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Thread: Electronic crossover questions - JBL L300

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    Electronic crossover questions - JBL L300

    I've been experimenting with bi-amping my L300's and had a few crossover questions. I currently have them set up in a "passive" bi-amping config, the internal xovers are split into two separate sections for the HF and LF. Each hooked up to their respective sets of binding posts. I have a 12wpc Fisher X-101ST el84 amp feeding the HF drivers, and a Crown Com Tech 800 on the woofers. These amps are controlled via a Juicy Music Blueberry pre. I am able to dial in a nice and balanced sound by tweaking the gain knobs on the amps, as well as the Lpads on the L300s.
    My question is, I keep reading about how superior an "active" biamped setup is with an electronic crossover - so I'm wondering if I am missing out on better sound, or maybe subjecting my amps to avoidable stress by not using an electronic crossover?
    From what I've read, with an electronic crossover you need to bypass the internal crossover completely and essentially wire the binding posts directly to the drivers? I can imagine how to do this on the woofers, but what about the tweet/mids - if I'm only using two amps?
    Or should I just leave it as is and relax?
    Any guidance would be great, thanks.

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    Senior Member ivica's Avatar
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    Quote Originally Posted by Crestwood23 View Post
    I've been experimenting with bi-amping my L300's and had a few crossover questions. I currently have them set up in a "passive" bi-amping config, the internal xovers are split into two separate sections for the HF and LF. Each hooked up to their respective sets of binding posts. I have a 12wpc Fisher X-101ST el84 amp feeding the HF drivers, and a Crown Com Tech 800 on the woofers. These amps are controlled via a Juicy Music Blueberry pre. I am able to dial in a nice and balanced sound by tweaking the gain knobs on the amps, as well as the Lpads on the L300s. My question is, I keep reading about how superior an "active" biamped setup is with an electronic crossover - so I'm wondering if I am missing out on better sound, or maybe subjecting my amps to avoidable stress by not using an electronic crossover? From what I've read, with an electronic crossover you need to bypass the internal crossover completely and essentially wire the binding posts directly to the drivers? I can imagine how to do this on the woofers, but what about the tweet/mids - if I'm only using two amps? Or should I just leave it as is and relax? Any guidance would be great, thanks.
    Hi Crestwood23,

    1. I think that not too much 'upgrade' can be get comparing single amp or dual amps driving passive networks,
    2. owing to the fact that the bass section of L300 network consist of 2.2mH coil and 20uF ( fn=750Hz) the interaction
    of the network and bass driver mechanical and acoustical parameters are weak so I would not expect too much
    'improvements' with active network driven bass driver.

    My experience with L300 clone is:

    1.- network upgrade to for VHF section ( LE85/ 2420J ) inspired by Mr.Nelson Pass work on L300 network upgrade.
    My network change attached
    2.- VHF upgrade to 2441J+2311+2308 ( 2441J + H93 + H90), May be easier can be ( and much, much more affordable) to find 2445J instead of 2441J.
    Problem can be to find a pair of horns H2311 (horn == H93), that perfectly fit L300 baffle hole from VHF driver.



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    Thanks for the reply ivica. I currently have the Nelson Pass networks installed. The HF section has been separated from the LF and is currently set up for passive biamping with 2 sets of binding posts for each cabinet. It has been my experience so far that a big sonic improvement is heard when I hook my tube amp up to the HF section, and the Crown up to the LF. Sound is much better than using either single amp and putting straps on the binding posts.
    I do not want to replace any drivers, just wondering if the sound will improve if I bypass the internal xover and go with an outboard electronic one.
    And if so, what's the best way to bypass the crossovers and adjust the internal wiring so the right drivers are being fed the right signal?

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    Senior Member BMWCCA's Avatar
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    Quote Originally Posted by Crestwood23 View Post
    And if so, what's the best way to bypass the crossovers and adjust the internal wiring so the right drivers are being fed the right signal?
    Simplest would be to use an electronic crossover set at the stock L300 high-pass point of 800Hz. Output the low frequency from the electronic crossover directly to the Crown and then to your LF driver bypassing your passive network completely. The HF output from the electronic crossover goes through your tube amp to the mid-range and HF drivers through what remains of the passive network. That way each amp will only supply the frequencies used by the drivers. If you're using a simple active crossover such as the Ashly XR1001 the levels between the LF and the rest can be controlled by the Ashly gain controls, or by input attenuators on the Crown. That's how I run my 4345s.

    There's a suggestion from Greg Timbers in the 4345 thread for running the 077 direct from a small amp using a simple resistor if you're game for going tri-amp. I never felt the need to try it on my 4345s.

    I'm not the best person to answer such a question but since no one else has chimed in yet . . .
    ". . . 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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    Thanks, that makes sense. So would the remains of the HF passive network affect the sound at all if signal is still passing through it? I guess it's the only option unless you tri-amp though.
    Looks like I'd need to get a mess of XLR to RCA cables for this - any recos on which to use?
    I assume the JBL recommended crossover points for all of the drivers are posted somewhere on this site if I do some digging...

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    Senior Member BMWCCA's Avatar
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    Quote Originally Posted by Crestwood23 View Post
    Thanks, that makes sense. So would the remains of the HF passive network affect the sound at all if signal is still passing through it? I guess it's the only option unless you tri-amp though.
    Looks like I'd need to get a mess of XLR to RCA cables for this - any recos on which to use?
    I assume the JBL recommended crossover points for all of the drivers are posted somewhere on this site if I do some digging...
    The Ashly uses XLR or 1/4" stereo phone plug (for balanced connection) or mono (for unbalanced) and the manual shows wiring for all. I use 1/4" mono interconnects between the Ashly and my Crowns so no adapters are needed. 1/4" to RCA adapters or vice-verse is easy to do depending on your needs. My pre-amp/controller output is RCA so I go RCA to 1/4" with a simple adapter probably known to all home-users of Crown pro amps. I don't bother with XLR since I don't have any and I don't need to be balanced for the short runs I'm using and the rest of the system isn't running balanced anyway so there's no benefit.

    If your network is of good design then you're not changing anything other than freeing up the amps to be more efficient.

    The L300 crossover specs are here: http://www.jbl.com/resources/Brands/... summit ts.pdf
    ". . . 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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    Quote Originally Posted by BMWCCA View Post
    The Ashly uses XLR or 1/4" stereo phone plug (for balanced connection) or mono (for unbalanced) and the manual shows wiring for all. I use 1/4" mono interconnects between the Ashly and my Crowns so no adapters are needed. 1/4" to RCA adapters or vice-verse is easy to do depending on your needs. My pre-amp/controller output is RCA so I go RCA to 1/4" with a simple adapter probably known to all home-users of Crown pro amps. I don't bother with XLR since I don't have any and I don't need to be balanced for the short runs I'm using and the rest of the system isn't running balanced anyway so there's no benefit.

    If your network is of good design then you're not changing anything other than freeing up the amps to be more efficient.

    The L300 crossover specs are here: http://www.jbl.com/resources/Brands/... summit ts.pdf

    OK bare with my dumb questions here - the more I dig into this I get a bit spooked by its complexity. I've attached a little diagram as I am a more visual person. Can you take a look and let me know what you think? Is it somewhat correct? Does the Ashly crossover go to 8500Hz or only 8000HZ? What does the "Response" knob do and what should that hypothetically be set at?
    Another question is the setting the levels of everything involved for peak performance - I fear blowing something up here! My pre has gain pots to adjust its output too, and I can adjust the output of the Fisher with its volume knob. Any idea on optimal settings for each piece?
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    Senior Member grumpy's Avatar
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    no. you could blow stuff up doing that (likely the ashly).

    If you want to tri-amp, you'll need six channels of amplification.
    As far as I can tell, you have four.

    I'd start here, with what you have, as a thought exercise:

    Use the Ashly unit in stereo and set both channels for 800Hz.
    Don't screw with the response knob (leave it at "6").

    Wire the crown directly to the woofer (but switch the wires vs. what's on the schematic ... the Ashly
    is 24dB/oct, so flipping the mid polarity vs. the woofer isn't necessary).

    Wire the Fisher to the .3mH inductor (instead of from the autoformer which should be out of circuit),
    leaving the low-pass and L-pad portions in place.

    Wire the Fisher to the 1uF cap in the HF string (leave the entire passive HF filter in place).

    If you're using the Pass version of the L300 filter, the idea is ... similar.

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    Heather [Senorita member] hjames's Avatar
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    Ashley DOES make a Stereo 3 way crossover if you want a pure electronic 3 way.

    http://www.audioheritage.org/vbullet...ossover-Review

    Ashly Audio XR-2001 Stereo 3-Way, Mono 4/5-Way
    http://www.parts-express.com/pe/show...number=245-209

    And the manual covers 3 models - XR1001,XR2001,XR4001 http://www.prosoundonline.com/wp-con...001_Manual.pdf

    I used their 2 way stereo xover when I biamped a pair of 4341 4 way monitors ... split at 290hz
    low side fed a 200w/ch amp for the woofers, hi side fed a matched amp that fed the existing passive and then the 10" midBass, LE85 and 2405 slot.

    I liked the way the Ashly XR1001 worked with that setup and would recommend it to anyone going that route ..
    2ch: Oppo, JoLida 502CRC, JBL L212, 18ti,240ti; Heath AS101, Von Schweikert VR4
    7.1: Oppo BDP103D, B&K, UREI 809A, JBL B460

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    Quote Originally Posted by grumpy View Post
    Wire the Fisher to the 1uF cap in the HF string (leave the entire passive HF filter in place).

    If you're using the Pass version of the L300 filter, the idea is ... similar.
    So if the existing Pass network I currently have is similar - should I leave well enough alone before I blow something up?
    I do not yet own the Ashly, and I'm not looking to tri-amp (baby steps). I'd rather not tinker with the existing crossover too much more as I'd like the option of going back to the passive in the future if I could.
    Is there any electronic crossover out there that would allow me to use the 2 amps I have into the 6 drivers of the L300's?
    if not, is it OK keep using them as I am with the Fisher feeding the mids/tweets and the Crown on the woofers, all through a split passive network and dialing the balance by ear?

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    Senior Member grumpy's Avatar
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    I'd enjoy your system as-is for now. You can always do more homework until you are comfortable with the concepts.

    Not a bad way to be enjoying them, meanwhile!

    6 drivers means six amps, three-way electronic crossovers + any required driver response shaping (EQ).
    Otherwise there will be passive parts involved.

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    Quote Originally Posted by grumpy View Post
    I'd enjoy your system as-is for now. You can always do more homework until you are comfortable with the concepts.

    Not a bad way to be enjoying them, meanwhile!

    6 drivers means six amps, three-way electronic crossovers + any required driver response shaping (EQ).
    Otherwise there will be passive parts involved.
    OK cool, thanks for the info and advice. Wow that's a lot of amps! I'll wrap my head around it abit more and decide if it's really for me. I am really happy with the sound currently and I don't want to screw it up, I'll just relax and enjoy!

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    Heather [Senorita member] hjames's Avatar
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    Quote Originally Posted by Crestwood23 View Post
    OK cool, thanks for the info and advice. Wow that's a lot of amps! I'll wrap my head around it abit more and decide if it's really for me. I am really happy with the sound currently and I don't want to screw it up, I'll just relax and enjoy!
    To clarify - 6 drivers means 6 CHANNELS of amps, 6 Mono amps, or more commonly, 3 stereo amps.

    Since you already have 2 stereo amps, you just need 1 more stereo amp (of comparable quality) to do it.
    2ch: Oppo, JoLida 502CRC, JBL L212, 18ti,240ti; Heath AS101, Von Schweikert VR4
    7.1: Oppo BDP103D, B&K, UREI 809A, JBL B460

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    Quote Originally Posted by hjames View Post
    To clarify - 6 drivers means 6 CHANNELS of amps, 6 Mono amps, or more commonly, 3 stereo amps.

    Since you already have 2 stereo amps, you just need 1 more stereo amp (of comparable quality) to do it.
    Got it, so that would mean one more low power tube amp that would then be dedicated to driving the tweeters only. And then the 3 amp setup would go through something like that Ashly 3 way crossover that you posted. Do I still need an EQ? Do you guys (and gal) think the sonic gains are worth the extra expense and complexity? Subjective question I know, but was it a "wow" moment when you went from passive crossovers to electronic?

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    Heather [Senorita member] hjames's Avatar
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    Quote Originally Posted by Crestwood23 View Post
    Got it, so that would mean one more low power tube amp that would then be dedicated to driving the tweeters only. And then the 3 amp setup would go through something like that Ashly 3 way crossover that you posted. Do I still need an EQ? Do you guys (and gal) think the sonic gains are worth the extra expense and complexity? Subjective question I know, but was it a "wow" moment when you went from passive crossovers to electronic?
    In my rig, preamp out signal went to the ASHLY crossover, then to the amps, then to the drivers.

    Here is what JBL top engineer Greg Timbers said about the 2405 slot tweeters re the big 4345 4 ways ...

    "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."

    If you want to read more, its from here:
    http://www.audioheritage.org/vbullet...l=1#post110349
    2ch: Oppo, JoLida 502CRC, JBL L212, 18ti,240ti; Heath AS101, Von Schweikert VR4
    7.1: Oppo BDP103D, B&K, UREI 809A, JBL B460

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