Power amp for jbl 4343

[pyonc]

[QUOTE=martin2395;362859]Yes, not bi-amped. The biggest problem I had was that I couldn't get the bass to blend with the rest of the units. /QUOTE]

Hummmmm..... Bass overwhelming enough to dump mids/highs? How coudd it be, with your active crossover? That's new to me. Maybe your xover with 24db/octave gets into play here, compared with the 12db/octave of 4343's passive network. Just my guess.
According to the theory, 12dB per octave crossover slope will not cut off as much information above certain Hz, 300Hz in 4343's case, as fast as a 24dB per octave crossover slope. And steeper slopes do add complexity to the crossover, however, and depending on the system configuration, may have no real sonic advantage over 6dB or 12dB slopes, according to the theory.

[martin2395]

It's not overwhelming at all, It's simply not blending well with the mid/high section. It's like I mentioned before - a 3 way monitor with subwoofer added.
24dB should be even better because it cuts the woofers quicker giving less overlapping between the woofer and the midwoofer.

An interesting fact: the bass blends better when you use the 'LOW' terminals on the back of the cabinent but it loses a lot of power , connecting the speaker cable directly to the 2231/2235 gives the tightest and most powerful bass.
I really think that the 3143 with that rubbish rotary switch (even cleaned) is the problem.

[pyonc]

An interesting fact: the bass blends better when you use the 'LOW' terminals on the back of the cabinent but it loses a lot of power , connecting the speaker cable directly to the 2231/2235 gives the tightest and most powerful bass.

Really? That's surprising. Direct connection to woofers, not going through back binding posts, produces such tight bass?
If that's the case, I just wonder what's the whole purpose of these speaker terminals on the back.
Not just 4343, but the entire line of big JBL speakers with binding posts on the back.

[BMWCCA]

Really? That's surprising. Direct connection to woofers, not going through back binding posts, produces such tight bass?
If that's the case, I just wonder what's the whole purpose of these speaker terminals on the back.
Not just 4343, but the entire line of big JBL speakers with binding posts on the back.

Duhh!

I imagine you guys have talked about and tried lots of things to get the most out of the system. I will mention a few things that I would do if I had a pair at home for my primary system.

• Get rid of the bi-amp switch. Hardwire it in which ever mode you want it. The switch is not that great.
• If you can work out bi-amping do so. The difference in the 2245H and 2122H will be amazing. The crossover will have to be non standard. Neither driver is flat around crossover so the voltage drives will need to be adjusted to get proper acoustic bandpasses.
• The network components should be updated and this isn't easy. All the capacitors should be polypropylene and you would want to use air core inductors where ever possible. I believe the 4345 used some tapped iron cores. Those are hard to replace with aircores because the surrounding network topology would have to change and all of the values have to be re-engineered. I would suggest leaving them alone unless you are really good at this stuff.
• If you can swing it, go to a biased network. The difference is unbelievable.
• The ring radiator hates passive networks. A major improvement in the upper range would be to drive the 2405 from its own little amp. You only need 3 or 4 v rms. The 2405 does 110 dB for 2.83v. It is padded way down in the system. There is little real power at those frequencies anyway. You only need to know the voltage output of the amp, power is irrelevant. The 2405 is about 12 ohms and won't draw much current. I would use some little chip amp with a 2ond or 3rd order low level highpass in front of it. Take off the passive network to the ring and just feed it straight. Make sure the amp doesn't make a DC thump on turn on or turn off. That will fatigue the diaphragm. The amp will also have to have really low noise characteristics as any hiss will be really loud directly into the ring. I used to use an old Marantz 1030 integrated amp to run my rings. I could separate out the power amp section and the tweeters always sounded really good.
• The L-pads aren't so hot either, particularly after all of these years. Once you have your preferred balance, it is fairly easy to measure each leg of the L-pad and replace it with fixed resistors.
• I notice from many of the pictures that the system is elevated on blocks. It is very good to get the 2245 up off of the floor to minimize midbass fatness.

BFT is my emphasis.

[pyonc]

Hi BMWCCA,
Thanks for posting Greg's insight on this matter.
I wish I were tech savvy enough to do as Greg advises...
Anybody has done this before, like Greg advised?

[BMWCCA]

Hi BMWCCA,
Thanks for posting Greg's insight on this matter.
I wish I were tech savvy enough to do as Greg advises...
Anybody has done this before, like Greg advised?

My 4345s "clones" came to me with all of those mods except the separate amp for the UHF. I also don't run them on stands but I do have them on casters.

[Goldjazz]

.... I would look into building one of Nelson Pass's Class A amplifiers that are on the DIY Audio website. The Pass F5 Turbo V3 is good for over 100 watts of Class A amplification. Good Luck, Paul[/QUOTE]

Yeah another 4343 owner recommended that to me. This is something I want to do eventually. I think I'll first focus my efforts on restoring the 43's. So I'd like something to drive them with as soon as theyre done. I'd love to go Class A, but as you know getting anything above 100WPC in Class A is not easy, your Krell looks awesome. That's why I wanna understand the power requirments for biamping the 43's, cause there's so many Class A options around the 100WPC but from what I understand that's not enough juice.

There is available a Perreaux PMF3150 http://www.perreaux.com/assets/file/...48-PMF3150.pdf which puts out 300W, CLass A driver stage, Class AB output. I've read elsewhere that damping factor is around 400. Could be an option for the bottom?

[Goldjazz]

So this is the project, I haven't got them yet. They're B's, the serial numbers are around the 18000 and are closely matched.

[pyonc]

So this is the project, I haven't got them yet. They're B's, the serial numbers are around the 18000 and are closely matched.

Nice pair! Don't forget to have your 2121 drivers and 2231A woofers reconed with genuine JBL kits.

[martin2395]

The recone's are NLA for a long time now. They only way to restore them is to put new surrounds

[richluvsound]

You beat me to it Martin. They look good enough to re-foam .
Just re-build the networks to a CC version .

Rich

PS ….. you might find the F5 Turbo lacking … Good for Bi-amping ,but no very competent gripping a 15"

[Goldjazz]

You beat me to it Martin. They look good enough to re-foam .
Just re-build the networks to a CC version .

Rich

PS ….. you might find the F5 Turbo lacking … Good for Bi-amping ,but no very competent gripping a 15"

Yep I'm hoping just a refoam is required for the drivers. As for the charged coupled network I need to read up a lot more. Here's a link that I found useful about its benefits as applied to the k2 that other novices like myself may find helpful
http://www.lansingheritage.org/image...500/page12.jpg

Without knowing anything at all about the subject my immediate concern would be the change in voicing. I'm inclined to start with a recap that members would deem not too much of departure from the original sound and start by experimenting with single and biamp and external x overs. Then trying fancy improvements. I want to get a baseline of the orignal sound first without the influence of old caps and go from there.

[grumpy]

I want to get a baseline of the orignal sound first without the influence of old caps and go from there.

Note that you can do this by building up a CC network, and -not- charging it.
A bit more money (more caps) but not much more work. Then the next level
of comparison is just a 9v battery away

That's a really nice speaker find (like a minimum effort fixer upper in a nice neighborhood).

[Goldjazz]

Note that you can do this by building up a CC network, and -not- charging it.
A bit more money (more caps) but not much more work. Then the next level
of comparison is just a 9v battery away

That's a really nice speaker find (like a minimum effort fixer upper in a nice neighborhood).

Cheers. Ok so if a cc capable can be built that yields the original sound and easily flick between the constanr bias being on or off that would be cool, I would try that. If anyone can link to a suitable thread own that would be appreciated. I could start ordering the bits and building it if its external.

[Goldjazz]

Still on the hunt for good amplifications options for these 4343's so if anyone's had particularly good results please let me know what you're using. Was just checking out the specs of the Sansui B2301 power amp, looking through the service manual. Seems Sansui believed it was a good match for the 4333 at least judging by this image.