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Thread: Is it sacrelege? Am I evil? (long) - 4343 xover mods

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  1. #1
    Senior nOOb 4343mod's Avatar
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    Question Is it sacrelege? Am I evil? (long)

    I have a pair of 4343's, #13602 & 16644.
    I bought these off of a friend who drove them with an Acoustat.
    (Jim Strickland Trans-Nova amp, before Hafler)
    This amp has a big DC pulse on power up. You could actually see the 15's flex outward for a moment! De-mag/re-mag service of the 15's at JBL in Northridge is needed to bring the sensitivity back to spec. Someday I will get to it.

    I initially used them with (2) 350W Jeff Rowland Model 7 monoblocks for a year or so, when a horrible thing happened. The cheese rotary switch on the left monitor started shorting at very high levels. The first 2 or 3 times, the Rowland would step into standby, like a thoughtful amp should. Then late one night when I was touching the face of god, inraptured in sonic nirvana, it happened again, and 1 output rail on the rowland went. (12) TO-3 transistors, toast. Rather send the 120-pound amp back to Colorado for repairs, I sold them both as-is to a local dealer. What a shame.

    That was the last straw. An incredible system, with almost limitless dynamics taken down by a $.50 part. Yes, these are rated at 150W, and saw 300+W regularly. Very convincing reproduction of concert levels! No, this disaster would never have happened with flea SE tube amps, I know. And I wouldn't need a towel next to the listening chair, either!

    It became evident to me that the design of drivers and cabinet were first rate, (obviously) and that JBL cut corners on hardware and internal componets. I, C, and R in the XO's were not up to what these speakers could and did deliver. the (2) 2 Ohm Ohmite series resistors in front of the 2420's were powdered grey from overheating, and that POS rotary switch in the binding post plate was blasted as if it saw arc from a MIG welder. All level controls were ALWAYS set to max; to turn them down, you might as well put cotton in your ears or listen with the flu.

    IMO, R is sonically destructive in a crossover. It should be used as little as possible, unless you like a veil between you and the music. Pots are the worst; fixed value parts should always be used when possible.

    Now, having seen the crossover schematic, and tanking up ideas with a friend, it became clear the XO slopes were more for withstanding abuse and protecting the horns from distorting, poor quality, low powered SS amps, and less for clean transmission of signal. The 2 big caps in each XO were 'Lytic cans! 25 year-old chemical capacitors are not what premium sound is about! What if I made purist 1st order XO's with beefy, quality (if not premium) parts?

    On to the debauchery!
    I removed the OEM crossovers, wire, binding posts & plates. I disconnected the pots, though they are still in the cabinets, acting as hole plugs. I made a couple of post plates to accomodate (4) pairs of posts each. These posts are wired directly to the drivers. I then made a couple prototype XO's with air core inductors, Solen metalized film caps, and Mills NI resistors. Some non-NI resistors have found their way into the circuit, as padding for the 2420's. I use a NOS Centralab rotary switch on each channel to select different I values across the 2420, ususally set to .15 or .20mH. All wiring is point2point with Wonder Solder. Wire is garden variety Belden 16 gauge, except the LF circuits, which are Belden 14 gauge.

    This arrangement allows for single, bi, tri or quad amping, as well as *gasp* active filtering with an outboard device.

    Using the (6) OEM T-nutted holes on the back of the cabinets, I put screws through from the inside, thereby giving me threaded studs projecting from the back. The XO boards are mounted on these studs. No cutting, drilling, or other permenent changes were made to the cabinets. Everything is reversible.

    On to the sound!
    There is not 1 area of reproduction that has not been improved with these changes. If you have heard 4343's in OEM form, all I can say is imagine upgrading all of your electronics and cables up a couple of levels. That approaches the magnitude of improvement wrought by this. The Bob Harley analogy of "looking through several dirty windows then through 1 clean one" applies here. Macro dynamics have not changed much, but the micro dynamics, the little sparkles and shimmers of detail are stunning. I can hear into the images so much farther and with greater accuity than ever before. The speed of attack and decay is astonishing! Those that have not heard a 2420 horn with a single cap and resistor in series are missing something.

    The bass response is more natural. Going from a 2nd order slope with an old, dried up 120uF 'lytic cap and tiny 20 gauge, 5uF inductor to 1st order with a 16 gauge, 9mH ERSE inductor is amazing. The boxiness is gone. The tonality and weight has taken shape like never before. The 15's play louder with less coloration. And the 15's are not even performing at spec sensitivity! Why would anyone use electrolytic caps in a high performance XO? And after 25-30 years, do you think the 120uF value is still stable? No way.

    All I can say is the OEM XO's are slow, veiled, garbled, soft JUNK.
    What a travisty to put this in front of such wonderful Alnico compression drivers.

    I welcome any JBL enthusiast in the Los Angeles area to drop by and have a listen. It may be a sin, but it sounds Soooo good.
    Any comments, slander or suggestions are welcome!

    Thanks for reading this, Andy Bacon

    System info:
    244VAC, 2-pole breaker out of a 100A load center into
    PowerStat 260V, 30A Variac, stepped down to 220VAC into
    Topaz/Square-D 5kVA Ultra-Isolator line noise supressor (transformer) lifted ground, ~120VAC into....

    Meridian 588 24-bit CDP, balanced out
    Harmonic Technology TruthLink, XLR
    Classe' CP-60 pre, balanced out
    Harmonic Technology TruthLink, XLR
    Crown Studio Reference1 or Krell KSA-200S
    Analysis Plus Oval9
    JBL 4343 Modded Macro Monitors!
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    Last edited by 4343mod; 10-17-2003 at 01:10 PM.

  2. #2
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Re: Is it sacrelege? Am I evil? (long)

    Originally posted by 4343mod
    What if I made purist 1st order XO's with beefy, quality (if not premium) parts?

    On to the debauchery!
    Whoa... Impressive, and beautiful syntax, besides !

    Any chance you could post a schematic of the final XO, and what slopes you elected to use?

    I would love the TasteTest, and will take the offer if I get close enough. Much to think about with my 4345's - regretably, for now I can only imagine the improvements you describe... , even though I think I lack for nothing!

    I think I'm getting that "Audiobeer Sensation"...
    bo

    "Indeed, not!!"

  3. #3
    Senior nOOb 4343mod's Avatar
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    I will post the OEM schematic that I got from JBL (don't remember what the model number is for the 4343 crossover) and my 1st order schematic when I find them. They have been burried and have been through 2 moves since I made the changes. I know they are around here somewhere!

    Thanks, Andy

  4. #4
    Senior Member Ian Mackenzie's Avatar
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    Andy,

    Excellent work and I admire Can Do Attitude, Enjoy.

    Yes, the cheap wire wounds ceramic power resisters scrub the sound somthin horrid compared to the Mills.

    Caps have also come along way in the past 25 years and I suspect your newer caps certainly grace the results you now have.

    I would turf the 120 uf electros (they sound cloudy & soft) and others and replace with a Solen or AEON and bypass with film & foil for starters, Hovland is better again but need to redraw on your mortgage got those.

    I accept 1st order slopes do have better transient transfer function and I hear this in my Century 100's but not sure on the final result with the 4343 response.

    Bo's 4345's xovers and my soon to be complete 4345 diy have tapped inductors to eliminate the fixed pads and power disipation issues.

    I find the variable faders however are useful for fine tuning the balance though, particularly when you have 4 drivers to trim and wifey who likes to move your cabinets around for the visitors in advance. The newer 100 watt faders from PartsExpress appear to be very good quality, but have not taste tested with Mills in comparison (nichrome wire vs well wire of some sort??)


    What is the Analysis Plus Oval9?

    Have fun......

    Ian






  5. #5
    Member JonFairhurst's Avatar
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    A sin? No. More like an act deserving sainthood.

    Painting black and white cow colors on a Paragon is a sin. Putting the best available components under the hood just makes the best use of an already great speaker.

  6. #6
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    "Painting black and white cow colors on a Paragon is a sin."

    Ooops!

  7. #7
    Senior Member Guido's Avatar
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    Re: Is it sacrelege? Am I evil? (long)

    Originally posted by 4343mod
    I welcome any JBL enthusiast in the Los Angeles area to drop by and have a listen. It may be a sin, but it sounds Soooo good.
    Any comments, slander or suggestions are welcome!

    Thanks for reading this, Andy Bacon

    For me it's too far to test it

    Anyway thanks for that post. Could you help us with a schematic of your mod X-over?

    This would be highly appriciated for shure!
    BLS Reference on Passlabs XA 30.5 + Everest DD66000 clone on Pass XA 100.5

  8. #8
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    I would love to hear a pair of biased 4343B's

    There has to be a way to get the good caps at a decent price. A Dayton 3.0 uF MPP goes for $1.67 and does sound a bit better than the Solen MPP that goes for $1.95 but the AudioCap PP&F that goes for $18.64 just blows them both completely away. It's just such a high price to pay, especially if you bias them. Just off the top of my head I would imagine a pair of biased 4343 networks would run nearly a grand?

  9. #9
    Your Memory Lives On RIP Tom Loizeaux's Avatar
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    I found your post on replacing the crossovers in your 4343s very interesting - since I have recently aquired and re-habbed a pair myself. Following advice I got here on the JBL Forum, I added bypass film/foil caps throughout the crossovers. I also only run these in the bi-amp mode, therefore going around the largest caps.
    I did not do a "before/after" test, but I find the results very satisfying.
    I wonder how much more detail and accuracy I might still find if I completely re-did the crossovers from scratch.
    Wouldn't putting jumpers accross the rotary switches, replacing all the caps and resistors, and hard wiring past the pots do the same job?

    I'm interested in hearing responses.

    Tom

  10. #10
    Senior Member Guido's Avatar
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    Hey Giskard,

    is this what you call a AudioCap PP+F ?

    I buy 3,3 uF for approx. 8 USD.

    If you have a bigger order then maybe I can help.
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    BLS Reference on Passlabs XA 30.5 + Everest DD66000 clone on Pass XA 100.5

  11. #11
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    Hi Guido,

    AudioCap

    They are from the Reliable Capacitor company.

    *****

    The price for them is just too high, especially for 10% tolerance, but they sound so damn fine.

    I've been told the Audyn-Cap is quite good and $8 sounds much better.
    Last edited by 4313B; 10-17-2003 at 05:30 PM.

  12. #12
    Senior Member Guido's Avatar
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    Normal price here is appr. 14 USD.

    So if anyone needs big caps in higher amount (think of the shipping Europe > USA) then I will be glad to help.

    Just drop an PM
    BLS Reference on Passlabs XA 30.5 + Everest DD66000 clone on Pass XA 100.5

  13. #13
    Dis Member mikebake's Avatar
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    Ian, what Parts Express fader are you refering to? Perhaps a link?

  14. #14
    Senior Member Ian Mackenzie's Avatar
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    Mike,

    Partsexpress.com

    Item 260-265 which I sourced locally

    Ian
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  15. #15
    Senior Member Ian Mackenzie's Avatar
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    These guys have some values of the Hovlands on special:

    They are a smooooooth wipped cream on the slots and affordable in those values

    http://www.welbornelabs.com/hov.htm

    Ian
    Last edited by Ian Mackenzie; 10-18-2003 at 12:52 AM.

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