HU Hiss

[tdonoughue]

Ok, so learning from the posts here, I decided that I am not happy with the present hiss from my system.

Amp and woofer info is below. I have Polks on all 4 spots in the tub. Stock HU. The 4 RCA outputs of the HU go to the amp; the first pair (front?) go direct to the 1-2 inputs of the amp; the second pair is split to 3-4 and 5-6. Fronts are then wired to 1-2, backs to 3-4, and the sub is on 5-6.

Power is run direct to batteries (basically--via ACR) for the amp with 1 ga wires (though the negative one is not as heavily stranded as the other, which I thought was the issue, but read on); stock power wiring for HU.

I read @David Analog , I believe, counseling to work backward from the source. I muted the HU. Still hiss. I unplugged the HU from the amp. Zero hiss. It all went away. Oddly, it went gradually. Each RCA that I pulled decreased it more and more until when I removed the last one it was silent. I believe that eliminates the power to the amp (or basically anything else about the amp) as the issue.

Problem is that I think now this tells me my HU is the issue. Anything that can be done about that? I mean other than throwing out the @#$^ and getting a new quality HU? Or am I missing a step or something simple here?

Thanks in advance for any advice.

 

[Bruce]

I would get a 1/8 (headphone) to two RCA cable and test the amp with a phone or MP3 player connected directly to it.

My guess is that you are right about the head unit but this would be a cheap test to confirm.

 

[txav8r]

I had the same hiss, and I accepted that it was the HU. Ironically, my new setup is very similar, except that I have two JL amps now, and 8 speakers...but the HU is a Fusion IP700i...no hiss at all.

 

[tdonoughue]

Crud. I was afraid someone was going to say that I had to buy a $500 HU to fix the problem...

Wait, let me see how this works: "But honey, they said this is the only thing that will fix it..."

Does it sell?

 

[txav8r]

I am re-reading your hookup and wondering what you meant with the RCA's. Several things are a bit confusing and questionable to me. First, the RCA's...all should be to the amp's 1/2 and 3/4 channel. Let the amp use the input to supply the sub. I don't remember for sure, but the out's off the HU may have a separate sub out, but 4 RCA's won't cover that. Second, your powering off the ACR? Your power needs to be off the battery directly or off the switch from the battery. Some guys have run off an ACR post just as a means of shortening cable runs, but they ACR wasn't crossed, it was just a point to point connection. Anything other than pretty much battery to amp can cause you ground loops however, so that may be a factor. Seeing your exact connection may help to determine if any of this could be an issue. I would try a straight connection to the battery before you just buy a new HU...but the HU will probably still be the culprit. The solution I used was to just turn the gain down on the amp, which made it less perceptible at normal listening levels.

 

[tdonoughue]

@txav8r , thanks, first. I appreciate the help working through this.

Yes, the HU has RCA outs for front/rear left/right (for a total of 4). There is no sub out. So I have front left/right going to 1/2 and rear left/right going to a split 3/4 and 5/6 (because I need input to 5/6 to run the sub). That was my first suspicion of an issue, so I unplugged 5/6 first. Still hissed...

So, to the power. I misspoke. I am not powering directly off the ACR, but rather directly off of the switch (the ACR then hooking both batteries + together). Standard BlueSea Add-A-Battery system (see https://www.bluesea.com/products/7650/Add-A-Battery_Kit_-_120A). So I have the amp wired to the house side of the switch, along with the accessory wire (which is powering the HU). Negatives are all hooked to a negative bus bar which goes to both batteries (also as shown in the link).

Now, for the sake of full disclosure, after I did the test, I did install a + fused bus to the switch. I left the amp directly on the switch and moved the accessory wire to the bus on a big fuse (30A?). No change. But I don't figure that will affect anything at this point.

 

[txav8r]

It is sounding like the HU, but it would be good if @David Analog just three his hat into the discussion. He has had meds this same test before and it isolated it to the HU. That clarion is a noise maker.

 

[Matthew]

I have a CMD8 with a JL M600/6 for my bow speakers, cockpit speakers and swim platform speakers. I also have a JL M200/2 bridged with a JL MX10IB sub. Since the CMD8 only has 2 RCA outputs I take the front output to the M600 and the rear output to the M200 then out the M200 to the M600 for the rear channels. This all works flawlessly but there is significant hiss after dialing in my JL amps input sensitivity with a multimeter (AC voltage output test speakers removed, 75% source output and 50hz and 1khz 0 dB reference test tone CD). Even with the CMD8 muted I get the hiss at low/muted volumes.

Short term I had to dial back the amp input sensitivity to help eliminate some of the hiss but want to take full advantage of the amps/speakers I purchased. I'd hate to hate to have to replace my like new CMD8 with something else...

 

[Glassman]

Here is an informative article:

http://www.termpro.com/articles/noise.html

I went to pains to make sure that I didn't run audio cables next to power cables. I also used the best quality shielded cables I could buy. I kept my runs to/from amp short as possible and I checked the boat for snakes.
I currently have no HISS from my stereo.

Hope you get yours figured out!

 

[Matthew]

Here is an informative article:

http://www.termpro.com/articles/noise.html

I went to pains to make sure that I didn't run audio cables next to power cables. I also used the best quality shielded cables I could buy. I kept my runs to/from amp short as possible and I checked the boat for snakes.
I currently have no HISS from my stereo.

Hope you get yours figured out!

It's definitely the HU as removing the RCA cables from the unit eliminates the hiss. I too took great care in routing and running of cables, speaker wires, RCA's, etc. For grins I am going to try an alternate source to take my HU out of the equation and see if that makes a difference in eliminating the hiss.

 

[Glassman]

It's definitely the HU as removing the RCA cables from the unit eliminates the hiss. I too took great care in routing and running of cables, speaker wires, RCA's, etc. For grins I am going to try an alternate source to take my HU out of the equation and see if that makes a difference in eliminating the hiss.

Yeah, unfortunately the head units aren't top of the line. Hope it works out for you!

 

[David Analog]

For noise diagnosis specifically you work backwards from the 'last' active component in the signal path, which would be the amplifier.
You do not need a substitute source in order to isolate the true cause of noise.
If the noise is the same whether the boat electronics are 'On' or 'Off' then it is not a matter of RCA cable quality or RCA cable path routing.
'Hiss' would be described as a constant "Shhhh" noise similar to a distant waterfall, with perhaps a bit more treble emphasis, that does not change with boat electronics engagement, that does not change pitch with engine rpm, and does not change with the audio volume (although may be masked by music somewhat at higher volumes). Just being thorough so that we are all referencing the identical noise.
Tower HLCD speakers will have hiss period at close proximity when at rest due to their extraordinary sensitivity and extra treble emphasis. Shouldn't be a problem when underway and shouldn't be a problem with conventional direct-radiating coaxials such as those used in-boat.
I'm curious if the gain level and noise (hiss) level, two different questions, is similar on CD, Aux, and FM sources?
Sometimes you have a gain inequity between interfacing equipment and that places too much responsibility for gain multiplication on one gain stage. And that is a certain prescription for hiss. Like for instance with an iphone with less than 1 volt out. Sometimes this can be corrected by a line-amp placed in the correct strategic location, whether before the Aux input or immediately after the HU output. Sometimes it's just terrible HU quality. But I'm a bit surprised that a Clarion would be noisily like a JBL HU for example.
I recommend using Odin with Earmark Marine for your marine audio purchases, and here is why. SUPPORT. He can walk you through the best tuning method that will reduce noise while still maintaining all your dynamic range. And he will lay out your initial system wiring scheme to avoid noise. Odin worked as a sound engineer where he set up the sound for hundreds of touring groups. And that is one complicated gig! So he is my best resource for gain structure and how it relates to noise.

 

[Geiger41]

Just turn up the radio real loud and all that hissing will go away

 

[internationalmarinemike]

We install many many in boats day in and day out. If you still are in need of any assistance please send me an email or call me in the office anytime. I find it tougher to type in an attempt to diagnose and issue such as this rather than walking you though it while you are at the boat. If I can't help you I will put you on with one of our senior audio technicians. We will support you even if you did not purchase your equipment form our company. In the end I just want you to enjoy your boat.

Mike

 

[Matthew]

It's definitely the HU as removing the RCA cables from the unit eliminates the hiss. I too took great care in routing and running of cables, speaker wires, RCA's, etc. For grins I am going to try an alternate source to take my HU out of the equation and see if that makes a difference in eliminating the hiss.

Interestingly enough I believe it is actually the XM source that causes the hiss. My CMD8 is nearly silent on FM, AUX and CD with volume turned down. Change to XM and the hiss presents itself. My tuner is the SXV200V1 installed with a Shakespeare SRA-25 antenna.

 

[biffdotorg]

Matthew, I know this is a truly old thread. But did you ever eliminate the hiss on XM? I am finding that I have a similar situation. I am good on all sources other than XM where the hiss is present.

As others have said, turn the volume up and it is not noticeable.

Thanks for anyone else's input as well.