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Thread: Charge Coupled Networks

  1. #1
    Administrator Robh3606's Avatar
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    Charge Coupled Networks

    I am going to change to a passive compensation for my 2344 horns. I am using the 4435 crossover and figured I would give it a try. I have schematics for several of them so the conversion looks easy with them as a reference and the information in the brochures on the site. Any of you tried to build/convert one or have any experience with them??

    Thanks Rob
    Last edited by Robh3606; 04-22-2003 at 09:10 PM.

  2. #2
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    Yes,

    Affirmative Will Robinson,

    Use the exact values JBL state, this will result in a smoother axial response within 3 db from 1 - 18 khz.

    Trying to design your own is a cow. Don't attempt it.

    I assume you are bi amping, so remember to use a hefty series non polarised capacitor to protect your compression drive(40uf).

    The concept of the charge coupled capacitors may yield some improvement as the series protection capacitor will need to be large, about 40 uf. This concept may help improve resolution. These capacitors can also be bypassed with 0.1 uf or smaller film foil types for improved performance.

    The components for the nominal crossover can be omitted.

    It is recommended that you include the pads to ensure the correct accoustic drive to your compression driver.

    The pads serve two purposes.

    The main 8 ohm pad controls the level +- 4db in the 2 khertz zone and is necessary to ensure the correct operation of the equ network. The pad in series with the equ network provides adjustment of the top end response.

    I would recommend quality capacitors like the Auricap or the Hovlands if you can in the equ netwrok, these will extract the best performance without the need to bias a lesser capacitor.

    Your graph should look like this, enjoy.

    Ian

    This graph is the 2122 H & 2344 with 2420 + Ti diamond bottle top at 9 ft mid way on axis with the 2122H and 2344 in my listening room.

    The mic is a Panasonic insert on a 3 ft aluminium tube with a custom battery mic preamp feeding WinAirr FTE driving a PC Sound card in the HP Pavilion 723A 2.0GHz.
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    Last edited by Ian Mackenzie; 04-23-2003 at 03:12 AM.

  3. #3
    Administrator Robh3606's Avatar
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    Hello Ian

    I have a complete parts set to build from. I plan on taking your sugestion and doing it complete from the start. When I did my own comps they were good but not as good as the JBL 44xx crossovers. I always had a slight hump and the last octave was always lower in amplitude than it should have been. Sounded good but not really there. I will be biamping so I don't have to worry about the woofer sensitivity like when I was running passive crossovers. That prevented me from building the original networks to begin with. I already had the 40ufs sitting around not used so I needed 4 5uf caps the resistors and a 9 volt batery and I am there. Just got the 5uf's just have to purchase the resistors. Let you know how it works out.

    Regards Rob
    Last edited by Robh3606; 04-23-2003 at 05:03 AM.

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    Rob,

    Cool,

    Have fun.

    Ian

    here's another graph, not as pretty, the blimp @ 15 khz is my TV Set.
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    Hey Rob,

    Tell us about the lastest on that sexy 4 way system in your avatar

    Ian

  6. #6
    Administrator Robh3606's Avatar
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    Not much to tell really. They were up in the den for a while. They are in storage at the moment until things get settled. I miss them and they were fun to build. Probably never find another NOS XPL200A crossover and 093TI mids again. I have a pair of ferrite woofers I want to try in them.

    Rob

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    Class A networks

    Hi Rob

    I'd love to hear about your sonic impressions after trying out JBLs' Charge Coupled Crossover topology. Considering the extra cost ( twice the quantity of caps & twice the mf value ) I wonder if its real positive benefit . Especially when compared to "transcapping" which is so economical . I haven't done it, as I'm still trying to decide whether to give titanium diaphragms ( on exponential horns not CD ) an "oil bath" ( inline or in the motor gap ) to dampen them down to the level of aluminum . I do remember that 2 years ago I did some testing comparisons and found that adding so called "fast caps" exacerbated things that I didn't like about 2426s on exponential horns. Seemed to add to an "overshoot" problem ( ie; unterminated transformer ) . But, "ADD" kicks in way too often these days and I just go back to my 288s for comfort . :o
    ( I think radio contolled relays toggling these things in and out of the circuit is the way to go to give a form of "blind taste-testing " ) .

    regards <> Earl K

  8. #8
    Administrator Robh3606's Avatar
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    Hello Earl


    "I'd love to hear about your sonic impressions after trying out JBLs' Charge Coupled Crossover topology. Considering the extra cost ( twice the quantity of caps & twice the mf value ) I wonder if its real positive benefit . Especially when compared to "transcapping" which is so economical ."

    Be glad too. I am very curious myself. They use it in most of the statement systems and the L250 Jubilee so there must be something to it. I already had the most of what I needed so I figured what the heck why not try it.


    ( I think radio contolled relays toggling these things in and out of the circuit is the way to go to give a form of "blind taste-testing " ) .

    You are reading my mind on that. I want to have a switch to drop the battery in and out. Just wondering what the time constant would be to bleed off the charge. May not be a quick on off thing.


    "oil bath" ( inline or in the motor gap ) to dampen them down to the level of aluminum

    Whats that??? Kind of like ferrofluid except not???

    Rob

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    Oil Bath ?

    Hi Rob
    "In the gap" would be ferrofluid & "InLine" would be big AC Motor Run style caps. As I said , I haven't pursued this , my interest iin this area is pretty dormant at this time . I'm satisfied with the "type - unknown" caps that I now use for DC blocking duties.

    re the ferrofluid; I have a pair of Selenium D205Ti 1" driver. It has a titanium diaphragm, uses an Altec style radial phase plug and has ferrofluid in the gap. The first time I heard these drivers I was surprised at how smooth sounding they were ( on small exponential horns ) . Testing revealed significant response dips/holes centered at @ 2.5 & 5 K ( right there that means I can't recommend others buy them ). My initial aural satisfaction was likely a reaction to these response nonlinearities as much as anything else . But the experience did get me thinking about using a bit of ferrofluid in gaps of drivers/horns which I feel are underdamped. Ferrofluid (like motor oil ) comes in many weights & blends. One needs the experience or guidance of others to help select the weight, the quantity , advice on clean-up, paper contamination realities & the need ( or not ) for extra gaskets. I shelved acting on the idea till more info presents itself .

    The ( A/B ) cap testing I did used toggle switches to flip the different types in and out of the circuit. This was while listening to just the compression drivers .

    regards <. Earl K

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    Great to see some diy tweeking happening.

    Tell us all know how it goes,

    Ian

  11. #11
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    Charge Coupled Network Topology

    Ok "Robh3606" , after several conversations I'm sold.

    I will probably start out charge coupling a pair of stock JBL networks that employ the standard metallized mylar and non-polarized electrolytic capacitors bypassed with polypropylene and polystyrene topology such as used in the original 250Ti. (polypropylene excels in speed and dynamics, polystyrene excels in spaciousness and three-dimensionality)

    I will then move up to polypropylene and foil capacitors without bypass capacitors. I can always add in polystyrene and foil bypass capacitors if the polypropylene and foil capacitors prove to sound too "compressed". However, by charge coupling, the limitations of the various dielectrics is theoretically supposed to be greatly reduced (as is overall distortion). Using a high quality film that will hold the charge is important, so I'll go with polypropylene and foil. The results are alledged to be stellar.
    Last edited by 4313B; 05-07-2003 at 02:00 PM.

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    An Example
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    4348 innards with the charge coupled network designed by Greg Timbers.

    Yeah Baby!
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  14. #14
    Administrator Robh3606's Avatar
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    Hello Rob

    I will be using the same capacitor combo as you. Glad you are giving it a try too. Maybe by the end of the week I can have one cobbled together. Those 40uf's are big mothers! Got some project boxes to but it all in but will probably have to strap those on!

    Rob

  15. #15
    mrdsp
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    Help... Giskard.

    Do you have any references which can explain in simple terms the theory behind transcapping. Is this an earlier attempt to deal with "limitations of various dielectrics"? On the surface it would seem that transcapping is a variation of bypassing a capacitor with a smaller one in order to negate the effects of series inductance (ESL) and/or resistance (ESR) of the larger device. If so it would then seem that charge coupling would greatly increase the ESL and/or ESR , yet the results are reported to be better. One might ask the question whether paralleling that charge coupled pair with a pair of 0.02 uF capacitors in its own charge coupled configuration would improve things further. Thanks!

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