keep losing top end :(

[jamlucas]

hi guys

 

I just need a little help. I have two jbl jrx100s, one of them keeps losing the top end, it keep coming and going, it is only happening on one of them so I am guessing its a cable problem or with the speaker itself? it has only just started happening in the last few days, usually during a show or when the venue is open and never when I am alone trying to figure out what the problem is?

 

Thanks for any help

[Shez]

Have you had a look inside the cab and checked for any loose connections? Input plate, crossover and driver.

[Dave SA]

JRX100 is a range. Which cabinet do you have?

[abbotsmike]

JRX100 is a range. Which cabinet do you have?

 

I was just thinking the same thing, but it sounds like it could be a dry joint or similar on the crossover board.

[ramdram]

Cheapest way is the substitution method. And apologies if you have done this/know about cabling, etc already of course.

 

This is one way to do the swaps, depending on what other kit you have. Other posters may recommend a different sequence of tests, so you will have to do what you decide. If I have made any errors in this no doubt they will be corrected, ** laughs out loud **.

 

You mentioned the hf is not always there...are the cables 2 core or 4 core. I have not googled the JBLs so this could be wrong, but may be relevant to similar queries, not yet posted in the forum(?).

 

Can you swap the spkrs/cables? This would tell you if the cable or the speaker is duff. You should keep your fingers crossed that the system uses 4 wire cable and there is a duff connection on either the +2 or the -2 terminals of the plugs; a bit of background:

 

http://www.blue-room.org.uk/lofiversion/in...php/t17810.html

 

and:

 

http://www.buyspeakercable.com/info_wiring...connector.shtml

 

If the cables are OK and connected properly then you can try a different pair of spkrs. If the speakers still lose hf then suspect the amp, so refer to last para.

 

If the problem disappears with the substitute spkrs then the original speaker is most likely to be the culprit .

 

You might then try opening the cab and searching for iffy connections and visible signs of distress to the crossover board components...burn marks say.

 

The JBLs may have an overload protection circuit which protects the hf driver. Presuming this is the case, this circuit may employ two light bulbs in a metal tube stuck onto the board with gunky stuff. Hopefully there will be a duff/dry solder joint on the bulbs to the board (they are inline bulbs btw, without a proper screw or bayonet fitting, and have two wires either end thru' the glass. These wires are soldered directly to the circuit board).

 

If the bulbs are ok and there is no obvious duff components then it may be the hf driver itself.

 

Again you can do the substitution thing. It would be sensible to write down a sort of truth table as you do this, so as not to get lost...and to use the same music or tones track for testing, (again, apologies to be stating the obvious).

 

IF the cables are OK and the speakers are OK (and you have tried the speakers on another system...) then you can suspect the amp itself.

 

Unless you are au fait with working on live kit, have the circuit diagram and a signal injector and decent multimeter then I strongly recommend you leave well alone.

Take the amp into the place where you bought it from or a repairer, who is an expert on amps. No doubt the BR cab help here provided they know where you are located. IT may be that there is a duff component in the amp which is affected by temperature as the amp warms up. This component may not be visibly damaged or appear "distressed" of course.

 

It may be the heat transfer paste on one of the power transistors/chips to the heat sink has broken down. You appreciate I am trying suggest anything could be causing this problem..it may have nothing at all to do with the transistors whatsoever.

 

If the amp is OK then you would need to think about other kit in the program chain.

 

HTH

[dboomer]

The JBLs may have an overload protection circuit which protects the hf driver. Presuming this is the case, this circuit may employ two light bulbs in a metal tube stuck onto the board with gunky stuff. Hopefully there will be a duff/dry solder joint on the bulbs to the board (they are inline bulbs btw, without a proper screw or bayonet fitting, and have two wires either end thru' the glass. These wires are soldered directly to the circuit board).

 

This is my best guess as well. They may also employ a PTC which requires "cooling down" before normal operation is resumed.

 

How quickly does it come and go? Minutes? Days?

[johndenim]

I once took a look at a pair of similar speakers for a friend.

 

I diagnosed the fault to be the HF protection circuit.

My friend took them to Electromusic in Doncaster, and they simply bypassed them!