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Alternator Whine - Detailed Post


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Disclaimer: 

I’ve done a lot of reading on forums such as this, articles on Crutchfield (including their noise flowchart), and some YouTube videos. I’ve looked over the system noise commandments thread (or whatever it was called) just a few minutes ago, but I think I’ve done most of those debugging approaches.


I’m posting in this section because my question is broad; I don’t know where the problem lies.

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Issue Description:

I’m getting some hiss and slight whine from my speakers. It isn’t terrible, but it definitely is there. The hiss is present when the motor is off or on. The whine happens when the engine is on and changes with RPM. In both cases the noise only occurs once the head unit has booted. You can kind of hear the hiss click on and off briefly during the booting process.

I only notice this with the front speakers. The rear are disabled and I don’t notice anything from the subs.

I don’t think I blew the pico fuse as I don’t think I unplugged the RCA cables with the HU on. But it’s hard to tell. 

There is NO hiss or whine when I run the front speakers of the head unit.

The amount of hiss and whine do not change with HU volume.

I don’t mind the hiss as you can barely notice it when the vehicle is running, but you can hear the whine while accelerating. I’m not very concerned about the hiss, but felt it is probably worth mentioning anyway.

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Setup:

2007 Honda Ridgeline

Pioneer 4400NEX

Morel Maximus 602 (front only)

3x Sundown SD3-10

Zapco ST-2X SQ

Zapco ST2000XMII

Harness kit from Crutchfield 

Amps are behind rear seat; I ran a dedicated hot AND ground 2 gauge wire from the battery. They feed into two distribution blocks that break out into 2x 4 gauge cables. The 4 gauge cables only run about a foot from the block to the amps.

I have a few RCA cables run back. One for the backup camera, one for subs, and two (left and right) for the front speakers. The cables are decent, shielded cables.

Speaker RCA for what it’s worth: https://www.amazon.com/dp/B00RXNVBBE/ref=cm_sw_r_cp_api_i_CEqQDbYA1JB2F

The radio is hooked into the stock harness (with an adapter of course).

Power is run on drivers side, speaker wire/RCA/amp remote are on passenger side.

Gain range for the amp is 0.2v to 8v. The HU is 4v RCA, so I tried the gain dead center. There was an unacceptable amount of hiss, so I dropped it back to a little under half. 

Assuming the gain is mostly linear, dead center is 4.1v, so it makes sense I need to be slightly under that. 

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What I’ve Tried:

1. Disconnect RCA from amp. Hiss and whine go away.

2. Disconnect RCA from head unit. Hiss and whine go away.

3. Dummy plug/RCA mute the RCA at the HU. Hiss and whine go away. This makes me think that the problem is NOT noise being picked up by the RCA run.

4. Ground HU to dash chassis instead of harness ground. Same amount of noise.

5. Ground HU to battery ground via 5 feet of 14 gauge speaker wire. Same amount of noise.

6. Disconnect antennae. Same amount of noise.

7. Remove HU the dash WHILE ON and moved it around. Same amount of noise and no fluctuation.

8. Ground RCA shield/ground/whatever to the head unit. This makes it much noisier. That seems odd since a general suggestion for noise is to ground the RCA to the HU for Pioneer models.

9. The voltage difference between the HU ground and (ground) distribution block is negligible. It reads 0v. It does have a slight reading of around 0.3 when I turn it to the 200m DCV mode.

10. I’ve unscrewed and re-seated the cable that runs from the battery to the chassis. 

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Additional Notes:

The alternator seems to be functioning as expected? I don’t know how old it is as I bought this vehicle only about 6 months ago, but I can see it is putting out 13.9-14.3 volts (at the cigarette lighter).

I have not performed the “Big 3” upgrade, but I’ve not noticed any dimming at all.

I’ve not check the resistance between the RCA ground and the HU with a DMM, but I did attempt to run a ground as described in #8.

The RCA for the speakers is longer than I needed, so the excess is coiled up behind the seat.

If all else fails, I might lower the gain a bit more - which regrettably entails removing the rear seat. I could compensate by increasing the source input gain on the HU.

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What I’m looking for:

Thoughts?

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I’ll look around for a way to turn it off.

 

Im curious where the problem would be coming from though. I have the dedicated ground line run.

The amp setup in the rear is quite straightforward.

I suppose I could try disconnecting the sub amp and double checking that nothing on the amp (namely mounting screws) are grounding out on the chassis.

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I decided to just do both.

I added an extension onto my multimeter so that I could reach everything. My multimeter reads a base resistance of 0.8 ohms.

Ill format my readers such that the first value is my measurement, the second value is my BASE resistance for the DMM, and the final result is the difference (or real resistance).

 

Battery to Amp ground: 0.8 - 0.8 = 0 ohms

Battery to dash chassis: 1.1 - 0.8 = 0.3 ohms

Battery to stock HU ground: 1.2 - 0.8 = 0.4 ohms (when I reversed the DMM leads....I got a reading of 0.5 - 0.8 = -0.3 ohms. I’m not sure how that is possible)

Stock HU ground to Amp ground: 1.4 - 0.8 = 0.6 ohms

Dash Chassis to Amp ground: 1.4 - 0.8 = 0.6 ohms

 

So as it stands - the gap is 0.6 ohms. But - connecting the HU directly to the battery ground (as I did last night) is equivalent to the first example (battery to amp ground) as I used EXACTLY the same cable as I did for my DMM extension. In that situation I still heard the whine. 
(in fact - I just tried again; no change)
 

Also - the different readout for battery to stock HU ground (based on the direction of my leads) is perplexing.

I don’t have a particularly amazing DMM though. It is a P30756 - so perhaps the accuracy isn’t up to snuff.

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I measured a bunch of different wiring configurations to give me a better picture of my options and the associated resistances.

As it currently stands though: I currently have the HU grounded to the stock harness ground. The amp is grounded by a 2 gauge line run straight from the battery. (Though it goes through a distribution block as it nears the amp.)

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in the past I have chased this issue and finally decided the power supply for the head unit was the issue and one of those inexpensive filters on the hu power fixed it 

did you try another music source on the amps?   I will bet its not there 

 

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