I've installed a couple of stereos in my time but this one has me confused. Mostly I'm not sure if this is because of the stock setup plus my new aftermarket stereo or if I am having grounding issues. I could use some opinions before I do anything else.

I installed KDC X704 - https://www.kenwood.com/usa/car/excelon/kdc-x704/
with this harness - but I think I should have bought a Metra-70-1786 and connected the RCAs directly to the preamp outs on the back of the new HU. Hindsight is always 20/20..

So now everything is working but I have fuzzy static noise when the speakers are set to the lowest volume setting with truck powered off. I did a bit of searching and it seems most noise issues are either caused by a bad ground, or from sending too much electricity through the amp. If I start the truck it doesn't grow with RPMs, like the alternator issues I've read about. I've tried regrounding the HU but that doesn't seem to help. So my question is should I buy a new Metra cable and skip the factory amp altogether, consider connecting a ground loop noise isolator, or am I missing something else?

I plan on installing an aftermarket sub and amp in a month or two but I want to see what the speakers sound like with the new HU so I can decide if I need new speakers as well.. Any ideas?

 

Any LED tail lights?

 

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Nope. I do have LED licence plate lights and in cabin lights. Are they known to cause issues?

 

I had this issue with the stock audio system. When the everything was off I could heard the faintest static noise through the speakers. The amp under the drivers seat had a swollen capacitor. Replaced it with a used spare and all was well after that.

 

You use the Kenwwod power amp as a preamp for the stock power amp. This causes a load mismatch (the stock power amp has an input impedance of several kOhm, while the Kenwood power amp is designed for 4-8 Ohm load). Also, a power amp is a bad preamp due to worse signal-to-noise-ratio as well as higher harmonic distortion. Using the Kenwood preamp outputs creates another problem: The stock power amp has balanced inputs while the preamp outputs are unbalanced. Since you want to replace the stock power amp anyway, you can chose one with unbalanced inputs, but you have to install shielded wires and this system is not as good as a balanced one.

 

This makes sense. So if I read that right, I can use the Kenwood power amp outs and then bypass the amp itself but I'll end up losing the sub (which is fine)?

Later down the road I'll add a sub and an amp. For now I'll try running the speakers without the stock amp. I found a pinout diagram for bypassing the amp, going to try wiring it up in a few.

 

You should be able to use the preamp outs to feed the stock amp under the drivers seat (with shielded wire) and use the speaker outs of the aftermarket head unit to power the sub.

 

Sure, you can drive the stock speakers with your Kenwood directly as long as the speakers have a minimum impedance of 4 Ohm. Disadvantages will be a little more more heat in the dashboard and you have to modify the wiring.

The other option is to convert the unbalanced outputs to balanced. This can be done either with audio transformers (cheap) or an active converter (I wonder why they are so expensive, which they shouldn't). A transformer has limitations in terms of signal quality. Too high input voltage will distort the signal due to saturation of the transformer's iron core. Frequency characteristics is also an issue. The optimum solution in terms of signal quality is an active converter. As I understand the Kenwood manual, the subwoofer output can be disabled. The stock power amp derives the subwoofer signal on it's own.

 

You can, but it comes with limitations: The effective signal is reduced by 50% and noise is fed into the power amp, because the signal is unbalanced (signal is referenced to ground where the amp picks up noise).

 

Bypassing the amp did the trick. I tested just the tweeters on the driverside A pillar to see if it would fix the static issue, then went ahead with the rest. I was able to pull the pins out of the harness connector so I didnt have to mangle things too badly. When I get around to running RCAs for a new sub maybe I'll do the speakers as well.

Thanks for the help!