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Amps for Maggies

Discussion in 'audio' started by murphydog, Oct 14, 2021.

  1. Jim Audiomisc

    Jim Audiomisc pfm Member

    Low capacitance means high inductance. Not sure that would be good for the frequency response - but it might protect an amp from the speaker load at HF.
  2. david ellwood

    david ellwood Kirabosi Kognoscente

    Why does low capacitance equal high inductance?
  3. Robert

    Robert Tapehead

    It does indeed, but the effect on response can be ignored for typical cable lengths for the slightly spaced conductor cables such as those from Linn and Exposure.
  4. murphydog

    murphydog Canine member

    Lots of suggestions. Thanks but looks as though they’ll be moving on as they’re not proving popular with the family
    and the second system room is tiny.
    Darren likes this.
  5. Darren

    Darren All Business

    Shame to be moving the family on MD. Its always a difficult decision, but in the end, your hifi must come first. I'm sure the family will come to recognise this given time and therapy.
  6. Gervais Cote

    Gervais Cote Predator

    It’s too long ago so I don’t remember all the details but it was a German version with a huge orchestra, album cover was brownish.......probably on Deutch Gramophone.
    Del monaco likes this.
  7. Del monaco

    Del monaco Del Monaco

    Maybe Ozawa with the BPO. It’s a thrilling piece of music.
  8. Jim Audiomisc

    Jim Audiomisc pfm Member

    Basic EM physics (simplified)

    c = constant/(L' x C')

    Where c is the velocity of the EM propagation, L' is the inductance/metre, C' is the capacitance/metre.

    Given that the value of c can't be higher than the speed in vacuo it follows that if you try to reduce the C' value beyond a certain level you find that L' has risen.

    Similarly, real materials tend to alter the constant in way that reduces the c value in the medium (cable).
  9. david ellwood

    david ellwood Kirabosi Kognoscente

    Theoretically yes, but in a six foot length of speaker cable?
  10. Jim Audiomisc

    Jim Audiomisc pfm Member

    Yes. The laws of physics apply regardless. However, as you realise, making the cable shorter will reduce *both* the series L and shunt C values. But for a given length you can't beat the above, so there will be a minimum on one value set by the value of the other.

    I suspect the reality in this case is slightly different. That someone says "choose a cable with lower capacitance/metre" as a way of indirectly saying "you need more inductance". Perhaps to avoid admitting a given amp isn't happy with the loading without sufficient inductance in the path. i.e. blame the cable. :)

    The snag with that is someone might simply use a much shorter cable, so not get the 'benefit' they expected.
    poco a poco and Del monaco like this.
  11. Del monaco

    Del monaco Del Monaco

    this forum.

    I love the new learning on this forum. It’s such a treasure trove of info.
  12. Jim Audiomisc

    Jim Audiomisc pfm Member

    I kept wanting to give the equation that ties the factors together. But have no idea how I can type symbols like mu sub-zero or sub-r into this! 8-]

    However, for anyone who wants to dig, it's one the points that comes out of the investigations wrt cables on my website. :)
    Del monaco likes this.
  13. Robert

    Robert Tapehead

    The Naim way, or at least it was for many years.
  14. daytona600

    daytona600 Registered User

    Ran stats for years & amp/cables make a huge difference into a 1ohm load
    2,000wpc monos @ 8ohm 100+ volts & 100a amps output stage normally 4/8 trannies
    these used 128 per channel virtually all amps are unstable or a fire risk into 1ohm load

    Stats are a capacitor, and amplifiers find capacitors very hard to drive. If the cable adds more capacitance, it only makes things that much worse for the amplifier.
    To an amplifier or speaker cable, ESLs appear as a capacitor, while magnetic speakers appear as a combination of a resistor and inductor An ESL is driven by a high-voltage, step-up transformer. T/x takes low voltage of an amplifier to the several thousand volts needed to drive an ESL

    transformers have leakage inductance. This inductance interacts with the capacitance of an ESL to form an L/C (inductance/capacitance) resonant circuit. This produces an undesirable, high-frequency, resonant peak in the frequency response of the ESL.
    this can destroy class D amps

    resonance must be kept in the 20-50 KHz + region so that it doesn't alter the high frequency response of the speaker. to get the resonance high is to build a transformer with very low leakage inductance.

    you want buckets of power + buckets of voltage for Stats
  15. AndrewR

    AndrewR pfm Member

    No it doesn't. Just ask a resistor.

    Perhaps you are purposefully coiling your flat gauge wire?

  16. Jim Audiomisc

    Jim Audiomisc pfm Member

    Nope, I was responding to a comment about cable.
  17. Jim Audiomisc

    Jim Audiomisc pfm Member

    The above is a good argument for choosing:

    1) An amp that is unconditionally stable.

    2) And if that means it needs a small output inductor, then its value should be low enough not to impact the audio band.

    It isn't an argument for simply choosing a cable with a high series inductance and/or resistance.

    Given (1) and (2) a modest length of cable shouldn't be a problem, either. if it is, you need to change something.

    BTW not all ESLs are simply 'capacitors'. cf for example the comments here

    And at HF/ultrasonic an input transformer can become like a capacitor. Just as a mismatched cable length+load can flip as you go to higher frequencies. cf some measured examples here

    more info here
  18. AndrewR

    AndrewR pfm Member

    Me too, particularly regarding a resistive / reactive network found in cables. A low reactance means BOTH low capacitance AND low inductance.

  19. Tony L

    Tony L Administrator

    Blimey, you’ll all be telling us cables make a difference next! ;-)
    Darren likes this.
  20. martin clark

    martin clark pinko bodger

    Yet, that may be/is most likely also true only in a defined frequency range. Not necc a useful one at that- by which I mean, without measurement (the way the so very many audio add-on sellers do stuff.)

    & Jim remains the physicists' physicist ... and not that we get many posting on our weird hobby interest here.

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