Amplifiers and engine noise

[tdr1213]

For you stereo electronic gurus. I installed a Cobra 5 channel amplifier and I'm hearing significant engine noise and there's also a loud pop when I change the channels. I believe it's engine noise because as I accelerate the tone of the noise changes.

The power is hooked directly to the battery via a quarter inch thick cable. Supposedly it's all quality stuff with large fuses, shielded speaker wires, etc.

Any ideas how to eliminate the engine noise?

 

[Faux4X4]

Make sure none of the speaker cables or RCA cables are near the power cable. You should run the power on one sied of the car and the wires on the other side.

 

[red91]

Make sure none of the speaker cables or RCA cables are near the power cable. You should run the power on one sied of the car and the wires on the other side.

X2...never run them together...

 

[jcnorman48]

I had a very serious problem with engine noise when I installed my stereo. It was really bad when I would use the turn signals as well. I had an old soundstream amp that died just after I installed it, bought a new alping 4 ch and the engine noise went away. You can buy a filter that goes on the rca's, never tried it, but I hear that it works. Run the power and the rca's on opposite side of the car. I placed a capacitor on the power/ground and that got rid of a bunch of engine noise and also kept the lights from dimming when I pounded. Caps are about $100 at a car stereo place but you can buy the same cap for <10 at a electronics shop. A 1 farad cap should do the trick. I bought mine at a JB Saunders.

 

["Wolz"]

Make sure your grounds are sufficient.

 

[rocwrlr]

am i correct in hearing that if there are abnormal noises through the stereo speakers relating to the engine that the voltage regulator on the alternator may be bad?

 

[DoriftoShoes]

I second the motion to check grounds and make sure power and speaker wires are separated. Everytime I've had someone come to me with this problem it has been one of the two.

 

[Ramsey]

in my experience it has usually been a bad ground

 

[Rawbrown]

don't just check the ground. but your ground should be the shortest run to the nearest solid body grounding point. don't run a long wire to the battery. if you bolt the amp under the seat, then thats where you should ground it. if the regulator is bad then voltage will reflect it. you can also pick up a ground loop isolater from radio shack for a few $. it will go inline to your amp inputs.

 

[Fred85]

general consensus in the audio world is that the amp ground should be no more than 18" long and the wire should be at least the same size as the power wire. Sometimes it's not neccesary, but you can also scrape away the paint on the grounding spot down to bare metal to get better metal-to-metal contact

But as stated above, the biggest causes of engine noise are usually grounds and wire routing

 

[rocwrlr]

http://ccs.exl.info/noise.html Nikola Tesla strikes again.

 

[Lou]

http://ccs.exl.info/noise.html Nikola Tesla strikes again.

Testla died pennyless.

The given explanation of a ground loop is sufficient to imply that they are bad--for the most part. 'Acts as an antenna' is misleading. They also fail to state that the ground should ideally be taken all the way back to the power source -- the battery -- inorder to eliminate any ground loops.

A 'ground loop' refers to a ground shared (e.g. car's chassis) among different circuits. If the current draw of one circuit is high enough it may induce noise in the other circuit that shares that same ground.

I've had a situation where I wired a headunit perfectly and still had ignition noise. In the end, it turned out that I actually had an ignition that was emitting alot of noise. I think it turned out to be a problem with the spark wires or dist cap.

 

[XJack]

I've had a situation where I wired a headunit perfectly and still had ignition noise. In the end, it turned out that I actually had an ignition that was emitting alot of noise. I think it turned out to be a problem with the spark wires or dist cap.

Just went through the same thing, but on a distributorless ignition. As mentioned a few posts up, Radio Shack carries a doo-dad (part# 270-054)that goes inline with the RCA's. It's a band-aid, but it generally works unless there is a larger wiring problem, such as routing, electrical short, etc.

I'd start with wire routing, and making sure you've got the fattest, shortest ground possible on all electrical accessories running on that circuit.

 

[xjj33p3r]

rewire the ground and see if that helps.

 

[tdr1213]

Thanks for the inputs!!!

I grounded the amp, with a short and thick cable, underneath the back seat into the floor. Unfortuneately, there's still significant engine noise.

There is one speaker wire that runs beside the power on the right side of the vehicle, I'll move that speakerwire to the otherside and see what happens to the engine noise.

If that doesn't do the trick I'll get the radio shack inline rca doohickie (#270-054).

Interestingly, I noticed I have the same engine noise running through my cb radio. Is this a common problem? It is grounded to the body as well.

tim

 

[5-90]

A "cheat" that's worked well for me...

Take a fat pen (say, 5/8" thick) or a dowel rod the same size.

Wind one end of the speaker leads (both wires) around the core six times. This is easiest if you are actually running new speaker leads, of course - and works best if you can do it right before the speaker.

Use tape or silicone to "fix" the coil in place, and remove the core.

Repeat for other speakers.

It also helps to leave a few free inches not in the coil - you may need to add or subtract a turn or two. I started doing this when guys would want cheap radios to not have alternator hum.

What happens, in effect, is that you form a "choke" in the line, which uses the "steadily-oscillating" magnetic field caused by the power hum to cancel itself out. The choke will allow the AF sounds (the part you want to hear) to go through unaltered. (I'm guessing - I've forgotten exactly why it works, but it works.)

If/when you have to run new speaker leads, take the time to make sure where the main front-to-back harness runs - it's usually on the driver's side of the vehicle. Put your power leads there, and run your speaker leads down the other side (which is usually empty under the doorsills.)

A small capacitor can also work - there's a formula for it, but I don't remember what it is.

There are several easy ways to get rid of noises like this, but I've found it most effective to eliminate it as close to the speakers as possible. A good amplifier kit will have a shielded set of RCA cables, and there should be a chassis ground screw by the RCA jacks on both the head unit and the amp - so anything picked up by the shield will be "drained" to earth.

An alternative solution would be to "choke" the power leads as described above (right before the device) - and I seem to want to recall using a 1" core for those coils (but I could be mistaken.)

There are also "noise filters" which are little more than condensers which go on the back of the alternator (this noise is usually "ripple" that makes it past the diode trios in the back of the alternator,) but they tend to be for lower-output alternators, and may not tolerate anything over, say, 80A output well...

5-90