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solenoide
01-11-2009, 06:49 AM
Hello,
i have just received my first pair of JBL ever.
Unfortunately the seller was so far that i had to trust him , he described the 4343 as "near mint".
As soon as i received them i realized that biamping wasn't possible.
I opened the speakers and i found that the crossover was rewired to eliminate the biamp switch.
36465

36466


Could you please help me with some suggestions?
Have i to rewire the 3143 as before? make a new crossover?(i will not be able to do it by myself)
May i separate the bass part from the rest so that i will be able to passive biamp the speakers?(i already own two power amps)
36469


Thanks

hjames
01-11-2009, 07:02 AM
I don't know how technical you are, so I make apologies now if I speak too complicated or too simply.

You don't want to feed full-range sound to your woofer alone, and don't want to send full-range with bass to your mid and hi side ...
Feeding fullrange signal to 2 parts of a speakers system is called biwire, and the big 4-way JBLs were not designed for that, they were designed for bi-Amping, which requires the use of an active crossover unit.

If you just want to get this working, the fastest approach is to skip the biamp switch anyway,
they have been known to fail when the switch contacts tarnish and wear.

This is kind of quick and dirty but will work for now.

You should have 2 sets of input connectors on the back of the cabinet.
One set should go directly to JUST the woofer. There should be no other connections to that pair or to the woofer.

The other pair of connectors should go directly to your internal passive crossover network.
The wires on the internal crossover that would have fed the woofer need to be taped up
so they cannot connect to anything and get shorted out.

This means that the second connector will feed signal to only the 10 inch mid-Bass driver, the horn driver and the slot tweeter.

You WILL need an active crossover to split your preamp out signals at 290-300Hz ... the LOW split output goes to the more powerful amp and then to your woofer-only connectors, the High split output goes to your cleaner amplifier and then to the high side connector.




Hello,
i have just received my first pair of JBL ever.
Unfortunately the seller was so far that i had to trust him , he described the 4343 as "near mint".
As soon as i received them i realized that biamping wasn't possible.
I opened the speakers and i found that the crossover was rewired to eliminate the biamp switch.


Could you please help me with some suggestions?
Have i to rewire the 3143 as before? make a new crossover?(i will not be able to do it by myself)
May i separate the bass part from the rest so that i will be able to passive biamp the speakers?(i already own two power amps)



Thanks

Robh3606
01-11-2009, 07:03 AM
Your PDF is not showing. Have you ohmed it out to see exactly what he did?? Can he provide you with a schematic?? Do you have an active crossover to use to biamp the speakers??

If you planned on doing a passive biamp from the outset it wouldn't have worked anyway. Having the switch wired out may not be a bad thing depending on how he hard wired it. If its set-up for fullrange you have your work cut out for you.

Rob:)

Robh3606
01-11-2009, 07:10 AM
Are you sure that schematic is correct?? If it is you can passive biamp them as is providing the High and Low frequency binding posts are really isolated. Just hook up one amp and change the connection from low to high to make sure they are isolated. To do it with an active now would not be all that hard either.

Rob:)

4313B
01-11-2009, 07:15 AM
Use this schematic for a bi-amp only version of the 4340/4341/4343 systems:

3140 network.pdf (http://www.jblproservice.com/pdf/Network%20Schematics/3140%20Network.pdf)

solenoide
01-11-2009, 07:29 AM
Hello,
thank you for your replies.
Sorry , i think i have confused some of you.
I have modified the original schematics just to let you know what i would like to do.(biwiring)
I have no technical skills and as far as i understand from your replies it is not possible to biwire the 4343 and passively biamp them without an external crossover( i do not understand why:barf:), is it correct?
I have an active crossover but i do not like it (Tannoy xO5000).
The problem is that the previous owner cut away all the original wires ( i can take better pics if necessary) and i won't be able to go back to the original wiring.( i have no skills and instuments to measure what he did)
I have also read all your precious efferts for new crossovers and upgrades but i will not able to make a new crossover by myself.
Is someone of you manufacturing and selling new crossover ? i live in Italy.

hjames
01-11-2009, 07:35 AM
If you are to do biwire, you need different circuitry in the cabinet than what JBL provided from the factory.
It can be done, but thats custom circuitry and its just not very simple for a non-technical person.

From a glance at the photos you provided I am guessing that the original JBL crossover in the metal box is intact, and that most of what the previous owner did was to simply eliminate the faulty biamp switch, which is a known weak point in those systems.

JBL originally made an active crossover unit for their studio monitors, they were customized for each individual model by the use of plug-in cards.
That's older tech now.
They later provided an adjustable crossover system, the JBL/UREI M552.
I used one of those on my biamped 4341s, but last year I replaced that with an Ashly XR1001 which seems to be better performance and quieter.
Depending on your budget there are other options that are quite good if pricier - but I am less familiar with them as I am more budget driven.



Hello,
thank you for your replies.
Sorry , i think i have confused some of you.
I have modified the original schematics just to let you know what i would like to do.(biwiring)
I have no technical skills and as far as i understand from your replies it is not possible to biwire the 4343 and passively biamp them without an external crossover( i do not understand why:barf:), is it correct?
I have an active crossover but i do not like it (Tannoy xO5000).
The problem is that the previous owner cut away all the original wires ( i can take better pics if necessary) and i won't be able to go back to the original wiring.
I have also read all your precious efferts for new crossovers and upgrades but i will not able to make a new crossover by myself.
Is someone of you manufacturing and selling new crossover ? i live in Italy.

porschedpm
01-11-2009, 09:49 AM
Your best bet may be to reassemble it and enjoy it full range using one amp. Then worry about converting to bi-amp after you've figured out what amps and active crossover you'll use and how to restore the wiring on the 4343 to accomodate bi-amping again. Or hard wire it for 'bi-amp only'.

I wouldn't recommend spending time trying to bi-wire these. IMHO, the gain in bi-wiring vs running conventional full range is not enough to justify essentially rewiring the crossovers to do it.

On the other hand, the gains in sound quality you'll get from bi-amping vs full range or even bi-wiring are significant enough to justify the the time and trouble to convert them back to bi-amp-able. Plus since the 4343/3143 were originally set up to accomodate bi-amp or full range operation, and it appears the previous owner merely hard wired the bi-amp switch to full range, to wire your 4343s to bi-amp only should be just a matter of reattaching the wires that were cut.

scott fitlin
01-11-2009, 10:04 AM
See the blue resistor? THAT is a Riken Ohm Carbon Compostion Resistor, AND I THINK THEY SOUND GREAT.

:D

solenoide
01-11-2009, 02:34 PM
I will bring the crossover to a technician , i found a picture of 3143 and my crossover looks quite different.
Also the soldering looks awful , i will ask the technician to bring the crossover to the original specs , switch included, maybe new caps and nothing else.
I listened to the 4343 in the afternoon and i won't be able to live with them , too bright and lean for me ( i am used to british speakers)
I really hope that with restored crossover they will sound different.

BTW , aren't Riken resistors 0.5 or 1W only? i can't see any 0,5 or 1 watt resistor on the schematic , shound't be 10 W at least?

Robh3606
01-12-2009, 06:02 PM
I listened to the 4343 in the afternoon and i won't be able to live with them , too bright and lean for me ( i am used to british speakers)


Try dialing down the midrange horn a couple of dB a bit. Then try the 2405. If they are set for 0 they may sound a bit bright. Might wabt to bring the 2121 up a bit as well. Do you have any pictures so we can see what they look like. Do the 10" migs have yellow surrounds??

Rob:)

solenoide
01-13-2009, 05:07 AM
Hello Rob,
I am listening with lpad for 2420 down to -2 , 2121 +1 and 2405 flat.
Surrounds are grey and looks very good , i will post some picture later.
Ciao

solenoide
06-20-2009, 09:21 AM
Hello,
after few months i have decided to take my 4343 but i still have to restore the crossover that was rewired to monoamp only.
I would like to build a rear input panel with 5 pairs of binding post in place of the rotary switch.(similar to the Tannoy FSM panel)
Could someone let me know if it is correct ? maybe there is an easier solution...
Thanks :)