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Thread: Modifying L150A's for bi amp use - Technical advice needed!

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    Senior Member DerekTheGreat's Avatar
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    Modifying L150A's for bi amp use - Technical advice needed!

    Hello everyone!

    Now that I've finally got my L150A's back on the road again I think the next project to get the most from them is modifying them for bi amp use. Here's what I intend to drive them with, either a pair of Marantz 250M's or 510M's. I've already got one 510M so I figure another 510M is the easiest route to go. However, there's a member here who is running 4345's using two older Crown amps (forget the model #) and I might go that route depending on what the budget allows.

    I'm new to pretty much everything. But from the research I've done so far, it looks like I can go two ways with the project:
    1) Bypass the internal crossovers completely and use something like an Ashly XR2001 or a pair of XR1001's.
    2) Modify the existing crossovers for bi amp use.

    #1 seems pretty straight forward, but I'm not sure how to set the crossovers up and would want advice there. Seems like 1 channel could cover the woofers but then I'd need two use two for the mids, 1 as a high pass and one as a low pass so that the midrange only plays 1100-3700hz and then just one high pass for the tweeters which handle everything above 3700hz. Is that the gist of it? What am I missing?

    #2 seems straight forward as well but with more work needed. First, I'd need someone kind enough to outline how the crossover network needs to be modified in order to isolate the 128H from the LE5-12 and 044 tweeter. Then I'd like to know which wires you fine folks would recommend to rewire it all as well as capacitors and binding posts. I'd also like to bypass the level pots for the mids & tweeters as well and would need wiring advice there. I'm kind of leaning towards this route but I don't see any spare L150A crossover networks available and while I realize the L112 is the same from a component standpoint, there are differences between the two, the main one being that the binding posts and the XO board arent fastened together. So I'm not sure if a board from an L112 will fit the plastic nibs on the inside of my L150A's. However, there are currently a pair of L112 XO's for sale on the 'bay.

    Semi related question:
    The pots for the midrange and tweeter.. They have a zero position and then positive and negative positions... My question is, aren't those things just variable resistors? If that is kind of how they operate, wouldn't "+3" (max position for them) be the same as zero resistance? On that note and if correct, isn't "0" actually some form of resistance the engineers incorporated into the system so that the frequency response at those positions is close to flat as possible like shown in the sales literature? Reason I'm asking is because I use an Audio Control C101 equalizer, and I've realized that the less unneeded signal I throw at my amplifier, the more headspace it has for signal I do want. So, I'm looking to use the C101 to attenuate the levels of the tweeters & mids rather than the pots by simply adjusting the pots to +3 and then pulling back on frequencies 1100hz-20khz with the C101. Hopefully this makes sense and someone could shed insight on this, I'd love clarification. Feel free to bash me as necessary haha.

    Thank you for your input!

  2. #2
    Administrator Robh3606's Avatar
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    It's not as easy as you think to bi-amp. You have to model the filter section for the midrange, remove the highpass pole/s and see what changes there are to the voltage drive. You may have to change part values in the other poles to keep the same voltage drive. All these crossover parts in a filter section "talk" to each other so removing one or more can have unforeseen consequence's.

    As far as Tri-amping with no network again you have to see what the voltage drives are to each driver. Using analog crossovers may not do the trick. May have to use DSP based depending of the individual voltage drives. An example being L2 which I believe has a significant DCR component close to 8 ohms and is used to flatten the rising response of the midrange driver. They are also 24DB L/R fixed slope and will not match the crossover slopes in the passive networks. The speakers may use the same drivers but with different slopes may not sum or sound the same. You won't have L150's anymore. That's fine as long as you understand the implications. If you really really like them leave them be.

    https://manuals.harman.com/JBL/HOM/T...L150A%20ts.pdf


    http://www.audioheritage.org/vbullet...The-LE5-Matrix

    JMHO I don't think the effort required to do this is going to be worth the results as far as a difference between passive vs. active all said and done.



    Rob
    "I could be arguing in my spare time"

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    Senior Member DerekTheGreat's Avatar
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    Really? The only thing I have to go by is my Northridge E90's downstairs. They're biampable and before I could do that to them I used the factory supplied shorting bars between the hi and low drivers. Those things improved quite a bit in sound quality and bass response when I moved to a receiver which supported biamp on it's own. I couldn't find a schematic for E90's specifically but here's one for E100's which operate the same way and use the same mid & tweeter. Only they've changed the crossover frequencies between the 90 and 100's.. https://manualzz.com/doc/19702299/
    But according to that, there is nothing special which detects whether you've got your stuff bi amped or not and then adjusts the network accordingly, which is why I thought I could modify a set of crossovers for the L150A's with a soldering iron, some fresh caps and two sets of binding posts..

    As for triamping, I just figured I'd use one of those Ashly crossovers or a DBX DriveRack 260 to handle the level adjustments and crossover frequency ranges for each of the drivers, dial it in by ear just like with equalization. I have yet to meet a speaker that didn't sound too forward to my ears initially. The detail & precision of them always goes up when I attenuate stuff between 900hz & 8khz, mostly the 900hz to 4khz range. But I'd also just use those things to lower the level down along with a microphone to get a baseline of where everything is.

    Speaking of equalizers, would you mind sharing your opinion on my last paragraph from my initial post?

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    Senior Member rdgrimes's Avatar
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    Quote Originally Posted by DerekTheGreat View Post
    Really? The only thing I have to go by is my Northridge E90's downstairs. They're biampable and before I could do that to them I used the factory supplied shorting bars between the hi and low drivers. Those things improved quite a bit in sound quality and bass response when I moved to a receiver which supported biamp on it's own.
    Not really a good comparison, nor did you have them in a true bi-amp. What you actually did was just increase the power a bit.

    My $.02 for the L150A is to just feed them copious watts and forget messing with crossovers. Although you could refurbish the existing XOs. My experience with them was 200+ WPC is best, more is better. At one point I tickled them with 1000WPC from a couple of bridged Carvers and they didn't break a sweat. IMHO, active crossovers and bi-tri amping is more likely to produce significant results with speakers a lot further up the food chain. And the existing OE crossovers are quite capable of resolving even high-res audio sources extremely well.

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    Quote Originally Posted by rdgrimes View Post
    Not really a good comparison, nor did you have them in a true bi-amp. What you actually did was just increase the power a bit.

    My $.02 for the L150A is to just feed them copious watts and forget messing with crossovers. Although you could refurbish the existing XOs. My experience with them was 200+ WPC is best, more is better. At one point I tickled them with 1000WPC from a couple of bridged Carvers and they didn't break a sweat. IMHO, active crossovers and bi-tri amping is more likely to produce significant results with speakers a lot further up the food chain. And the existing OE crossovers are quite capable of resolving even high-res audio sources extremely well.
    what he said
    well put mister

  6. #6
    Senior Member DerekTheGreat's Avatar
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    I appreciate the responses fellas, I really do! I'm trying to learn here.

    Indeed, not a good comparison but the only actual one I have to go by. It was true bi amp though? The Marantz SR7005 downstairs is a 7.1 receiver with switchable amps for the 7.1 aspect.. So in SPKR-C mode it uses the amps that would normally drive the center surrounds to drive the L&R channels. I've got a set of wires going from one bank of the receiver's amps to the E90's tweeter & mid section and another set of wires going from that other set of amps to the woofers of the E90's. How is that not biamping?? Crucify my ignorance where you see fit but from what I've read, that's how it's done... And with the set up running like that, I noticed that when driven hard, there was noticeably less break-up in the upper & mid ranges and the bass was more.. present. Even when driven to what I felt certain was clipping range before. So with that experience in mind, that's why I was curious about going that route with my L150A's.

    As mentioned previously, am open to going alternate routes. When I had my 510M serviced, it was rated at 305WPC on both channels before clipping. Sounds great now that things are as they should be thanks to edgewound and his company, Upland Loudspeaker Service. Trying to drive them with the old Marantz 4300 is what nudged me off the fence to go old school component Marantz. Which is something I did to channel my dad.. But I did indeed fall in love with the Marantz sound. It blew away the Harmon/Kardon, RCA and Yamaha receivers I had lying around for comparison. So I don't mind feeding them more power but what amps would give me that sweet, smooth warm sound like I've got with my Marantz 510M? Also, when you drove them with 1000watts did you curtail the low end at all? Greg Timbers himself said the 128H isn't really suited to subwoofer duties but these things do dig low. Last night I played with them and noticed if I leave the 30hz adjustments flat at 0dB, whoo boy do those woofers move a whole lot compared to -6 or more dB attenuation. I can only imagine how they'd move with more than double the horsepower if you know what I mean lol. 'Cause if it wasn't for those clip lights flashing, I'd have tried to drive them harder. Oh and according to Marantz literature about the 510M, those are meant to light up & flicker before clipping happens, that there is something intrinsic to the circuitry that when approaching that point, it'll hold some juice to the indicator lights so the user sees a flash. That full on illumination is when actual clipping is reached..

    UPDATE: I played with the potentiometers for the mids & highs last night. Control run with them dialed back at ~-2.3 for tweets and ~-2.6 for mids vs +3 across the board didn't really have an impact as to when I saw the clip lights flicker on the 510. So I dialed them to 0 everywhere and used the C101 to attenuate the harshness like I've done for other speakers.

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    spend some time listening to music
    just listening to some music

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    Senior Member DerekTheGreat's Avatar
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    How should I go about modifying the factory crossover?

    Would anyone with electrical knowledge be kind enough to outline how rebuild & modify the factory crossovers for bi-amp use? Or at least recommend an amp with 500watts per channel or more which has a sound similar to my Marantz 510M & 3600 preamp combo?

    There is this guy who offers ready made crossovers for the L150A and many other models:
    https://www.ebay.com/itm/153430117101
    But I've messaged him twice now with no response regarding if he'd make a network which supports biamping. He hasn't responded in regards to what he'd like for a pair of his standard crossovers either. So I'm not sure I'd take the gamble with his stuff based on his lack of communication.

    So short of that guy, my only option is redo the things myself. From the factory schematic I know what values to use for capacitors and inductors, but what brands would you guys run with and what type of wire? Also, if no one recommends a mightier amp, what needs to be done to properly bi amp these things? Thank you for your time and assistance, it really is appreciated.

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    Quote Originally Posted by DerekTheGreat View Post
    Would anyone with electrical knowledge be kind enough to outline how rebuild & modify the factory crossovers for bi-amp use? Or at least recommend an amp with 500watts per channel or more which has a sound similar to my Marantz 510M & 3600 preamp combo?

    There is this guy who offers ready made crossovers for the L150A and many other models:
    https://www.ebay.com/itm/153430117101
    But I've messaged him twice now with no response regarding if he'd make a network which supports biamping. He hasn't responded in regards to what he'd like for a pair of his standard crossovers either. So I'm not sure I'd take the gamble with his stuff based on his lack of communication.

    So short of that guy, my only option is redo the things myself. From the factory schematic I know what values to use for capacitors and inductors, but what brands would you guys run with and what type of wire? Also, if no one recommends a mightier amp, what needs to be done to properly bi amp these things? Thank you for your time and assistance, it really is appreciated.

    Derek,

    What you are wanting to do is called "Passive Bi-Amping" ( versus Active Bi-Amping ).

    Two amps are still used but Passive Bi-Amping uses the speakers builtin passive crossover components .

    Perhaps you should try that contacting that seller one more time, this time using a change of language ( terminology ) within your communication .


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    Senior Member grumpy's Avatar
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    Other than adding a pair of terminals and clipping one connection (ok, two connections to prevent blue-smoke-type boo-boos), I'm not seeing this (passive bi-wiring 'mod') as being particularly difficult.

    The L150A schematic was posted above, I believe. Also, aren't the L112 and L96 networks the same?

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    Quote Originally Posted by grumpy View Post
    Other than adding a pair of terminals and clipping one connection (ok, two connections to prevent blue-smoke-type boo-boos), I'm not seeing this (passive bi-wiring 'mod') as being particularly difficult.

    The L150A schematic was posted above, I believe. Also, aren't the L112 and L96 networks the same?
    yes, the L150A is a L112 in a bigger box with a passive radiator instead of a port
    networks are identical same as driver compliment

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    JBL Custom Work

    Just contact these guys, tell them what you want and they'll fix you right up

    Arguably the best JBL custom shop there is

    Well established and 100% legit

    here ya go:
    http://jbl43.com/?mode=f3

  13. #13
    Senior Member DerekTheGreat's Avatar
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    Quote Originally Posted by Earl K View Post
    Derek,

    What you are wanting to do is called "Passive Bi-Amping" ( versus Active Bi-Amping ).

    Two amps are still used but Passive Bi-Amping uses the speakers builtin passive crossover components .

    Perhaps you should try that contacting that seller one more time, this time using a change of language ( terminology ) within your communication .

    Thank you Earl, I will try that again using "passive Bi-Amping" instead of "Bi-amping" like I was. That is exactly what I want to do; use two amps with the built in crossover, just modified to support it of course.

    Quote Originally Posted by grumpy View Post
    Other than adding a pair of terminals and clipping one connection (ok, two connections to prevent blue-smoke-type boo-boos), I'm not seeing this (passive bi-wiring 'mod') as being particularly difficult.

    The L150A schematic was posted above, I believe. Also, aren't the L112 and L96 networks the same?
    Thank you for your response, grumpy. Indeed it was, and I had previously downloaded the schematic myself for reference. I originally thought the same thing but another member posted this which made me question what I'm about to do:
    "Robh3606:
    It's not as easy as you think to bi-amp. You have to model the filter section for the midrange, remove the highpass pole/s and see what changes there are to the voltage drive. You may have to change part values in the other poles to keep the same voltage drive. All these crossover parts in a filter section "talk" to each other so removing one or more can have unforeseen consequence's."

    If I can ignore this and do like you say, then I am eyeballing these L112 crossovers:
    https://www.ebay.com/itm/153782685687
    But when I went to put my 128H's back in place, I noticed that while the crossovers may be identical, there look to be slight differences in the boards themselves and wiring lengths which mean the L112 board might not fit where the original L150A board is and the wires won't reach. The L150A board is mounted mid cabinet away from the terminals whereas the L112 board is fastened directly to the terminal board.. I don't know the dimensions between them though, so just drilling holes in the new boards to fit the plastic nubs on the L150A's cabinets might not do it.

    Lastly, while I can make out where the caps & inductors are in the schematic, I really can't read them as well as you guys can. And the board isn't exactly laid out as obvious as that schematic so if you wouldn't mind tossing a fella a bone by indicating where to cut and splice in the second set of terminals that would be incredible. Also, while I'm there, I'd like to rewire & redo all components from caps to inductors if you guys think it is worth it. But what brands of stuff to use (wire, caps & inductors) and where to source them? Also, could I get rid of the pots without affecting the crossover network in a negative way or would things need to change? Based on the schematic, they just look like variable resistors, so it seems like if I got rid of them, I'd need to measure what they are currently and replace them with that resistor, right? (Currently all four are set to "0")

    Quote Originally Posted by Michael Chavez View Post
    yes, the L150A is a L112 in a bigger box with a passive radiator instead of a port
    networks are identical same as driver compliment
    Please see my response to Grumpy's response, your input here is appreciated. I don't want to go spending ~$150 only to have to resell the things..

    Quote Originally Posted by Michael Chavez View Post
    Just contact these guys, tell them what you want and they'll fix you right up

    Arguably the best JBL custom shop there is

    Well established and 100% legit

    here ya go:
    http://jbl43.com/?mode=f3
    Thank you Michael! I had a look around, even when translated I'm not sure how to email them my request. And Grumpy has me feeling confident I can modify the network easily to support passive biamplification.. Which button would I click on to send them an email and do they understand English or should I translate it first??

    Thank you for the responses fellas! Truly appreciated, please keep them coming.

  14. #14
    Senior Member BMWCCA's Avatar
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    Before I'd spend $150 on two L112 crossover networks that I'd still have to modify, I'd go out and find a pair of L7s which come as bi-wired and even provide for active bi-amping through an internal jumper connection. But that's just my opinion.

    I own L112, L150A, and two pair of L7s (among others). The L112 I've owned since they were new and they've always been a second system. L150A I bought . . . just because I liked the idea of an even more robust L112. L7 I bought because I'd read so much about them and they were offered three houses down the street. I liked them so much I bought a second pair when they came up 100-miles away—for the same price ($200). In my humble opinion, they blow away both the L112 and L150A which I really do like.

    I would think more power feeding the L150A without modifying anything would likely produce the same result as active bi-amping, but then what do I know—I bi-amp my 4345s because they're designed for that and I have no other choice.
    ". . . as you have no doubt noticed, no one told the 4345 that it can't work correctly so it does anyway."—Greg Timbers

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    Senior Member DerekTheGreat's Avatar
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    Quote Originally Posted by BMWCCA View Post
    Before I'd spend $150 on two L112 crossover networks that I'd still have to modify, I'd go out and find a pair of L7s which come as bi-wired and even provide for active bi-amping through an internal jumper connection. But that's just my opinion.

    I own L112, L150A, and two pair of L7s (among others). The L112 I've owned since they were new and they've always been a second system. L150A I bought . . . just because I liked the idea of an even more robust L112. L7 I bought because I'd read so much about them and they were offered three houses down the street. I liked them so much I bought a second pair when they came up 100-miles away—for the same price ($200). In my humble opinion, they blow away both the L112 and L150A which I really do like.

    I would think more power feeding the L150A without modifying anything would likely produce the same result as active bi-amping, but then what do I know—I bi-amp my 4345s because they're designed for that and I have no other choice.
    You're the same guy I referenced in a similar thread about biamping
    Indeed, I think about 5 or 600 watts would do it, but I need a recommendation of which amp or amp preamp combo would give me the warm, sweet sound I like from my Marantz 510M & 3600 preamp combo. I don't really want to move away from that as I built it to channel my father. And as for replacing the 150A's, that's a possibility, although they'd go downstairs. I've got close to $3k in them, so selling them would hurt my butt just wayyy too much at this point and I do like the sound quite a bit. There are plenty of L7's for sale though. I was looking to maybe purchase a set of XPL-200A's in the distant future to replace the L150A's...

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