# Alternator whine issue - it's the amp !



## weng (Jun 7, 2006)

Finally I have isolated the source of the alternator whine. Have swapped a few other amps in my car that played without any noise, so the amp is the culprit.

Now I am working on rectifying the amp. What parts should I look for / replace to get rid of the annoying noise in the amp ? 

Please help !

edit - the amp is a Tru C7.4T


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## cvjoint (Mar 10, 2006)

You know, for the longest time I thought I was getting alternator whine from the amps too. Sometimes it would be quiet, sometimes just plain loud. It turns out the RCAs were the problem. Have you moved any of the RCAs at all? Even the slightest move closer to the chassis will induce noise.


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## chad (Jun 30, 2005)

weng said:


> Please help !
> 
> edit - the amp is a Tru C7.4T


And the rest of the rig?


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## weng (Jun 7, 2006)

Nothing is changed or moved when swapping amps. RCA is layed from front to back under the seats. Have also tried a temporary pair of RCAs from the HU to amp thru the cabin and noise is still there. But no noise for other amps

I run off a DRZ9255 to the amp and from the amp back to the speakers. Nothing else in between. Amps that I have swapped for testing include Tru TO3 4.150, Genesis DM, Adcoms, PGs, Poweramper tube amp, Hustler tube amp, Linear powers all of them whining free. All in the same car with nothing else changed during trouble shooting.

Have also upgraded the alternator, the big 3s, second battery at the boot, 0awg negative back to the front batteries, but without luck


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## cvjoint (Mar 10, 2006)

did you try the other amps over the same frequency? I'm not sure the whine is still there after you LP etc


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## Mooble (Oct 21, 2007)

How well is the amp isolated from the chassis? Do you screw the other amps down as well, or just lay them on top when you test them?


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## weng (Jun 7, 2006)

Tested the whine with volume turned to zero and step on the gas pedal. Its at the same crossover point, same setting. Nothing is changed, just plain swapping of amps

Yes, other amps are screwed down. In fact the C7 is out of the car now, am enjoying music from other amps, minus the noise 

Anybody who have success in repairing amps that caused alternator whine ?


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## kyheng (Jan 31, 2007)

Maybe a blown RCA input's earth like Pioneer HU? Anyway you can repair it yourself if you have the knowledge or send to an eletrical repair shop to do the job. It should not cost much.


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## 14642 (May 19, 2008)

Measure the resistance between the head unit's RCA center pin and the shield. You should read 0 ohms. If it's more--like a few hundred ohms, then measure the resistance of the RCA input on the amplifer. If there's any continuity, try a ground loop isolator between the head and the amp.


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## Nitr0racing21 (May 25, 2008)

Could it be your alternator going bad?


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## weng (Jun 7, 2006)

kyheng and Andy, thanks for the suggestion ! I will check the RCA input first thing. 

Are there any other possible faults that I should check in the amp ?


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## weng (Jun 7, 2006)

Nitr0racing21 said:


> Could it be your alternator going bad?


I have tried 3 alternators 

And the issue is there is nothing wrong with like 10 other amps in the same car, same system.


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## 14642 (May 19, 2008)

You're not looking for something broken as much as you are looking for incompatibility. Ideally, there's one audio ground in the system or the entire signal chain is balanced--balanced outputs and differential inputs. 

Unfortunately, some head unit manufacturers try to split the difference and put a resistor between output hot and ground. That causes current to flow and creates a ground loop, especially if the amplifier manufacturer does the same thing and sticks another resistor inbetween the signal hot and shield. 

Real differential inputs don't care about any of that and just amplify what's different between hot and ground. All amplifiers should be built that way. when you're shopping for amps, stick an ohm meter on the shields between the channels. If you measure continuity between the shields or a resistance between shield and hot, look for another amp. Same goes for head units. They should be either O ohms or an open circuit. If you read some bizarre resistance that rises for awhile and then stops, that's a capacitor and is probably OK, unless the shield is continuous to chassis ground. 

Not understanding this is what causes so many problems for folks who try to integrate with factory heads and factory amps. We 're used to thinking about signals as low level and high level. To us, low level means not much voltage and shield is ground somewhere in the system (usually at the output of every piece of gear, but not on the input (hopefully). High level means lots of voltage and nothing is ground. Many OE systems use balanced output and differential input(nothing is ground) and either high or low level. The input sensitivity is set by a resistor network in the amplifier that sets a maximum input voltage to prevent the signal from overdriving the A/D convertor in the amp--which IS the input section. Hooking up a speaker-level signal to that input if the resistor network is designed for a 1V signal sounds crappy--very distorted and digital clipping is really ugly. Hooking up a single-ended head unit's RCA output to the signal doesn't cause clipping, but it unbalances the inputs and causes noise. Despite it's bad reputation as a band-aid, the ground loop isolator is the only fix for this problem. The transformer inside reflects the impedance (provides a fake load) and allows balanced circuits to remain balanced. Occasionally, they attenuate the bass. all good systems ought to have an EQ and with the EQ you can put the bass back in.

The ground connection to signal shield is a home audio thing and is less problematic at home because power supply ground can be isolated from audio ground more easily. One day, there won't be any more single-ended outputs anywhere and everyone's lives will be easier.


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## chad (Jun 30, 2005)

Andy Wehmeyer said:


> You're not looking for something broken as much as you are looking for incompatibility. Ideally, there's one audio ground in the system or the entire signal chain is balanced--balanced outputs and differential inputs.
> 
> Unfortunately, some head unit manufacturers try to split the difference and put a resistor between output hot and ground. That causes current to flow and creates a ground loop, especially if the amplifier manufacturer does the same thing and sticks another resistor inbetween the signal hot and shield.
> 
> ...




It cannot be stressed more!

See, my standardization rant... it's not just a rant....


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## weng (Jun 7, 2006)

Thanks Andy for the detailed info ! Will troubleshoot again...

As for the ground loop isolator, it makes me thought of the following situation : When a man couldn't bring a hot blonde reach orgaism like the other 10 men could with ease, give that man a vibrator   just j/k


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## 14642 (May 19, 2008)

Interesting analogy. Less hassle with the non-human pleasure-giver. I'd opt for the isolator.


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## chad (Jun 30, 2005)

Isolators got a REALLY bad name in car audio but in essence they are merely isolation transformers, which when quality ones are purchased sound just fine and have a flat phase response much higher and lower than a sound system. Problem is that the ones you can buy for $9.95 have poor transformers in them, that saturate easily and can attenuate the extremities.

Transformers ave been and are used all over the place in audio, there is no reason to think of them as a band-aid when solving compatibility issues.


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## 14642 (May 19, 2008)

Right.


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