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In Reply to: A clue to an explanation. posted by Al Sekela on April 2, 2007 at 12:29:33:
Al,I think you made several very good points. I've been using homebrew, unshielded interconnects for years. When I first built them I thought they sounded better than anything else I'd tried except that the high end was a little "tizzy". It occurred to me that I may have made a fine, high Q antenna system, so I matched them. They had a Zo~300ohms so I built some end gadgets that had a build-out resistor for the source (~200ohms) and a 300ohm termination at the load end. That seemed to do the trick.
I was just trying get good sound so I didn't make any measurements, but anecdotally I think this supports your advice.
Follow Ups:
For these, dynamic loading with R-C networks may be a good compromise.
While I didn't dissect them, I did measure the output impedance on the sources I was using and they all seemed to be a pretty flat 100 ohms so I just assumed that they had an internal series resistor. As near as I could tell the ~600ohm total load wasn't causing distortion problems but it's probably on the edge unless they used good line drivers.Had I heard problems my plan was to just use a bigger build-out and turn up the volume. The line really only needs to be matched at the load end.
But using a cap is a good idea and may make the scheme usable with a wider variety of equipment and lower Z lines. Perhaps a COG mono would do the job. I'd be loath to add much dielectric absorption.
What I did probably isn't optimal. I'm not a very good audiophile as I tend to stop messing with the equipment when I'm happy with the sound. These days it's computer software, the wretched "players" sound varies with type, versions, settings, lunar phase... At least they are easy to A/B test.
Rick
My Wadia 861 seems to have a good, strong set of output drivers. I did not notice degradation when I first tried loading the cables with 600 ohms at the amps, but, upon further refinements, it became clear that the sound was better with higher impedance.
Well, you've managed to plant a definite seed of doubt. I think I was so pleased with how much better my system sounded after changing the interconnects that I just didn't bother to drag the distortion analyser in from the garage.At a guess I'd suppose the Wadia to have a stouter output stage, if anything, so I'd better revisit mine.
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