Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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Re: May I comment?

Posted by Jacques (A) on July 8, 2006 at 05:33:34

In Reply to: May I suggest? posted by real_jj on July 7, 2006 at 21:55:22:

Good presentation. Some remarks however (please don't get upset of these, realjj, and don't ask for apologies...)

• Pages 7 to 7 , I would have liked him having a word for differential current breakers, triggered above 5mA fault. It saved so many lives here (p7 and 6) since it is mandatory. Some of your US lives could also be saved this way too, if EEs lobbies cry loud enough as make it a public health issue. Whitlock is way conscious of the problem, not of its existing and proven solution.
• the thing presented on page 8 should be forbidden (as it is here) : it is not fool-proof. We human species are fools...
• Myth page 12 makes me tickle. A voltage is the measure of a difference of potential (defined from the electrostatic field mathematical structure, but it's another topic) . A difference means two points of measurements. If I decide that MY ground (or more exactly the copper covering the test table in my lab) is at reference 0V, it is. It is enough for my uses. As for other grounds, I just don't care.
  I don't see any clue in this "myth". Why did he write that?
• Page 14, Myth: most Noise is Caused by improper AC Power Wiring.
  I agree with his explanation p14, 15, 16 (see note below). However, noise can be caused also by interwiring neutral and ground in outlets. It's a very common problem, and is a source of much noise if several equipents are connected together (a default current flowing through the interconnect, which develops large common mode noise. On balanced interconnect, fine (as long as CMRR is good enough at the frequencies of the perturbation), on unbalanced, this common mode noise is seen as differential (more on pages 31 and following). I wonder he didn't notice it.
• MYTH:These Voltages and Currents can be Eliminated
  SHORT ‘EM OUT” with massive copper bus bars
  Experiment to find a “better” or “quieter” ground
  well, if you designed badly your equipment, or are trying to interconnect badly designed equipment, that's often the way to go. For example, those ground lift switches on pro audio systems, whose use if often related to stupid grounding scheme in the equipment (confusion signal return and chassis ground being the main culprit).
  Route noise to an earthground where it disappears
  He's right, it's a stupid idea
  Make the electrician fix “his” problem
  If the problem relies on intermixing neutral and ground, as often the case, thats a good thing to have the electrician fix his crappy work, don't you think?
  Install equipment to “purify” the “dirty” ac power
  he's confusing several issues here. Raw AC power sometimes cannot afford a level of quality complying with a system requirement would the culprit be power interruptions, brownouts, harmonics, RF noise CM and DM etc etc. That's why UPS do exist and are used in industry. By writing this, he behaves here like the guy who has good knowledge of a narrow topic, and therefore thinks that everything is related to the topic he knows best.
  Does an earthground really stop noise? Think about all the electronics in a 747 ...
  It is a marketing hype argument, not a solid one. On the contrary, everything is well grounded on a plane. It carries its earthground reference with it, but it's a real neat ground. In many areas, even done in order to let a lightning stroke pass through it without melting anything away.
• page 24, Unbalanced versus balanced InterfaceLacks the Common Mode Input Impedance Zicm, and the Common Mode Ouput impedance Zocm (for the later, its schematics seems even to imply that the this Zocm is R0/4 )/. Curious for a transformer manufacturer, for which those impedances being high is quite the best justification for using them...
• page 26, MYTH: Impedance Implies Level Odd myth. In which tribe did he hear about? But the Earth is huge.
• MYTH: Audio Inputs and Output Should Be Impedance Matched that was an old myth common in the telecom community up to the '60s (before the digital era), since it was often true on their systems thanks to their huge length. But for everybody under 90, it seems just of an historical interest. Am I wrong? Or the only one under 90?
• Pages 30 to 35Unbalanced Interfaces He is so true! I would like people interested in audio know those paragraphs by heart forward and backward. Then prof johnston would make a peer-review test (the peers being inmates too)
• MYTH: Expensive Cables Stop NoisesI would like the team of virgins he talks about pet and cuddle him for having written this page. Expensive cables have two main purposes: be used as tonality controls since they are banned from audiophile frontplates, be a social symbol of the hidden kind, those your neighbors won't know about (or wouldn't understand), but that you know you own and can afford (like giving anonymally to a charity). Still better if you're not so sure of their magic action. Oh, as for his reward, maybe, he would prefer a team of boys instead of the weaving virgins? OK with me, granted, I keep the virgins.
• page 37 to 45. again pages to know by heart forward and backward. For those who don't understand while at the same time are dazzled by the clarity of the quantic-based explanation of some known magic metallic undercutting waste of an Asian stamping press delivered in a crystal box, I would advise to add the adjectives "quantic and entangled before every other word of those pages 37 to 41, and then to learn it by heart. Thinks should then be clearer (that's paedagogy, boy).
• pages 45 to 77. Excellent. I wonder why he gives so neat explanations now, after having ignored the Common Mode Input Impedance Zicm, and the Common Mode Ouput impedance Zocm on page 24. Maybe his brain works on tubes, and needs some warming. No problem, I will ignore those early pages. Or make me think of musicians just before the concert, emitting distracious sounds to set pitches...
• page 78 and 83: to know by heart forward and backward.
• remaining is fine

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