HELP Alternator Buzz

[Ryan]

Trying to help out my uncle. He has a 55 chevy, 427. Installed the aftermarket stereo with an amp in the trunk. System sound great with the engine off. With the engine running, I get a buz though the speakers. Disconected the alternator and ran it off the battery. The buz went away. Any help would be greatly appreciated.

Ryan
Rnakamura@aol.com
405-824-6538

 

[zam70]

What kind of amp?
Now days 99% of the time, engine noise is a fault of the equipment used.
other than that, make sure the chassis & engine ground at the battery is good and that the alternator is in good working order.
Make all grounds as short as possible and check to make sure none of the signal cables are crushed or pinched.

also, make sure he is using resistor style plugs and wires (no solid cores). If he is an old scholl hot rodder, this is probably the problem.

 

[Ryan]

The amp is a coustic 480 qe, battery is in the trunk. Battery to frame, Engine to frame. SP wires are supression type. Just swaped out the alternator with another used one. The GEN light on the dash came on. That might be another bad alternator. May just buy a new one. With the other alternator, there was still a buz audible.

 

[zam70]

PART of the problem is the amp. It's not a bad amp but the Coustics did not have good power supply isolation....you might have to use a filter.

 

[GNandTTA]

Did you run the power wire and RCA's on the same side? They should be on opposite sides. Try disconnecting the RCA's from the back of the radio and see if the noise goes away. Also try running a new set of RCA's from the radio to the amp OUTSIDE of the car. This will eliminate the possibility of the noise being inductive.

 

[AZ Vic]

In my experience, alternator whine has always been a bad ground somewhere. I have bought the filters and they never did any good.

Isn't it the speaker wire "higher voltage" line the one you have to worry about "cross modulation" with the RCA's most?

Either way I would definitely run the extra set of RCA's outside and see if that takes care of it.

It may be your head unit. Do you have any speakers that are connected directly to the head unit? Try doing that so you might eliminate or isolate the source.

Double check your grounds and voltage at the head unit and the amp. The best way is to use a good Volt Ohm Meter. I would be lost without my Fluke You should have less than 1 ohm across any two grounding points ie. head unit to batt, amp to batt, here's an important one - alt to batt. You may have a bad ground through the mounts of the alt.

How did you run the power wires for the deck? The old connections may be bad. I would suggest running new wire for both the ground and the power if you have not allready done so.

hope that helps,

Vic

 

[GNandTTA]

Isn't it the speaker wire "higher voltage" line the one you have to worry about "cross modulation" with the RCA's most?

Not sure, I've always run speakers wires along side RCA's and never had a problem. Have, seen, and fixed many many problems with RCA's being to close to 12v wires and grounds. Either way, with todays equpiment being better, your right, the filters are rarely needed anymore. It is usually RCA plugs picking up EMI from current carrying wires (power and ground).

Also often overlooked are passive crossovers. The inductors often pick up EMI as well. Many times just rotating the crossover away from the offending wire(s) will eliminate it.

 

[ross87t]

I guarantee it is because he has his RCAs running along side his power wire.

Ross

 

[zam70]

Personally, I HATE the filters and wouldn't suggest using one (and have never used one). HOWEVER, in the case of some amps (Coustic being one) they have NO internal filter/ isolation. I would usually suggest getting a different amp, I didn't see that as a good solution in this situation.

On another note, in the 17 years and thousands of installs, I have NEVER solved a noise problem by relocating the power wire/signal wire from each other. I'm not saying it doesn't happen, I've just yet to see it myself.

Common causes:
Amp gains to high
pinched/crushed/shorted or bad signal cable.
poor signal ground reference from amp to headunit.
junk or bad equipment (x-overs, EQs & amps)
Bad alternator diodes
Bad body/dash, amp grounds

There's alot of good suggestions in this thread, just follow them and trouble shoot the system.

 

[GNandTTA]

I have NEVER solved a noise problem by relocating the power wire/signal wire from each other.

Probably because you know better than to run them together in the first place.

There are alot of variables that determine if RCA wires pick up noise. The biggest being the output impedance of the head unit. Most all good brands now make sure the output impedance is under 500 ohms. The real goods ones like Eclipse have it under 100 ohms. Output voltage also matters alot. Most good brands have at least 4 volts now.

HOWEVER, in the case of some amps (Coustic being one) they have NO internal filter/ isolation.

But any amp that produces over 30 watts per channel has a filter in the switching power supply. The whole purpose of a switching power supply, besides raising voltage, is isolation. But you are right, most manufacturers add a filter inside the amp as well.

 

[IrvJr]

I had 3 Coustic amps in my setup. 1 for the sub (360 model), old, like 12 years old. But it worked good. I just replaced that for a RF sub amp. But my 2 other Coustic amps (model 160's) run my deck and door speakers and they whine. Even with the stereo off, so i know it just those 2 sets of speakers running off the Coustic amps, and i have tried everything, filters new grounds.
I believe it is the old inferior designed amps. I am going to replace them soon for a RF 4 channel amp and reduce the clutter and hopefully lose the noise.

Scott