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Discussion Starter #1
Feedback or "hiss" sound in new system - only starts after several minutes of play

I asked this in my Build Thread, but it may go unnoticed there...

Vehicle - 2016 Ram Crew Cab
Using factory 8.4 Uconnect (non-alpine)
Axxess AX-DSP-CH5 T-Harness
Hertz MLK Mille Legend 165.3 Components (front)
Hertz MPX Mille PRO's 165.3 Coaxial (rear doors)
JL Audio FiX 82
JL Audio TwK D8
Rockford Fosgate Power T400X4ad
Rockford Fosgate Power T750/1bd
Alpine R-Series R-W12D4

I need a little assistance. All equipment was purchased new from authorized dealers. Installed by professional installer with 30 years experience.

There may be something wrong with either my FiX or TwK. When I first turn the system on, it's PERFECT. No noise whatsoever. Just perfect silence, at all volumes, until I send a signal from Bluetooth or some other source. I've tested for the absence of any noise with the engine running and off. I've paused the signal and turned the volume up all the way on the DRC-200 and there is absolutely zero background or electrical noise. THEN...after about 15 minutes, a faint electrical sounding "hiss" starts. It's a constant hiss and increases in volume as I turn up the DRC-200 or turn up the gains on my front stage amp. The subwoofer signal is clean with no noise at any volume. Signal is ran from the HU to the FiX then optically to the TwK. Analog signal is then fed to the amps. The DRC-200 controls the gain of the TwK. My HU volume was set at 34 out of 38 when the TwK was tuned. My amps were level matched using JL set up disk.

It's important to note that the hiss (sounds like electrical feedback maybe) is not present for approximately 15 minutes, then just magically appears. It doesn't matter if I'm driving or just sitting in the driveway. My installer believes the noise originates before the amps.

I'm leaning towards something being wrong with either the FiX or TwK. It's almost like something internal warms up, and causes the feedback. I can turn the truck off and come back after an hour or so and the noise is gone, but comes back like clockwork after about 15 minutes. This further leads me to believe that whatever is causing the noise cools down and doesn't cause issues until it heats back up.

I've read numerous threads about noise with the FiX or TwK, but no one else seems to report that the noise only starts after a few minutes of playing the system. My installer is at a loss. He's installed these items countless times and states that he hasn't seen another example of the signal being all but perfect like mine and only developing an issue after a few minutes of use.

I don't want to let this go for long in case I need to send something back to be replaced.

Thoughts???
 

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Discussion Starter #2
My main Power wire (1/0 gauge) is ran to the middle of the amp rack and splits from there. I've read that the amps should be 18 inches from the power supply. I'm closer than that, but that doesn't explain why it only starts after 15 minutes.

The amps have fans. I'm going to check to see if the noise corresponds to one of the amp fans turning on.

I'm almost certain that all of my grounds are good. If it was a grounding issue, wouldn't the hiss be constant?

I plan to check all of my RCA's tomorrow to ensure one isn't causing the hiss.

Something else that's strange. When using Bluetooth, the Output LED light on the TwK stays amber...should turn green. However, it's obviously sending an EQ'd signal to the amps. It turns constant green when using a USB cable or thumb drive instead of Bluetooth or when using XM for signal. This HU doesn't have a CD player.
 

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Re: Feedback or "hiss" sound in new system - only starts after several minutes of pla

Can you bypass the JL parts and go directly to the amp? Just to try to isolate it further.
 

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Re: Feedback or "hiss" sound in new system - only starts after several minutes of pla

Something getting warm with a bad capacitor in it. Start with the signal path, processors and so on. Is the hiss persistent with muted audio? Start with pulling the RCAs from the first part of the signal path and work your way to the amps.
 

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Discussion Starter #5
Something getting warm with a bad capacitor in it. Start with the signal path, processors and so on. Is the hiss persistent with muted audio? Start with pulling the RCAs from the first part of the signal path and work your way to the amps.
Yes...the hiss, once it starts, is constant with music or while music is paused or muted.
 

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Re: Feedback or "hiss" sound in new system - only starts after several minutes of pla

Can you locate a specific channel? If so that will help slightly, I stick with my statement above, disconnect RAC's till it goes away.
 

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Re: Feedback or "hiss" sound in new system - only starts after several minutes of pla

Are you sure its not the fan for that amplifier coming on? I know these dumb questions can be annoying but its worth asking them anyway. You can bypass both DSP's with a music player and cord that allows 3.5 mm jack to RCA direct into the amplifier. This would eliminate the DSP's as the possible source of the hiss if it was still there and then I would start looking at that amplifier or possible sources of interference for it.
 

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Discussion Starter #9 (Edited)
Update: Didn't have a lot of time today to play the system. Drove the truck for about 30 minutes running some errands. No issues. Perfectly quite. Zero noise or hiss...even with no signal and at full volume. As far as I could tell, the amp fans never came on. I sat in the truck for 45 minutes this evening. Played the music as loud as I dared given the late hour. The noise never came back, but I'm 100% sure the fans never came on either.

I'll play the system tomorrow until the fans start up. If the noise comes back at the same time, we've solved our mystery. If so, I'll work to isolate the amps and RCA cables until the fans can come on with no noise/hiss introduced to the signal.

Will update tomorrow. Thanks to everyone for their feedback.

I don't want this to take away from how AMAZING this truck sounds. To my ears, it's absolutely perfect. I can not find any negative to the SQ. I doubt seriously that I'll go active. It's hard to imagine it improving the SQ enough to justify the expense. I'm so very happy with how this has turned out. I feel confident that I'll figure out the little "hiss" issue that appears to only be introduced when the amp fans turn on.

Thanks!!
 

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Discussion Starter #10
Update...I haven't been able to reproduce the circumstances that caused the hiss. It's been so damn cold down here that my amp fans aren't coming on. I jammed for an hour listening to Pink Floyd, and nothing. Just perfect sounding music with absolutely no noise. I even had the heater going. Maybe tomorrow...LOL.

I'm convonced that the fans are what caused the hiss sound. Once I can verify this, I'll move things around a little to isolate the amps.
 

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Discussion Starter #11
Update to this thread in the event someone stumbles upon it. The amp fans were not to blame. The hiss or feedback sound was caused by a custom made ohm load device used to send a signal to the FiX 82. We swapped it out for the JL LSA-4 and it’s gone. Period. No noise whatsoever. I should have used the LSA from the start. Anyway...all’s good and now I’m moving on to a “hybrid” 3 way active up front. More on that soon.
 
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