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Thread: The continuing saga of the charge coupled network

  1. #1
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    The continuing saga of the charge coupled network

    I thought that I would continue the discusion on the topic. Sorry Widget . Everyone, or most, here know that charge coupled networks do work, the proof is in the pudding. The senior members her don't take to kindly to "JBL bagging" so please make sure that no one does. JBL spend quite a lot of cash on R&D so you can guarantee that when they introduce a new idea it will actually have merit. For all the members who are non beleivers I would recomend building a very simple CC network and do a listening test. I understand the technical aspects of the CC network and how it works in practice but there is one point that I dont understand at all. JBL compare how it works with Class A verse Class B amplifiers. For those that don't know, Class B crosses the "zero point" whereas in Class A the waveform is basically "pushed" away from the zero point by a fixed DC voltage. In this way the waveform never crosses the zero point so we get a purer sound. The bias viltage to get pure class A operation needs to be higher than the maximum peak input voltage though.
    My question is this. If we apply a signal to our xover of say 40 volts, which for arguments sake is 200 watts into 8 ohms, how can a 9volt supply fully bias the main signal? Would it not need to be at least half of the peak to peak input voltage?
    To my way of thinking a 9volt supply will only fully bias an 18volt peak to peak signal. Am I correct?

    P.S. I know this is getting to be a very tired topic but I would like to know this final detail. So jump in.

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    Please keep this thread clear of all posts until December 6th.

    Thanks.

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    I was asked to make a brief response to this last post, so here it is. The capacitor biasing is something that has existed for many years. Tube equipment does it automatically since there is usually a large DC offset between stages. Some early transistor amps/preamps had two polarized caps in series with the center point going to ground through a large resistor.

    I personally became aware of this technique for speaker systems through communications with Ed Meitner, currently of EMM Labs. He is a wealth of information regarding these "tricks" to help linearize or improve the sound of passive components.

    It turns out that the bias trick actually increases measured IM distortion and the higher the bias voltage, the greater the increase. It is not by a great amount, but it is measureable. The sound imporvement (or change) is very rarely perceived as worse and is never linked with a increase in IM distortion. The sonic effect is one of smoothness, increased spaciallity, detail and stuff like that. IM has a muddling or confusing effect so I doubt that this particular steady state measurement is explaining the sound difference either way.

    Simply put, we are striving to create a class A situation but as was just pointed out, depending on the bias voltage with respect to the voltage across the capacitor, we may only have an "A" condition up to a particular drive level. So if it makes you happier, consider the change to be class AB, but heavily biased to A. You must also keep in mind that the voltage across the input terminals of the crossover network does not tell you what voltage or current is applied to any individual component. Some parts block signal and others shunt signal so the loading on a particular part is not obvious. For the most part, the caps are well taken care of with 9 volts, even at healthy drive levels. The obvious choice for 9 volts is the small cheap battery and holders that are available. No current is involved so a smoke detector battery and holder is a natural choice.

    We did do one system with 18 v (M9500). Certain of the Japanese reviewers thought it was an improvement. I can't personally tell any difference. I am also told on a regualr basis (again by our Asian customers) that the battery must be changed at least every 90 days and that the sound degrades after that. Once again, I have not been able to "hear" any difference after 90 days and the battery is certainly still good for many years from a voltage standpoint.

    What playing around I have done with initial application of a battery to a biased circuit (that has not been previously powered up) is that it takes about 3-5 seconds for the soundstage to change. I have tried to measure the voltage level in that time period and it seems that several volts is all that is necessary to accomplish 90% or more of the improvement. Once a circuit has been energized, it is nearly impossible to return it to zero. You have to individually short out each cap and leave them shorted for a while or else they will creep back up somewhat. If you replace the battery with a short and play the system for a while, the caps will start to bias themselves, although not to anywhere near the same degree.

    You can take this opinion for what it has cost you. I have been very pleased with biasing for many years. I use it in all applications that involve a capacitor and I have rarely been disappointed. Results may vary so if it doesn't do it for you that is okay too. It cost a bloody fortune to implement as it requires 4 times the capacitance and double the capacitor parts count. The network size gets huge as well. Inspite of this, I have never heard a capacitor type that didn't improve (or change) including the nearly perfect teflon variety.

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    Dang. Amateur speakerdave's Avatar
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    Mr. GT,

    It's very nice of you to come address the peanut gallery.

    Thanks,

    David

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    Senior Member Ian Mackenzie's Avatar
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    2nd that ...

    Greg has again offered us some great insights .

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    Hi Greg,

    Thanks for the answer to my question. I knew the theory behind it but had not read the correct answer. Everything that I read conflicted in some way. Its all very simple really. Hopefully now the debate will stop raging.
    Once again, thanks for the answer. I did not think that my question would invoke a response from the man himself.

    Allan.

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    Quote Originally Posted by gtimbers View Post
    I was asked to make a brief response to this last post, ... I have never heard a capacitor type that didn't improve (or change) including the nearly perfect teflon variety.
    Hi Greg,

    Nice talk You gave and way comprehensive. I dropped You a PM.

    Thanks!

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    Senior Member Doc Mark's Avatar
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    Hello, Greg,

    Thank you, so very much, for your comments on this topic! I know it's been a hot topic here at LH, and your thoughts on all this are very much appreciated!

    It's also very nice to see you so involved with those of us who have loved JBL components for so many years. At a NAMM show, many years ago, I met Mark Gander and was happy to have quite a bit of time with him, discussing a JBL project I was hoping to undertake. It was he who first suggested that I move on past the LE15 woofers, and explore the possibilities of the 2235H. Many years later, I have found his suggestion to have been absolutely dead on the money, and love the 2235H woofers!

    Since I became an LH member, I've read several of your own comments on such things as 4-way systems, and have found them to be very well thought out, and with much merit. Like I did that day with Mark, I really do appreciate your taking the time to share your thoughts and experiences with "things JBL", and how to best make use of the components we all love so very much! Here's hoping you will visit us now and then, and I will always look forward to any and all information you wish to share with us. Take care, and God Bless!

    Every Good Wish,
    Doc
    The only thing that can never be taken away from you, is your honor. Cherish it, in yourself, and in others.

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    Senior Member jblsound's Avatar
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    Thanks Greg for that info.
    Having biased a pair of custom L212s almost 5 years ago, I totally agree with your statement about sonic effect is one of smoothness, increased spaciallity, detail.

    And like you say, it cost a bloody fortune. The C-C crossovers for the L212s cost me $150/ea, which consists of one card for each driver.

    The cost to do a pair of my PT800s I've figured to be at least $225/ea, as the caps required are quite a bit larger than needed for the L212.

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    G.T., Thanks so much for your explanation and further details on how CC networks were used and experimented with. I had the exact same question of bias voltage and I'm happy to have heard answers and practical experience.

    A colleague of yours, Tom Swem, has recently joined again to comment a bit on a prototype speaker he has. Not sure these were ever "official" L400 prototypes but interesting nonetheless. The thread is here:

    http://www.audioheritage.org/vbullet...ad.php?t=23098

    Regards,

    Bart


    Mini,

    Some more information and enlightenment can be had from other GT posts, notably this one on his reflections and analysis of the 4345. Many of the issues you had questions about, especially directivity, crossover and network design, as well as driver integration, are touched on here:

    http://audioheritage.org/vbulletin/s...5&postcount=27
    When faced with another JBL find, Good mech986 says , JBL Fan mech986 says

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    RIP 2010 scott fitlin's Avatar
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    Hello Mr. Timbers, and thank you for your in depth explanation of biasing caps, and theory of operation.

    Based on your wisdom, and the schematic provided by a forum member, I am going to have a friend who is a wiz at this type of thing fabricate some some boards for me, and take it from there!

    I'm already anxious to hear what the results will be.

    Thank you, and have a GREAT holiday season,
    scottyj

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    Senior Member jblsound's Avatar
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    Quote Originally Posted by scott fitlin View Post
    Hello Mr. Timbers, and thank you for your in depth explanation of biasing caps, and theory of operation.

    Based on your wisdom, and the schematic provided by a forum member, I am going to have a friend who is a wiz at this type of thing fabricate some some boards for me, and take it from there!

    I'm already anxious to hear what the results will be.
    The improvement will be superb. I would suggest using Solen polypropylene caps.
    Last edited by jblsound; 12-04-2008 at 06:07 PM. Reason: spelling

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    I have added the inital question and Greg's response to the Technical Section as would be appropriate.

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    Quote Originally Posted by jblsound View Post
    The improvement will be superb. I would suggest using Solen polypropelene caps.
    Agree, and since the Solens are the recommended cap by almost everyone, that IS what I am ordering!

    I have one more question, since I use six horns and drivers powered by 1 amplifier, do I make two biased cap boards, amp feeds boards , 1 per channel? Or six individual biased cap boards, 1 per driver?

    Cause I'm not really sure!

    Thank you for your input,
    scottyj

  15. #15
    Senior Member jblsound's Avatar
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    Quote Originally Posted by scott fitlin View Post
    Agree, and since the Solens are the recommended cap by almost everyone, that IS what I am ordering!

    I have one more question, since I use six horns and drivers powered by 1 amplifier, do I make two biased cap boards, amp feeds boards , 1 per channel? Or six individual biased cap boards, 1 per driver?

    Cause I'm not really sure!

    Thank you for your input,
    It would depend on how much space you have. When I did my L212s, the original XO was on one 4x7 card, that fastened to the side. But I had to build a card for each driver as the caps are twice the size and twice as many. That took up a lot more room.

    Plus I think its better to have one card (board) for each driver.

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