Successfully installed new amp with existing HU and no hiss

Well, you didn't leave very much time for a response.

I have an Alpine MRX-V70 5-channel amp running off the factory HU with no hiss. I'm using a pair of Infinity Kappa 62.9i in the front doors and a Pioneer TS-SW3001S4 in the back. All factory speakers are removed except the squawkers which are disconnected. No hiss. I don't have the gain cranked up though. There might be some hiss if I do. But at that level, it's loud even at minimal volume.

 

I have a amp installed, Polks in the door. "Normal Gain" There is none. You adjust to your liking, I have mine adjusted about 9 o'clock, any more and it is hisssing, not much but it does. If you have hiss, and your at zero gain, then I would look at the RCA cables if they are used. Make sure your screw connectors are very tight, and the ground cable from the amp, is close to the amp and it is secured to the bare metal frame.

 

Absolutely! Mine even has 3 processors and it has zero noise.
Here is my system:





What kind of noise are you getting? Steady high hiss or does it sound like an alternator whine?

Two things I'd check: Your grounding point and your gains. what does your grounding point look like? Where did you tap it and how big of a wire are you using? Where did you route the signal wires? Sometimes if you have multiple units (amps, xover, etc) they can create a ground loop. I would suggest using a ground distribution block and tap it on a clean, solid chassis area. You can also get a ground loop isolator, but I suggest locating a good grounding point first.

Second thing is the gain setting. You can google proper gain setting for a more thorough explanation, but in a nutshell, you want to play music at near 90% volume, then on your amp, adjust the gain starting from 0 and slowly turn it up just before clipping occurs. The hissing occurs when amp gains are cranked all the way up unnecessarily. The gain knob is not a volume control, it is used to match the voltage of the source unit.

Another source of noise is when your source has a very low preout voltage (1.5v or below), since this will make you turn the gain all the way up. In this instance, you will need a line driver to bump the preout voltage to 4v or higher.

If there's a constant hiss on your tweeters, this tells me that one of your gains is not set correctly.

 

Hiss not a head unit problem, I kept the dash speakers

 

Unfortunately, being a high end/professional shop doesn't mean they have competent installers
I've seen botched jobs and bad installs that came from high end shops.

Did you mean speaker level inputs? What Alpine amp do you have? Give me the model name and we'll lookup and see if it even has speaker level inputs. Regardless, I don't like the idea of directing speaker level signal to the amplifier. Not only it will introduce noise, but in some amps, it gives you a turn on/off pop. My JL Audio 700/5 amp is capable of accepting speaker level inputs, but I still insisted on using a LOC. It's just 'cleaner'.

This is the LOC I use - I bought it at Frys and you will need two if you're running 4 channels:
FRYS.com | AXXESS

Your stock head unit is fine, I'm almost 99% sure that adding a LOC will fix the noise issue. This is exactly what I encountered before I bought the LOCs.

 

I used a Polk 660 for a while, it had a awful pop on power down, I could control some of it with controls on the amp, but I changed it to a Kicker 4 channel amp, no pop, and clear sound. Different sound then the Polk, but at least it is not popping.

 

Before you go any further, may I ask where did you get the speaker level outputs? Is it coming straight from the back of the stock HU or did you simply just tap from the kick panels?

If you have the resources to try another amp, you can certainly try that too.

Which power wire? If you're talking about the amp power wire then I would say yes. The LC6i does not need a big gauge power wire like your amps do.

 

I'm starting to think that his amp has an issue... some amps ARE very picky with inputs.

 

The MRV-F300 accepts speaker-level inputs, but I would still try a LOC.

It's possible to have a faulty amp, but if you bought it brand new, that may not be the case. I need you to try a LOC and go through the RCA inputs of the amp. I have 5 amps at home - a mix of RF, MTX and Xtant from my previous car. When I bought the Prius in November, I tried ALL of them using the speaker level inputs and NONE worked, even though the amps are capable of taking speaker level inputs. All I got was a noisy signal on the speakers. I added a LOC and it instantly gave a clean output.

 

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