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Thread: Performance series + DIY

  1. #16
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    Fortunately I had these pics. I used a pice of 1/4 inch plywood for the mounting board. The pic with the board in the box shows that it is resting on a layer of sand before I covered them with sand.

    If you are looking at the schematic, while viewing these, you can see where I tried to keep the components for each driver in some sort of order, with the woofer on the left , mid in the center, tweeter on the right, for the pic of the crossover in the box. The underside of the board is flipped left to right, and you can sort of tell that by the color of the wire ties.

    For installation, I just removed the binding posts and crossover from the PT800, and ran the wires in through the holes where the binding posts are. So I could easily put everything back to stock, with no signs of molestation if I wanted to.

    But I don't forsee that happening........
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  2. #17
    Senior Member Don Mascali's Avatar
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    4406, 4412A, L100, L100t3 (3 pair), L1, L7, 4645C, 4660A, 4695B, SR4735 and various DIY JBL Pro loaded systems.

  3. #18
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    Smile Aha!

    I see things that were hidden before. Thank you!
    Out.

  4. #19
    MJC
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    looking at that box, I will probably need to built a slightly bigger box for a CC xo, as the number of caps will double.
    Using Mills resistors, Jantzen coils and Solen caps will cost $450~475 for a pair of PT800s. Or about 50% more than the cost of my pair of CC xo for the L212s.

  5. #20
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    Quote Originally Posted by MJC View Post
    looking at that box, I will probably need to built a slightly bigger box for a CC xo, as the number of caps will double.
    It's easy to see why JBL didn't cc them. No room at all.

  6. #21
    MJC
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    Quote Originally Posted by 4313B View Post
    It's easy to see why JBL didn't cc them. No room at all.
    Although the PT800s are about the same size as the L212s, it was easy to CC L212 with its open back. I cut up three cards the same size as the original, one for each driver. Mounted one to the left side, one to the right side and one accross the opening, to the wide side of the speaker array.
    For stand alone PT800s JBL could have provided bases similar to the L212 bases and housed the cc xo inside, and/or added them to the PS1400.

    There is one thing I would not have thought of, until reading through this thread, adding sand to the box, good idea.
    Last edited by MJC; 12-04-2007 at 04:40 PM. Reason: add thought

  7. #22
    MJC
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    parallel caps best when of equal value?

    While going over the xo for the PT800s to develop a parts list for cc xo, it became obvious that I would have to mate caps in parallel to get the capacitance values needed for each half of each series pair.
    Then the question that came to me, is it better for each cap, of parallel pairs to be of equal value, or at least close, or to use totally unmatched, in value, for each parallel pair?
    To my way of thinking, it would be better to have parallel pairs as close as possible to equal capacitance for best results. Would this be right?
    Or does it make no difference?

  8. #23
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    Quote Originally Posted by MJC View Post
    While going over the xo for the PT800s to develop a parts list for cc xo, it became obvious that I would have to mate caps in parallel to get the capacitance values needed for each half of each series pair.
    Then the question that came to me, is it better for each cap, of parallel pairs to be of equal value, or at least close, or to use totally unmatched, in value, for each parallel pair?
    To my way of thinking, it would be better to have parallel pairs as close as possible to equal capacitance for best results. Would this be right?
    Interesting question and one that I just faced. When I built the XOs for my L,C,R with LE175-HL-91s, the mids called for 16.5 mF cap. I wanted to stay with one brand and use ALL Solens and made up this value using two 8.2 mF Solens (16.4 mF total).

    When I ordered parts to build the XOs for the four surrounds that are to use 2425J, I also wanted to use the two 8.2 mF Solens. But I only ordered enough parts to build one of the surround XOs (and a few extra parts to get quanty discount where applicable) with the reasoning that I could build one and "tweek" it before ordering the parts for the other three.

    Meanwhile, Domino was building similar (but not identical) XOs for his project that also use the 16.5 mF cap for the horn. In his case, he used a 16 mF Solen and a 0.47 mF Janzen (16.47 mF total).

    Domino wasn't happy with the sound and decided to replace them with AuraCaps, so sent me the Solen/Janzens. So one set of surrounds will use two 8.2 mF Solens while the other two will use the 16 mF Solen and 0.47 Janzens. Also Domino sent me four 1.5 mF Janzens that will be used in the HF compensation network. (The L,C,R use Solens in the tweeter network.)

    In my case, all caps (Solen and Janzen) in all XOs receive Theta Audio-Cap 0.01 mF bypass caps, that in theory, should impart a similar (but not idential) sonic signature on all of the caps regardless of brand.

    I really doubt that I will hear a difference because of brand or because of the way the values were paired.

    In theory though, I would think that a large and small cap together could outperform two medium caps, much in the same way that a by-pass cap works. I had always heard (maybe incorrecly) that a smaller cap can react faster to transients than a larger cap.

  9. #24
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    Quote Originally Posted by MJC View Post
    While going over the xo for the PT800s to develop a parts list for cc xo, it became obvious that I would have to mate caps in parallel to get the capacitance values needed for each half of each series pair.
    Then the question that came to me, is it better for each cap, of parallel pairs to be of equal value, or at least close, or to use totally unmatched, in value, for each parallel pair?
    To my way of thinking, it would be better to have parallel pairs as close as possible to equal capacitance for best results. Would this be right?
    Or does it make no difference?
    Here's the matrix I posted a few years ago for the Solen pairs. I just select the two closest value pairs.
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  10. #25
    Dis Member mikebake's Avatar
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    You had/have L212's; did you give us a comparison somewhere to the PT800's? Also, do you still have the sub1500's?















  11. #26
    MJC
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    Quote Originally Posted by mikebake View Post
    You had/have L212's; did you give us a comparison somewhere to the PT800's? Also, do you still have the sub1500's?
    I've still got all 7 L212s, one pair cc, which I have setup with Citation amps and a turntable.
    And I still have the pair of SUB1500s in the HT.
    As you might expect, the L212 and PT800 are quite similar, if for no other reason, than they more/less share the same basic design. Both 3-way in boxes that are close to being the same size.
    But when it comes to movie soundtracks, the PT800s are much faster, I suppose due to them being 100% Ti.
    One slight difference, in comparing the main L/R of each, is that the main L212 were cc, where as the PT800s are stock.
    The PT800 seems to be more airy, open, althought the cc pair of L212 are also much more so than when they had original xo.

    AS Ti Dome has stated, on another forum,
    In 5.1 multichannel music (DTS, DD, DVDA, SACD) the sound is immaculate. No sub is needed whatsoever. The sound is full, open, spacious, refined, clear, and dynamic. It's truly the most seamless musical experience I've had outside of a concert hall or music venue. In some cases, it's better than the live show.
    But as skeptical 1, who started this thread, almost a year ago, has said, upgrading the xo improved an already very good system. Although he only built a by-pass xo, using higher end components. But I plan to build cc xos, for the main L/R first and then probably for the center.
    At this time I think I'll have to skip doing the surround PT800s, as they are hanging on the walls, as there isn't enough room inside the PT800 boxes. Or so it would seem. I suppose I could cut out the sheetrock behind the speakers and mount a the xo boxes in the wall and re-mount the PT800 in front.

    This is how the front end of the HT looks now. Notice that the sub boxes are square, as they were built to match the L212 boxes. I bought a pair of PT800 grilles for the subs.
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  12. #27
    MJC
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    One thing I've never had the chance to do is compare a PT800/PS1400 stack to the PT800/SUB1500 stack, as I don't have even one PS1400.
    Although I get a very good bass with a Crown K2 amp driving the SUB1500s I can't drive the stacks as a unified full range speaker, as can be done with the PS1400 in the mix.
    If I were to replace the Crown with plate amps and use their xo then I could run a true full range, bi-amped stack. Although I don't know if there would be any advantage compared to using the K2 amp and the bass management in the H/K receiver.

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