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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: RE: We don't want to talk about it with the type that hang out in Prop Heads. posted by Steve Eddy on February 12, 2011 at 08:27:05:
What SE has shown, is essentially accurate. However, the mysterious distortion comes ONLY when certain cables are plugged into the analyzer, osc out to test in. This is a very easy connection that is BUFFERED on both sides from extra concern about loading, small impedance differences, etc.
Just within the last hour, I was able to find an RS cable that measures WORSE than the VDH reference, without too much trouble at all. I also found an RS cable that measures very much like the VDH cable. The main factor that seems to create this difference, is that the GOOD RS cable is well used with the test gear, and it is part of my lab stock.
The tests that SE has posted are only 3, of dozens and dozens of measurements of a whole lot of cables. This is what I found in general:
First, cable cost does NOT seem to be the major contributor in this test. Some very cheap cables (including SE's test units) measured good to very well in this test. Some other cheap and some very expensive cables, like the VDH and the JPS that I use to establish my baseline, have always tested well.
Second, it MIGHT be the ground return, or the shield that is to TRUE distortion producer. IF SO, then this should be looked into, because most real hi fi systems may be equally sensitive to this distortion generation, as much as the ST1700B.
Third, my test equipment is dated but works well enough for this test, but it is not 'idiot proof' and may be difficult to interpret if done on an absolute scale, BUT COMPARISON between the cables can be easily noted, and it should be obvious that among the 3 tests, the RS looks the worse. Also, the sameness in the test samples is usually the test equipment residual, and should be ignored. This is one of the problems with the ST1700 systems, they were designed for consistent performance to 100dB, NOT 120dB and this requires modification of the test equipment to lower the residual, or else to systematically ignore the test equipment residual. The test equipment that I am using TODAY, is completely unmodified, and actually shows a slightly higher test equipment residual than my personal unit, which the screen shots shown were measured on, that was slightly modified to LOWER the oscillator residual.
Fourth, my first hypothesis was that I was looking for 'microdiodes' as I have seen similar behavior in potentiometers. However, it might as well be 'microgaps' instead. In any case, it acts like a 'dead zone' at 0 V. We usually call this crossover distortion, a general definition.
Fifth, I first thought that I was paralleling the test that VDH did many years ago, but HIS measurement level was much lower, maybe 60 dB lower, and that is a separate issue.
Sixth, I found that my 'bad examples' often became fairly good examples, IF used over a period of several hours, so I found that I had to REMOVE the BAD cables and put them aside, IF I wanted to use them to show the problem in future. Previously, I might leave the test equipment running with the cable installed, and a week later, the cable measured much better. I suspect it is 'break-in' that is being shown, in this case. Any questions, anyone?
Edits: 02/12/11 02/12/11 02/12/11 02/12/11
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Follow Ups
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - john curl 10:12:06 02/12/11 (12)
- My thanks to both of you for the data and info. - rick_m 17:07:22 02/12/11 (3)
- RE: My thanks to both of you for the data and info. - Steve Eddy 18:06:19 02/12/11 (2)
- Who's Bruno? -nt - rick_m 07:23:28 02/13/11 (1)
- Bruno Putzeys... - Steve Eddy 07:52:49 02/13/11 (0)
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - Steve Eddy 11:31:18 02/12/11 (7)
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - john curl 12:05:44 02/12/11 (6)
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - Steve Eddy 12:37:56 02/12/11 (5)
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - john curl 13:25:13 02/12/11 (4)
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - Steve Eddy 14:08:20 02/12/11 (3)
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - john curl 14:29:28 02/12/11 (2)
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - Steve Eddy 15:04:36 02/12/11 (1)
- RE: We don't want to talk about it with the type that hang out in Prop Heads. - john curl 16:13:42 02/12/11 (0)
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