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Thread: "Charged Coupled" crossovers?

  1. #31
    Senior Member pierce's Avatar
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    Quote Originally Posted by spkrman57 View Post
    Usually the shelf life of the battery is the same as with several million ohms of resistance in series.

    I would check them once a quarter to verify the voltage to be sure.

    Also, the capacitors when hooked up the 1st time will need some time to fully charge to their potential. Sometimes that may take up to 24 hrs to maximum performance. Also, removing the battery will take about the same time to notice the lack of bias.

    I hope I'm right with this information.

    Regards, Ron
    a capacitor is charged to 63% after R*C seconds, so 2.2 megohms into a 20uF capacitor (typical for what I've seen) would be 63% charged in 44 seconds. another 44 seconds would charge 63% of the remaining 37%, or 87% in 88 seconds. another 44 secs makes it to 95% (in about 3 mins total) whereupon we're deep into the diminishing returns (95% of 9V is 8.55V, which should be sufficient bias...)




    the 72uF caps in that design of the k2.5500 above would take almost 4 times this long, but still not hours.

  2. #32
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by pierce View Post
    ... but still not hours.
    You have not taken into account the strange behaviour of the electrones at the surface of the foil. It will take more time for the full effect than the classical physics want to tell you.

    Btw. the nominal 9 volt batterie should not have less than 7 volts.
    ____________
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  3. #33
    Senior Member pierce's Avatar
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    Quote Originally Posted by Hoerninger View Post
    You have not taken into account the strange behaviour of the electrones at the surface of the foil. It will take more time for the full effect than the classical physics want to tell you.
    I do not believe in Magic.

  4. #34
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by pierce View Post
    I do not believe in Magic.
    It is not magic but solid-state physics.
    a capacitor is charged to 63% after R*C seconds ... (and so on)
    This law can't describe it all as there is only a definite number of charges so loading can not go on undefinitely.

    Further the dielelctricum (I called it foil) is regarded as an isolator, right? But when the voltage is too high than there is current. It is acceptable that there is more to the charges in the dielectricum than simply polarisation.

    Charge coupling demonstrates that there is an influence in a very small amount of voltage when the voltage crosses zero volts. This is audible at low levels but not at louder ones. 9 volts seems to be sufficient.
    ____________
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  5. #35
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    Quote Originally Posted by pierce
    I do not believe in Magic.
    - IME, it's best to just implement the topology ( it's certainly cheap enough ).
    - Delay trying to answer the "why" questions till later / then ones' personal observations can contribute something meaningful to the discussion .

    >< cheers

  6. #36
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    I would have to agree with EarlK. Thinking about it too much you will just come up with ideas why it won't work. The major hurdle for me, and I have asked why and I got a resonable explanation, was the fact that a 9v bias would only work perfectly if the input voltage was below 9v. One would think that it would be prudent to raise the bias level abouve what the maximum input voltage would be. I would like to try a higher voltage but I think the additional benefits would be very small. Also, if something goes wrong with the crossover, the 9v source has much less of a chance at killing you drivers. Just try it. It does work.

    Allan.

  7. #37
    Senior Member jblsound's Avatar
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    Quote Originally Posted by Allanvh5150 View Post
    I would have to agree with EarlK. Thinking about it too much you will just come up with ideas why it won't work. The major hurdle for me, and I have asked why and I got a resonable explanation, was the fact that a 9v bias would only work perfectly if the input voltage was below 9v. One would think that it would be prudent to raise the bias level abouve what the maximum input voltage would be. I would like to try a higher voltage but I think the additional benefits would be very small. Also, if something goes wrong with the crossover, the 9v source has much less of a chance at killing you drivers. Just try it. It does work.

    Allan.
    According to Greg Timbers, no matter what the input voltage is no single conponent in the XO will have a voltage more than 9 volts. I believe that post is in this thread a year or two ago. Tho it might be a different thread.
    Living in the Land of the Sun

  8. #38
    Senior Member Steve Schell's Avatar
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    As I understand it the input signal peak to peak voltage would have to be twice the polarizing voltage, or 18V in the case of 9V bias, before the signal would swamp the bias. One direction of swing will momentarily increase the bias while the other direction will decrease it. If the input signal happened to reach or exceed 18V PtoP, all that would happen would be that one side of the signal peaks would be subject to the zero crossing nonlinearities that have been avoided with the bias. It is doubtful that this would be audible. In fact, if any of the speakers I listen to regularly receive an 18V swing I don't want to be anywhere close!

  9. #39
    Senior Member pierce's Avatar
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    my comment about Magic was in reference specifically to Hoerniger's statement ...

    You have not taken into account the strange behaviour of the electrones at the surface of the foil. It will take more time for the full effect than the classical physics want to tell you.
    odd how a foil which can change polarity at megahertz speeds would have a memory for a dc charge that required conditioning it for hours.

    I have no issues with the basic concepts of biasing capacitors... And I can see how the dielectric hysteresis that this bias circumvents are only an audible issue for small signals, that if you have a large enough signal to exceed 9V peak across the filter caps, the tiny amount of distortion would be insignificant.

  10. #40
    Administrator Robh3606's Avatar
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    With a DC bias why would the cap loose the bias due to an AC signal??? AC and DC have a different set of rules. You also have very long time constants involved. I don't see how you could swing the cap through 0 volts with a 10ms peak no matter what the voltage when you have a 20 second time constant to work against. That battery is always there so it is always trying to charge the capacitor. The AC see's the battery and resistor as an open and the load as a couple of ohms. It's no surprise where the AC is going.

    Rob
    "I could be arguing in my spare time"

  11. #41
    Senior Member pierce's Avatar
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    Quote Originally Posted by Robh3606 View Post
    With a DC bias why would the cap loose the bias due to an AC signal??? AC and DC have a different set of rules.
    actually, AC and DC follow exactly the same set of rules, its just that AC is changing in time while DC isn't, so this complicates the circuit analysis, and takes it from simple arithmetic into the realm of calculus and differential equations when you add reactive signal elements like inductors, capacitors, transformers (and, of course, at a high enough frequency, *everything* has reactance)..

    the DC 'bias' is added to the AC signal. if the AC signal is +/- 5 volts, and your DC bias is +9V, the net affect is a AC signal that ranges from +4 to +14 volts. if the AC signal is +/- 12 volts with the same 9V bias, then your net signal will be -3 to +21 volts.

  12. #42
    Administrator Robh3606's Avatar
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    actually, AC and DC follow exactly the same set of rules,
    You can pass DC through a capacitor or a transformer?? What about the time constant to charge the cap?? Does it just go away when you apply an AC voltage??

    Rob
    "I could be arguing in my spare time"

  13. #43
    Senior Member pierce's Avatar
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    Quote Originally Posted by Robh3606 View Post
    You can pass DC through a capacitor or a transformer?? What about the time constant to charge the cap?? Does it just go away when you apply an AC voltage??
    you cut off the interesting part...

    its just that AC is changing in time while DC isn't, so this complicates the circuit analysis, and takes it from simple arithmetic into the realm of calculus and differential equations when you add reactive signal elements like inductors, capacitors, transformers (and, of course, at a high enough frequency, *everything* has reactance)..

  14. #44
    Administrator Robh3606's Avatar
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    its just that AC is changing in time while DC isn't, so this complicates the circuit analysis, and takes it from simple arithmetic into the realm of calculus and differential equations when you add reactive signal elements like inductors, capacitors, transformers (and, of course, at a high enough frequency, *everything* has reactance)..
    When you look at a circuit you look at it for both AC and DC analysis. For example you can have multiple sections in an amplifier that are capacitively coupled but are electrically isolated for DC and work under different DC voltage and bias conditions.

    Maybe I am wrong but I think you are looking at it as if the AC and DC are the same or act the same in the same circuit. If you do a simple DC and AC analysis to a charge coupled capacitor circuit they look very different.

    In your example you have the AC voltage crossing zero volts. What is the DC voltage doing?? Seems to me it's not moving, based on simple addition or subtraction used in the example. If the DC bias doesn't change the capacitor never goes to zero volts.

    Rob
    "I could be arguing in my spare time"

  15. #45
    Senior Member pierce's Avatar
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    Quote Originally Posted by Robh3606 View Post
    In your example you have the AC voltage crossing zero volts. What is the DC voltage doing?? Seems to me it's not moving, based on simple addition or subtraction used in the example. If the DC bias doesn't change the capacitor never goes to zero volts.

    AC is volts changing over time, while DC is constant volts. volts is volts.

    Electronics engineers tend to prefer to simplify things and treat DC and AC as distinctly different things, it certainly makes the math more tractable, but in fact, there's a continuum of behaviors, as the frequency approaches zero, the AC approaches DC

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