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Thread: Low capacitance cables

  1. #51
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    These is a very old Siegfried Linkwitz post on the subject:

    Let's put a little realism into high frequency loss due to long interconnects.

    I just measured 2 nF capacitance for a 5 m RCA connector cable that I use with Pluto. That is 400pF/m rather than 100pF/m or less which is typical for interconnects.

    If the output impedance from the pre-amp is 1kohm (high) and the input impedance of the power amp is 10kohm, then the effective impedance is 10k//1k or 910ohm.
    With the 2nF cable this gives a low-pass 3dB cutoff frequency of Fc = 1/(2piRC) = 87 kHz, which is still far above the needed frequency range. With a typical capacitance cable the cutoff would be at 350 kHz. If the passive pre-amp has 10kohm output resistance Fc would still be 70kHz.
    Kevin

  2. #52
    [Industry Expert] Addicted to Best! DaveC's Avatar
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    Yup, C is not the problem that causes highs to seem dull in some cables, although it is misunderstood or misrepresented by some to be an issue. Low-C is not an indicator of good-sounding cables either.
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  3. #53
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    Quote Originally Posted by Speedskater View Post
    These is a very old Siegfried Linkwitz post on the subject:

    Let's put a little realism into high frequency loss due to long interconnects.

    I just measured 2 nF capacitance for a 5 m RCA connector cable that I use with Pluto. That is 400pF/m rather than 100pF/m or less which is typical for interconnects.

    If the output impedance from the pre-amp is 1kohm (high) and the input impedance of the power amp is 10kohm, then the effective impedance is 10k//1k or 910ohm.
    With the 2nF cable this gives a low-pass 3dB cutoff frequency of Fc = 1/(2piRC) = 87 kHz, which is still far above the needed frequency range. With a typical capacitance cable the cutoff would be at 350 kHz. If the passive pre-amp has 10kohm output resistance Fc would still be 70kHz.
    3dB down at 87KHz is certainly not good enough for me. I want to see each of my components with B/W of 100kHz. Why would I want less for my cables? These roll-offs are additive. 1dB down at 30kHz for a cable may result in 3 dB down or more for the system.

    It's like trying to measure a signal with frequency components of 1.5MHz with a 2MHz B/W scope. If you don't mind an inaccurate reading...

    Capacitance is certainly not the ONLY attribute that makes a great interconnect cable, but an important one. More important than resistance and inductance.

    Steve N.

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