Hi.

First I want to say that i have a car audio deck hooked up to my laptop as an audio system. Everything is fine when the laptop doesn't have the dc converter hooked to it. But when I plug it in to charge the laptop a background noise shows up in the speakers (humming noise- goes louder when power supply heats up)- so i thought the dc converter is not working right- I got one that have an option to hook it up to 115V of wall socket or a 12V DC (car cigarette lighter)- the noise dissappears from the audio when I use the PC PS to provide the 12V DC (the same PS that the radio is hooked up to)- however then a "noise" shows up on my external monitor thats hooked up to the wall.... it shows up as horizontal lines moving vertically through the screen - like a ripple... not quite sure what to do.... any ideas? Please let me know as its really frustrating...

I tried putting the magnetic ring on the audio cable before as SAYAL staff advised, but it didn't work- same ring is on the power cable for the laptop....

 

It's probably a Ground Loop ('hum loop').

As long as only one item (ie. the amp) is connected to something external, the only signal on the audio cable is the audio you want.

Once you connect the laptop to power as well, you have the possibility of externally induced currents, which get superimposed on the audio.

This is commonest with two seperate items that both have AC supply grounds, but can happen due to capacitive coupling within power supplies etc.

The simplest way to remove the problem is probably to use an audio transformer in the audio cable to the amp.

More info on the problem:
http://www.aqdi.com/groundloop.htm

Audio isolating transformers at Radio Shack:
http://www.radioshack.com/search/index.jsp?kwCatId=&kw=ground isolator&origkw=ground isolator&sr=1

 

It's probably a Ground Loop ('hum loop').

As long as only one item (ie. the amp) is connected to something external, the only signal on the audio cable is the audio you want.

Once you connect the laptop to power as well, you have the possibility of externally induced currents, which get superimposed on the audio.

This is commonest with two seperate items that both have AC supply grounds, but can happen due to capacitive coupling within power supplies etc.

The simplest way to remove the problem is probably to use an audio transformer in the audio cable to the amp.

More info on the problem:
http://www.aqdi.com/groundloop.htm

Audio isolating transformers at Radio Shack:
http://www.radioshack.com/search/index.jsp?kwCatId=&kw=ground isolator&origkw=ground isolator&sr=1

Is it possible to eliminate the noise by just plugging the supply of both components to a same socket? If they have a same ground plane, I think it can eliminate the noise.

 

Is it possible to eliminate the noise by just plugging the supply of both components to a same socket? If they have a same ground plane, I think it can eliminate the noise.

I have tried that already....

rjenkins thnx for answer

not sure what to do still since the "amp" is the cd deck which only uses mini jack connection (conversion from mini jack to RCA and RCA to mini jack?)... beside with that noise canceled device would I loose quality? (that's the whole reason for running this setup)

P.s.
I found this one eBay:

http://cgi.ebay.ca/PAC-SNI-1-3-5-GR...emQQptZLH_DefaultDomain_0?hash=item3efe43e9ec

but the build quality is not really promising (most expensive eBay has to offer)

 

It's not noise cancelling, it's just coupling transformers that eliminate the direct connection between the two items, so there cannot be a ground loop.

The one on ebay looks worth a try, I'd not worry about the casing as the specs look fine.

I generally use modem transformers (like off scrap 56K PC modem boards). These have extremely good frequency response and low distortion. It's quite possible these are also used in the commercial units as they are very cheap and excellent qualty.

 

It's not noise cancelling, it's just coupling transformers that eliminate the direct connection between the two items, so there cannot be a ground loop.

The one on ebay looks worth a try, I'd not worry about the casing as the specs look fine.

I generally use modem transformers (like off scrap 56K PC modem boards). These have extremely good frequency response and low distortion. It's quite possible these are also used in the commercial units as they are very cheap and excellent qualty.

Can you possibly make a picture of one from the modem board? (or describe how it looks? - I work at the lab in the university and they throw out bunch of old computer equipment all the time- i might be able to scavenge something....

 

http://tncomputersunlimited.com/user/cimage/broadcom-modem.jpg

I just found one like that- anyone can tell me how to use the transformer from it to break the ground loop?

 

k so i hooked the laptop converter to the PS, and lifted the ground from the monitor- as far as i know ground is to there to protect the device from surges - is there anything else I should worry about when the ground is lifted?

 

If the problem is resolved by lifting the ground, you have proven it is a ground problem. Now you can get a ground isolating device to decouple the laptop and keep the safety of the ground.

 

yes, that would be correct resolution if the ground loop isolators were reasonably priced- and they still maintain a bit of the noise as far as the reviews I read online are correct.... the device im talking about is some humx product that costs $70 - now I wont mind paying that much if it was some fancy electronic - however it appears to be fairly simple build so the item is way overpriced.... if you can advice me a source that I can find it for a fair price I wont mind buying it.... thanks

If the problem is resolved by lifting the ground, you have proven it is a ground problem. Now you can get a ground isolating device to decouple the laptop and keep the safety of the ground.

 

http://www.amazon.com/Tripp-Lite-ISOBAR4ULTRA-Protector-Suppressor/dp/B0000513O4
This is what I use. I actually use the 2 outlet version for around $25. (see below)
http://www3.shopping.com/xPO-Trippe-Lite-Isobar-2-ISOBAR2-6

 

http://www.amazon.com/Tripp-Lite-ISOBAR4ULTRA-Protector-Suppressor/dp/B0000513O4
This is what I use. I actually use the 2 outlet version for around $25. (see below)
http://www3.shopping.com/xPO-Trippe-Lite-Isobar-2-ISOBAR2-6

It doesn't say anything about terminating of the ground loop.... I wouldn't mind paying some more for 4 or even 6 outlet bar like that but how do i know they will have ground loop protection?

 

I have used them on studio instruments and amps with great results.. But I cannot say for SURE it was ground loop hum and not AC line noise. But one of the bass amps I use has a ground-lift option that did kill the noise in the amp, and after I used the isobar, I didn't need the ground lift anymore.

 

I have used them on studio instruments and amps with great results.. But I cannot say for SURE it was ground loop hum and not AC line noise. But one of the bass amps I use has a ground-lift option that did kill the noise in the amp, and after I used the isobar, I didn't need the ground lift anymore.

Ok, thank you for the info- I will try it regardless since this is defiantly worth the price looking at all the reviews and sturdiness of the item. Thanks!

 

ever wonder to find out how the connections are made by the OP?

 

ever wonder to find out how the connections are made by the OP?

would be nice to know....

 

tell us or show us how you made the connections.

 

tell us or show us how you made the connections.

I thought you were going to enlighten us ...

 

I'll like to know if it is you termination that is producing the hum

 

Rifaa was asking to see your (LaZyLuke) wiring layout for your components. If your connections are improperly terminated, you can be picking up much interference.