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Kona KL-Box hum problem

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Andreas Friedrich
Kona KL-Box hum problem
on Feb 9, 2009 at 6:29:33 pm

Hi, everyone,

I've encountered a problem that makes me slightly nervous. Maybe you've had the same issue?
I've been editing on my FCP system (Dual Quad 3 GHz, FCP Studio 2, Kona LH and KL-box) for more than a year now with no problems at all. Recently I hat to edit a nice project outside my office, so I packed up my gear and set it up at the customer's office, using the octopus cable instead of the box.
When returning to my office, I connected everything the way it was before, using my KL-box again, and found my analogue audio humming. In search of the error, I stripped the box from every cable connected and left only the active monitor speakers. The hum persists even when only the bare box ist on my desk with nothing connected but the active speakers via balanced XLR.
Any Ideas? I've had the box exchanged, the new one does just the same. Using the breakout cables is my workaround, everything works fine without the box.
Having this kind of error is pretty hard on my self-confidence, so if you have an idea... ;-)

Thanks very much in advance,

Andreas


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Bob Zelin
Re: Kona KL-Box hum problem
on Feb 10, 2009 at 1:39:49 am

encountered a problem that makes me slightly nervous. Maybe you've had the same issue?
I connected everything the way it was before, using my KL-box again, and found my analogue audio humming. In search of the error, I stripped the box from every cable connected and left only the active monitor speakers. The hum persists even when only the bare box ist on my desk with nothing connected but the active speakers via balanced XLR. I've had the box exchanged, the new one does just the same. Using the breakout cables is my workaround, everything works fine without the box.

REPLY - so you are telling me that you simply disconnect the KL box, use the break out octopus cable and the hum is gone ? I don't believe it. The KL box has both XLR and RCA outputs. Monitor from first the RCA outputs, and then the XLR outputs - do they both "hum".

HUM is usually caused by a grounding problem. Simply, you have stuff plugged into outlets on 2 sides of the room. This is what I suggest. Plug in only your MAC, monitor, speakers, and mixer to one AC outlet strip that is plugged into one outlet on your wall. UNPLUG EVERYTHING ELSE. You don't even need to playback audio to hear hum - silence is an excellent way to hear hum. MAKE SURE that nothing else is plugged into any electrical outlet (other than your lamp !). Listen first to the XLR output of the KL box, then the RCA output of the KL box. Both humming ? OK, get your breakout cable, and bypass the KL box. Use the XLR outputs of the breakout cable. Do you hear hum ?

If you hear hum from the KL box, but not from the octopus cable, using the same XLR cables to your mixer or speakers, then I am guessing that its not the KL box, but the cable harness that AJA sends out that goes between your KL box and the Kona LHe.

AC ground issues is the #1 cause of audio hum. Unplug all those things from the wall, and use only ONE OUTLET STRIP to do these tests !

bob Zelin





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Andreas Friedrich
Re: Kona KL-Box hum problem
on Feb 10, 2009 at 12:55:50 pm

Thanks Bob for your quick response.
I don't want to seem stubborn about ist, but I still don't get it. Using only one outlet is easily done here, since there's only one in the editing room.
I disconnected everything else - even the lamp, just to make sure - and left only my Mac, monitors, mixer, and speakers.
Still the hum persists, at least on the XLR outputs. The RCA outputs are perfectly silent. In addition to that, the hum on the XLR outputs becomes louder whenever I touch the surface of the breakout box or connect the multipin cable between the box and my Mac, yes, even when I connect the second speaker to the second XLR outlet.
Connecting the same setup via the octopus cable produces the silence we all enjoy to hear. And, yes, it's the same set of cables from there. I exchanged the cables as well to make sure, the result is the same.
As far as I know, the breakout box is just a passive connector, no active components inside. Still it doesn't behave the way the octopus cable does. So I tried to find anything unusual without having to open the box: There's a connection between pin no. 1 in the analogue XLR input and the chassis of the box (and, by that way, to all other signal grounds). I'm not sure, but this doesn't seem to fit, since XLR ground and common ground shouldn't be the same, should they? They aren't connected in the octopus cable.
Forgive my possibly stupid questions, I just don't understand how this phenomenon comes to happen.

Thanks again,

Andreas


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Bob Zelin
Re: Kona KL-Box hum problem
on Feb 11, 2009 at 2:00:37 am

your questions are not stupid. Replies below -

Using only one outlet is easily done here, since there's only one in the editing room. -
REPLY - this is good. You don't have a CABLE TV hookup to your montior do you ?


I disconnected everything else - even the lamp, just to make sure - and left only my Mac, monitors, mixer, and speakers.

REPLY - this is good.

Still the hum persists, at least on the XLR outputs. The RCA outputs are perfectly silent.

REPLY - well this is strange. If the Kona KL box was bad, both XLR and RCA outputs would both cause hum. Did you say that they sent you a NEW KL box ? Because if they did, it's your cables. Obviously, if you connect from RCA to your Mixer, and then XLR to your mixer- these are TWO DIFFERENT CABLE SETS (one RCA ends, one XLR ends). I ASSUME that you are plugging into the 1/4" tip ring sleeve stereo phone plug input of your mixer - am I correct ?


In addition to that, the hum on the XLR outputs becomes louder whenever I touch the surface of the breakout box or connect the multipin cable between the box and my Mac, yes, even when I connect the second speaker to the second XLR outlet.

REPLY - if you have replaced the KL box, then you have an audio cable problem. For your tests, you should have a RCA to 1/4" stereo phone plug (KL RCA out to mixer), and XLR to 1/4" stereo phone plug (KL XLR out to mixer).


Connecting the same setup via the octopus cable produces the silence we all enjoy to hear. And, yes, it's the same set of cables from there. I exchanged the cables as well to make sure, the result is the same.

REPLY - the Octopus has XLR connectors. The RCA ouputs of the KL box are RCA, not XLR. so these are different cable sets. But you said that the RCA's were silent, and the XLR's had the hum. Is this correct ? Confirm that you are going into the 1/4" line inputs of your audio mixer.


As far as I know, the breakout box is just a passive connector, no active components inside. Still it doesn't behave the way the octopus cable does. So I tried to find anything unusual without having to open the box: There's a connection between pin no. 1 in the analogue XLR input and the chassis of the box (and, by that way, to all other signal grounds). I'm not sure, but this doesn't seem to fit, since XLR ground and common ground shouldn't be the same, should they? They aren't connected in the octopus cable.
Forgive my possibly stupid questions, I just don't understand how this phenomenon comes to happen.

REPLY -
you have a custom cable from AJA that goes from the Kona LHe to the AJA KL box. HAS THIS BEEN REPLACED ?

Bob Zelin





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Andreas Friedrich
Re: Kona KL-Box hum problem
on Feb 12, 2009 at 2:28:16 pm

Hello again,

thanks again for your patience. As to your question on the exchange of the box: yes, they sent me a (hopefully) new one. At least it was sealed and packed like my first one. The AJA KL-cable was exchanged as well.

[Bob Zelin] "I ASSUME that you are plugging into the 1/4" tip ring sleeve stereo phone plug input of your mixer - am I correct ?"

I dit that at first, using adaptors from RCA to 1/4" jack, all perfectly silent, then tried the RCA in on the mixer (yes, there's a pair of those) - which gave me the same fine result.
I also tried leaving the mixer out of that line, connecting the speakers directly: fine with RCA, fine with 1/4" jack adaptors from RCA, hum as soon as I came from the XLR output.
Just to have left nothing out, I tried adapting a mono 1/4" jack from the XLR output (bridge between pin 1, ground, and pin 3, sig-), and the hum became definitely less, but didn't disappear entirely. I think this makes sense in a way, but still doesn't give me a clue.
Again: The octopus cable behaves as I expected, no humming, all perfectly silent. It's just the XLR outs from the box.
As I mentioned before, I don't have to rely on the box, the octopus cable is a near-perfect workaround. But interesting, nonetheless.
Thanks again, best regards,

Andreas



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