k120 cutting out - cause?

k120 cutting out - cause?

Postby GratefulMets » Sat Sep 20, 2014 8:24 am

Hi Folks,

What would cause a speaker to cut out intermittently? I nabbed two NOS K120 speakers off craigslist, and both worked great for a while, but now one of the speakers cuts out completely, intermittently. It can run fine for a while, and I cant find a 100% consistent action to make it fail. I've confirmed it's not the wiring in my 2x12 cab by swapping connectors and having the same result. So, which component of the speaker would this indicate is failing or needs repair?

Thanks all
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Re: k120 cutting out - cause?

Postby hippieguy1954 » Sat Sep 20, 2014 8:48 am

It's a long shot, but have you checked the wires coming off the back side of the speaker terminals to make sure they are making good contact?
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Re: k120 cutting out - cause?

Postby czyfingers » Sat Sep 20, 2014 9:03 am

I have a K120 that had pretty much the exact same symptom you've described. After ruling out all the obvious...connections cables etc. I ended up shelving it for a while, out of frustration. Eventually I got it out and set it up on the bench with music playing through it and a meter connected until it cut out. When it stopped, it was showing an "open" reading. I eventually figured out through process of elimination that one of the single strand voice coil leads on the cone itself had become stressed and cracked under the black goop they're covered in. I carefully scraped away the black covering enough to isolate and find the break with the meter. With nothing to lose, I layed a tiny bead of solder across it, tested it to make sure it no longer cut out for a few days and recovered the area. It's worked ever since and been 4 or 5 years. That's one possibility...or it could be a similar situation be deeper than that. Like in the coil under the cone, which would mean it would have to be reconed to be repaired. That's assuming all the external connections are confirmed good. I'd reccomend checking all that you can see first, then try to get it to quit with a meter connected. Then gently prod around and see what gets it to start working again. This may give you an idea of where the problem lies. That was my approach...there may be a better one.
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Re: k120 cutting out - cause?

Postby tatittle » Sun Sep 21, 2014 9:05 am

Sounds like one of those curses that follows Mets fans in particular :lol:

I concur with the above post...it must be a bad connection somewhere that is completely breaking. I would get a multimeter set to ohms (lowest setting) and see what the numbers reveal. It doesn't sound like it is blown or going so much as a bad connection somewhere. I have had to clean the posts before on old JBL's...they had a high DCR reading; but this sounds like a true break either between the posts and the rear cone entrance or under the glue as noted above.
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Re: k120 cutting out - cause?

Postby GratefulMets » Sun Sep 21, 2014 9:50 am

Thanks for the replies. I'm as qualified to dig into the guts of my electronics as Omar Minaya was to build a baseball team! But that didn't stop him from trying, so I guess I'll give it a shot. Hopefully my results dont resemble Oliver Perez. And worst case, I know what to tell a qualified tech if I need to.

Thanks again. #metsin2015
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Re: k120 cutting out - cause?

Postby tatittle » Sun Sep 21, 2014 9:59 am

yeah...as soon as someone else has the rights to the speaker/player it will reach its full potential lol.
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Re: k120 cutting out - cause?

Postby MikeInMarin » Sun Feb 12, 2017 12:47 pm

I have a similar problem, where my K120 (bought on eBay last July, never move it, sit's in my studio in cabinet) completely cut out and is dead as of last night. I have ruled out the cables from the amp, as well as the connectors on the speaker. No matter what I do, I get zero sound.

Can anyone post some info about how to open the speaker and check for a broken wire inside, as was mentioned above ? I would be happy to go buy a multimeter (i should have one anyway), but I was hoping to at least be able to do some kind of visual check first.

Thanks.
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Re: k120 cutting out - cause?

Postby MikeInMarin » Sun Feb 12, 2017 9:26 pm

UPDATE: I unsoldered the tinsel leads (after testing with wires from my MC50 directly to connector posts and then tinsel lead wires on underside of speaker...nothing) and rubbed wires on exposed wire holes on inside of speaker. Still nothing. So there must be a cut in the voice coil wire itself.

Doesn't seem to be any way to get to that wire that runs the inch or so on the speaker to the voice coil....I heated and scraped some glue away, but still nothing. Don't know how to get below it any further to replace actual wire coming out of voice coil.

So looks like I am out of luck. The JBL I have was re-coned and in amazing shape, but I guess they did a shitty job with the voice coil wire.
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Re: k120 cutting out - cause?

Postby tatittle » Mon Feb 13, 2017 12:53 pm

I didnt see a refernce to it working after it cut out on you Mike. So you may have just blown the speaker. Did it distort before it stopped working?
The advice above is assuming the speaker works sometimes. Do you get a DCR reading ever above 0? If it is traditionally blown the break is inside the speaker and generally requires a recone. A recone likely didnt having the power capacity of the original, though it certainly could have. I suppose there are instances where the blown speaker could be repaired vie careful surgery, but that is beyond my ability.
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Re: k120 cutting out - cause?

Postby MikeInMarin » Mon Feb 13, 2017 2:33 pm

tatittle wrote:I didnt see a refernce to it working after it cut out on you Mike. So you may have just blown the speaker. Did it distort before it stopped working?
The advice above is assuming the speaker works sometimes. Do you get a DCR reading ever above 0? If it is traditionally blown the break is inside the speaker and generally requires a recone. A recone likely didnt having the power capacity of the original, though it certainly could have. I suppose there are instances where the blown speaker could be repaired vie careful surgery, but that is beyond my ability.


tatittle - Thanks for responding. No, the speaker just completely died instantaneously. No distortion, not intermittent cutting out. Very weird. Seems like the voice coil wire got cut. I cannot get to it w/o cutting the cone or cap out. Not sure I want to spend the money getting it fixed either but I am going to ask a local amp guy or two. In the meantime, I just ordered another K120 off Reverb.com. Hopefully, this one will actually last.
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