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Thread: Repair/Rebuild 3110 crossover

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    Member wpod's Avatar
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    Repair/Rebuild 3110 crossover

    Greetings- I picked up a pair of 3110 crossovers on Ebay cheaply (not working) and now I have a few questions.Upon first glance, I noticed that a few of the resistors need replacing due to a crack and a couple of broken leads. I figured that it would be best to just replace them all (4 per crossover) with Mills NI-ww resistors.Any problem with with using a non-inductive resistor in place of those sand cast "white coffin" resistors? Next I thought I'd measure the two inductors and the four capacitors to make sure they are still at their original values. Assuming that they are still within spec, I'd like to bypass the caps with some .1uf or .056uf Russian teflon caps ( if they all fit). Is there anything wrong with this idea? There's not much that I can do with the inductors (3.3 mH, 2.14 tapped) except trim and resolder the leads. Should I replace the two pole-three position switch or will a good cleaning take care of it if it's in good physical shape? I'm missing the knobs that go on to the switch shafts, are these still available from JBL or anyone on this forum?I'm also missing the ten screws (per crossover) that hold the thing together.What type, size and thread was used for this? I'd also like to get a couple of empty steel crossover boxes (with or without cover w/binding posts) in case I'm not pleased with the behavior of the 3110 in my system (4648A bottom, 2445J on 2380 horn and 2402 tweeters. I'm currenty using (and pleased with) a 2nd order homemade crossover with premium components (cfac inductors,oil and teflon caps,NIww resistors).The trouble is that the cossover is just sitting open on top of the bass cabinet. If I had a couple of empty crossover boxes , I could put my components inside of it and mount it properly in the rear of the cabinet. I use just a 1uf Vitamin Q cap for the crossover for the tweeter ( in case you were wondering). Any help will be greatly appreciated. Thank you, Paul

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    RIP 2011 Zilch's Avatar
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    1) Mills will be fine.

    2) Bypassing is fine.

    3) Not much can go wrong with inductors.

    4) A good cleaning will restore the switch.

    5) JBL may still have knobs.

    6) 10 screws? It was 4 pop-rivets per on the lid, originally. I use #8-32 x 1/4" self-tapping screws to replace them.

    7) No empties here, alas....

  3. #3
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    Quote Originally Posted by wpod
    I'm currenty using (and pleased with) a 2nd order homemade crossover with premium components (cfac inductors,oil and teflon caps,NIww resistors). The trouble is that the cossover is just sitting open on top of the bass cabinet.
    - Keep the networks external .
    If I had a couple of empty crossover boxes , I could put my components inside of it and mount it properly in the rear of the cabinet.
    - Be carefull what you wish for .
    - Don't assume placing cfac or aircore coils in or even on metallic surfaces is some benign exercise in component relocation .

    - To test for the influence of a metallic surface on a inductor; build a self resonating LC circuit ( just tune the L & C to the same frequency or Fc, / use the highest "Q" components you can find ) .

    (i) Attach an applicable transducer to a source of pink noise / then monitor ( watching an RTA is the easiest ) the "peaked" response of the driver / all the while placing/moving the coil into or even close to the metallic surface in test.

    (ii) If the metal has sufficient magnetic conductability you should see the "purpose built resonant peak" flatten & broaden out .
    - This flattening represents a significant loss to the "Q" of your tuned LC circuit.

    (iii) I've done this exercise and was surprised to find that to duplicate the effect ( of; lowering the inductors' "Q" by adding series resistance ) it took upwards of 4 or 5 ohms added in line with the inductor .
    - ( So much for any significant investment in those coils sporting lower DCR figures ).
    - In my ad-hoc test, I used a .56mH ( 16 gauge ) Solen aircore sitting ontop of a metallic lid belonging to a Budd-style/Hammond project box ).
    -I also placed the coil into the project box with not much of a notable difference to that of simple placement ontop of the single metal surface ( ie; the lid ) .

    (iv) Luckily ( & as another complicating factor to all of the above ) lower "Q" circuits can often be better sounding than high "Q" circuits .

    (v) I haven't tried this exercise yet with laminate or ferrite core inductors / but it's worth the investigation .


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    Member wpod's Avatar
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    Very Interesting- Thank you

    Earl- Thanks very much for the info. Beleive it or not, when I tried to see if the cfac inductor would fit into the case, I noticed that they were made of steel and not aluminum. It crossed my mind that there could be a problem, but I dismissed it figuring that if the steel was ok for the stock inductors, that it would not bother the cfac either. My original idea was to locate the components in some nice wooden cigar boxes ( complete with larger binding posts) on top of the cabinet. Perhaps I should stick with my original plan. I had also thought of using an aluminum box to contain the components, any idea if the cfac would be effected by the aluminum? Thanks very much, Paul

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    I had also thought of using an aluminum box to contain the components, any idea if the cfac would be effected by the aluminum?
    - Short answer ; I don't really know. I don't have any cfac coils to test against various metallic surfaces. I'm speculating that cfac(s) will react in a similar manner to a regular wire-type airwound coil .

    - The project box I was testing is made by Hammond. Hammond labels this ( 1590 ) series of boxes as being constructed of "diecast aluminum alloy".


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    knobs

    need knobs??



    sub
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