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

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Re: Sorry, chap, and a right answer.

Posted by Jacques (A) on April 25, 2006 at 01:48:08

In Reply to: Sorry, chap, and a right answer. posted by real_jj on April 24, 2006 at 20:32:17:

First, I'm speaking from a US point of view, and there are some very leaky power supplies over here in the colonies.
So why doesn't the King's colonial administration outlaw power supplies with too bad a current spectrum the way we do in our decadent and fallen continent? Would be good for all parties: power companies, distribution companies, consumers, even employment market since you would have to hire competent engineer to design those new breed power supplies.

Second, anything with a diode brige creates harmonics, you'd better have a pretty good RFI filter even for that.
You're right (I never argue against that fact!). However, a pretty good RFI filter is not enough if you let the wiring around the diode resonate on its stray capacitance and inductance, or the components around the diodes resonates thanks to parasitics components (xformers with their interwiring capacitance etc). The wiring around the diode has to be done in a proper way not to resonate and not to radiate E, H and EMI fields. The way it's done in many so-called high-end audioequipment is just funny in these matters. And also: critically damped (at the VHF impedance of your wiring, which means you have to calculate it, and measure it with a network analyser). When I see the wiring in many so-called high-end equipment with PS at 50/60Hz, I do understand why they cannot use a SPS at 500KHz!

Third, I can and do measure crap on the power lines. (this in the USA) It's there, in plain sight, even before the harmonic analysis. One can see glitches and flattening where bridge-rectifier supplies start to operate, etc.
I know. Recording those events is what power network dataloggers are made for. Not only in the US can the main become crappy: more in the US for 3 reasons:
(1) average final user's lines are longer in the US. The country is large.
(2) the voltage being half than ours, the same perturbation is 3dB higher in Bushland.
(3) the TT interconnexion scheme, with neutrals connected to earth at the xformer and all the users premises, is prone to mix common-mode and differential modes perturbations and to cancel the effect of line impedance in isolating remote perturbation sources. So, you get a "pool" of all the perturbations occuring on the mains connected to your HT transformer, even if/when the source is remote. By contrast, on a TI network, you get perturbations only from your neighborhood, remotes ones are well attenuated. (but I understand that the size of your country and its high keraunic level in many areas precludes the use of TT networks. Also historical reasons.).

Don't claim something is wrong until you consider the context and the consequences of picking a fight with somebody who does know what they are talking about.???
Waooo, ticklish you guy! Can you point out where I "claimed something is wrong"?
I just say, and I say again that a correctly designed switching PS does not inject in the network perturbations above the levels set in the standards. Because it cannot, or won't pass the certification if it does.
I also say that equipment can be built in order to work on very perturbed power networks. As a layman matter of facts, think of devices like self dialysis apparatuses that people use at home. A perturbation-induced event that would bug out the microcontroller or some measure and you're dead and the company is sued down to its roots. However, it works. Reliably. Even in non controlled electrical environment. They just applied the stringent standards for life-sustaining equipment, and went a little farther.
My concern there was not to bash you, which would be childish, but to defend correctly designed PFC'ed switching power supplies from being the culprits for sending crap on your networks, which is way not true...

My other concern was about the fact that it seems so hard to the high-end audiocommunity to switch to PFC'ed switching power supplies from the crappy transformer/rectifier/storage cap scheme.

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