AC Noise

[rmkrause]

Most of us have a transmitter and I'm sure most of us have AC hum or noise if you will. My noise comes and goes with the action of the lights. I've ordered a power conditioner and will install to clean the power going to the transmitter,computer etc. When running the show on a laptop and on the internal battery no noise. It's too bad the battery won'd last all night. Does anybody have further suggestions?:?

[Guest wbottomley]

rmkrause wrote:

Most of us have a transmitter and I'm sure most of us have AC hum or noise if you will. My noise comes and goes with the action of the lights. I've ordered a power conditioner and will install to clean the power going to the transmitter,computer etc. When running the show on a laptop and on the internal battery no noise. It's too bad the battery won'd last all night. Does anybody have further suggestions?:?

Maybe the laptop is too close to the transmitter. PC's and FM transmitters have trouble which in turn the pc wins.

Seperate the two and it should improve a lot.

[rmkrause]

It's about ten feet away.

[Greg Young]

I don't know what transmitter you are using, but the "hum" you describe may be due to an audio ground loop, and/or 60 cycle noise/poorly rectification on the power input side.

You can use simple chokes (R Shack sells split ones that you can wrap the leads through (aim for 6 or 7 times)) for both the power and audio leads.

Be sure not to use the same choke for both!

Essentially these will function as common mode chokes.

This often provides a simple, and relatively inexpensive fix.

Good luck,

Greg

[Max-Paul]

For what we are doing there are several different sources of noise. I think you have done a dandy job of Iding the source of your noise.

You told us that the noise seems to rise and fall with the activity of your lights. And that when you were using your laptop on batteries it went away. So, I think that you have taken the right step in getting an line condictioner. Now it may work with the computer and radio wall wart plugged into it. But I suspect that you might want to keep the computer off of the condictioner and only plug your radio transmitter into it.

Some of the other sources can be the computer power supply and or the computer. RF getting into the audio leads. AC noise getting into the audio leads. And one other possible source is another distant radio station skipping in, in the evening or night time.

Good luck, but I think you are on the right track attacking the 120VAC line noise.

[-klb-]

There is a good chance of it being a ground loop as well, with the described behavior. Especially if line filtering does not take care of it. Radio Shack also sells a car audio ground loop isolator. In reality, it is just a simple, symmetric unun, or unbalanced to unbalanced transformer. It will pass the audio signal at a slightly reduced level, with the ground potentials isolated from each other. Especially if the transmitter and computer are on different circuits, this may be exactly what you need.

[rmkrause]

I know for sure it's coming from the AC line. When I unplug the power and go on the laptops battery all the noise goes away. I got a isolator coming and when it gets here I'll post the results.
Dick :?

[Greg Young]

That should do it. I suspect a common mode choke would work as well, and it would be less costly.

Let us know how you make out!

[Jerry Budelman]

Another simple thing to try is to lift the ground connection on your laptop power supply (if it has one). Use a three to two pin adapter. This worked for me in the past.



Jerry Budelman

[chuckd]

Are you getting an isolation transformer or a 'power conditioner'? Or, does your power conditioner have a built in isolation transformer?

High end audio guys know that one of the best way to get dirt out of your audio is by using a power isolation transformer. Simple conditioners (like Monster Power, stuff like that) won't touch your problem, as they're primarily designed to filter higher frequency noise.

I've never actually witnessed a snap-on EMI choke do much of anything to this type of noise, as they are simply designed for much higher frequencies (think video, USB, network, etc). You can look at their noise filtering spectrums in spec sheets, and quickly realize that this is way out of the audio range.

[rmkrause]

I've gotten a power conditioner and still have the problem. What isolation transformer would you recommend? P.S. Thanks for your help.

[chuckd]

First (and far cheaper), are you powering the PC/transmitter from a completely separate circuit than the lights? If not, try that first. Run a long extension cord from somewhere else in your house if you have to.

Secondly, I never connect the PC to the transmitter unless it's through an audio ground loop isolator. Radio Shack has a cheap model that's not too bad, but JK Audio makes a much better unit (meaning 'more expensive'), called the Pureformer.

Lastly, if none of that stuff helps, you might look into this:

http://www.cdw.com/shop/products/default.aspx?EDC=414708

However, none of this stuff is absolutely guaranteed. Every noise problem is different. These are just the usual steps that we try to eliminate the problem.

But, I can tell you that some of us do have whisper quiet FM transmitters. It just takes some dilligence.

[-klb-]

Here is the audio ground loop isolator I mentioned above. It may be the same cheap RS one that Chuck mentioned.

http://www.radioshack.com/product/index.jsp?productId=2062214

They usually have it in stock at the store, but it can be a pain to find sometimes.

[-klb-]

Also, at the same time you are checking that the computer and lights are on different circuits, have you checked to see if there is any difference with the transmitter on the same, or different circuits as the PC?

[rmkrause]

OK guys, the problem is solved! Whom ever suggested the Radio Shack ground loop isolator was right on the money. Got one yesterday and 98% of the hum is gone. The power conditioner did not work maybe if it had an isolation transformer it would have. The best place I've found to put it is between the audio output of the computer and the audio gear and transmitter. Thanks for your help and suggestions.
Dick

[Greg Young]

chuckd wrote:

Are you getting an isolation transformer or a 'power conditioner'? Or, does your power conditioner have a built in isolation transformer?

High end audio guys know that one of the best way to get dirt out of your audio is by using a power isolation transformer. Simple conditioners (like Monster Power, stuff like that) won't touch your problem, as they're primarily designed to filter higher frequency noise.

I've never actually witnessed a snap-on EMI choke do much of anything to this type of noise, as they are simply designed for much higher frequencies (think video, USB, network, etc). You can look at their noise filtering spectrums in spec sheets, and quickly realize that this is way out of the audio range.

Chuck, it depends on the value of the ferrite material selected.

There are chokes designed for just about any frequency, from low audio all the way up to microwaves....

Snap ons are not as effective as wrap arounds, but if you stack up enough beads, they can work as well, again depending on the job they are designed for.

[rmkrause]

Final word on hum. I installed a Tripp-Lite isolation transformer on the AC line feeding all my equipment, transmitter,mixer,etc. Hum gone and music sounds terrific.

[rmkrause]

Morning Jeff, I hear a lot of people complain about the Remsey 30. I have one and it's just fine and I'm comparing it to a EDM which I also have.

[rmkrause]

Jeff,
I looked up how to make a DC power supply, but how do you use it. Does it replace the "wall warts"?
Dick:)

[rmkrause]

That's good to know. I spent a lot more money that you did but now I'm a happy guy with my system. It was amazing what a clean power supply did for the transmission, big big improvement. Thanks again for the information.
Dick