| Dan2 |
i know there have been many threads on this topic, but i went through them and couldn't find a solution to my problem.
i want to hook up my mids to my amp (located in the trunk). it is a 4 ch and 2 run my sub, so i just hooked up the back mids, switched to high pass filter, started the car and got alternator niose coming through.
first i thought it was the rca cable, cos it runs with the power cable. so i hooked another cable up to the head unit (temperary, over the seats etc) and still got the noise.
i checked the ground wire, from gnd on amp to battery gnd was about 1ohm (or 10 ohm, cant remember) between them. so i hooked up a ground wire straight from amp to battery, still got noise. but i did use a thin wire, which i thought was ok cos i didn't crank it up.
i also checked the rca jacks on the head unit and the amp. the negative terminals are shorted to the chassis of both the amp and head unit.
so now i wonder if i just have a crappy amp with bad (or no) noise filters in the signal line. oh yes that reminds me, if you switch the lpf on the noise goes away - but then so does the music!!!
i dont have too much time or money to play around with - i am hoping its something simple i am missing. or else i will just stick to using the head unit's amps. |
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| Perry Babin |
| You need to re-check the resistance from the RCA shield on the amp to chassis ground with no RCAs plugged into them. It can't be 0 ohms to ground. If it is, the amp is defective. |
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| zigzagflux |
Typically, the chassis of the head unit is tied to the car frame, just by nature of the mounting. If the RCA shield is tied to the frame (which you measured to be the case), there's a likely source of noise. Same goes for the amp.
Also verify, at least for testing purposes, that the amp frame is isolated from the car frame. As Perry mentioned, disconnect the RCA leads before measuring any further. |
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| Perry Babin |
The head unit's shields are virtually always connected directly to the case of the head unit (and therefore chassis ground). The amp's shield can't be tied to chassis ground. If they are, there will be a ground loop and noise. The amp input shields need to be able to float.
On Rockford and MTX amps, there is a diode that sometimes shorts (when someone allows a 12v source to contact the shields). This causes the RCA shields to become shorted to chassis ground and will cause noise. |
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| MatthewS |
| quote: | Originally posted by Perry Babin
The head unit's shields are virtually always connected directly to the case of the head unit (and therefore chassis ground). The amp's shield can't be tied to chassis ground. If they are, there will be a ground loop and noise. The amp input shields need to be able to float.
On Rockford and MTX amps, there is a diode that sometimes shorts (when someone allows a 12v source to contact the shields). This causes the RCA shields to become shorted to chassis ground and will cause noise. |
Perry, don't most pioneers heads make an exception to this rule? Could swear I remember their low level outputs no being tied to chassis ground.
- Matt |
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| Perry Babin |
In virtually all head units, the shields are supposed to be tied to the case of the head unit. Pioneer uses a fuse to protect the vehicle if someone allows a 12v source to contact the shield of the RCA cable. This is a common mistake and the fuse opens. The following page covers it briefly.
http://bcae1.com/images/rca/tempora...ieldrepair.html |
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| ppia600 |
| quote: | Originally posted by MatthewS
Perry, don't most pioneers heads make an exception to this rule? Could swear I remember their low level outputs no being tied to chassis ground.
- Matt |
Haha, the pioneers are most DEFINATELY tied to ground if working properly. What amp are you using? And yes on a good amp that actually uses a seperate power supply instead of just some 12v ic amp, the rca inputs shouldn't be connected to ground. (of course make sure the rca cables aren't connected when testing) |
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| MatthewS |
| quote: | Originally posted by ppia600
Haha, the pioneers are most DEFINATELY tied to ground if working properly. What amp are you using? And yes on a good amp that actually uses a seperate power supply instead of just some 12v ic amp, the rca inputs shouldn't be connected to ground. (of course make sure the rca cables aren't connected when testing) |
Are you laughing at me to be rude? or do you just think I'm that funny?
It was a legitimate question. I had a very old pioneer CD deck that one day, out of the blue, during normal operation began to develop an 'echo' effect. When I took it apart to look for ground damage I didn't find a direct tie to ground, and I didn't find an inline SMT fuse either. What I found was each ground line running to a SMT transistor.
My assumption at the time was that pioneer was either attempting to 'filter' the ground to reject ripple and noise, or that it was some sort of balanced arrangement. I was 17 the last time I saw it, and that was a long and inexperienced time ago. Either way I don't think it was an outrageous thing to mention here. It' wasn't directed at you, and I'm not the one in need of help here.
But thank you for attempting to marginalize my intelligence. Whatever makes you feel superior I guess? :confused:
- Matt |
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| Perry Babin |
| The transistors were probably muting transistors. They clamp the audio to prevent pops. The muting transistors are not active when audio is present at the RCA jacks. |
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| ppia600 |
"and I'm not the one in need of help here" ???? Chill out dude, you are jumping to conclusions WAY too quickly. First, do a search and you will understand why I mentioned them being DEFINATELY grounded. Second, I wasn't poking fun at you. The pioneer rca grounds are supposedly known for being delicate, its been mentioned many times. But since you obviously measured them to ground the deck should be ok. Just in case you noticed I also tried to give some helpful info. You still haven't mentioned what amp it is by the way. That would be helpful, some of these guys (me included) might be able to help diagnose the problem if you shared that piece of info. This is one of the few good sites where you don't have to worry about snobby responses. Everyone tries to be helpful.
| quote: | Originally posted by MatthewS
Are you laughing at me to be rude? or do you just think I'm that funny?
It was a legitimate question. I had a very old pioneer CD deck that one day, out of the blue, during normal operation began to develop an 'echo' effect. When I took it apart to look for ground damage I didn't find a direct tie to ground, and I didn't find an inline SMT fuse either. What I found was each ground line running to a SMT transistor.
My assumption at the time was that pioneer was either attempting to 'filter' the ground to reject ripple and noise, or that it was some sort of balanced arrangement. I was 17 the last time I saw it, and that was a long and inexperienced time ago. Either way I don't think it was an outrageous thing to mention here. It' wasn't directed at you, and I'm not the one in need of help here.
But thank you for attempting to marginalize my intelligence. Whatever makes you feel superior I guess? :confused:
- Matt |
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| sousmielie |
| Hi, I had the same type of problem, traced it to the head unit. The RCA's ground on the radio pcb has a very small resistor to ground which somehow went open circuit... Thus I had no ground with my input signal to my amp... Fixed it 2 days ago |
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| MatthewS |
| quote: | Originally posted by ppia600
"and I'm not the one in need of help here" ???? Chill out dude, you are jumping to conclusions WAY too quickly. First, do a search and you will understand why I mentioned them being DEFINATELY grounded. Second, I wasn't poking fun at you. The pioneer rca grounds are supposedly known for being delicate, its been mentioned many times. But since you obviously measured them to ground the deck should be ok. Just in case you noticed I also tried to give some helpful info. You still haven't mentioned what amp it is by the way. That would be helpful, some of these guys (me included) might be able to help diagnose the problem if you shared that piece of info. This is one of the few good sites where you don't have to worry about snobby responses. Everyone tries to be helpful.
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Now look at the first words out of your mouth. Then scroll back up to the top and look at the posters name, does it match mine?
I'm not the one who needs the help. :xeye:
- Matt |
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| sousmielie |
| quote: | Originally posted by ppia600
"The pioneer rca grounds are supposedly known for being delicate, its been mentioned many times.
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This part is true, my head unit is a pioneer... :hot: |
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| ppia600 |
| quote: | Originally posted by MatthewS
Now look at the first words out of your mouth. Then scroll back up to the top and look at the posters name, does it match mine?
I'm not the one who needs the help. :xeye:
- Matt |
You are the one that stated that near the bottom of your first post, are you not? You seriously need to chill. I wasn't poking fun at anyone including you, so why did YOU get offended in the first place???? I was poking fun at the delicate pioneer grounds, why can't you see that by now. C'mon dude??
:confused: |
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| Dan2 |
i must agree that i have always had helpful responses from you guys, and i do ask some pretty stupid questions!
| quote: | Originally posted by zigzagflux
Also verify, at least for testing purposes, that the amp frame is isolated from the car frame. |
the amp frame is connected to power ground, which in turn is connect to car frame. i know this cos i sometimes touch my screwdriver on the frame while screwing down the 12v and get sparks (even when gnd is disconnected, from caps i guess). is this wrong??
just checked, and the RCA ground IS SHORTED to the amp case. this must be where the ground loop is coming from. so what is the next step?????
it is a jensen amp, 1000w 4ch. i got it for free from a friend cos he said it was blown - but all channels work (maybe he was using it for his mids) |
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| Perry Babin |
If an amp has issues with its case being grounded, it is VERY poorly designed. Many amps connect the heatsink directly to ground. Others use a capacitor to shunt high frequency noise from the sink to ground.
If the RCA shields of the amp are shorted to chassis ground, I'd expect to find that someone had been in the amp and connected a jumper between the two grounds.
Is the ground terminal of the amp shorted to the case also? |
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| sousmielie |
| Is it one of those black jensens with the chrome in the middle? I think I might have one laying around... model xa-ja320? Those amps aren't too badly designed. I'd say open up the amp and post some pics... I've seen these amps blow the resistor between 12v gnd and the amp gnd, someone may have bridged the resistor out? :cannotbe: |
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| sousmielie |
| Also I'd say to make sure your head and rca's are fine, use an extension cord with a small radio with rca in and run your head into the radio... |
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| Dan2 |
this one's model number is xs-ja420.
i rechecked my measurements and found that the case (heatsink) is shorted to power gnd, and there is about 10ohms resistance between power gnd and rca gnd. i also found the resistor between pwr gnd and amp gnd - a 1W 10R resistor (so that right)
the glue around all the screws has not been broken so i don't think the board has been taken out, although there is one small wire that looks like it was added on - but the 2 components are already connected through the PCB. :confused:
i will put pictures up a little later. (by the way how do you put big pictures up??? i always struggle to compress them to add as an attachment) |
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| sousmielie |
| The 10ohms sound right... That is the one I was talking about. So that part is fine. Heatsink should be connected to power ground... So that part is fine. You don't get any noise with the car just on acc without the motor running or do you hear a faint noise? Did you check your head unit? Check the resistance between the gnd of the rca cable and the chassis. ie. without the rca being plugged into the amp |
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| Perry Babin |
| I don't have much experience with jensen amps but 10 ohms seems low. The lowest I've ever seen was 100 ohms. Most amps use values between 270 and 1k ohms. What are the color bands on the resistor? |
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| ppia600 |
| I've seen some of the jensen amps have a voltage problem in the input circuit. The ones witht he sliding plastic window over the crossover controls. Can't remember what was actually wrong though. ??? |
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| sousmielie |
| quote: | Originally posted by ppia600
The ones witht he sliding plastic window over the crossover controls. |
Think those where the blue ones, I still have a 2ch one laying around...
The 10 ohms are fine, I've seen it in a couple of amps... |
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| Perry Babin |
| I would expect them to have engine noise with 10 ohm resistors. Do you know if engine noise is a common problem with jensen amps? |
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| sousmielie |
| I've found this amp, opened it up and found that it has no filter coil on the 12v input... The other jensen that i have has one. Also this amp has a 22ohm resistor in series with a 10nf cap between gnd's. As far as I can remember this never had a problem with noise. Is your alternator and engine well grounded? |
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| sousmielie |
| Inside...No Filter... |
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| sousmielie |
| see post 20. should be low resistance. measured with everything off to chassis |
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| Perry Babin |
Inductors are not necessary on the B+ input to prevent noise. They wouldn't have any significant effect on the low frequency noise that's produced by the alternator.
The isolation of the secondary ground is what prevents noise in most of these budget amps.
The 22R in series with the 10nF cap is a snubber. It's connected across the transformer's windings to damp ringing on the square wave. |
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| Perry Babin |
| sousmielie, if possible, unplug the RCAs from your amp and measure the resistance from the amp's RCA shield to one of the speaker terminals that are NOT used for bridging. |
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| sousmielie |
| quote: | Originally posted by Perry Babin
sousmielie, if possible, unplug the RCAs from your amp and measure the resistance from the amp's RCA shield to one of the speaker terminals that are NOT used for bridging. |
I know, but what I'm checking is just to check that the rca shields on the head unit are grounded without removing the head unit. When my rca out went, there was a resistance of about 5Mohm. Now its just the resistance of the long wire. |
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| Dan2 |
the resistor between amp gnd and pwr gnd is definitely 10R, thats what i measured and it says 10 ohms on the PCB. Perry, if i change the 10r resistor with a 100R would that be ok? or would it disrupt the whole design? cos i also got another amp here - a 250 W sony xplod amp - the resistance from amp gnd to pwr gnd is about 5Kohms.
there is a large inductor by the pwr input in the Jensen amp.
i just measured the resistance from the rca shield on the cable (disconnected from amp but connected to frontloader) to pwr gnd of amp, it measured 2 ohms (about)
as far as i know the alternater is well grounded - its a 96 model nissan sentra and i have no other electrical problems with it (charges fine too)
i have the pictures on my computer but they are too big to put as an attachment (about 300kb) |
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| sousmielie |
| quote: | Originally posted by Perry Babin
Inductors are not necessary on the B+ input to prevent noise. They wouldn't have any significant effect on the low frequency noise that's produced by the alternator.
The isolation of the secondary ground is what prevents noise in most of these budget amps.
The 22R in series with the 10nF cap is a snubber. It's connected across the transformer's windings to damp ringing on the square wave. |
True, but aren't those inductors needed to keep noise from the amp entering the cars electrical system? |
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| Perry Babin |
There isn't much noise in an amp that's properly designed and in good working order. The filter caps across the B+ and ground terminals filter most of the noise. The inductance of the power wire is enough to stop anything that's left.
For the most part, Rockford, SoundStream, MTX and Zapco don't use filter caps on their B+ input. |
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| ppia600 |
| And those filters can limit "instantaneous" current the amps need during transients. |
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| Dan2 |
| so......can i just swap out the resistor???? |
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| Perry Babin |
I don't see a problem with changing the resistor to a higher value.
With no RCA cables plugged in, confirm that one end to chassis ground is 0 ohms and the other end to the RCA shield is 0 ohms. That will confirm that this is the resistor that connects chassis ground to secondary ground.
After you change it, mount the board back into the heatsink and clamp the transistors down tightly to the sink. Insert a 10 amp fuse in the B+ line in case the amp has a problem with the higher value resistor.
If the engine noise was relatively minor, this may solve the problem. If the noise was extremely loud, this probably won't solve your problem. |
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| Dan2 |
well if that doesn't solve my problem then i will probably just leave it as my sub- amp.
thanks for all the help guys ;-) |
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| Dan2 |
i recently got a new set of front speakers, and decided to try and fix my amp so there would be no engine noise. i replaced the 10 ohm resistor with a 100 ohm, and it did nothing. then i pushed the resistor to 2k2 ohm, stil tons of noise. then i went back to the head unit to check the RCA output grounds - this is where its gets interesting:
measuring the the RCA ground to head unit chassis -> 0 ohm. this seemed right, but as a last resort i physically tied the RCA ground to the chassis with a piece of wire and the noise went away!!!!
so for anyone reading this with the same problem, do the mod that Perry suggested - even if your measurements look right.
thanks again to everyone for your input. |
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| jol50 |
| I just put a refurb pioneer HU in and took an alpine out, now at low volume the alternator comes in. Had this with pioneer 20yr ago and they still can't get it right.:rolleyes: It does seem to be louder on the right than left, I'll have to find time to test it out. Reconnecting the RCA made no difference. |
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| gonzalez |
| I THINK YOU ARE RONING THE POWER CABLE ALONG THE RCA CABLE IF YOU RONG THE RCA IN ONE SIDE AND THE POWER IN THE OTHER SIDE AND YOU ARE FREE FROM ENGINE NOISE |
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| gonzalez |
| THIS MIGHT HELP YOU OUT |
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