Quote:
Originally Posted by faranks
U.S. amps are located in the left rear quarter panel along with the cd changer. I can't really think of any reason why tapping into a post-amplified signal could have any effect on the preamp section, especially causing it to turn off...
Noise that becomes amplified after the signal or ground shield makes contact is typically caused by what is called a ground loop. All this essentially means is that there is a significant difference in resistance (impedance) between the ground for the source unit and the ground for the amplifier. Countless times I have seen this to be a product of cheap electronics with worthless internal filtering. You could use a ground loop isolator, but you should have power to spare because it will reduce your signal input. Additionally, it is odd that your are getting induced noise through your subwoofer. Does your amp have a low-pass crossover? Induced noise is often in the frequency range much higher that 20-100Hz that is the typical range of a subwoofer.
You may also want to try a different location for your amplifier ground. If it is not a very good one, the amp will try to pull a ground through the RCAs, which is not in the design of any of the components.
1) Try a new ground first, make sure that you have scraped away the paint that is on the chassis, so that you can make a clean metal to metal connection. (Make sure that you are not putting a screw into gas tank or brake lines etc!)
2) Try to ground the RCA outer shield on the amplifier with inputs plugged in.
3) Last resort, try a ground loop isolator or replace your head unit with an aftermarket one. This would be my vote since it is easy, and you can gain bluetooth handsfree, ipod link, dedicated preamp outputs, satellite or HD radio etc. etc. This is simple since you can just wire up a basic harness and feed the factory amp a high level signal. The only downside to that is if you have a weak sub amp and you can't turn your deck up very high, it throws the ratio off and is tough to get much bass.
Hope this helps
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hi Faranks, THANKS for the xmas present! and here's what i've done soon after kids opening their presents
here's progress:
i tried grounding the RCA outer (i'd never have tried this if you hadn't told me not to worry!). that seems to do the job!
diagnosis: so that means ground loop? so i removed my ground cable from the chassis to check, i think that seems to be the root cause potentially. it has other components on it so i can't scrape off the paint there and i've loaned my drill to a friend, so i'm gonna drill a proper hole, scrape the paint and re-connect the ground (maybe tomorrow as i have xmas stuff today)
in the meanwhile i will run today with the RCA outer grounded.
IF grounding properly, and then grounding the RCA doesn't work i will fix a ground loop isolator. shouldn't be a problem i guess cos i do have ample power. my gain control on the amp is set to around 25% of its capacity.
some clarifications:
1. when i said when i connect the speaker wire to the subwoofer amps RCA outer it knocks the radio off, as i'm working on the high-level out, it could very well be that its the amp that it knocks out not the head unit right? cos either way the result is no sound. so that might explain why it goes dead..
2. re. the noise i get: yes i have a low level filter and in low mode it can be turned right down to 30Hz (range from 30 to 100 i think). that cuts out most of the noise but still leaves a 'pumping' sound, very low down and routine.
my amp is a JBL GT02060 (
Slutsteg JBL GTO 2060 GTO2060 - Kp Slutsteg p BRC.se) ;
sub is a JBL GT01202D (
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pls let me know if you have any other thoughts.
also can you help me with a rather fundamental clarification please - when connecting the high level output to the RCAs does the +/- matter, or can i just connect either way? (that does sound stupid but i've figured that connecting either wire from the high level out to the middle (not outer) wire of the RCA makes the sub pick up sound.
thx so much, i'm happier today and hopeful of proper sound on my xmas run!
merry xmas faranks!