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Thread: 4412 Charge-Couple Help

  1. #1
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    4412 Charge-Couple Help

    Iím new to the forum, this is my first post.
    Iím in the process of restoring a pair of 4412 monitors. While looking for information on recapping the crossovers I became interested in charge coupling them instead. I read Greg Timbers article and many posts on the subject on this forum and elsewhere and looked at some schematics using this method and decided it may be doable. Iím hoping someone here would look at my plan and make suggestions for improvements.
    One question I have, is since these crossovers already have bypass caps, are there still gains to be had by biasing them?
    Iíd like to keep this as simple as possible, the current plan is to remove the electrolytic, mylar and bypass caps, solder some leads in place of the electrolytic and mylar, and connect them to poly caps mounted on a separate board, reusing the other existing components.
    I redrew the N 4412 schematic to show the changes and included a drawing of what the modified crossover would look like.
    I had to parallel two caps in most cases to exactly double the value of the originals, which makes for a lot of parts. Iím using a 2.2 meg ohm .25-watt resistor on the battery simply because thatís what was shown in the article, and on the Century Gold schematic.
    Any help and advice would be greatly appreciated
    Bill
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  2. #2
    Junior Member LarryM's Avatar
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    4412 CC crossover

    Hi Bill,
    Your CC'd capacitors are correct. R4 though, cannot feed all the capacitor pairs. Do you see that you have connected all cap pairs together. It would sound bad and could damage the tweeter. Run 4 different 2.2Meg resistors from the battery + terminal to each pair of caps. That will isolated each pair from each other.

    Bypass will still help, but you only need them on C2 and C4. One should go across each cap in the cap pairs. You would need 4 total per speaker. I like the .01uf Audiocap PPT theta's. They are not cheap though. About $6 each from Parts Express. Many others brands are available too.

    Your right. CC caps are much bigger and more of them. Its expensive too. I question even doing the LF section anymore. It is the most costly leg to implement, takes the most real estate and IMO has the least impact on sound. I suppose others may differ.

    Good luck,
    Larry

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    Senior Member pos's Avatar
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    WKOTTD, while you are at it why not separate LF from mid/HF to allow for biwiring/biamping like in the LSR6332?

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    Quote Originally Posted by LarryM View Post
    Hi Bill,
    Run 4 different 2.2Meg resistors from the battery + terminal to each pair of caps. That will isolated each pair from each other.

    Bypass will still help, but you only need them on C2 and C4. One should go across each cap in the cap pairs. You would need 4 total per speaker.

    Your right. CC caps are much bigger and more of them. Its expensive too. I question even doing the LF section anymore. It is the most costly leg to implement, takes the most real estate and IMO has the least impact on sound. I suppose others may differ.

    Good luck,
    Larry
    Larry, Iím going to forgo biasing the LF, I did notice when I was looking at schematics that some were, and others were not. I did however add a bypass cap to the LF, only because thatís how it was originally configured.

    I did not know about both biasing and bypassing caps. I updated the schematic to show how I understand what you said. I also included the additional resistors.
    Thanks for the help
    Bill
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    Quote Originally Posted by pos View Post
    WKOTTD, while you are at it why not separate LF from mid/HF to allow for biwiring/biamping like in the LSR6332?

    I hadnít thought of that, mostly because I know little about it.
    Since your reply Iíve started to do some reading about it. My impression so far is that biamping might be worthwhile and looking at the Century Gold schematic it appears to be something I could do. If nothing else, itís an opportunity to learn something new.
    Thanks
    Bill

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    Senior Member Ian Mackenzie's Avatar
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    On the K2 systems they steered away from bypassing and use straight Solen Fast Caps 250v with charge coupling.

    I would do this on the mid and hf filters first to access the subjective improvement before doing the expensive LF filter

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    I know this is an old thread, but I just recently completed the restoration of these speakers and wanted to thank those who provided advice and answered my questions, about Charge coupled crossovers, preventing me from screwing up. I also wanted to share the results
    The speakers sound WAY better, much clearer and more detailed, the timbre of vocals and instruments is amazing. Sound stage while not any larger is more centered and defined.
    I donít know how much of this is due to the crossover mods because of the other work done. These were in rough shape (but cheap) when I bought them from a studio that went out of business. The cabinets had deep scratches, smashed corners, and many screw holes. Every peg was broken off the grills. One tweet was open, both damper foams were rotten, and the woofers had the foams glued on the wrong side of the cones with way too much glue.
    It took some work to fix all that, but some bondo, new veneer, and 15 coats of lacquer fixed the cabinets. Re-drilling and some epoxy repaired the grills. A used tweeter and new damper foams off e-bay fixed the tweeters and off-center sound stage. And finally, new OEM recone kits were installed in the woofers by Midwest Speaker.
    This is the sixth stereo system Iíve had in this room and these are by far the best sounding speakers.
    Thanks
    Bill
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    Mate they look absolutely mint. I can't believe how much better they look with the baffle veneered. Well done.

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    They are gorgeous! I guess they also sound terrific, I think tweeters servicing brings back some of the original great sound even if no CCed, it's mandatory but sadly almost never done :'(
    Well done!

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    Senior Member DavidF's Avatar
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    Nice to see the end product. The workmanship looks first class and so they must sound quite nice, too.
    David F
    San Jose

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    Congratulations! A beautiful job... so nice to see the results.

    Thank you for sharing!


    Widget

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    Senior Member SteveJewels's Avatar
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    Very nice!

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    Amazing work, WKOTTD !

    BUT: With due respect, I'm in severe doubt that Ľcharge couplingę plastic foil capacitors will improve anything at all. At least one has to be pleased if there's no deterioration afterwards. Why? As shown in all related schematics, all capacitors that are to be charge coupled are replaced by two specimen with double the capacitance. Two caps in series necessarily will show increased ESR. A high ESR in a filter network surely won't improve sound quality.

    Then the bias voltage needs to be higher than the maximum peak voltage that has to be expected over the capacitor. Hence, with a 9 V battery and 8 ohms impedance, any effect will be limited to an output power of just 5 watts.

    If one states some better sound quality from charge coupling, he has to be asked if he had performed a double blind test. Did he really listen to two speakers that are identical besides the charge coupling? And if you alter more parameters than one, as it has been done above, how can you assign some effect to just one of them?

    The only positive effect that I perhaps might attribute to charge coupling would be if one replaces a non polar electrolytic by two polarized ones in back to back. But remember: The polarisation voltage needs to be higher than the maximum signal voltage peak to have the 'lytics polarized the right way in any instances!

    Best regards!

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