One of my KRK v8 hums and I don't know what to do - diyAudio
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Old 5th July 2012, 02:57 AM   #1
vvd is offline vvd  Germany
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Default [Solved] One of my KRK v8 hums and I don't know what to do

greetings DIYers,

I am not a electrical engineer and not really a DIY guy (I wish I was) so I am asking you for help. I want to gather some knowledge about my issue to educate myself so that I am hopefully able to justify possible rapair costs.

Here is my issue:
for some years now one of my good 'ol KRK V8 hums slightly, even with no connected audio cable. The hum is constant and has never changed during the years. I've made a recording as i thought it might help a technician to identify the issue (In the recording I am moving the mic from the woofer to the tweeter, back to the woofer and back to the tweeter again):

http://prodatum.sf.net/tmp/hum.mp3

for comparison: the same recording from the silent monitor (BTW, the hiss of the tweeter is not audible normally, I cranked up the recording levels quite a bit):

http://prodatum.sf.net/tmp/nohum.mp3

I've also made a frequency analysis from the hum of the woofer:

Click the image to open in full size.

My power line is AC @ 50Hz, and there's a peak at 50Hz, but also one at around 150Hz. Does that tell you guys something? It doesn't to me... i think it's interesting tho', and might be a hint?

So yeah, I have no clue about electronics... Could this possibly be repaired easily? You know, it's expensive gear and people might think oh, he has lots of money, let's just sell him a new amp or something. I don't want to be fooled/spend too much money.

Thank you!

PS: Both monitors are on the same power line.

Last edited by vvd; 5th July 2012 at 11:13 PM. Reason: marked as solved
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Old 5th July 2012, 03:32 AM   #2
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Hi,
That it is a sound like an open input. Did you try shorting the input to see if the sound goes away?
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Old 5th July 2012, 03:46 AM   #3
vvd is offline vvd  Germany
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Quote:
Originally Posted by tauro0221 View Post
Hi,
That it is a sound like an open input. Did you try shorting the input to see if the sound goes away?
i'm not sure if i know what you mean, sorry. do you mean the problem might be somewhere on the audio input side (but inside the box, since no audio cable was connected), eg before the amp/crossover or whatever the audio goes into first? like a broken ("open") audio-connector or something like that?
is shortening the input easy to do? I have no experience with those things but i'd love to try it.

edit: does shortening mean physically disconnect?
also, there is an electrical shock warning on the back. What do I have to do to get a shock? I may then decide to avoid it.

Last edited by vvd; 5th July 2012 at 04:10 AM.
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Old 5th July 2012, 07:32 PM   #4
vvd is offline vvd  Germany
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i took it apart, this is how it looks from the inside:
KRK V8 guts

my question would be: is there anything dangerous about playing with these parts? again: i am no electrical engineer.
and: is there anything i could try yo get rid of the hum?

thanks again!
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Old 5th July 2012, 10:38 PM   #5
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re:'What do I have to do to get a shock?' - ignore the warning.... If you don't know about electrical safety, LEAVE IT ALONE, you could die.....
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 5th July 2012, 11:03 PM   #6
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What I mean by shorting the input it is take an RCA cable and tie together the two wires.
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Old 5th July 2012, 11:13 PM   #7
vvd is offline vvd  Germany
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Well, I ignored the warnings from all my friends and strangers and disassembled the box. I was about to bring it to a pro for inspection when i reconnected the woofer and tweeter just to try it (heck, you never know, right?). Powered it on, and voila, no hum. I then reassembled the box and it is noise free now!
Well, good, awesome! But WTF? I did nothing but open the box, disconnect the drivers and reconnect them. Fixed?!
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Old 6th July 2012, 05:03 AM   #8
puppet is offline puppet  United States
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... gotta love it when stuff fixes itself.
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