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  #1  
Old 07-28-2010
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Noise filter ??

Long ago, when I was big into car audio installs I used to get these little coils (about 1" in diameter) that connect in-line with the positive wire on a head unit that would isolate alternator whine. They worked really well, but it's been a long time since I've used one.

After 20 or so years, I don't have anymore of 'em and I can't think of exactly what they're called.

I've got a little alternator whine in the stereo & I'm going to be adding a new sub amp shortly. I have a couple of the RCA inline filters that cut some of the whine, but if I mute the stereo I can still hear a tiny bit of noise.
You can't really hear the noise with the stereo volume on 1+, but when I mute it, there's a hint of noise.

I've made sure to run the RCA's down the pass side at a 90* angle to any other wires while running the Power to the amp down the driver side at a 90* or 45* angle to any other wires to avoid any EMF.

I currently have an inline RCA filter going to ch 1 & 2 of my amp (mids) and it helped a lot, but there's still a little noise I'd like to kill. Ch 3 & 4 are currently bridged for my sub, but I'm going to run all 4 channels for my 4 mids as soon as I get my new sub amp installed - thus doubling the noise I'll have from the mids.

Does anyone know what that little coil/filter/thingy is called or where I can find one online???

I'd like to install one in the power wire of the head unit to see if it'll help.
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Old 07-28-2010
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Inline noise surpressor? - sounds like what your looking for.
When you upgraded the alternator did you upgrade the cables? usually changing the one from the alt to pos, and the one to the block helps fix this. Would recommend a 1/0 ( or 4ga )if you havn't already done it....

Try this to eleminate the rca's....

if you have a filter in the rca line thats helping it may just be a problem with the rca's , unplug the rca's going into the amp, then take a seperate rca and plug the white leads into the input the l/r channels and see if you get whine, ( this will check that its not in the amp itself, if you have a whine still, make a better ground) if you dont have a whine, then plug your normal rca's into the amp but disconnect them from the head unit, and start the truck, mute as you have pointed out and see if its there ( this will check the rca's even using a rca filter you can still be picking up noise...)

If you still have the noise issue then pop a noise surpressor on the incoming power line to the radio... they are cheap and usually not needed anymore, but the other checks are free so I usually do them first....
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Old 07-28-2010
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I believe its called a choke coil sir, its a type of inductor used to do exactly what you describe, filter out higher frequencies.

Did it looks similer to any of these?



some headunits still have them in a little enclosed plastic box in line with the power, at least one i just repaired did but its a few years old.
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Old 07-28-2010
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CHOKE COIL!!!

Why couldn't I remember that?!?!?

I've used some that had a rectangular bracket for mounting & some even had a clam shell cover with the wires coming out.

I had (probably still have it somewhere) a DIN sized EQ that made a ton of noise unless I had one of those connected inline with the power.... after that it was quiet as a church mouse.
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Old 07-28-2010
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lol yeah bud we all seem to forget all the things we need only when we need them, myself included, theres a billion different shapes and styles but they all do the same thing, maybe one day someone will make a choke for people, giving us the ability to make them to... "as quiet as a church mouse" haha

Last edited by edge2k; 07-28-2010 at 10:29 PM. Reason: Spelling fail.
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Old 07-28-2010
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...I upgraded to 1/0ga wire for all power & grounds with the new ALT.

I even ran a new wire down to the starter with 1/0ga.

The grounds are all connected together now too. I ran the battery to the header panel, header panel to frame, frame to block all with 1/0ga.

I could probably use higher quality RCA's too, but I didn't have any "good" cables that were long enough to reach from the H/U all the way around to the amp.

If the inline choke filter @ the H/U doesn't help, I might try new RCA's from the H/U directly to the amp(s).
I'm on the verge of upgrading the old Sony to something built within the last 2 decades, so that may solve the problem completely.

Luckily, it's not detectable with road noise or when the volume is turned on.

I've never really been concerned with volume or SPL, I try to focus on crisp, clean, tight, noiseless systems. This little whine has been bugging me for years, I just never got around to doing anything else about it.

Funny, now I'm going from 200w to 1500w (more like 750w RMS) for my sub... but at least now I'll be able to control the front/rear speakers with the H/U's fader.
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Old 07-28-2010
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Quote:
Originally Posted by edge2k View Post
lol yeah bud we all seem to forget all the things we need only when we need them, myself included, theres a billion different shapes and styles but they all do the same thing, maybe one day someone will make a choke for people, giving us the ability to make them to... "as quiet as a church mouse" haha
HA,

That would be called a "mouth muffler".

I'd buy stock in that company.
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Old 07-29-2010
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Also, not being an audiophile but a Amateur Radio Operator, GROUNDS are very important.
Battery to Frame to Block being a biggy.
As you said you replaced all of the wires with larger 1/0 ga wire good but what about the AMP itself how is that grounded.
To me, being a newb in this area, I would think a separate ground bact to the battery would be the best bet to reduce noise.
Also, you mentioned that fact that you replaced the wire to the starter, I assume you mean the power wire, a trick to help the starter and give any noise noise generated there, a direct route back to the battery is to run a separate ground wire 1/0 to one of the starter mounting bolts.

Just thinking out loud, a way to learn...
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Old 07-29-2010
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I never thought about running a 1/0ga from the battery directly to the amp/distribution block.
It might help eliminate any noise generated from the amp(s), but if the noise is coming in through the radio's power/ground, I'll still be S.O.L.

Right now the old amp is grounded to the body via a big brass grounding block, bolted down with copper bolt, washer & nuts. Made sure to sand the metal on both sides to bare metal & sprayed some WD-40 before I tightened everything down.

The other day I had an idea... running a new power wire to the head unit from the 1/0ga power distribution block, controlled by a relay that's triggered by the original radio power wire... so the radio will be getting power basically directly from the battery, but it will only be energized when the key is in acc/run like normal (radio won't be on all the time).
Same could be done for the head unit's ground as well (except for the relay).

The only issue I can see with this setup might be if the relay introduces it's own noise into the mix.

I might try this if the noise filter choke on the head unit's power wire doesn't help... not to mention I'm looking for some better quality RCA's so I can run 3 sets from the dash back to the amp(s). I only have 2 sets of RCA's in my current head unit, but all the new ones I'm looking at have 3 sets (front/rear/sub). Thought it'd be nice to have a little control up front instead of the daunting task of climbing in the back & wriggling around to get to the amp settings.
Man, I wish I still had all the Phoenix Gold & Monster Cable RCA's I used back in the day.

Oh, I did run a new 1/0ga power wire to the starter. Even the frame ground that was buried under the steering linkage got upgraded & moved forward with 1/0ga cable.
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Old 07-30-2010
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Quote:
Originally Posted by buggman View Post
I never thought about running a 1/0ga from the battery directly to the amp/distribution block.
It might help eliminate any noise generated from the amp(s), but if the noise is coming in through the radio's power/ground, I'll still be S.O.L.

Right now the old amp is grounded to the body via a big brass grounding block, bolted down with copper bolt, washer & nuts. Made sure to sand the metal on both sides to bare metal & sprayed some WD-40 before I tightened everything down.
Maybe not SOL but maybe close. once the noise gets into the body it can go anywhere.
The idea of running the ground back to the battery is to use the battery as the filter.
How about this, cover both a power and ground wires with one of the hollow braided straps, ground the strap close to the battery; this should help bleed stray electrons to ground close to the battery and back in the negative grounding side of the battery, sort of a path of least resistance thing. That is if you run both wires to the battery...

Quote:
Originally Posted by buggman View Post
The other day I had an idea... running a new power wire to the head unit from the 1/0ga power distribution block, controlled by a relay that's triggered by the original radio power wire... so the radio will be getting power basically directly from the battery, but it will only be energized when the key is in acc/run like normal (radio won't be on all the time).
Same could be done for the head unit's ground as well (except for the relay).

The only issue I can see with this setup might be if the relay introduces it's own noise into the mix.
Yes on the relay noise, not always a good thing but the idea of powering the amp off of a relay that is either powered by the same wire as the radio or the "delayed on" wire coming from the back of the radio could be interesting.
Not sure what to call the wire on the back of the radio but there is one there that sends a signal out after the radio is turned on. (I watched a DVD/Parking Brake By-Pass Vid and they mentioned using that wire, a relay and grounding so the ground would happen after the Radio is turned on).
When choosing a relay get one that needs to be sw’d on and sw’d off, a latching rely like master sw; this would eliminate any constant power to the relay and in turn reduce noise. Not sure what that will do to the amp/stereo system but just thinking, remember I am no stereo/auto electrical tech so beware of my ideas.


Quote:
Originally Posted by buggman View Post
I might try this if the noise filter choke on the head unit's power wire doesn't help... not to mention I'm looking for some better quality RCA's so I can run 3 sets from the dash back to the amp(s). I only have 2 sets of RCA's in my current head unit, but all the new ones I'm looking at have 3 sets (front/rear/sub). Thought it'd be nice to have a little control up front instead of the daunting task of climbing in the back & wriggling around to get to the amp settings.
Man, I wish I still had all the Phoenix Gold & Monster Cable RCA's I used back in the day.
Good quality Connections will make a difference, I will have to remember that when my unit comes in, didn’t even thing of cabling yet !

Quote:
Originally Posted by buggman View Post
Oh, I did run a new 1/0ga power wire to the starter. Even the frame ground that was buried under the steering linkage got upgraded & moved forward with 1/0ga cable.
One the main things forgotten about in an automotive system is the ground. You ran a new ground to the frame and maybe to the block but the one thing on the engine that uses a LOT of current is the starter and although you ran a new power wire to the starter, the current needs a path back to the battery so you need a good ground connection near the starter too.
The extra ground will reduce where and tear n the over all electrical system.


I am sorry for carrying on about grounding but that is one of the major problems with electrical systems.
You might do one more ground wire, run from the frame ground mounting point to the body of the vehicle; normally there is a ground strap from the body to the frame but it is little and not up to the extra current of high powered radios and amps and all of the extra lighting and the such added by Electrical Geniuses like myself and others.

Good Luck on the install, I wll use some of the info for my install too, if the stuff ever gets here.

Last edited by Scrambler82; 07-30-2010 at 09:01 AM.
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Old 07-31-2010
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So... I've been out working on the truck all day.

I got the new amp temp. installed with 2x 8ga cables for pwr/gnd and so far no problems.

With all 4 channels of my old amp now going to the 4 midrange speakers, I can still hear a tiny amount of whine when the truck is running & the head unit is muted.

I added a second inline RCA filter for the other 2 channels of the amp & it mostly eliminated the noise, but it killed my bass... there's 50% less bass from the sub (running the sum output from the 4ch amp).
So removed the filters & wired everything back together & it sounds better.

While I was at it, I removed the bezel (broke my darn 12v port!) and tried the RCA filters at the head unit. Killed the noise 100%, but killed the bass again. I'm still waiting for my choke filter for the head unit's power (it already has a tiny noise filter that's not doing it's job) & I'll install it whenever it comes in to see if it helps.

If all else fails, I guess I can live with a little whine whenever I hit the mute button.
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Old 07-31-2010
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Iv always hated those inline noise filters, for exactly the same reason loosing signal strength, what type of rcas are you using exactly. do they look like they have a pretty decent shielding, that could be a good cause of the problem there, if you disconnect the rcas with the amplifier still on is there still a noise? It could possible be the amplifier itself causing it the whine due to a ground loop with something else in the truck, if you care to check the resistance between the ground terminal at the amplifier and the location you grounded it, ideally you would want 0 ohms, if it has a high value id look for another location with as low a value you can find, on bare metal. Maybe that will help? Good luck =D
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Old 08-01-2010
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My RCA's are RCA brand, I believe. The jackets are fairly thick, but you know how some companies fake good shielding with thicker plastic.
They're not high end stuff, but they were the only ones I had that were long enough at the time & I just never got around to changing them.
If I get a new head unit, I'll grab some better RCA's with better shielding.

When I moved the RCA filters directly to the head unit (instead of right at the amp) all the noise disappeared completely.
I didn't have a chance to install anything else on the head unit's power (still waiting on the one I ordered), but that will hopefully clean things up.

I'm on the verge of buying a new head unit anyway & I'm sure anything made today is leaps & bounds better than my old one.
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Old 01-07-2012
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This is an old one but a lot of usful info and problems that all of us face.

buggman,

How did this turn out, did you get rid of the noise ?
AND what did you do ?
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  #15  
Old 01-07-2012
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For some help when dealing with vehicle electrical noise , turning to HAM operators is a good move.

http://www.eham.net/articles/1076
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