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Thread: Alternative to tapped inductor in 3110a or 3115a?

  1. #1
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    Alternative to tapped inductor in 3110a or 3115a?

    Greetings,

    I have a multitude of 2225H, 2445J (with 2380 horns), and 2404H drivers that I am trying to put to use. I would like to build something similar to a 4673 clone but the tapped inductor of the 3110a and 3115a crossovers have me stumped. Is there any way around them using multiple standard inductors?

    I have seen the 3110 equivalent HP filter that gets around the tapped inductor, but I need the "a" version to go with the CD 2380 horns.

    I have used the Behringer CX4300 in the past but I want to keep this a passive crossover.

    My next question is how much of an issue is CD compensation if the 2404Hs are blended in at 5kHz?

    Thanks for any input.
    Robert

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    Senior Member Baron030's Avatar
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    Hi Robert

    You cannot use multiple standard inductors simulate a tapped inductor. A tapped inductor acts like a transformer. And since, there are not separate primary and secondary winding, these devices are often referred to as Autoformers or Autotransformers. I don’t know of anyone that is manufacturing these devices, so unless you can track down some JBL crossovers. You might need to wind your own coils, which is not something that should be attempted without test equipment to measure the inductance.
    And due to the necessary inductive interaction between taps, I would recommend using an iron core rather than an air core design. Rewinding an Erse Super Q coil would be a good starting point for such a project.

    Here is a link to the inductance ratios that would be needed:

    http://www.audioheritage.org/vbullet...hread.php?5376
    http://www.erseaudio.com/Products/Su.../ESQ55-16-3300


    Baron030

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    Thanks for the info, Baron030. I am comfortable with modifying an existing inductor or creating a new one from scratch. I am also familiar with the theory of transformer windings but I need to read up on the mechanics of winding multiple taps. I have now read through many of the autoformer threads here but they seem to dwell on the theory more than the execution of the tapped inductors.

    I guess my biggest question is do you just start with the primary inductance winding (say 3.3mH) and then wind the secondary coils over the primary according to their calculated ratios? Are the secondary coils connected to each other? Then I notice you mention that there are not seperate primary and secondary windings.

    Thankfully I am not in a hurry to finish this project as it appears that I still have quite a bit of reading/learning to do.

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    Senior Member Baron030's Avatar
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    Hi Robert

    Here is how I would attempt to make a tapped 3.3mH coil for the 3110a crossover. I would start with a 3.3mH Erse 16 gauge Super-Q coil and some additional 16 gauge magnet wire and an inductance meter. The reason for the additional magnet wire is that when you are removing windings from the Erse coil. The insulation is going to come off that wire because Erst cements the wires together with enamel or varnish. Start by removing windings and while measuring the inductance until the coil’s inductance is reduced to 2.97mH. Keep track of the length of the wire removed and the number of turns removed and record those values. Then continue removing windings and measuring inductance until the inductance is reduced to 2.7786mH. Again record the length and number of turns of wire removed. Then continue removing windings and measuring inductance until the inductance is reduced to 2.4717mH. The wire lead that is closest to the iron core is “Lead # 1” and the outer wire lead is “Lead #2 = -6db”. Attach some new magnet wire to “Lead #2”, it should be a few feet longer than the total amount removed. Start rewinding the coil until the inductance is back up to 2.7786mH and then form a loop marking it as “Lead #3 = -8db”. Continue rewinding until the inductance is 2.97mH and then form another loop, marking it as “Lead #4 = -10db”. And then continue rewinding until the inductance is back up to 3.3mH and marking it as “Lead #5”. While winding you will want to brush some varnish to cement the winding together. Needless to say this is all very labor intensive.

    Baron030

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    Wow, thanks for the explanation. That sounds very straight-forward. I'm sure it will be a very tedious process but the concept sounds simple enough.Thanks for the info.Robert

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    Has anyone reworked the 3110a to have a fixed HF gain of -10db and not use L3 and S2?

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    Senior Member Baron030's Avatar
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    Crossover Network Rotary Switch

    Well, without having an actual JBL network on hand to do an exact comparison. This is my best guess as to the correct switch for the network. I am pretty sure that JBL is using an Electroswitch brand rotary switch. But, without actual physical measurements I am not sure which Electroswitch switch series is being used. (“C4”, “D4”, or “D7”) Electrically, any of these 3 series should work and could be interchangeable. Now, there are some key words that must be followed when ordering this switch. The switch should have “Solder Lug Terminals”, “1 deck”, “2 poles per deck”, and “3 or more positions” and “Non-Shorting”. And have adjustable rotation stops. So, if the switch has more then 3 position, you can reposition some stops to limit the shafts rotation to just the required 3 positions.

    Actually, for the 3110A network a “1 poles per deck” switch would work.

    While a N1200 network would require “2 poles per deck”

    Considering cost and availability, I would have to say that the “Electroswitch D4G0205N” switch would be my best guess and it should work for this application.
    Mouser Part # 690-D4G0205N

    Baron030

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    Hi Robert

    Just to give you an idea of just much additional wire that you might need on have on hand for this project. Taking into account the DC resistance of the Erse Super Q coil is 0.187 ohms. And the fact that 16 gauge wire has 4.094 ohms per 1000 feet. This coil has total of about 46 feet of wire in it. Assuming a turn ration of 0.0512 for the -6 db tap, this would suggest that you will be removing about one half of the wire, or about 23 feet. So, for a pair of crossover networks , it might be best to buy a one pound spool of wire and have some to spare.

    Link: http://www.amazon.com/Magnet-Enamele.../dp/B000IJXXSY


    Baron030

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    Cool 18 ga I-Core

    Quote Originally Posted by Baron030 View Post
    Hi Robert Just to give you an idea of just much additional wire that you might need on have on hand for this project. Taking into account the DC resistance of the Erse Super Q coil is 0.187 ohms. And the fact that 16 gauge wire has 4.094 ohms per 1000 feet. This coil has total of about 46 feet of wire in it. Assuming a turn ration of 0.0512 for the -6 db tap, this would suggest that you will be removing about one half of the wire, or about 23 feet. So, for a pair of crossover networks , it might be best to buy a one pound spool of wire and have some to spare. Link: http://www.amazon.com/Magnet-Enamele.../dp/B000IJXXSY Baron030
    Did you slip a decimal there? 0.0512 suggests one half? I think the 16 ga coil is probably overkill for the HF driver, I had a 2.5mH 18ga on hand. I had ordered it by mistake (PE 266-556) and added wire to make it a 3.3mH, so taking that wire off gave me a good idea of how much wire this would take, about 12 feet. I unwound the 2.5 down to 2.47 and spliced on some new 18 ga wire. Here's what it took: Tap 2 to Tap 3: 9.75 turns, started with 4' wound on about 3'. Tap 3 to Tap 4: 6.75 turns, started with 3' wound on about 2'. Tap 4 to Tap 5: 11.5 turns, started with 5' wound on about 4'.

    Super glue holds the windings from moving. Used a whole small tube, it was just opened for another project and I knew it would go bad before I needed it again, so I used it all.
    Attached Images Attached Images     
    Last edited by 4343; 06-13-2012 at 01:22 PM. Reason: Pics
    Mike Scott in SJ, CA
    Drive 'em to the Xmax!

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    Senior Member Baron030's Avatar
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    Did you slip a decimal there? 0.0512 suggests one half?
    Hi 4343
    Oops, Yes I did slip/flip a decimal! The correct turn ratio for a -6 db tap is 0.5012. Actually, you are probably right about using a 16 gauge coil for the HF driver is over kill. An 18 gauge coil would be a lot cheaper.

    Maybe this would be better starting point:
    http://www.erseaudio.com/Products/IQ.../ELC54-18-3300

    Baron030

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    Senior Member Baron030's Avatar
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    I should say this now, just in case this all blows up in my face.

    The tap inductance values that I posted are based on calculations and are not based on actual measurements from a 3110A crossover network. And there is one other possible flaw in my logic. And that be that the tapped “secondary” winding of the coil must be closer to the core then the “primary” windings. This would mean that you would need to start with a 0.33mH core (-10db tap) and then add winding to you reach the full 3.3mH.

    If anyone in the Chicago area has a 3310a crossover and would not mind me taking some measurements of its tapped coil. Please contact me and I would most gladly post the actually measured values here. And this offer also applies to any JBL network that has a tapped coil. I think we need to document these tapped coil networks. Because hand winding tapped coils is not rocket science and the cost of inductance meters has come way down.

    4343 that sure didn’t take you very long to make that tapped coil. I sure wish you didn’t live so far away. I would sure love to CLIO test that coil to see if the all the tapped voltage drive levels are right or not.

    Baron030

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    Senior Member 4343's Avatar
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    Cool

    Quote Originally Posted by Baron030 View Post
    Hi 4343
    Oops, Yes I did slip/flip a decimal! The correct turn ratio for a -6 db tap is 0.5012. Actually, you are probably right about using a 16 gauge coil for the HF driver is over kill. An 18 gauge coil would be a lot cheaper.

    Maybe this would be better starting point:
    http://www.erseaudio.com/Products/IQ.../ELC54-18-3300

    Baron030
    I'd rather start with this one:

    http://www.erseaudio.com/Products/IQ.../ELC54-18-2500

    and add wire to get to the specified inductance for each tap. If you are going to unwind and then add new wire anyway... I suppose if you had the proper varnish, you could re-coat the wire you remove, but I have new wire, but not the varnish. (Super Glue only works to hold the wire in place, it's almost impossible to use it as a coating without getting stuck!)

    BTW, those are both out of stock at present, PE sells the exact same ERSE made coils at a bit of mark-up, and they are in stock for someone in a hurry, despite the photos, they have the same mounting bracket included:

    http://www.parts-express.com/pe/psho...number=266-556

    http://www.parts-express.com/pe/showdetl.cfm?Partnumber=266-560


    Mike Scott in SJ, CA
    Drive 'em to the Xmax!

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    Senior Member 4343's Avatar
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    Cool

    Quote Originally Posted by Baron030 View Post
    I should say this now, just in case this all blows up in my face.

    The tap inductance values that I posted are based on calculations and are not based on actual measurements from a 3110A crossover network. And there is one other possible flaw in my logic. And that be that the tapped “secondary” winding of the coil must be closer to the core then the “primary” windings. This would mean that you would need to start with a 0.33mH core (-10db tap) and then add winding to you reach the full 3.3mH.

    If anyone in the Chicago area has a 3310a crossover and would not mind me taking some measurements of its tapped coil. Please contact me and I would most gladly post the actually measured values here. And this offer also applies to any JBL network that has a tapped coil. I think we need to document these tapped coil networks. Because hand winding tapped coils is not rocket science and the cost of inductance meters has come way down.

    4343 that sure didn’t take you very long to make that tapped coil. I sure wish you didn’t live so far away. I would sure love to CLIO test that coil to see if the all the tapped voltage drive levels are right or not.

    Baron030
    Just happened to have the right coil close at hand, and as I said, it was ordered by mistake, so I only have the one. And I just realized my 2385's have 2446H's on them, so I will need to swap them with the 2445J's on my big lenses to make use of a passive XO anyway.

    PM me your address, I'll send it out ASAP.
    Mike Scott in SJ, CA
    Drive 'em to the Xmax!

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    Would using 4 aircore inductors (2.47; 0.30; 0.20; 0.33) in series be a bad idea?

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    Quote Originally Posted by Baron030 View Post
    Actually, you are probably right about using a 16 gauge coil for the HF driver is over kill. An 18 gauge coil would be a lot cheaper
    That's good news. I have an 18awg 3.5mH coil laying around that I could tryout. Now I just need to get an LC meter and I'll be good to go.

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