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View Full Version : JBL 4320/4333 with 3120A crossover problem, lost bass response



MadsKaizer
12-30-2013, 05:58 AM
Hey All

I hope you can help me in the right direction to find out what is wrong with my speakers. The bass response is completely gone from my right speaker.

The problem is not my tube amplifier, I checked its balance, bias etc, all is good, switching the speakers around the problem stays with the right speaker. Playing with the balance it is very obvious there is no bass output from the right speaker compared to the left.

My speakers: http://www.audioheritage.org/vbulletin/showthread.php?34611-JBL-4320-4333-Upgrade&highlight=

Crossover schematic: http://www.jblproservice.com/pdf/Network Schematics/3120A Network.pdf

I opened up the crossover and can see that the UHF driver is connected through a 3,3uF capacitor from the HF tap. The components I could measure without taking the components out measured fine and visually there seem to be no faults.

Any ideas on what to look at when the bass response is gone is most welcome.

grumpy
12-30-2013, 07:09 AM
The components I could measure without taking the components out measured fine and visually there seem to be no faults.

... and the woofer itself is working? (not having said this was measured directly, or tested with the crossover bypassed)

script56
12-30-2013, 08:08 AM
I had the same problem. Had to remove cone assembly spider and all and found the voice coil came loose from cone and became stuck in voice coil gap

MadsKaizer
12-30-2013, 08:24 AM
... and the woofer itself is working? (not having said this was measured directly, or tested with the crossover bypassed)

All drivers are working, LF, HF and UHF, there is just a huge lack of bass in LF and HF drivers output. The components I mentioned are those inside the crossover unit.

LF driver (2231A) measures 6-7 Ohm, deviates doing measure.

HF driver measure (2470) 10.5 Ohm

UHF driver was not desoldered as I do not have time right now for that.

The nomimal impedances for LF are 8 Ohm and 16 Ohm for the HF and UHF.

MadsKaizer
12-30-2013, 08:34 AM
I had the same problem. Had to remove cone assembly spider and all and found the voice coil came loose from cone and became stuck in voice coil gap

It is both my LF and HF driver that lacks the bass response, that is why I suspected the crossover at first.

Mr. Widget
12-31-2013, 11:06 AM
It is both my LF and HF driver that lacks the bass response, that is why I suspected the crossover at first.What do you mean the HF driver is lacking in bass response?


Widget

MadsKaizer
12-31-2013, 04:34 PM
What do you mean the HF driver is lacking in bass response?


Widget

When I compare to my left speaker, all voice in HF lacks bass response, as in there are no deep tones, only the high pitched tones. The LF just lacks punch and depth. It is like a high pass filter suddenly was added.

MadsKaizer
01-02-2014, 11:07 AM
The problem have been fixed.

Turned out to be a bad solder joint from the flexible wires from the cone to the terminals on the bas driver. The solder joint looked okay, but re-soldering them really helped, the swinging resistance measurement is now stable at 6R6 Ohm.

The high resistance might have pulled the crossover down so the response also changed for the HF/middletone/horn driver.

subwoof
01-02-2014, 04:16 PM
you might find that the litz wires are corroded and this will happen again and again - many of my 2213's and 2203's had a similar affliction so my reconing center replaced the wires completely. It's a good long-term maintenance project.