jl audio 1000.1 amp prblem - diyAudio
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Old 24th March 2009, 05:12 AM   #1
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Default jl audio 1000.1 amp prblem

my baby has layed down on me....

my cd players rca jacks stopped working and took my amp with it.... help perry, im bassless

anyways....it powers up fine. no protection...idles at 1.5volts...
you can hook a speaker up to it and no weird noises or anything.

but if i hook my new radio rca jacks up, the amp just humms out of the speaker.....i can unhook the rca jacks , and touch the input rca jacks on the amp and it makes the same humming noise...

testing for dc voltage with the black probe on the chassis ground. red probe on the positive speaker wire, i get 57.84v dc

testing for dc voltage with the black probe on the chassis ground. red probe on the neg speaker wire, i get 57.90v dc
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Old 24th March 2009, 05:32 AM   #2
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Have you checked the shield ground on the head unit's RCA output jacks?

Check for DC voltage on the RCA shield of the amp. There shouldn't be any significant voltage.
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Old 24th March 2009, 05:50 AM   #3
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i went ahead and got another cd player to replace the non working alpine..it needed to be replaced a while ago. i wished i would have done it sooner now.....
i picked up a kenwood kdc ps909 , no speaker wires, just 3 sets of rca jacks......kinda old , but it works great...lol


the jl amp does the humming thing with the newer cd player hooked up to it...but this kenwood is good. i can hook up another amp to it , and it has good audio....
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Old 24th March 2009, 07:02 AM   #4
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I think you still need to check both.
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Old 24th March 2009, 07:33 AM   #5
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i dont have the alpine in front of me right now, it gave it to a buddy who said he could fix it....i just didnt want to bother with it...amps are my thing...lol

but the kenwood has no dc voltage on the rca jacks. all 3 sets..reads -0.001 v
ac voltage fluctuates from 0.00v to 0.98v ...thats with a low volume on the cd player ..
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Old 26th March 2009, 02:14 PM   #6
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the alpine is history....i tried to get it back from my friend , but he took it and junked it out for parts......

would the 2 op amps right near the rca jacks keep the sound from being amplified?
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Old 26th March 2009, 02:39 PM   #7
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It's very strange that the power supply is producing rail voltage and it produces a hum when you touch the RCA jacks. This really seems like a signal source problem.

It's unlikely that the op-amps have failed. If you're 100% sure that the signal source isn't the problem, you could start troubleshooting by confirming that you have 15v on pins 4 and 8 of the op-amps.
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Old 26th March 2009, 04:34 PM   #8
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one rca jack will humm a little louder than the other one when you touch it.. does the same thing when you plug each rca up to the amp..

readings from the op amps right near the rca jacks
opamp 1 u-50
pin 4 -14.21v dc
pin 8 14.20v dc

opamp 2 u-51
pin 4 -14.21v dc
pin 8 14.22v dc

Click the image to open in full size.

are the other 3 ic's on the left side of the pic (u1,u2,u3) opamps to?
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Old 26th March 2009, 04:56 PM   #9
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ok, i turned the low pass filter off, and turned the gain up a little , and i can hear some voices coming out of my sub now, but it still has that awful humming noise ....
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Old 26th March 2009, 05:09 PM   #10
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You checked the DC on the Kenwood head unit. You were supposed to check the continuity between the shield and ground. Is that 0 ohms?

You gave an AC voltage. Where was that read from (black and red probe placement)?

Yes. The other op-amps are likely NJM072s.
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