Mixers/Consoles Hum when video system patched in

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Djruss84

Member
I have been racking my brains on this issue I have been having. Every time I try to take an audio out feed from my audio consol and plug it into our video recording system a hum emulates from the house PA. I have tried every possible solution I could think of to resolve this. I have tried ground lifts, hum eliminators, using the same power source as the pa, using a power source from a completely different panel, nothing stops the hum. It does not matter what output I use on the board either weather it's an aux, bus, sub out or record out there is a hum in the pa only when I try to feed the video system. The board is a mackie vlz24-4 and I am trying to feed a DVD recorder. What am I missing here? To get sound for our video recordings I currently am using a in ear receiver to feed the DVD recorder which is not the proper way but it works and no hum. Has anybody experienced this and if so how did you solve this?

Thanks in advanced
Russell
 
I've never had any issues like you mentioned before. What brand is the DVD Burner and what cabling and connection's are you using to patch it in? Have you tried hooking up the DVD recorder as you did and then remove the video feed isolating the DVD burner from your video feed and see if the hum go's away?
 
I believe that it is a Sony DVD recorder. I custom made 1/4" ts to RCA cables useing belden 9451 cable going directly to the DVD recorder. I also tryed balanced out of the board into a direct box with a ground lift switch then RCA out to the DVD audio in. I even went balanced into the video switcher then out to the DVD recorder the hum was still there. It also happened when we tryed going into a VCR too. I also tryed doing as you suggested and removed all video connections problem was still there. I then thought that it was the cable transmitting system we use to send video to monitors located throughout the building. I purchased an expensive Jensen catv isolator but this was not the cause either. I have never not been able to isolate a hum but this one is persistent and will only go away when I do not feed audio directly to the video recording system. I even tryed the audio out on our audio recording and as soon as it was plugged in hum appeared. Also if it helps the pa is a Bose panaray system that was custom made and installed by Bose.
 
My first instinct would be to put an isolation transformer on between the console and the video system.
(As a general rule, I would always isolate anything I was sending to broadcast - for a whole range of reasons I won't go into here...)
 
the power supply on your recorder could be sending high frequency noise into the mixer, as frequently happens with laptop supplies, the wireless link does not transmit this noise.Is your gain structure right? this will make the situation much worse if you are not running your mixer at full output. Gain structure is crucial in noise problems.A ground lifted passive DI box, with the desk running at high level and the amps set as low as possible should vastly reduce or eliminate the problem.
 
I have already tryed the direct box with a ground lift and an iso transformer. Gain structure is properly set up and there is no change in frequency or level of the hum when i adjust the gain. What is also odd is i can not see the hum on the consols VU meter or hear it in my headphones but i can see the signal lights on the amps showing the hum. When the ground was lifted at the amps the hum did not go away either. I am begining to wonder if the mackies power supply is begining to die and any time i try to put any more load on the outputs the power supply emmits some odd voltage on the outputs or something. I really have never not been able to resolve an issue like this. My next step is going to be renting a different consol to see if that is the issue. Might be a good time to convince the venue to go digital.
 
I have similar issues!! with different end-of-line device!!

I notice my issue with an older wall mounted backstage announce speaker that worked fine before I burrowed equipment and put back. I run an M7CL, and unfortunately traced the issue all the way to the console. I've tried unplugging unbalanced inputs and got better results, but not completely gone. I tried switching that send cable to a different monitor omni out and buzz became 1/2 as loud in both speakers. That's when I had to take a day away from our sound system.

First noticed with my radio receiver. when m7 channel is on buzz is lessened, turn the send to BS Ann. and it gets louder proportional to send volume. If I unplug the receiver from the console the buzz changed pitches slightly. I've run 200 feet of extension cord to get the amp on same power strip as board. The only change being I then had an ugly orange cord hanging through our lighting coves. BTW: the amp and board were/are on same iso-ground panel.

I'm thinking my problem is two or three fold. buzz on ground. Buzz injected on signal +/-. I hope the amp isn't failing, worse yet M7CL failing.
 
Have you tried putting a di or hum eliminator at the amplifier, you may ground lift the signal but still have an earth loop through the power.
 
David Ashton said:
Have you tried putting a di or hum eliminator at the amplifier, you may ground lift the signal but still have an earth loop through the power.
Click to expand...
Just ried powering the amp through an Grounding adapter(allows you to plug a grounded Edison plug into an ungrounded receptical) and removing the grounding tab on the adapter. The result is unnoticed if there is a change. I'm thinking the main issue is the buxx is being injected onto the positive or negative signal wire.
 
Russell didn't say, but I'll bet he is trying to use the 1/4" TRS main outputs of the console, while the amps are driven from the XLR main outputs. If that's the case, I know exactly what the problem is. The TRS and XLR outputs of the Mackie are paralleled on the pin2/tip side of the balanced output stage (the ring side is just "impedance balanced" with a resistor). By using both jacks simultaneously, the line to the amps is becoming unbalanced, which reduces the ability of the input stage of the amps to reject hum and noise. The console is not properly designed to allow both of the main outputs jacks on each channel to be used together.

The fix is to use a different pair of outputs to feed the video recorder. Try the RCA tape outputs, which are buffered from the main outputs. Or, set up a post-fader mix for video on the aux sends.
 
As i said before it does not matter which output i use. I have never tryed using the secondary main outputs because I always like sending seperate mixes for recordings. Also today when i tryed patching in a second professional cd recorder the hum occured again. Now i have determained that the issue is not just because i am feeding a video device but the hum will occur any time i add a load to the output to the board. While the hum was happening i tryed some more troubleshooting. I lifted the ground to the bose system eq and this did not solve the issue. I then put a direct box in line between the consol and amp racks and lifted the ground that way. This too did not fix the problem. I then tryed an eb tech hum eliminator and you guessed it the problem was still there. I am now convinced that the mackie is on its last legs and the internal power supply is ready to go.
 
I thought that it was a video issue until I tried the cd recorder which has balanced in. I now know it happens any time i add an output onto the board. It does not matter if it is video or audio.
 
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