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Hi,I bought a surplus iso-transformer (Ericsson) some time ago.. Although it did lower the noise floor of my system I could still hear the switching transient noise when I turn off the lights in the living/listening area using in-wall light switches ('popping' noise from speakers especially when volume is up). Does the "screening" between the primary and secondary windings of an iso-trannsformer limited in attenuating souch noise???
The light bulbs are warm white 7W energy-saving types. I live in a condo apartment but at least the mains for audio has its own high current circuit breaker. The mains V here is quite on the high side, most of the time 10V higher than what is normal (the darn electric co. won't do anything about it). I step down the V using my spare Automatic Voltage Regulator. BTW, the switching noise is there w/ or w/out the the AVR. Thanks for any comments.
fred
Follow Ups:
(1) It's likely that your light circuit makes a loop somewhere, I mean 2 wires carrying current not laid out close to each other, so, when switching, the di/dt causes a strong RF magnetic pulse though the loop area. To avoid recabling your lights, use a RC damper in parallel with the switch, as other people advised you.
An important concern here: or buy a built RC damper, or DIY your own with a 100ohm resistor and a 0.1 uF cap, but, in the later case THIS CAP SHALL BE AN X TYPE, I REPEAT THIS CAP SHALL BE AN X TYPE: SHALL BE, NOT SHOULD BE. Would I have to insist more?(2) to get rid of your overvoltage, i drawed a little schematic you can download here (see link below). Its main advantage is that using a 100W transformer, you can fix mains rated at several KW. And safely, and without resorting to quantum a**holes, oh, sorry, dots.
The schematics are drawn for a 127V mains, because, since you worry for those feable 10V, I guess you live in a low mains continent.
Hi Jacques,Thank you for the .pdf schema. I appreciate your help. And yes, x-rated caps are mandatory. There are lots of them types (rated for 250VAC mains) that can be ordered through our local RS-Comp.
Our mains V here on average should be 230V/60Hz, but our condo building gets 240 and even sometimes 245V in the evenings. What's worse is my 3kV iso-trannie steps up the voltage even more to 10V again (!), getting me around 250V at most times! The other taps in the secondary are way lower than 220V to be of any use.
I won't really worry about the 10V overvoltage if my phonostage's power trannie would not saturate (when I'm near the unit I could hear the mild vibration) and the unregulated DC filaments of my DHT tubes goes way up increasing distortion and shortening its life. That's why I used my spare Matsunaga automatic voltage regulator to step it down a bit. I plug-n all my electroncs (amp/preamp, turntable, etc) to the AVR-> Iso-Trannie. If I can implement your transformer trick (with a friend's help) I could use the AVR for non-audio stuff.
Oh BTW, Jean Hiraga is one of my heroes....Best,
fred
...
Supress at source....using supression caps.
Noise as you describe is broadband RFI from the spark at the switch - isolation transformers can't help here.To get rid of the noise you just need to wire a contact suppressor across the switch, which will snub the spark when the switch opens. These are available commercially at low cost, or - if you are confident at DIY - make your own from a mains-rated 10 to 100nF cap in series with 100ohms.
Is the 7w bulb a flourescent ? If so, it's bad news because it emits a lot of RFI both into the air and onto the AC line it's on. Also, IMHO the 100 ohm R sounds somewhat high. I'd try an 8-10 ohm. Also, the R should be a carbon composition rated @ 0.25 or 0.5w as they are much more "lossy" that any other R's. The cap is there to shunt RFI to Gd. and the R to dissipate as much of that RFI as possible rather than dumping it onto the neutral leg of that circuit.Happy Listening !
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