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Old 20th February 2012, 04:52 AM   #1
Bonsai is offline Bonsai  Taiwan
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Default Noise

I thought I'd just share this with you. I was working on my new power amp this weekend, and using an overhead light fitted with a CFL lamp - rated I believe for the equivalent output of a 100W incandescent. The attached picture you see is the output from the amp - about 60KHz at 70mVpk-pk. The amp has a filter on the front but is exposed and about 1m from the lamp. Turn the lamp off, and the amp output is quiet as a mouse.

There's a lot of garbagae around now with these new lamps. I recommend you keep them away from your workbench, and you find something else for your listening room as well.

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File Type: jpg CFL Radiated Noise.JPG (35.5 KB, 196 views)
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Old 20th February 2012, 05:17 AM   #2
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Default yeppers

This thread discusses CFL nastiness also. Looks like similar noise band as well.
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Old 20th February 2012, 10:22 AM   #3
DF96 is offline DF96  England
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Radio amateurs and short wave listeners have been suffering from CFLs for years. The cheaper ones often omit the suppression components, like many Chinese SMPSs. Even when present, the suppression probably won't work down to audio frequencies.
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Old 20th February 2012, 01:07 PM   #4
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i had to replace the flourescent lights illuminaing the back of my record (LP) shelf with a string of LED christmas tree lights. Too much noise in the hifi.
I'm fairly annoyed anyway at the single source nature of CFL's. In the stores I am offered the opportunity to buy 50 different brands, all made in the same country, probably the same factory. My electric utility gives CFLs away, paid for by my base service fee - we are supposed to use CFL's as a patriotic gesture to avoid wasteful domestic coal production.
I found a few CFL's 5 years ago assmebled in City of Industry, CA. The one I operate in the room with the hifi does not present a sound problem. It is obviously an inferior product, deserving bankruptcy.
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Old 20th February 2012, 01:12 PM   #5
DF96 is offline DF96  England
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In the UK we have some choice. CFLs seem to fall into two price bands. It may be (not sure) that the higher price ones (typically from known brands such as Philips or GE) emit a bit less interference and may last longer.

LEDs won't always help, as they may be driven by a cheap SMPS.
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Old 20th February 2012, 01:20 PM   #6
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You know what? The one that caused the interference was from the big European company.

The only way to solve this problem is legislate and demand that these things meet minimum standards. And no wiggle room either.
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Old 20th February 2012, 01:28 PM   #7
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Yes, I once had a DVD player from Philips which generated interference (made in China of course). Got my money back and bought a Sony. Much better - I guess the Japs are more suspicious of Chinese factories so insist on things being done properly.

The legislation exists, certainly in EU, but it is rarely enforced. The political will is currently to encourage/force adoption of CFLs etc, so inconvenient truths like poor EMC performance are ignored. In the UK it would be a job for local Trading Standards officers, but they are more interested in serious safety issues and fake designer labels.
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Old 20th February 2012, 02:16 PM   #8
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Welcome to the world of noise measurement, and WHY I only have incandescent lamps in my lab.
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Old 20th February 2012, 04:47 PM   #9
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Try replacing with halogen, excellent light output yet still a filament. CFLs are rubbish when it comes to EMI no matter where they come from.
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Old 20th February 2012, 05:31 PM   #10
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The new fluorescent lamp we got for the kitchen recently has been quite unconspicuous in terms of RF emissions so far, even down on 160m. (Maybe not that surprising, as it's sold by what appears to be a joint-venture involving Osram.) The one it replaced (about 9..10 years old) had been much worse, at shorted tube length.

ESLs haven't been much trouble either, as long as I keep antennas like 0.5 m to 1 m away (scaling with power, an 11 W Osram emits less than a 23 W Philips). And that's stuff that's SUPPOSED to pick up RF.

The worst interference sources here are a plasma TV (Panasonic eventually wised up and by about 2009 apparently modified their panels so they'd be RF-tight, but this model precedes that by a few years), and as it is much closer to my antennas, the SMPS inside my ethernet switch (about 10 years old; no CE anywhere in sight, I don't think that really was legal at the time).
Plasmas are a real pest on MW and lower SW. Their direct radiation (when using unshielded panels) is readily detected from meters away.

I'm not sure how RF from florescents/ESLs would get into amplifiers. While they do involve some high-impedance nodes, normally they have a metal case which is connected to circuit ground somewhere. RF filtering on the input may not be effective at a few 10 kHz yet, but a low source impedance or even a short on the input should keep that down, too.

BTW, when using LEDs for biasing, note that they also work in reverse. Something to keep in mind.
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