Hello All,

I have 2 different installs where cat5E was used to transmilt line level audio. On both locations we have a hum in the audio feed. We have tried both soldering RCA plugs to the cat5E directly as well as using Baluns. Either way we get the same result. In one job the run is only about 69 feet or so. In the second it is just shy of 400. In both we have a good strong audio signal to the amps. The Hum is very low but it is volume dependant. Any ideas???

Thanks

Robbie S

I would first check to make sure you are not close to any AC lines. If thats not it then you have a ground loop ploblem.

Where are the volume controls: are they in a pre-amp before the cat5, or are they in the amp after the cat5?

We are not near any AC source. It doesn't sound like the typical AC noise I've heard before.

The first system is running from line level output of a computer sound card into an input on a Denon A/V Receiver. I have tried adjusting the line level out on the computer but it seems to make no difference.

The second system has an AM/FM Stereo receiver running 2 pairs of speakes locally off the receiver's volume control. We then ran a Cat5e From the TAPE OUTPUTS to the inputs of an Audio Source 2 Channel amp at the other side of the complex. The Audio Source Amp has an internal volume control as well. It drives one pair of speakers in the building it is located in.

Thanks

Robbie S

I've run into this before trying to tie in a Grand piano into the audio in a bar. The output out of the piano was very week so it forced me to gain the amplifier very high which caused the hum to get unbearable. After trying every trick in the book I tried using an inexpensive line driver maid by Audio Control for a car application. It boosted the pre amp signal high enough to allow me to gain down the amp lowering the noise floor low enough that it was unoticeable. I hope that helps.

Bob

This sounds to me like a ground loop problem. Sometimes when people are grounding their recpticles they go to a different ground than the AC Panel. What I ould do first is lift the ground on the Audio equipment if the cord is using a gorund. ALso it could be transformer interference. I ran into this problem when the customer had halogen lights and the transformer was in the ceiling. When my wires was up against the transformer I had a hum. Once I moved it away it was fine. When running a liine level audio anywhere over 50 feet we always use shielded mic cable. Whenever it is over 100 feet we use a line level amplifier. Hope this helps.

Mike

If you have used a Balun with the CAT5e, most likely the culprit is not a ground loop. Another reason is the volume dependant problem.

Please specify your source and your amplification. The more detail in your question and configuration, the quicker this can be resolved.

Robbie, got get one of these .... [Link: radioshack.com]

Also pick up a 1/8"mono to RCA adapter. Take a listen to the output of the source and see if the noise is there with the portable amplifier. Let's try and rule out problems with the source first.

Stop back on this thread an tell me what you find. You can be sure we can get rid of the offending noise.

Try this - get the hi volt at both ends on the same phase of the electrical system. Worth a shot. Typically balanced line drivers eliminate this.

Try swapping audio sources. Some sound card configurations from PC's can be inherently noisy. Also, check your gain staging on the sound card sorftware

Mike is right on the money, if you have two different devices that are not on the same phase at the A/C panel you can get ground loop hum. I would HIGHLY recommend getting a Jensen Transformers ground isolator http://www.jensentransformers.com/ they work great. let us know if that does it for you.