Any idea what's wrong with my K120?

[vlchilders]

Hi all - I'm new to this forum and hoping this newbie question doesn't come off as woefully idiotic!

I have a JBL K120 I'm using for guitar. Recently the speaker started acting up. Basically, I can fire it up and it will play beautifully for a few minutes, then it may crackle a little bit before going silent or just die altogether. If I give it a little more or less juice, just moving the power amp volume around a little bit it will sometime wake up again briefly. But not always.

If I shut everything down and wait 1/2 hour or so, I can bring it back to life (usually), but same problem repeats. I've tested it with several different amps and speaker wires and got the same issues, so I'm pretty confident that the speaker is, in fact, the problem.

Anyway, any diagnosis or prognosis is much appreciated. This is killing me!

[Eaulive]

Possibly a broken solder between the cat's wisker and the cone or the connector.

[jcrobso]

SWAG= Scientific Wild Ass Guess.
You could have break in the wire of voice coil, when the speaker is cold your OK. But after a while the voice coil gets warm and opens up and the speaker dose not work until it cools off.
Maybe Edgewound has an idea.

[vlchilders]

Possibly a broken solder between the cat's wisker and the cone or the connector.

Just went through and doesn't look like a solder problem, at least not anything immediately visible?

[vlchilders]

SWAG= Scientific Wild Ass Guess.
You could have break in the wire of voice coil, when the speaker is cold your OK. But after a while the voice coil gets warm and opens up and the speaker dose not work until it cools off.
Maybe Edgewound has an idea.

If that's a side effect of a broken voice coil, certainly sounds plausible to me. Is this something that can be repaired or am I basically screwed?

[jcrobso]

At lot depends on where the break is, but generally it needs to be reconed.
I suggest you PM edgewound he is a JBL pro service pro.

[vlchilders]

At lot depends on where the break is, but generally it needs to be reconed.
I suggest you PM edgewound he is a JBL pro service pro.

Will do. Thanks for the advice!

[Audiobeer]

I'd hook up a speaker in its place and see if it's in the amp?

[vlchilders]

I'd hook up a speaker in its place and see if it's in the amp?

Definitely the speaker. I PM'd edgewound and sounds like voice coil is the problem. It's unfortunate what it costs to recone these bad boys. Have to decide now if I buy another one or cough up the dough....

[subwoof]

one easy test to see if the braided wires ( litz ) are the problem.

Hook the speaker directly to a music source ( like a receiver ) and without moving the cone, move each wire carefully with your fingers to see if the sound interrupts. If so then a simple wire replacement ( by a PROFESSIONAL ) will fix the problem. The wires often fatigue and break where the solder ends when wicked into the braid.

I have seen many cones with this problem over the years and it's a 10:1 ratio compared to intermittent coils.

sub

[vlchilders]

one easy test to see if the braided wires ( litz ) are the problem.

Hook the speaker directly to a music source ( like a receiver ) and without moving the cone, move each wire carefully with your fingers to see if the sound interrupts. If so then a simple wire replacement ( by a PROFESSIONAL ) will fix the problem. The wires often fatigue and break where the solder ends when wicked into the braid.

I have seen many cones with this problem over the years and it's a 10:1 ratio compared to intermittent coils.

sub

subwoof - I just hooked it up and tried this. I had to run the volume on the receiver pretty low to keep the speaker from dying, but when I pushed around on the braided wires I was able to generate some crackling and breakup.

I called the local JBL guy and he said he thought my problem could very well be intermittent leads. However, he said the problem can't be fixed anyway because of the "glue" holding the leads to the cone -- he says they can't be removed? Basically, he said a recone would still be necessary.

He seems like a good guy, but is he just wrong on this one?

[Eaulive]

subwoof - I just hooked it up and tried this. I had to run the volume on the receiver pretty low to keep the speaker from dying, but when I pushed around on the braided wires I was able to generate some crackling and breakup.

I called the local JBL guy and he said he thought my problem could very well be intermittent leads. However, he said the problem can't be fixed anyway because of the "glue" holding the leads to the cone -- he says they can't be removed? Basically, he said a recone would still be necessary.

He seems like a good guy, but is he just wrong on this one?

That was my first impression, those lead wires.
Now it CAN be fixed but it involves some work on the cone, (melting or scraping the glue) and it can lead to some damage on the cone.
There's chance that your cone will never look the same again, but yes, it can be fixed, however it's not the JBL purist way if you catch my meaning ;-)

[subwoof]

The hardened glue on the thin paper cone is a problem BUT one trick that works is to use a quality 40 watt soldering iron and poke the tip into the center of the bubble. the glue will melt ( and STING your eyes) and when it reaches the eyelet, add a tiny bit of thin solder to whet the joint.

As SOON as the solder melts, pull off the braided wire from underneath with a pair of small needle nose pliers.

Then REMOVE the iron and let everything cool off.

The goal here is to melt the solder, remove the wire and be FAST about it.

Later when you want to replace the leads, use a piece of solder wick to clean out the eyelet but be very careful of the thin aluminum wire that is inside of it ( the actual voice coil lead ). the glue usually comes off with heat and patience but remember the paper is very thin and you just cooked a little.

I have done this many time with good success but it's best practiced on a number of truly burnt cones first to get the technique down.

sub

BTW - I did this on a bar top once during a band break on a K120 ( twin ). free drinks all night...hic

[Eaulive]

The hardened glue on the thin paper cone is a problem BUT one trick that works is to use a quality 40 watt soldering iron and poke the tip into the center of the bubble. the glue will melt ( and STING your eyes) and when it reaches the eyelet, add a tiny bit of thin solder to whet the joint.

As SOON as the solder melts, pull off the braided wire from underneath with a pair of small needle nose pliers.

Then REMOVE the iron and let everything cool off.

The goal here is to melt the solder, remove the wire and be FAST about it.

Later when you want to replace the leads, use a piece of solder wick to clean out the eyelet but be very careful of the thin aluminum wire that is inside of it ( the actual voice coil lead ). the glue usually comes off with heat and patience but remember the paper is very thin and you just cooked a little.

I have done this many time with good success but it's best practiced on a number of truly burnt cones first to get the technique down.

sub

Yup, I agree with everything there

[SMKSoundPro]

Yes, that's how its done. Although I don't recommend doing it on a bartop, unless thats your only option. The pool table has more room to spread out on!

Geez Subwoof, is there anything you haven't done on a bartop during a gig?

Scotty.