Windows 2000 laptop, loud hum on mic in

[SCPD]

I just installed RR software on a windows 2000 laptop and I have a cable going from the headphones jack on the scanner into the mic jack on the laptop. With this setup I am getting a loud "hum" in my feed. I tried to adjust the mic input level via the speaker control with little change - I have the mic bar is only 1 to 3 pixels above 0 and I still get the noise. The volume control on the scanner is around 1/4 and the squelch is around 2/3. What adjustment am I missing? I think the input level into the laptop is somehow not the same as what I have adjusted to. I am going to install winamp with a VU-meter add-on to see just where the input level is.

Any other thoughts on where to look?

 

[LordJ]

Google 'Ground Loop'

 

[exportdawg]

I just installed RR software on a windows 2000 laptop and I have a cable going from the headphones jack on the scanner into the mic jack on the laptop. With this setup I am getting a loud "hum" in my feed. I tried to adjust the mic input level via the speaker control with little change - I have the mic bar is only 1 to 3 pixels above 0 and I still get the noise. The volume control on the scanner is around 1/4 and the squelch is around 2/3. What adjustment am I missing? I think the input level into the laptop is somehow not the same as what I have adjusted to. I am going to install winamp with a VU-meter add-on to see just where the input level is.

Any other thoughts on where to look?

This is what you need. It should get rid of the hum. Had to use it on my feed and it eliminated the hum. Highly recommended
Ground Loop Isolator - RadioShack.com

*You will have to buy a few small adapters(to connect to a 3.5mm jack) but they have them at the store too*

 

[SCPD]

I did Google ground loop isolator (thanks for this tip) and there is one on hold at my local radio shack. I'm not sure this is the issue. I had a similar setup using an old 386 box (running freebsd and shoutcast) with no hum noise. After reading some other posts (http://forums.radioreference.com/li...d-loop-isolator-not-removing-hum-my-feed.html and http://forums.radioreference.com/st...-please-hum-despite-ground-loop-isolator.html) I am going to try some other troubleshooting. One thing I did change between the old 386 setup and the laptop setup is where the scanner power supply get plugged into. I will start here and work my way up the ground loop.

 

[exportdawg]

I did Google ground loop isolator (thanks for this tip) and there is one on hold at my local radio shack. I'm not sure this is the issue. I had a similar setup using an old 386 box (running freebsd and shoutcast) with no hum noise. After reading some other posts (http://forums.radioreference.com/li...d-loop-isolator-not-removing-hum-my-feed.html and http://forums.radioreference.com/st...-please-hum-despite-ground-loop-isolator.html) I am going to try some other troubleshooting. One thing I did change between the old 386 setup and the laptop setup is where the scanner power supply get plugged into. I will start here and work my way up the ground loop.

If it does not work, you can always take it back. Here is a picture of the connectors you will need. Make sure you get 3.5mm (Stereo-2 black lines on the tip, not mono-1 black line)
http://ecx.images-amazon.com/images/I/41yWV1iYrsL.jpg

 

[SCPD]

I started the troubleshooting by changing the location where the laptop plugs in - no change. I then changed the location of the scanner power supply location - no change. I then shut down the scanner completely and still no change. I then unplugged the scanner end of the audio cable leaving it still plugged into the laptop - still no change (I thought this was odd as there is no connection on the other end). When I unplugged the audio cable from the laptop, the hum went away - no real surprise there.

So I installed the ground loop isolator with no change - still got the hum. From here I started to unplug each side of the isolator. The only change in the hum volume was when I unplugged one side from the laptop end. From here I swapped the sides of the plug so I have the white plug from the ground isolator plugged into the red side of the adapter (RCA to 3.5mm adapter) and the white side open. This eliminated most of the hum however the sound quality coming from the broadcast sounds "tinny". (See attached png file)

Any thoughts on why this cable setup works?

I think I will spend the time and resurrect my FreeBSD 386 box using shoutcast.

 

[exportdawg]

I started the troubleshooting by changing the location where the laptop plugs in - no change. I then changed the location of the scanner power supply location - no change. I then shut down the scanner completely and still no change. I then unplugged the scanner end of the audio cable leaving it still plugged into the laptop - still no change (I thought this was odd as there is no connection on the other end). When I unplugged the audio cable from the laptop, the hum went away - no real surprise there.

So I installed the ground loop isolator with no change - still got the hum. From here I started to unplug each side of the isolator. The only change in the hum volume was when I unplugged one side from the laptop end. From here I swapped the sides of the plug so I have the white plug from the ground isolator plugged into the red side of the adapter (RCA to 3.5mm adapter) and the white side open. This eliminated most of the hum however the sound quality coming from the broadcast sounds "tinny". (See attached png file)

Any thoughts on why this cable setup works?

I think I will spend the time and resurrect my FreeBSD 386 box using shoutcast.

Had mine at first plugged in the same way at first, and still had the hum. You have to have it separated . Dont plug that splitter right into the computer, have about 4' of 3.5mm audio line or more plugged in.

My suggestion (how mine is done)

4' or so of 3.5mm Line plugged into Computer. and the other end of the 4' line, connect the Isolator/connector and attach it to another 4' or longer 3.5mm cable to the scanner. You want to keep the isolater in the middle of the feed lines (hope that make sense)

*You may have to get a 3.5mm to 3.5mm Female/Female adapter if you dont have one*

 

[SCPD]

Had mine at first plugged in the same way at first, and still had the hum. You have to have it separated . Dont plug that splitter right into the computer, have about 4' of 3.5mm audio line or more plugged in.

My suggestion (how mine is done)

4' or so of 3.5mm Line plugged into Computer. and the other end of the 4' line, connect the Isolator/connector and attach it to another 4' or longer 3.5mm cable to the scanner. You want to keep the isolater in the middle of the feed lines (hope that make sense)

*You may have to get a 3.5mm to 3.5mm Female/Female adapter if you dont have one*

So something like this:

Scanner - 3.5mm jack_4' cable_3.5mm jack - Fem/Fem - Ground Isolator - Fem/Fem - 3.5mm jack_4' cable_3.5mm jack - Laptop mic in.

With this setup are both RCA plugs used?

 

[exportdawg]

So something like this:

Scanner - 3.5mm jack_4' cable_3.5mm jack - Fem/Fem - Ground Isolator - Fem/Fem - 3.5mm jack_4' cable_3.5mm jack - Laptop mic in.

With this setup are both RCA plugs used?

You got it, and yes, I would use both RCA, but you can try it both ways. I hope it works for you, if it does not, I am at a loss of what could be causing the issue. You have done everything right in your potential problem areas. But I have a suspicion this will fix you up. (I hope)

 

[exportdawg]

One more thing, I would not have the Isolator touching metal/computer if possible or cords that carry power, that can give you interference also.

 

[dovy6]

Sorry I'm a little late to this party, but for the future, I found a site selling these ground loop isolators for very cheap: AUDIO GROUND LOOP ISOLATOR | AllElectronics.com $6.00 each. I've used all electronics.com before they are a great website. (I am not affiliated with the site in any way)

 

[exportdawg]

Sorry I'm a little late to this party, but for the future, I found a site selling these ground loop isolators for very cheap: AUDIO GROUND LOOP ISOLATOR | AllElectronics.com $6.00 each. I've used all electronics.com before they are a great website. (I am not affiliated with the site in any way)

Great Find, Thanks!

 

[SCPD]

I was able to fix my hum issue - I ended up re-building my old 386 box with FreeBSD and darkice to act as my stream server. I think the issue I was having was with the laptop itself. There must have been something wrong with the mic in port which was causing the hum. With my 386 box setup the hum is gone and I am much happier with the feed quality.

Thanks for the help here with my initial hum issue. All suggestions were helpful with the troubleshooting process.

 

[AK4FD]

I actually have the SAME problem too! I'm running a Windows 7 laptop with the ScannerCast software from RadioReference and using the mic port on my laptop to broadcast as well. The problem I've found is the "humming" only happens when I plug my scanner into the wall using the adaptor it came with, when I just use rechargeable batteries there's no hum and my feed is loud and clear (listen for urself), so I'm running my feed 24/7 of changing rechargeable batteries every 12 hours til I can figure out the problem. It only hums when there's a power source plugged into the scanner... Any ideas anyone???

 

[AK4FD]

Hey guys I just wanted to update y'all on my "humming" situation... I FINALLY was able to plug in the wall adapter into my scanner and not hear a hum anymore on my feed... Turns out the problem was I was using a stereo cord for my scanner-to-mic input on my laptop, I switched to a mono cord and it's perfect now, listen for urself! Thanks to all for ur helpful advice and hopefully this will help anyone else with a hum problem on their feed, make sure ur not using a stereo cord...


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