Amp installation help needed

[jaynana]

hi, i have a 2004 X5 with nav, cd changer, no dsp. and i'm trying to install an amp+sub(JBL).

i've got power, ground, signal connected all ok.

issue is when connecting the sound/signal to the amp (RCAs)

i've got the speaker outs from the factory BM54 as below:
http://www.xoutpost.com/articles/x5/...formation.html

so basically the rear right + rear left.

when i connect one of those to the first RCAs inner the sub starts working; but the moment i connect the first RCA outer wire itself the radio knocks itself out.

and i have to remove that outer, and restart the radio to get any sound from it.

amp works if i connect only the inner cable of the RCA but that's no good because then it gives out ambient noise (i believe because then its not properly grounded?).

can anyone help me understand what i'm doing wrong here pls?

[faranks]

w/o knowing the exact specific wires that you tapped into...
I have always took my signal from the rear door outputs off the amp, not the head unit, this is a full range signal. There must be something the head doesn't like about the low level outputs having it's resistance load changed.

Another alternative you could try, slightly unorthodox, would be to leave the outer shield of the RCA unnattached as how you got sound w/o interruption, and ground the outer shield of the amp's rca. Simple to just take a piece of ground wire and try this quickly. Do not worry, no harm can come of this, but it may have no result also.

[jaynana]

thanks faranks, that's an interesting suggestion, i will try that and let you know if that works!

its actually not the low level output from the head unit but the high level output from the amp that i'm taking. i think its probably different to what you may see in the US, in europe , its a BM54 amp which is located right next to the battery.

wiring i picked up is as in below (2002 radio module with nav)
http://www.xoutpost.com/articles/x5/...formation.html.

but interestingly my colours were slightly different (probably cos this is teh european model):
blue/purple, blue/gray: right rear
yellow/purple, yellow/gray: left rear

i will try your suggestion tomorrow. at the same time, any other suggestions you can think of please, like adding a resistor, or capacitor to the line, etc, to kill the noise?

cheers

j

[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

[jaynana]

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

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 - Köp Slutsteg på BRC.se) ;
sub is a JBL GT01202D (ƒn�[ƒ}ƒ“�AJBL‚ÌŽÔ�Ú—pƒTƒuƒE�[ƒtƒ@)

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!

[faranks]

right, so I guess I should have clarified a bit, I took for granted that you were using a hi-low level input converter (a box that steps down voltage and turns speaker leads into RCA leads). If you are not using this, and just running the speaker level into a spliced RCA, then you are introducing much more input voltage to the amplifiers preamp than it was ever designed to handle...this is probably (one of) the source of the induced noise. Some amps have a high level input area that is designed to receive an already amplified signal, I am not familiar with that amp though.

This would also explain why you are able to have your gain down so low, your input signal is so hot it is disproportionate. Additionally, you will want your low pass crossover to be set around 80Hz, if it's down much lower you will be missing out on some music.

lastly, the +/- doesn't really matter as long as you're only using one. if you are using 2 (sets) then you just have to be consistent, if they are opposing then they will be out of phase with each other and you won't get much sound. The sub can be out of phase with the music and you will not be able to tell mostly due to variances in room acoustics.

Merry Christmas!

[jaynana]

Originally Posted by faranks

right, so I guess I should have clarified a bit, I took for granted that you were using a hi-low level input converter (a box that steps down voltage and turns speaker leads into RCA leads). If you are not using this, and just running the speaker level into a spliced RCA, then you are introducing much more input voltage to the amplifiers preamp than it was ever designed to handle...this is probably (one of) the source of the induced noise. Some amps have a high level input area that is designed to receive an already amplified signal, I am not familiar with that amp though.

This would also explain why you are able to have your gain down so low, your input signal is so hot it is disproportionate. Additionally, you will want your low pass crossover to be set around 80Hz, if it's down much lower you will be missing out on some music.

lastly, the +/- doesn't really matter as long as you're only using one. if you are using 2 (sets) then you just have to be consistent, if they are opposing then they will be out of phase with each other and you won't get much sound. The sub can be out of phase with the music and you will not be able to tell mostly due to variances in room acoustics.

Merry Christmas!

Hi Faranks

I'm not using a hi-low level input converter as my amp is supposed to be able to handle speaker level outs (although yeah, gain at 25% and still earth shattering base (when it works) may indicate that i probably should be converting to low level inputs)

i''ve also set the low pass filter to around 80Hz.

ok, now with regard to my pumping noise, here's what i've done:

1. I ran (around 30miles) with the RCA grounded yesterday. sound improves when RCA is grounded, but the pumping noise comes up intermittently. so its not entirely gone.

today i drilled a new hole, scraped the paint and did the ground newly, with a 4mm cable.

i then tried the following, hoping that the ground now was good:

1. removed RCA outer grounding, and tried to connect the car speaker outs to the RCA outer. bang! the radio knocks itself out.

2. thought ground could still be bad and made a parallel ground with a 1 1/2ft 4mm cable from the chassis to the amp. still no difference (when i connect the car speaker out to the RCA outer radio goes out)

then i got a bit brave and tried a few other things:

3. removed the RCAs entirely, and then tried to touch the car speaker outs to the RCA outers (RCA inner now disconnected). the moment either cable touches the RCA outer the radio goes out!!

so it now looks like my car head unit or car amp really really hate the RCA outer of my external amp

if you have any further thoughts on above pls let me know,

here's what i plan to try out next:
1. drive around another 40miles or so today (now that the amp is newly grounded (and RCA is grounded) i'm hoping that the pumping noise would have gone away entirely- not even intermittent i hope.

2. if that doesn't work, buy and fix a ground loop isolator? links to 2 units below:
Skytronic Ground Loop Isolator: Amazon.co.uk: Electronics
Ground loop isolator audio noise hum removal: Amazon.co.uk: Electronics

3. alternatively before trying that out, should i fix a hi-low input converter. does that isolate the ground as well? below is what i've found:
FLI Audio Line Level Car Rear Speaker Wire To RCA Converter: Amazon.co.uk: Car & Motorbike
Speaker to RCA Converter / High to low Line Level Converter: Amazon.co.uk: Car & Motorbike

is that the type of thing you suggest faranks?

cheers

j

[faranks]

the RCA preamp section of the amp is designed to accept an un-amplified signal.

If you are going to use the low level RCA input, you need to get a hi-lo adapter to reduce signal. This also solves your physical issue of converting a speaker wire into an RCA.

If this amp has a hi-level input, then it will have a separate connector or terminals that are designed to accept spkr wire, not an RCA.

[jaynana]

Originally Posted by faranks

the RCA preamp section of the amp is designed to accept an un-amplified signal.

If you are going to use the low level RCA input, you need to get a hi-lo adapter to reduce signal. This also solves your physical issue of converting a speaker wire into an RCA.

If this amp has a hi-level input, then it will have a separate connector or terminals that are designed to accept spkr wire, not an RCA.

ok, my amp has no speaker wire input; it only has RCA input. so then its best to fix a hi-low converter.

but is that going to fix my problem faranks do you think? would that help me with the issue i'm now finding out - that i can't seem to get the cars speaker wire to touch the RCA outer cable at all?


thx

j

[faranks]

I can't promise that using a hi-lo converter will solve your noise problem, but it is the correct way to do what you are attempting to accomplish, and doing it the way you are can cause problems, obviously.