Hi, everybody. Thanks for the add! I have a JL Audio 450/4 amp that has an issue that I'm hoping is easy to fix.
I've connected it to three different input sources with varying results:
1. Receiver on boat - audible noise whine without engine running (didn't start engine), frequency hunting and varying without obvious reason.
2. Iphone plugged directly in using battery in garage for power - very minimal hum, sounded great otherwise. All 4 channels producing powerful, clean sound. Hum slightly louder in right channels.
3. Iphone playing through JL Audio bluetooth adapter (that is normally playing through my garage's system with absolutely no noise, hum etc). Adapter is powered by 12 VDC power converter (cheap plug in adapter from Amazon). Very loud static comes through all channels. No noise plays through garage receiver but similar noise is present as I plug RCA's into the back of that receiver before outer ground terminals contact. Once ground terminal contacts, noise stops. Not the case on this amp. Noise is continuous on all channels.
Similar results when in 2 or 4 channel input mode.
I know next to nothing about diagnosing these amps, but it seems that the issue is in the input stage somewhere. It also seems that there is a missing ground connection or something to that effect. I assumed that the outer (ground?) connections for the RCA terminals would have some continuity between each other so I measured them, but they measure a consistent 3 megaohms between each other. The output RCA's measure approximately 0.5 ohms between outer terminals. I measured a couple of PPI amps I have laying around and they measured 20 ohms between outer terminals.
I did my best to search this forum and I saw mention of confirming that the input board was fully seated, so I pulled the amp apart, lifted and replaced the board with no change. When the board was out, I noticed some of the coating on the bottom of the board that covers the RCA input solder joints was a bit crusty, so I scraped the loose stuff off with my fingernail and brushed it away, thinking it may be somehow creating a bridge between the inner and outer RCA terminal connections. No change in function.
I apologize for my improper terminology and I'm here to learn. Thanks in advance for any advice you guys have! Thanks! Mike
I've connected it to three different input sources with varying results:
1. Receiver on boat - audible noise whine without engine running (didn't start engine), frequency hunting and varying without obvious reason.
2. Iphone plugged directly in using battery in garage for power - very minimal hum, sounded great otherwise. All 4 channels producing powerful, clean sound. Hum slightly louder in right channels.
3. Iphone playing through JL Audio bluetooth adapter (that is normally playing through my garage's system with absolutely no noise, hum etc). Adapter is powered by 12 VDC power converter (cheap plug in adapter from Amazon). Very loud static comes through all channels. No noise plays through garage receiver but similar noise is present as I plug RCA's into the back of that receiver before outer ground terminals contact. Once ground terminal contacts, noise stops. Not the case on this amp. Noise is continuous on all channels.
Similar results when in 2 or 4 channel input mode.
I know next to nothing about diagnosing these amps, but it seems that the issue is in the input stage somewhere. It also seems that there is a missing ground connection or something to that effect. I assumed that the outer (ground?) connections for the RCA terminals would have some continuity between each other so I measured them, but they measure a consistent 3 megaohms between each other. The output RCA's measure approximately 0.5 ohms between outer terminals. I measured a couple of PPI amps I have laying around and they measured 20 ohms between outer terminals.
I did my best to search this forum and I saw mention of confirming that the input board was fully seated, so I pulled the amp apart, lifted and replaced the board with no change. When the board was out, I noticed some of the coating on the bottom of the board that covers the RCA input solder joints was a bit crusty, so I scraped the loose stuff off with my fingernail and brushed it away, thinking it may be somehow creating a bridge between the inner and outer RCA terminal connections. No change in function.
I apologize for my improper terminology and I'm here to learn. Thanks in advance for any advice you guys have! Thanks! Mike
Check the shield ground on the boat head unit. What is the resistance between the RCA shields (nothing plugged into them) and the case of the head unit?
Are any other amps being used in the boat?
Sometimes, JL amps don't like signal sources without a grounded shield.
JL uses a balanced input. There is no direct connection to ground.
Does the noise sound like this?
http://www.bcae1.com/temp/cooleditmixedoscillator01.wav
Are any other amps being used in the boat?
Sometimes, JL amps don't like signal sources without a grounded shield.
JL uses a balanced input. There is no direct connection to ground.
Does the noise sound like this?
http://www.bcae1.com/temp/cooleditmixedoscillator01.wav
Thank you for the reply, sir! I had been reading your posts prior to posting this issue and it was apparent that you are quite knowledgeable...I was hoping you would eventually reply and you were on it!!
You nailed the sound of the noise on the boat. It was slightly louder in two of the channels (left channels I believe).
There is a JL 1000/1 sub amp connected as well. I don't hear any noise coming from it. It is a class D amp and is connected to the sub, so I'm not sure these frequencies would be audible through it anyway. No hum or anything coming from it though.
The RCA shields are grounded to the receiver case (less than 0.2 ohms on my inexpensive multimeter, most of which is probably in the probes).
You are obviously on the right track. As I attempted to describe, the noise is dependent on the source, and the three sources do not make any discernable noise when connected to other amps. The boat receiver (a new JVC KD-T91MBS) does not generate any noise when connected to my PPI A300.2. The bluetooth adapter does not make noise when connected fully to the home receiver I have in my garage. However, the same noise that is generated when that bluetooth adapter is only partially connected, when the center pin is making contact, is the noise that is playing through the 450/4 when the RCA is fully connected (center and outer ground). I imagine is it from the 60 Hz wall power that is being rectified to 12 VDC. In my experience, it is common for amps to make noise when connecting the RCAs after the center pin makes contact but before the outer connection is made, but the noise disappears once fully connected. It is as though the signal is never fully grounded or balanced on this 450/4.
Hopefully my rambling makes sense! I'm trying to give you meaningful info and you seem to be on the right track already!
I doubt it matters, but this is a used amp that I am connecting for the first time. I bought it as a supposedly fully functional amp but I don't have the history of it. It appears to be in good physical condition and I don't see any signs of distress on the boards, with my untrained eye of course.
Thanks again for your help!!!
You nailed the sound of the noise on the boat. It was slightly louder in two of the channels (left channels I believe).
There is a JL 1000/1 sub amp connected as well. I don't hear any noise coming from it. It is a class D amp and is connected to the sub, so I'm not sure these frequencies would be audible through it anyway. No hum or anything coming from it though.
The RCA shields are grounded to the receiver case (less than 0.2 ohms on my inexpensive multimeter, most of which is probably in the probes).
You are obviously on the right track. As I attempted to describe, the noise is dependent on the source, and the three sources do not make any discernable noise when connected to other amps. The boat receiver (a new JVC KD-T91MBS) does not generate any noise when connected to my PPI A300.2. The bluetooth adapter does not make noise when connected fully to the home receiver I have in my garage. However, the same noise that is generated when that bluetooth adapter is only partially connected, when the center pin is making contact, is the noise that is playing through the 450/4 when the RCA is fully connected (center and outer ground). I imagine is it from the 60 Hz wall power that is being rectified to 12 VDC. In my experience, it is common for amps to make noise when connecting the RCAs after the center pin makes contact but before the outer connection is made, but the noise disappears once fully connected. It is as though the signal is never fully grounded or balanced on this 450/4.
Hopefully my rambling makes sense! I'm trying to give you meaningful info and you seem to be on the right track already!
I doubt it matters, but this is a used amp that I am connecting for the first time. I bought it as a supposedly fully functional amp but I don't have the history of it. It appears to be in good physical condition and I don't see any signs of distress on the boards, with my untrained eye of course.
Thanks again for your help!!!
Try leaving the JL 1000 off to see if you get noise in the boat.
Try connecting the RCA shields on the JL to the amp's main ground terminal to see if it affects the noise on the other sources.
Try connecting the RCA shields on the JL to the amp's main ground terminal to see if it affects the noise on the other sources.
Thanks, is there a slick way to connect the shields to ground other than wrapping a wire around them? I'll give those things a shot tomorrow. Have a good evening!
You can solder a wire to a short cable, barrel connector... anything that you won't mind soldering a wire to. Alligator clip jumpers may work, depending on the RCA connector style.
Grounding the RCA’s on the bench with the Bluetooth input completely solves the issue. Grounding either side of channels 1 or 2 takes care of noise in both 1 and 2, and grounding 3 or 4 takes care of both 3 and 4. The ground does not span the two sets of inputs, not surprisingly. I imagine the same fix will solve the issue on the boat but it’s not as easily accessible.
What is the long term fix for the issue? Is there a way to fix it inside the amp or do I need to run external grounds to the RCA’s? I can’t imagine they were able to sell a new amp of this caliber with this issue.
As another side note, the RCA’s on the boat are new JL audio marine cables.
Thanks a million for the help!!!
What is the long term fix for the issue? Is there a way to fix it inside the amp or do I need to run external grounds to the RCA’s? I can’t imagine they were able to sell a new amp of this caliber with this issue.
As another side note, the RCA’s on the boat are new JL audio marine cables.
Thanks a million for the help!!!
There may not be a problem. Car head units have a grounded shield (and have for 40(?) years. The amps are designed with that in mind. Many can deal with floating shields but not all of them.
If the problem in the boat is the noise that you heard in the file that I posted, the problem probably won't be solved with a ground and grounding the shields in the wrong location may cause other noise problems.
The noise in that file is what happens when you have two non-synchronized oscillators. You need to see if the noise is there without the 1000 being powered up.
If the problem in the boat is the noise that you heard in the file that I posted, the problem probably won't be solved with a ground and grounding the shields in the wrong location may cause other noise problems.
The noise in that file is what happens when you have two non-synchronized oscillators. You need to see if the noise is there without the 1000 being powered up.