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.
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.
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.
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.
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.
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.
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/temporaryrcashieldrepair.html
http://bcae1.com/images/rca/temporaryrcashieldrepair.html
MatthewS said:
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)
ppia600 said:
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?
- Matt
"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.
MatthewS said:
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?
- Matt
MatthewS said:
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.
- 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??
i must agree that i have always had helpful responses from you guys, and i do ask some pretty stupid questions!
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)
zigzagflux said:
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)
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?
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?
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? 
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.
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)
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.
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)
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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