volume fade only while engine runs?
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=96598
Printed Date: May 15, 2024 at 2:47 PM
Topic: volume fade only while engine runs?
Posted By: lexelite
Subject: volume fade only while engine runs?
Date Posted: August 23, 2007 at 5:25 AM
Car: 2000 Lexus SC400
System: Stock Nakamichi Headunit and System
Xtant X603 Amplifier for front + sub channel only
Main Issue: Extreme Volume Fade that returns to normal volume and fades back intermittently while standing.
Other symptoms: Momentary loss of balance control on HU, problem occurs on all source inputs.
Note: (1)Setup fully functional for 2 months w/o any issues or additional modifying. (2) Alternator tests good at 15.10 while running with the amp on. (3) Isolated Xtant amp by removing power and problem persists through the HU direct powered rear channels.
Backstory:
The volume on the stock NAK HU disappears w/o warning. It will go from full volume to no-sound over various bumps (even my aftermarket amplifier running half the system is following along with the act). Figured it was a bad fuse or two.
Replaced all radio fuses thanks to the OEM manual, but problem persists.
Everything will play clear and loud as long as the car is in the ACC or ON position. As soon as the engine is running, the volume fades back to the "intermittent" mode (somewhere between no volume and way too loud). As soon as the engine is killed, the clarity and volume returns immediately.
Tested this while standing still and it is the same results.
What gives? Help...
Replies:
Posted By: sarcomax
Date Posted: August 23, 2007 at 12:17 PM
How are you providing the signal to the amp? Is it your stock alternator that is pushing over 15 volts to a 12 volt system? I have had customer vehicles with bad voltage regulators that have had similar effects on the audio system. A guy with a 70's bronco had a decrease in output power with the motor running, and if he reved the motor everything would shut off. metered the truck and found a 15.5 volt idle, and a 24 volt peak when he reved past 4 grand. He had polk momo amps.
Posted By: lexelite
Date Posted: August 23, 2007 at 5:32 PM
The signal to the amp is a built-in line-in connection for the Xtant X603. No line converters here.
The stock alternator before my amp pushed about 15.4 continuously. The power regulator is built into the alternator. Replacing the alternator is over $200 in just parts.
I would like to be sure that this will solved the audio problem before making such a large investment.
Is there anyway to be more sure, or any other possibilities first? 
Note: Several 12V sources inside the car still read 12V with the car on so the regulator still has to be functioning somewhat.
Posted By: i am an idiot
Date Posted: August 23, 2007 at 9:03 PM
Mark Levinson system?
Posted By: lexelite
Date Posted: August 23, 2007 at 9:18 PM
i am an idiot wrote:
Mark Levinson system?
No. The Nakamichi was the premium system before Lexus inked a deal with Mark Levinson.
Still looking for answers though..
Who else can chime in? Mods?
Posted By: lexelite
Date Posted: August 23, 2007 at 10:49 PM
Is there any way to isolate the stock NAK headunit or stock amp as the problem?
The headunit uses a balanced 5 wire input into the amp, so I am not sure how to test the signal. Or furthermore, how to test the amp's integrity either.
ideas?
Posted By: swerve
Date Posted: August 24, 2007 at 7:32 PM
that 15.4 volts from the alternator sounds a little too high. we had the same problem with an 04 malibu that ran 15 volts, 12 volts at idle everything was fine, start the car then nothing intermittent on/off from the deck. had the car checked out by gm and sure enough the regulator was bad in the alternator and they replaced the alternator and everything works fine now. also the guages read 13 volts even though it was more than that at the battery.
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git yer swerve on!
Posted By: DYohn
Date Posted: August 25, 2007 at 10:04 AM
Yep, sounds like the alternator/voltage regulator to me. Take the car to your local auto parts store and have them test the alternator. ------------- Support the12volt.com
Posted By: lexelite
Date Posted: August 25, 2007 at 4:21 PM
DYohn] wrote:
Yep, sounds like the alternator/voltage regulator to me. Take the car to your local auto parts store and have them test the alternator.
I didn't know that they could test the regulator. I thought they only checked if the output was above 13v or so.
I will look into this further.
Thanks for the support guys.
Posted By: i am an idiot
Date Posted: August 26, 2007 at 11:43 AM
Just to eliminate the alternator from the puzzle, without having to go get it checked. Why not disconnect the charge wire. If the problem goes away then the alternator may be the problem.
Posted By: lexelite
Date Posted: August 26, 2007 at 5:20 PM
i am an idiot wrote:
Just to eliminate the alternator from the puzzle, without having to go get it checked. Why not disconnect the charge wire. If the problem goes away then the alternator may be the problem.
Simple and effective. I like it. If this fails to solve the issue, then the issue lies in the HU, stock AMP, or wire short.
Posted By: i am an idiot
Date Posted: August 26, 2007 at 7:06 PM
I am not familiar with the Nak system. But the Mark Levinson systems do have amp problems that cause the radio to lose all control and also lose audio. This has been confirmed as the amplifier problem. If you determine that it is the amp, It might be an easy fix. Just let me know if you determine that it is the amp.
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