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  1. #26
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by dean_martin
    The input impedance of the amp is 20k Ohms. The preamp I'm considering has an output impedance of "less than 500 Ohms."
    You should have no issues at all. I am particularly sensitive to this question in that I don't use my preamp at all when playing the CD source. I go direct to amps via precision DACT attenuators. That results in a less favorable impedance multiple although my tube amps help with their 137k input impedance. My situation does, however, require using low capacitance cables.

    rw

  2. #27
    Forum Regular hermanv's Avatar
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    According to the data sheet my Levinson DAC has an output impedance of less than 6 Ohms and the Pass Labs an input impedance of 11K (unbalanced) giving a ratio of 1833 to 1, great.

    Unfortunately I have a passive pre whose input impedance avarages about 3.9K Ohms and whose output impedance tends to be half that (it depends on volume setting). So I end up with a ratio of more like 11000/1950 or 5.6 to one. The system sounds great, numbers are usefull, don't get too carried away with what is a minimum acceptable number.

    THD (Total Harmonic Distortion) has the unfortunate limitation of not telling you which harmonics are most present. SET amps are notorious for having poor THD specs, but all their problems are usually with low order even harmonics such as second, or fourth. SS amps can have the opposite problem, small numbers, but lots of odds of high order such as 5ths, 7ths, 11ths or higer.

    Most people think SETs sound relaxed and clean while they find SS gear with high distortion to be grating and fatiguing. It's seems to be these high order harmonics that our ears find most offensive. This could be because it is quite difficult to create these with accoustic instruments, mainly brass and violins tend have high order harmonic content and they are generally considered instruments that have "bite". None of this shows up in the data sheets so THD doesn't provide much help.

    IM could help; all amplifiers that distort at all will create sum and difference producs;
    suchs as f1 +/- f2
    and 2f1 +/- f2
    or 2f2 +/- f1
    I have seen reviews of amplifiers with very high intermodulation distortion that the reviewer claimed sounded great, but most well regarded SS amps have good IM numbers. Lots of negative feedback helps IM numbers but tend to move single frequency harmonic orders up higher. A trade off. Charts are better than just specs, but require more skill or knowledge to read.

    It's all complex enough that your ears are your most reliable guide.
    Herman;

    My stuff:
    Olive Musica/transport and server
    Mark Levinson No.360S D to A
    Passive pre (homemade; Shallco, Vishay, Cardas wire/connectors)
    Cardas Golden Presence IC
    Pass Labs X250
    Martin Logan ReQuests.

  3. #28
    Do What? jrhymeammo's Avatar
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    Quote Originally Posted by E-Stat
    My situation does, however, require using low capacitance cables.

    rw
    Hey E-stat,

    Could you tell me some ballpark figures on low capacitance cables? I'm in a process of searching for a pair of XLR right now. I havent decided on the length at this moment, but it's be either 1 or 3m. 3m of Silver Streaks could be rather costly. I'm currently using DH Labs BL-1 and they are absolutely the worst sounding cables I've tried in my system. But a pair of Air Matrix could be a different story.

    Thanks

  4. #29
    Music Junkie E-Stat's Avatar
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    Quote Originally Posted by jrhymeammo
    Could you tell me some ballpark figures on low capacitance cables?
    Blue Jeans cable has some low cap interconnects for about $32/meter. I use somewhat pricier JPS Labs cable.

    Quote Originally Posted by jrhymeammo
    I'm currently using DH Labs BL-1 and they are absolutely the worst sounding cables I've tried in my system.
    I have some of those in the single ended flavor. While they are a tad "tizzy" at the top, I find them pretty decent.

    rw

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