一切從Concert開始......

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An absolutely another story is RFI. This frequency is millions times higher than the AC frequency. It behaves like radio-wave and it can penetrate the gear. What it does inside is this:

1. creates fast oscillations in magnetic field of transformers
2. becomes amplified by transistors, tubes and op-amps
3. mixes with digital signals and creates errors
4. interferes with various clocks and oscillators
5. moves operating points of devices
6. Causes erratic behaviours of integrated chips
7 can be reproduced as sounds above hearing threshold but causing us to be tired and annoyed.


The problem is that the RFI can enter gear DESPITE the galvanic separation by transformer and  despite filtering effect of capacitors in power supply. The RFI becomes the Trojan Horse of AC grid power system  in our gear.

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Getting rid of these is a bit tricky. But my advice is - that our intervention is focused on hundreds of kilohertz and not close to 50 Hz AC.  So the intervention is very gentle, very low order, and  nothing to do with our regular current feeding the gear.

xover

The filtering is achieved by two opposite effects: parallel capacitive shorting and series inductive blocking.
The kindergarten explanation for non-engineers is that for high frequency - a capacitor presents a SHORT, and coil - presents a high resistance (impedance).


So a RFI noise rides by the AC cabling to our house very happy, like a Porsche on the autobahn. But when it arrives to the filter - the road becomes blocked by the coil. Oh shit thinks the noise, getting through is gonna be real tough.  But then it notices an alternative route - an easy one - via a cap. It chooses the easy route and ends up in the ground. Dead.  That's our noise trap. That applies of course  to very dumb Porsches only.  This method does not affect the AC performance because the cap is VERY small and the coil has a DC resistance of milli-ohms. Literally - of a foot of thick wire. So the impulse response of the AC source to the amplifier demand is not limited. We say that the supply is NOT CHOKED.

xover

The audible effect depends on many many factors - the circuits in gear, the internal filters commonly built in, the ground quality and arrangement in the house, the type of devices playing together etc. It is IMPOSSIBLE to predict the degree of improvement, but strangely - the result s are very consistently proving in every house that:


1. The change is audible
2. The change is Positive
3. The negative effects do not exist at all (trade-offs)
4. Every gear responds more or less
5. Every owner hears it and accepts it.
6. Noone wants to go back to raw AC

xover

What you should hear - is that the musical event becomes more real, instruments better separated, threads easier to follow, like more microphones were used. Timbres become more natural, the woods, the brass, the drum skins, the strings - all sound more "analogue".


The switch back to no filter is perceived like a bad thing,  the filter is very addictive.

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[線路圖]

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Schematic Key


  ______ = wire connection


  o = junction where wires or leads are connected/soldered together


  ) = wire connection skipping over another wire, no junction


  H= Hot AC line or (L/Live)


  G = Ground


  N = Neutral

xover

-Parts Descriptions-



For AC Line Filter Schematic

C1,2, 3 = 0.1 uF 250 VAC metallized polyester AC line rated for
continuous use across the line, which is designated as "X" type caps.
C4 = 0.01 uF 250 VAC metallized polyester AC line rated cap as above.
L1, L2 = 50 to 100 uH powdered iron rod core inductor with DCR less
than 0.03 ohms.

For AC Surge Suppressor and Filter Schematic

B1 = Circuit breaker, 5, 10 or 15 amps as appropriate, thermal type.
V1,2 = Harris Metal Oxide Varistor 150 VAC rated
C1,2,3 = 0.047 uF 250 VAC metallized polyester AC line rated for
continuous use across the line, which is designated as "X" type caps.
C4 = 0.01 uF 250 VAC metallized polyester AC line rated cap as above.
L1, L2 = 50 to 100 uH powdered iron rod core inductor with DCR less
than 0.03 ohms.


-Capacitors-

These are metallized polyester AC line rated capacitors, rated for
continuous use across the AC line, UL and other safety agency listed.
For any capacitor placed across the AC line, I recommend use of
fully rated AC line parts, which are designated as an "X" type.
They are 250 VAC rated, and can be used with European voltages as
well as for US lines.