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KRK Rokit 5 faint buzz, bad capacitor?
Old 25th May 2012
  #1
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ersheff's Avatar
 

KRK Rokit 5 faint buzz, bad capacitor?

Hello.
I've been dealing with a faint buzz in both of my original KRK Rokit 5's for quite some time now. Different houses, power conditioners, different power cables, etc didn't solve it. The buzz is there as soon as they're powered on and doesn't change with the volume control or whether or not anything is plugged into the audio input speaker.
So, undoubtedly, the noise originates from within the speaker itself.
I ran across another guy online who had a really loud, bad buzz in his. It turned out to be an obviously leaking capacitor.
I opened mine up to check it out and, while no capacitors are obviously leaking, the exact same one in both speakers looks to be ever so slightly bulged.
I've attached photos- the cap on top in both is the suspect.
What do you think? Could this be the problem? Is it worth attempting to replace the caps?
Thanks!
Attached Thumbnails
KRK Rokit 5 faint buzz, bad capacitor?-img_0293.jpg   KRK Rokit 5 faint buzz, bad capacitor?-img_0295.jpg  
Old 25th May 2012
  #2
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LeeYoo's Avatar
 

Hi.
That bulging cap definitely needs replacing.
With a quality Low ESR cap.
Get one with a higher voltage rating if you can fit it.
Leo..
Old 25th May 2012
  #3
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I don't know if those caps are causing all of the problem, but it seems as if they were being run very close to their stated voltages for long periods of time. They should get replaced as the starting point in your troubleshooting.

Dennis
Old 25th May 2012
  #4
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Thanks, folks!
I just got one of the bad caps removed.
It's a 1000 microfarad 35V, also has a temp marking of 105C.
Are these the numbers I need to pay attention to?
Are you saying that I can up the voltage on the next one so long as it fits?
Thanks!
(P.S. This is all pretty new to me. The only caps I've replaced before were on my guitar's tone pot.)
Old 27th May 2012
  #5
Gear Nut
 

I have the same speakers - they always had a buzz when using the RCA unbalanced inputs, but no buzz when using the balanced inputs. Since I really never need the RCA inputs, I just never really cared enough to look into it further.
Old 27th May 2012
  #6
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I'm always using the balanced inputs. And, like I mentioned, the buzz is there whether or not anything is even plugged in and it doesn't change with the volume pot on the speaker itself.
I ordered 50V 1000 microfarad caps, though I have resigned myself to the distinct possibility that replacing those caps won't change anything. I was hopeful simply because someone else online who had a completely failed cap (the exact same as the bulging ones in mine) had an extreme buzz in his speaker.
That being said, they were clearly the only affected caps in each speaker, so I might as well replace them now.
Old 27th May 2012
  #7
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Is the "buzz" a 120hz or (100hz) hum? If so, the cap could very likely fix the problem.
best,
Ike
Old 28th May 2012
  #8
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Really? That's great to hear. It's definitely a 60/120hz thing.
I would know by now if it weren't for that fact that the local Radio Shack didn't stock the cap I needed. But they should be here in a few days.
Old 28th May 2012
  #9
Gear Head
 

ersheff,
I hope the cap solves your problem. Someone brought me a one of these KRK's. It buzzed more out of the tweeter and I believe that we had it narrowed down to a bad IC, but had a tough time getting a replacement. (I think they're still mixing on headphones over there, but cest la vie). Best of luck.
Old 30th May 2012
  #10
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I just finished replacing those caps with higher voltage replacements (50 vs the old 35).
Got them all put back together and... the buzz is gone!!!



I can't understate how awesome it feels to do a little research on a problem that you've had with some equipment for a few years, perform a repair that you knew nothing about a week ago, and have it all work out.
I wonder- the first thing I tested them out with is Grizzly Bear's Veckatimest.
Is it possible that replacing this cap actually improved the sound of the speakers?
I swear they're considerably more detailed with better imaging (that vocal came from dead center in front of me) than they had before, but I'm fully prepared to accept that as a placebo effect.
Maybe it's just that I've gotten so used to ignoring the buzz that now with the buzz gone I can finally hear everything that's there!
Thanks everyone for your help.
Old 30th May 2012
  #11
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Nice one! In answer to your question, you effectively lowered the noise floor of your speaker at 120hz, so yes, things should be clearer.
Best,
Ike
p.s. It ain't a buzz, it's a hum!
Old 30th May 2012
  #12
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ersheff's Avatar
 

Quote:
Originally Posted by Ike Zimbel View Post
p.s. It ain't a buzz, it's a hum!
Thanks, Ike.
I'm curious- what differentiates a buzz from a hum?
I'm very familiar with frequency ranges and have an intermediate knowledge of digital synthesis (oscillators and harmonics and additive and subtractive and whatnot).
Are you saying that I heard 120hz simply because it's a partial above 60hz, which would be the real signal present? Or is there an electrical reason why 120hz would be produced INSTEAD of 60hz?
For me, it was a buzz because the noise only came out of the tweeter, so I was only hearing the remnants of whatever partials of 60hz were being allowed to pass through to the tweeter. But I'd really like to learn more if I'm mistaken or misled!
Old 30th May 2012
  #13
Gear Addict
 

Quote:
Originally Posted by ersheff View Post
Or is there an electrical reason why 120hz would be produced INSTEAD of 60hz?
Yes. Because full-wave rectification is used (since it allows more efficient use of the transformer), then the ripple that the caps see is double the mains frequency, or 120Hz in the US, 100Hz in EU.

Of course, the mains isn't a perfect sinewave, because all kinds of loads get connected to it and it gets distorted, so you also get harmonics coming thru. Those harmonics were what you were hearing thru your tweeter, the buzzing noise.
Old 30th May 2012
  #14
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Ike Zimbel's Avatar
 

Couldn't have said it better myself!
Best,
Ike
Old 30th May 2012
  #15
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ersheff's Avatar
 

Coooooool.
I love learning new stuff.
Old 31st May 2012
  #16
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KnMn's Avatar
 

Man, this was satisfying to read. OP identifies problem, comes up with a possible fix, resolves problem. And then I learned a little bit about ground hum. Just great.
Old 2nd June 2012
  #17
Gear Maniac
 

Hi guys.

I have one of these units as well, with what's probably the same issue.

I was wondering if the op or indeed anyone else could tell me how hard it was to pull the speaker apart and how difficult it ended up being to remove the cap? I'm pretty good with a soldering iron, but I am a bit anxious about tearing things apart, particularly given all the screws etc that these have.

Stratman
Old 3rd June 2012
  #18
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The only screws you need to remove are the ones all around the outside edge on the back.
You may need to push something through the port from the front of the speaker to pop the back off. I used one of my roommate's percussion mallets (handle end).
There are only 5 cables connecting the back section to the rest of the speaker- 2 for the woofer, 2 for the tweeter, 1 for the light on the front. All of these were easily unclipped.
From there, removing the caps was probably the hardest part since you have to carefully locate the correct solder joints on the bottom side of the circuit board. Also, I have a ****ty little solder sucker, so I had to try a few times to get the cap loose, including a little wiggling action. The cap is stuck to the board with some kind of adhesive. It's a weak adhesive, but still enough for you to need to use a little force. Rock it back and forth and you shouldn't have any problems.
Make sure you note where the negative side of the cap was connected.
Soldering the new ones on was a piece of cake.
Old 4th June 2012
  #19
Gear Maniac
 

Quote:
Originally Posted by ersheff View Post
The only screws you need to remove are the ones all around the outside edge on the back.
You may need to push something through the port from the front of the speaker to pop the back off. I used one of my roommate's percussion mallets (handle end).
There are only 5 cables connecting the back section to the rest of the speaker- 2 for the woofer, 2 for the tweeter, 1 for the light on the front. All of these were easily unclipped.
From there, removing the caps was probably the hardest part since you have to carefully locate the correct solder joints on the bottom side of the circuit board. Also, I have a ****ty little solder sucker, so I had to try a few times to get the cap loose, including a little wiggling action. The cap is stuck to the board with some kind of adhesive. It's a weak adhesive, but still enough for you to need to use a little force. Rock it back and forth and you shouldn't have any problems.
Make sure you note where the negative side of the cap was connected.
Soldering the new ones on was a piece of cake.

Hi ersheff,

Thank you for your reply.

Since mine are out of warranty, I went and opened them up, your description gave me some confidence that it wasn't going to be a disaster.

I'm a bit unsure about the 35v cap. I've attached some pictures below. Neither unit seems to have a cap I'd call geometrically round in this position (but this could be normal?) - I do find it suspicious though that out of *all* of the caps, there is a very definite red residue on top of these two (but not iron oxide red orange though), and none of the others. I looked about inside the box, but I couldn't see what else could have generated the "red" that I can see smeared on both caps in varying amounts, but I couldn't find anything. I know some of the other goop on some of the other areas looks a bit bad (poor manufacturing!) but generally looks clean. Any thoughts?









Stratman

Last edited by Stratman; 4th June 2012 at 11:24 AM.. Reason: Link to image was wrong
Old 4th June 2012
  #20
Gear Addict
 

The red stuff is some paint or glue. Nothing to worry about. Replace the big caps even if they don't look bulged, they may have just dried out. Leave the rest alone for now.
Old 4th June 2012
  #21
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As long as it's low voltage anyway, another way to check for a dried up capacitor is by paralleling a new cap with the same ratings as the old capacitor. This can be done with alligator leads or by just tack soldering the new component onto the solder tabs of the older part. Always be cautious of the components polarity, negative to negative and plus to plus. Sometimes this saves a lot of trouble shooting time. Sometimes I don't even tack solder the new part to the old, but just hold the leads to the solder tabs of the older part, again taking into consideration of its polarity. Doing it this way takes a bit more care and finesse so that the leads don't spring off onto something you don't want them to thus the possibility of shorting something out.

These are just trouble shooting short cuts that do save time, but may not be for everyone's technical abilities. (This is called a disclaimer), lol.

Dennis
Old 4th June 2012
  #22
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Ike Zimbel's Avatar
 

What's happening with R-108? It's hard to tell, but in the last pic, it's either in shadow, or possibly burnt.
Best,
Ike
Old 5th June 2012
  #23
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I am going to stay out of this since I barely knew what I was doing with my own. shied
But, good luck getting it fixed, Stratman. Seems like some of the other characters in this thread might be able to help you out.
Old 5th June 2012
  #24
Gear Maniac
 

Hi guys.

Wow, several replies. Never thought I'd see more than one.

=======

Th3_uN1Qu3 you're probably right. The red stuff isn't from the cap itself. With regards to replacing that cap, at worst I get no real improvement, but at least I will be less likely to have the issue of a cap being pushed too close to its limit and dieing early.

Hi Ike - R108 has black goo on it. KRK gooped up the end of the cables on that part of the board and were quite liberal with it. FYI the speakers as per the op's case both *work*, just aren't "hum" free (despite plugging in at other locations etc). I would be surprised if R108 was a problem. -10,000 points to KRK for being messy though. The workmanship on these cards in places is just abysmal.

=============

I feel embarrased to say the following. I have found 2 1000uf caps I have from a chorus unit I built a little while ago spare. They were bigger than I needed previously, but they are 63V 1000uf Low ESR 105 deg and will fit as far as I can see. So that'd help me to replace the ones with the red stuff on them. But the embarrasing bit is, my soldering iron tops out at 35W and whatever KRK has used for solder here seems to require considerably more heat than a 35W iron generates, I couldn't get any solder to come off onto my braid! Ah such is life. My guess would be I might need 50W or higher. Might be able to get one of those cheap at an auto shop or see if I can lend a bigger iron, otherwise I'm stuck.

Audiotech - I think there just really isn't much room here to try this sort of thing, but I do appreciate the hints. I am always learning with DIY and if there was a bit more room and I felt I was less hamfisted, I would consider your suggestion.

Assuming I progress further with a hotter iron, I'd certainly be happy to post more pictures of what I've done and what things look like in these. I'm surprised given how many not so flattering comments there about the innards of these that someone hasn't done a full deconstruction guide.

Quote:
Originally Posted by ersheff View Post
I am going to stay out of this since I barely knew what I was doing with my own. shied
But, good luck getting it fixed, Stratman. Seems like some of the other characters in this thread might be able to help you out.
Thanks ersheff. I wouldn't be here now contemplating the "surgery" if it weren't for your thread!

Stratman
Old 5th June 2012
  #25
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ersheff's Avatar
 

You might be right about the soldering iron. I used a 70w Hakko on mine. I bought that at work mainly to do cable and headphone repairs. Didn't realize it was so high powered (relatively speaking).
Old 5th June 2012
  #26
Gear Addict
 

Agreed on the iron. I have a cheap 60W power controlled jobbie (no temperature feedback, just power control), and it gets pushed to its max setting sometimes. It mostly sits at 2/3 output. Lead-free solder is used almost exclusively nowadays due to environmental regulations, and it has a higher melting point than oldschool Sn-Pb solder, hence you need a more powerful iron. I always use 60-40 Sn-Pb when doing repairs tho. The only thing i've found leadfree better at, is soldering together large chunks of metal, like heatsinks or cases.

I used to have a 25W iron which just didn't cut it when it came to removing big parts with thick leads, like capacitors or inductors, and a 80W (no power control at all) was too much and kept oxidizing the tips really fast.
Old 5th June 2012
  #27
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Ike Zimbel's Avatar
 

Whatever iron you get, just remember that you are dealing with double sided circuit boards, which means the parts are soldered all the way THROUGH the board. You need to desolder them to the point where they come out with no force applied. One trick is to gently rock them while desoldering the leads.
Old 11th June 2012
  #28
Gear Maniac
 

Hey guys,

I'm back. I got a 30W/60W switchable iron for a reasonable price from a hardware store. At 60W things worked a treat. Getting the cap out was quite straight forward (happy to post some pics).

Now for the good news. I believe changing the cap has got some noise out of the audio path. Hurray! The only problem I have now is that there is still a noise and I reckon maybe it's the transformer or the transformer is picking up some interference. It doesn't seem to matter if something is plugged in to it or not.

Have a listen here:


I can't do much about the ambient noise at the moment. I do my surgery away from other audio equipment and the second I started trying to do this there was a load of traffic outside, including an ambulance. From the clip you can hear this hum/buzz thing that's going on in the lower frequencies. I'm on 240v..50hz hum?

Any thoughts or suggestions?

Stratman
Old 18th June 2013
  #29
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RatsRatsRats's Avatar
Quote:
Originally Posted by Stratman View Post
Hey guys,

I'm back. I got a 30W/60W switchable iron for a reasonable price from a hardware store. At 60W things worked a treat. Getting the cap out was quite straight forward (happy to post some pics).

Now for the good news. I believe changing the cap has got some noise out of the audio path. Hurray! The only problem I have now is that there is still a noise and I reckon maybe it's the transformer or the transformer is picking up some interference. It doesn't seem to matter if something is plugged in to it or not.

Have a listen here:


I can't do much about the ambient noise at the moment. I do my surgery away from other audio equipment and the second I started trying to do this there was a load of traffic outside, including an ambulance. From the clip you can hear this hum/buzz thing that's going on in the lower frequencies. I'm on 240v..50hz hum?

Any thoughts or suggestions?

Stratman
That is EXACTLY the sound my VXT6s are producing, they're not even 2 months old! They also pop anytime I turn on an EQ band.... each band does it.... even with it staying flat.... never did it before.... pops when pausing music too.... more like a click actually. Gibson is giving me the run-around and I took them to a "local" repair shop, said nothing was wrong.... what a waste of gas that was.... 50 miles each way.
Old 20th June 2013
  #30
tomcc
Guest
Has anyone tried to mod the rokits by changing the Opamps? I am thinking of changing the JRC4580 to Lm4562s. Also looking for schematic
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