Low level hum?
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=82226
Printed Date: May 21, 2024 at 12:32 PM
Topic: Low level hum?
Posted By: punkbastard
Subject: Low level hum?
Date Posted: August 29, 2006 at 1:40 PM
I was just curious. When you hook up an amp and sub to a factory headunit through an LOC and use the vehicles accessory wire as an amp turn on, why do you get a low level hum when the car is on and radio turned off? It only happens sometimes from what I can gather but i've never known why it does that. My only line of thought is that since the radio is off tne there is no input voltage to the LOC, hence no input signal at the amp and maybe there is some kind of feedback problem. Anybody who can explain this to me would be very much appreciated
Replies:
Posted By: jettagli03
Date Posted: August 29, 2006 at 1:45 PM
its not an always thing. i've done many setups with LOC's and never gotten a hum. its getting some kind of interferance somewhere.
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Posted By: Flakman
Date Posted: August 29, 2006 at 1:56 PM
With the amp on (even with the radio off) the interference can now be amplified. Are power and ground solid? Are you using quality RCA Cables? There are things to check...possibly even where you are running the RCA cables. There have been threads regarding whether or not noise will propogate when running power next to signal, but this is something to look at as well. ------------- The Flakman
I feel strange. I have deja vu and amnesia at the same time.
John | Manteca, CA
Posted By: electrostatic
Date Posted: August 29, 2006 at 2:21 PM
to troubleshoot mute the amp using muting plugs and post results. muting plugs are easily made by jumper-ing an rca connector's leads together. then connect them to the input channels of the amp. if the noise goes away your problem lies further up the signal chain, i.e. loc, headunit, etc. ------------- Prove your connections, use a meter!
I promise, I'll behave!
Posted By: punkbastard
Date Posted: August 29, 2006 at 2:30 PM
Its not on a car that I am working on now or anything, I have just seen it in the past and wanted to know why it happens. Most recently I saw it on a car that I did a remote start, sub and amp in off of the factory deck. I didn't hook up the accessory wire that powers the radio at first so when I remote started, the car was on meaning the amp was on but the radio wasn't and there was that noise, once you put the key in or once I hooked up that wire, it worked fine with no noise. Every other time I have seen it that has been the case, radio off = noise, radio on = no noise. If there was interference due to poor cables or wiring than it would show itself all the time right?
Posted By: electrostatic
Date Posted: August 29, 2006 at 4:09 PM
my bad!
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Prove your connections, use a meter!
I promise, I'll behave!
Posted By: Flakman
Date Posted: August 29, 2006 at 4:29 PM
Now you're getting a bit out of my realm. I will defer to the older...oops, I mean more experienced members  ------------- The Flakman
I feel strange. I have deja vu and amnesia at the same time.
John | Manteca, CA
Posted By: punkbastard
Date Posted: August 29, 2006 at 6:39 PM
ha ha, nice. I tend to think a bit too deep in to things, can't help it. By the way your signature is now my headline on myspace, thats funny.
Posted By: punkbastard
Date Posted: August 29, 2006 at 6:40 PM
All I know for sure is that I have never had this problem using the exact same equipment with an aftermarket radio. Thats why i think it has to have something to do with either the LOC or using accessory as an amp turn on.
Posted By: stevdart
Date Posted: August 29, 2006 at 10:06 PM
Close, but I believe it has to do with the regular speaker wire that connects the LOC to the factory wiring. These wires, if not twisted, will act as antennae (so to speak). Use wires that are twisted together to prevent this interference. The area behind the deck is a hot spot for picking up noise, so even short lengths of connecting wire should be twisted, even if they are just the little wires that came attached to the LOC. These are input signal wires prior to amplification, not speaker wires, and that is why they should be twisted and regular speaker wires from the amp don't need to be. (Twist + and - around each other.)
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: punkbastard
Date Posted: August 29, 2006 at 10:24 PM
I think I should add something to stevdarts post just to make sure there is no confusion. When he says to twist + and - around each other, he does not mean to strip the shielding off the wires and twist them together, leave the shielding on and kind of braid the wires. Now, a question for stevdart. I emailed Perry Babin, the guy that runs bcae1.com about this and he said that when the deck turns off, the speaker outputs from the onboard amp are left floating, meaning not electrically connected to anything which can allow the transformer in LOC to pick up noise. How does that sound to you?
Posted By: INSTALLER_MSS
Date Posted: August 29, 2006 at 10:49 PM
this sounds accurate. try to see if the factory amp has a remote turn-on lead from the radio (some factory setups have them, some don't). if you can't find one and the customer just can't stand the noise then try simply putting a toggle switch on the turn-on lead running into your aftermarket amp so he/she can turn the amp on and their on will. signal wires are really bad about picking up noise like stevdart said. make sure all your RCA's are as afar away as possibly from the power wire, computers, and large factory harnesses. also try adjusting the gain levels on the LOC (assuming you are using an adjustable one)...turn the gain down but the bass boost up on the amp for the sub if it gets too low.
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"If a man made it, another can modify it...it just takes some thinking."
"If you ask questions, you're a fool for 5 minutes; if you don't, you're a fool for a lifetime."
Posted By: stevdart
Date Posted: August 29, 2006 at 10:50 PM
I would say that Perry Babin tops the list of people I enjoy learning from. I'll remember that. My experience with LOCs is limited, but I haven't heard any noise problems as you described. I will use long lengths of twisted speaker wire to connect the LOC, and place it close to the amplifier. The connecting RCAs are one foot or less in length. You say that just turning the deck on, with no volume at all to mask the noise, stops the hum? Hummmm....... The LOC in question is not grounded to chassis, is it? And is it one that is of high quality and has isolated circuity to prevent ground loop? Whether it is capable of picking up noise when the connected deck is off or not, it is still connected to the amp via RCA cables and has to remain a suspect...as well as all grounding involved in the install. ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: INSTALLER_MSS
Date Posted: August 29, 2006 at 10:55 PM
another thing...if the amp is mounted with screws to the body, it can create a ground loop from having multiple ground points (the frame/chassis of all radios, amps, etc. are actually grounds used for internal electronics). try mounting a piece of mdf to the body, then use short wood screws to mount the amp to the wood. just because you can't hear the noise when the radio is playing doesn't mean it isn't there, it could just be drowned out by the audio signal. a good rule of thumb as well is to use "twisted pair" or at least "shielded" RCA cables. this will help reject these little annoyances...good luck
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"If a man made it, another can modify it...it just takes some thinking."
"If you ask questions, you're a fool for 5 minutes; if you don't, you're a fool for a lifetime."
Posted By: punkbastard
Date Posted: August 29, 2006 at 11:05 PM
yes, simply turning the deck on will stop the noise. I'm starting to think I'm crazy cuz nobody else knows what I'm talking about. The noise isn't alternator whine or any other kind of inducted noise it is as though a test tone cd was playing a low frequency track on repeat but it is very loud. As soon as you turn on the deck it goes away. The LOC I used when this happened last was a peripheral, before that I believe it was install edge. Perry's explanation is really making sense to me because it is the only possible cause I have heard yet that has to do with the radio turning on and off any other noise I would be able to hear under other conditions but with the deck on (revving engine with volume down to here alternator whine for example).
Posted By: punkbastard
Date Posted: August 29, 2006 at 11:05 PM
Hey I got a star finally! Woo hoo!
Posted By: stevdart
Date Posted: August 29, 2006 at 11:20 PM
punkbastard wrote:
Now, a question for stevdart. I emailed Perry Babin, the guy that runs bcae1.com about this and he said that when the deck turns off, the speaker outputs from the onboard amp are left floating, meaning not electrically connected to anything which can allow the transformer in LOC to pick up noise. How does that sound to you?
Oh, then I misunderstood what he said. I read that to mean that the LOC could not pick up noise when the deck is off. But now, by what you just said, I realize it is entirely the opposite, that it can pick up noise because the deck is off. I had thought that the LOC could pick up noise either way...deck on or deck off...if something was not up to par with the setup. But this sounds like a voltage mismatch hum, this sub frequency tone. Such as when the amplifier gain is set too high for the deck's output signal. First, test to see if the LOC is the culprit (or anything upstream) by removing the RCA inputs at the amp. Some good troubleshooting has been given in this thread, and you should now work through a troubleshooting procedure to isolate the cause. ------------- Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: punkbastard
Date Posted: August 29, 2006 at 11:48 PM
Yeah i dont really know how a transformer works or anything so I can't say why this is true but the next time I have a customer who wants to do this typ eof setup I will definitely put on my investigators hat and do some pokin around.. Thanks everybody for all your thoughts and ideas. One last thought. People ask me alot why I chose the career I have instead of doing something else that I guess is more meaningful. This type of thing is why. There are so many other things you can study and fields you can work in that have solid concrete answers to your questions that you can look up in a book very easily. But it seems like so much of this industry is kind of up in the air and you really have to put in some time to really understand it instead of just sayin "hey there it is, it works, forget it". Thats exciting. Maybe im just a rambling idiot who puts too much thought into things, yeah im gonna go with that.
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