power, dozens of massive subwoofers (if it's not 12"+ then it's not worthy of being called a subwoofer), and banks of deep-cycle batteries to sustain the immense current draw without clipping output (we specialized in SPL competition systems, typically in the range of 150+ dB). It's been many years since I was deeply involved in that scene, but the technology really hasn't changed much.With the gear and setup you are describing, you shouldn't have any of those problems. Honestly it sounds like shitty RCA cables or a bad amp. Possibly a bad crossover module, if your amp has a dedicated input filter or if you have an external one.Some things to check:Try a different amp. Not just a different unit, but a different model and brand.Use shielded RCA cables. Not the cheap thin crap. Good cables will generally be two to three times as thick as crap ones, and will be much more difficult to bend or twist (so plan your wire routing accordingly).Don't use cables that are any longer than absolutely necessary. A few feet of extra cabling looped back on itself and tied up with a plastic tie wrap makes for a pretty good way to add inductive feedback. Don't allow your cabling to get pinched, smashed, or bent in too tight of an angle.Your vehicle is almost certainly a high percentage of composite materials (or at least exotic alloys) that aren't like the steel unibody shell of most cars. The metal of the cabin might even not be a very good ground at all! Don't assume that any exposed metal will function as a suitable grounding point - no matter how solid it looks. You need to measure the conductance and not rely on assumptions.Run the power/ground for your amplifier and head unit on one side of the cabin, and signal wires on the opposite side. Don't run them next to each other. Don't run the signal wires next to other wiring harnesses that are part of the car itself (if you can help it).You said that you are using 2-gauge wire (probably fine), and I assume that it is stranded and not some crazy solid bus wire (yes, I've seen someone try to use that before). Make sure that your connectors are crimped to that wire extremely well. We used a hammer and chisel for this when I used to do high-end audio installs. Heavy-gauge wire takes a lot of elbow-grease to wrestle into submission.Make sure all of your wiring splices are done properly. Noise can enter the system from many non-obvious connections. No "pigtail" style twist connectors, no electrical or duct taped splices. No "no cut" snap-on connectors. At a minimum, use high-quality crimp connectors, or if you are looking for perfection then solder + heatshrink tubing.No floating wires. Not even that display brightness wire for your head unit.Make sure that the amp ground returns directly to the battery. Don't try to complete the ground circuit using the chassis. Use the same gauge wire for the ground as you used for the positive supply.If you are using intermediate devices like active crossover modules, equalizer, etc then make sure that they are also grounded properly.Use proper battery terminals that are designed to handle your heavy-gauge amp supply/ground wire as well as everything that the car needs. I can't overstate how important the battery terminal connection is. Also, be sure that the terminals of the amplifier itself are similarly robust.

author: MacAttak
author_rank: Unknown
timestamp: May 20, 2013, 11:01:35 pm
content: Also, in some cases you can simply just shorten the distance between head unit and amplifier by moving it. If the amplifier is mounted in the rear of the trunk then you could easily cut out 30% to 40% of the signal wiring distance by just moving it to a position right behind the rear seats, or even place the amplifier under a seat (depends on size of amplifier and cooling airflow).There are also alternator filters available, I assume you already have one installed.A quick web search also pulled up this page, which is mostly pretty good info:http://www.crutchfield.com/S-6uyOpnDFK0T/learn/learningcenter/car/noise_suppressors_installation_guide.htmlIt is correct about your ground ideally being short, but that also relies on the chassis being a good conductor back to the battery compartment (which yours might not be). It also assumes that you have a beefed-up ground cable from the battery to the chassis. Most cars have a wimpy grounding cable there - not nearly enough to handle the current needs of a decent audio amplifier system.

author: c4757p
author_rank: Super Contributor
timestamp: May 20, 2013, 11:11:41 pm
content: Quote from: MacAttak on May 20, 2013, 10:50:58 pmWe normal people call that "keep your music in your car and out of my living room"...QuoteWe normal people call that "copper rods"...QuoteSeems overcomplicated to me. Noise isn't going to seep in through taped splices or twist-on connectors. It seems to me like audio people make their stuff much harder than it needs to be, with lots of noise myths and grounding myths and connection myths and whatnot. I seriously don't see why it's too hard for high end audio stuff to just use properly terminated differential connections for signals and other modern practices.

author: Mike Warren
author_rank: Unknown
timestamp: May 21, 2013, 02:41:16 am
content: Quote from: c4757p on May 20, 2013, 11:11:41 pmNo, but anywhere you have high resistance can contribute to problems. As someone who's been involved closely with the car audio industry for nearly 30 years, I can assure you there are times when this matters. Because of the high vibration inherent in this environment, any substandard connections are likely to cause issues in the future.QuoteThere is a very large amount of misinformation floating around, including some in this thread. It's not really a hard thing to solve, but every situation is different. You need to conduct tests to show where the problems lie (and there is usually more than one cause). Cars are a terribly noisy environment, and many manufacturers of equipment simply don't design their products properly. I've even seen it from the large manufacturers from time to time.QuoteMostly because of backward compatibility. But that will still not eliminate all the problems.It really is reasonably simple in 99% of cases if you understand ground paths, but often even professional installers don't understand it. The noise on the ground of a car is so high that the slightest problem will usually be audible.

author: c4757p
author_rank: Super Contributor
timestamp: May 21, 2013, 02:46:04 am
content: Quote from: Mike Warren on May 21, 2013, 02:41:16 amDifferential signals can be backwards compatible if implemented right. Diff->single: Leave off the inverting line. Single->diff: Ground the inverting line. Even better, in the single->diff case, you could get a semi-differential system by using shielded cable and connecting the shield at the differential (receiving) end not to ground, but to the inverting input. Obviously you'll have 2x gain or attenuation, but that's not a big deal. Just make sure it's symmetric about ground.

author: Mike Warren
author_rank: Unknown
timestamp: May 21, 2013, 03:03:32 am
content: Quote from: HooRide on May 20, 2013, 09:17:49 pmIf you are still getting noise with the amplifier not connected to anything, and the car battery is still being properly charged, then (bar one possibility (see below)) you have a faulty amplifier. What brand and model is it?When you run the amplifier by itself, the only possible places for the noise to get in are via the power or via the speaker wires. Having noise induced into an amplifier via the speaker wires is almost unheard of these days. I'm assuming you have used standard figure 8 speaker cable. If you've run 2 individual wires that are not parallel to each other, you should fix that first.You need to work through the problem logically.Firstly, isolate the amplifier and only one speaker. If you still have noise, disconnect that speaker and connect one of the others. If you still have noise, there has to be something wrong with the input filtering or internal grounding of the amplifier. Assuming you don't have a seriously faulty battery or alternator, but either of those would show up as other electrical problems in the car. If one of your negative speaker wires is shorted to ground, then it is possible (but unlikely in a properly designed amp) you are creating a ground loop within the amplifier itself.Change the amplifier to one that does work properly, or find and fix the fault in your current amp.Until you have the noise out of the amplifier, there is no point in going any further.QuoteThese symptoms are typical of ground loop problems, and that is, by far, the most common cause of car sound system noises.

author: Mike Warren
author_rank: Unknown
timestamp: May 21, 2013, 03:12:23 am
content: Quote from: c4757p on May 21, 2013, 02:46:04 amThat requires training for installers. And besides, it's not necessary. With properly designed equipment, installed according to the instructions, there is almost never a problem.Actually, most modern amplifiers do have differential inputs. The shield of the RCA does not go to ground, but rather to the negative input of a differential input amp. But the noise level is so high in cars that this is not 100% effective. It also causes problems when equipment is mixed from different manufacturers.For example, for quite a few years, Pioneer were getting the ground for their head unit output pre-amplifiers from the RCA ground, thereby eliminating the most common ground loop path. the problem was, if you connected a Pioneer head unit to an Alpine amplifier (which use the pseudo-differential amp) the system wouldn't work.

author: c4757p
author_rank: Super Contributor
timestamp: May 21, 2013, 03:21:01 am
content: Well yeah, because they're sneaking it in like that. How much training does it really require to say that some inputs and outputs use two wires, and to join a two-wire device to a one-wire device, omit the one marked (-)?

author: smashedProton
author_rank: Frequent Contributor
timestamp: May 21, 2013, 03:28:02 pm
content: Try cranking up the gain on the head unit. But lowering the gain on the amp. That may be what you need