Poor man's guide to remove power supply noise from audio

Gip · 11-22-2006, 01:41 PM

Intro

Well... You just connected your notebook to a car power adapter and to the amplifiers... But... WTF! You hear a very loud buzz from the speakers, and you can barely hear the music playing on your PC! Please, help me Mastro Gippo!

Example of a noisy environment:

Car -> DC-DC Inverter, 12V to 19V -> Laptop -> 3.5mm Jack to RCA cable -> Amplifiers

Here is the solution!

What you need:
-2 old modems (56K or lower, with the little transformer)

(get them from your nearest dumpster)
-the 3.5mm Jack to RCA cable (or whatever connector you need)
-soldering iron and standard stuff
-optional but recommended: a proto-board

Before you start
Standard disclaimer: I'm not responsible if you break your stuff or die. This method works for me and for that kind of noise. It won't eliminate any other kind of noise. Please do this only if you know what you are doing, and ask help to someone that knows electronic better if you are in doubt.

Let's go!

Carefully remove the tranformers from the modem PCB using the soldering iron (heat one pin and gently pull the transformer, then heat another pin, then another, then the last, repeat until the transformer falls into your hand - warning, hot pins!). Beware, these transformers are very fragile and you can break a pin if you pull out too heavy!
Now you should have two transformers, just test them to check if they work using an ohmeter.

The windings should have an impedance (resistance...) of 150ohm.
Cut the adapter cable in half, or at the point that suits you best, strip a bit of wire out of the ends and pre-solder them.
Solder the transformers on the proto-board, then solder the cables following this schematic:

I'm not so good at paint, so I added 2 pictures of the finished product so you can get an idea of the circuit. The white wire is only for holding the other two wires,so I don't break them if I pull too hard.

The end!
Connect the cale between the PC and the amplifiers... And it's done! Total cost: about 10$.... (even less if you already have the two modems, or if you find them for nothing).

And the quality??
This circit will not add any interference/distortion to your signal. You may have some impedance issues (the signal should increase a bit in amplitude) but the output will be 99.999999% the same as the input.

I hope you apprecate this topic and maybe make it sticky... I'm very busy at wok, but I will try to give support to anyone who needs help.

Bye
Gip

Rob Withey · 11-22-2006, 01:48 PM

This is simply a ground loop isolator.

Ruffy · 11-22-2006, 01:50 PM

interesting
if i have induced noise i'll try it

Gip · 11-22-2006, 01:51 PM

Quote: Originally Posted by Rob Withey

This is simply a ground loop isolator.

A poor man's ground loop isolator....

Nomader · 11-22-2006, 02:25 PM

considering i bought my ground loop isolator for 12 euros then this is a veeeeery poor man's groung loop isolator

but nice to read how to do it and have fun to make

Chris31 · 11-22-2006, 03:39 PM

That is called "a poor man, 2 spare modems, other bits and alot of time" solution.

I think the poor man with no spare modems would just buy the premade one

Nice tutorial though

Ruffy · 11-22-2006, 04:50 PM

Quote: Originally Posted by Chris31

That is called "a poor man, 2 spare modems, other bits and alot of time" solution.

I think the poor man with no spare modems would just buy the premade one

Nice tutorial though

I have spare modems, many of them. Most people that have build computers through the years have at least one.

I also I have RCA jacks and mini 1/8" plugs, same thing as above.

With alittle knowledge of the tools anyone can make it in like 10 minutes or less. I know I could.

A Premade one can be bought for under $20. But wheres the thrill of making something yourself with that?

Hell you can buy those transformers for $2-5 each and make your own for under $10

Ruffy · 11-22-2006, 04:58 PM

transformer
http://www.allelectronics.com/cgi-bi...:600_OHM_.html
$1.00 x 2

or

http://www.allelectronics.com/cgi-bi..._600_OHM_.html
$1.00 x 2

+

http://www.allelectronics.com/cgi-bi...CA_JACKS_.html
$1.25

+

http://www.allelectronics.com/cgi-bi...RF_BOARD_.html
$0.75

+ shipping = $11.00
At those prices you might as well buy extra parts and make several of them to make up for the high cost of shipping

Chris31 · 11-22-2006, 05:41 PM

Cool

How about a nice project box + gromets for the board to finish it off?

Ruffy · 11-22-2006, 07:02 PM

Quote: Originally Posted by Chris31

Cool

How about a nice project box + gromets for the board to finish it off?

a true poorman dont need no sticking project box

he wraps it up in 19 cent electrical tape!

You could use a film canister, as if people still buy film...

Gip · 11-23-2006, 01:44 PM

Quote: Originally Posted by Ruffy

I have spare modems, many of them. Most people that have build computers through the years have at least one.

I also I have RCA jacks and mini 1/8" plugs, same thing as above.

With alittle knowledge of the tools anyone can make it in like 10 minutes or less. I know I could.

A Premade one can be bought for under $20. But wheres the thrill of making something yourself with that?

Hell you can buy those transformers for $2-5 each and make your own for under $10

Well, I must admit it, this tutorial is mainly for people like you (and me), who have tons of "junkies" too hard to throw away because "you never know..."!
And I must ABSOLUTELY quote "A Premade one can be bought for under $20. But wheres the thrill of making something yourself with that?"!!! Are we the same person?

Btw, I'm not really a "poor man", and I don't think that everyone having enough money and effort to spend in a carputer is a REAL poor man, but I simply LOVE the challenge of efficiency. I always want to obtain the best results with the smallest effort... And I succeed most of the time! Sorry for you guys that prefer to buy premade things, paying more and learning nothing, but I'm a geek and I'm proud of it! Well, actually I'm not a real geek, since I have a girlfriend, but who cares!

PS: my circuit is wrapped up in 19 cent red electrical tape...

Rob Withey · 11-23-2006, 02:31 PM

Quote: Originally Posted by Gip

Sorry for you guys that prefer to buy premade things, paying more and learning nothing, but I'm a geek and I'm proud of it!

Some of us are geeks that already know how stuff works, and recognise that sometimes the most efficient way to get stuff done is to buy a mass produced device.
I'm surprised you didn't wind your own transformers...!

Gip · 11-23-2006, 04:10 PM

Quote: Originally Posted by Rob Withey

Some of us are geeks that already know how stuff works, and recognise that sometimes the most efficient way to get stuff done is to buy a mass produced device.
I'm surprised you didn't wind your own transformers...!

Touche...

But what about the satiafaction! Btw, I myself already know how and why this stuff works, you surely can imagine that I haven't tried to put every single component of a modem pc board in series of the audio cable to find out tha the transformer works better!

You will be surprised to know that in the past i even wond (mmmh... past of "to wind"? sorry for my english.....) my own transormers...

Ruffy · 11-23-2006, 05:20 PM

Quote: Originally Posted by Gip

Touche...

But what about the satiafaction! Btw, I myself already know how and why this stuff works, you surely can imagine that I haven't tried to put every single component of a modem pc board in series of the audio cable to find out tha the transformer works better!

You will be surprised to know that in the past i even wond (mmmh... past of "to wind"? sorry for my english.....) my own transormers...

wound. You were on the right track with the word. The English language is not friendly.

miwise · 11-23-2006, 05:37 PM

worked nicely for me. I already had a ground loop isolator (from radio shack) b/w the computer and both amps, but I was getting a loop b/w the sub amp and highs amp. I installed this b/w the 2 amps. Worked great!