Comments on Existence is Wonderful: EMC Engineering: What Does It Mean?

So, I take it you would consider it rude behavior ...

2011-05-09T01:08:43.675-07:00

So, I take it you would consider it rude behavior on my part to construct and use an old-fashioned spark-gap transmitter? (Snork!)

I have read of people making aluminum foil beanies...

2011-02-24T15:57:53.201-08:00

I have read of people making aluminum foil beanies for themselves, to stop the alien mind-control rays. I have always poo-pooed that silliness, thinking that if they knew what they were doing, they would make them out of mu-metal.
What can you tell us about mu-metal and its ability (or lack thereof) to block magnetic influences?

(reply to jimf, part 2): ...Both DACs had ...

2011-02-22T11:00:28.504-08:00
(reply to jimf, part 2):

...**Both** DACs had that exquisite smell of cooked electronics after the adventure.

Heh, I am *quite* familiar with that smell. Its presence generally prompts at least a few cracks about how one has "let the magic smoke out" [of the electronics].

Electromagnetic interference, indeed! It's gonna cost me to have those two DACs fixed. I'm just lucky nothing else was fried (including the speakers and subwoofer). The system continues to play, using an older (Tripath) Class D amp, and a third D/A converter ahead of the preamp and crossover.

Well, good it continues to play with the old bits at least. Though I am not sure you've experienced an EMI/EMC issue so much as a "poor circuit protection" issue, which would (in my experience) fall in the realm of survivability/reliability. EMC principles definitely factor into designing against things like what you experienced, though...I am wondering whether perhaps (in addition to any physical damage to the device, per your suspicion) someone didn't take differing ground potentials (between, say, the tube parts and the digital comps) into account and set the scene for a voltage to build up somewhere it shouldn't have.

(This is especially likely if the burnout happened right when the system was first plugged in and connected.) Good luck getting it properly repaired, at any rate...

(reply to jimf, part I): jimf wrote: I purcha...

2011-02-22T10:59:45.711-08:00
(reply to jimf, part I):

jimf wrote:

I purchased a (used) Class D power amplifier for one of my stereo systems. As you may know, a Class D amp is quite different from a traditional amp using either solid state or vacuum tube output stages as linear amplifying devices. A Class D amp switches its output devices on and off at an ultrasonic frequency (hundreds of kilohertz up to megahertz) in a "duty cycle" corresponding to the amplitude of the audio input signal (it's called "pulse-width modulation", as you no doubt know).

Yep, I've heard of Class D amps and PWM. Never played with them on stereo systems, though.

Anyway, I own and use several Class D amps based on Tripath chips, and they sound great IMO, but I wanted to try out another design -- in this case, a B&O "ICEpower"-based design. So the amp incorporating the ICEpower modules is an H2O S-100, bought, as I say, used on a trading site called Audiogon.

Okay, now you're speaking "audiophile"...I've never heard of Audiogon or the designs of which you speak, so I will have to take your word that that sort of thing can make a difference sound-wise! :P

So the amp arrived, and I hooked it up, and to cut to the chase, it **fried** two (in a row!) D-to-A converters **upstream** of the amp, while leaving the entire rest of the system (including two intervening components -- an active crossover and a preamp, both tube-based) undamaged.

o_0 o_0...wow. How bizarre. But not entirely unsurprising the tube-based stuff survived! Any idea what the D-to-A converters were (as in, what chip/model no.)?

The amp's designer says he's never heard of such a thing, but since I subsequently found evidence (the audibility of loose components rattling around in the case) that the amp may have been damaged in shipment, it's going back to the manufacturer for repair...

Ew, yeah...rattling is generally not a good sign. At my last job we actually had a qualification test for new units that literally involved shaking them upside-down to make sure there weren't any loose parts or metal bits. This was important not just because it's bad for stuff to be loose, but because even a tiny piece of metal (e.g., a component lead that was cut off during assembly) can result in nasty short-circuits if it happens to fall across a PCB or set of connector pins, etc.

My best (barely educated) guess is that the ultrasonic switching signal from the (undoubtedly malfunctioning) amp leaked out through its **inputs** back through the crossover and the preamp (leaving them unaffected, possibly because they're tube units) and into the **outputs** of the D/A converter(s), frying some or all of their (solid state) circuitry.

I couldn't say for sure without examining the hardware myself, but your conjecture at least sounds reasonable.

CPP: Regarding cell phone interference, as far as ...

2011-02-18T10:35:27.484-08:00
CPP: Regarding cell phone interference, as far as I know the EMC consensus is that there is a *small* chance for cellular/wireless devices to specifically interfere with aspects of the plane's navigation systems. You are right, though, that if that were actually a terrible risk more stringent measures would likely be taken.

Really the main reason (as far as I know) that people are told to turn off their phones is because cell phones can get "confused" when they can see multiple towers simultaneously. This can result in, among other things, your service being shut off because the phone "thinks" it may have been stolen or something. I don't know why they don't just tell people that on planes, though...maybe they figure it's tl;dr for most passengers or something. But the short version is basically that turning off your phone while a plane is landing is generally much more about protecting your phone service than about protecting the plane!

H., it is not ALL electronics that need to accept ...

2011-02-18T09:41:25.507-08:00
H., it is not ALL electronics that need to accept ALL interference of all types/levels. For one thing, there's sort of a priority hierarchy. As in, regulatory entities may set different limits for different types of devices, Consider, for instance, the situation in a hospital where you have some sort of life-support machine operating. You are not likely to see that same kind of FCC sticker on the life support machine, because obviously it is more important for that machine to operate than for someone's portable CD player to operate in that room (not that those two things would necessarily interfere with each other, but you get the idea).

Basically, the disclaimer you see about having to accept interference is there so people using (mainly) "consumer electronics"-type items don't get the idea that they can complain about interference caused by, say, police/fire signals, and also because there is really only so much you can do (especially within particular cost/material constraints) to make interference a complete non-issue. It is, therefore, pretty normal for people to have to do things like be careful what things they are plugging into the same outlet in their house and have to orient or arrange their various home electronics differently. It would be impractical to design and build absolutely everything to not interfere with anything else or be vulnerable to interference from anything else. A lot of it is therefore about compromise and gradually just figuring out what makes the most sense to protect the most.

> To prevent electrical/electronic > devices...

2011-02-18T08:39:28.145-08:00
> To prevent electrical/electronic
> devices (and their subsystems)
> from interfering with proper
> functioning of other devices
> (or subsystems within the same
> device)

I had an unfortunate taste of this quite recently.

I purchased a (used) Class D power amplifier for one of my stereo systems. As you may know, a Class D amp is quite different from a traditional amp using either solid state or vacuum tube output stages as linear amplifying devices. A Class D amp switches its output devices on and off at an ultrasonic frequency (hundreds of kilohertz up to megahertz) in a "duty cycle" corresponding to the amplitude of the audio input signal (it's called "pulse-width modulation", as you no doubt know).

Anyway, I own and use several Class D amps based on Tripath chips, and they sound great IMO, but I wanted to try out another design -- in this case, a B&O "ICEpower"-based design. So the amp incorporating the ICEpower modules is an H2O S-100, bought, as I say, used on a trading site called Audiogon.

So the amp arrived, and I hooked it up, and to cut to the chase, it **fried** two (in a row!) D-to-A converters **upstream** of the amp, while leaving the entire rest of the system (including two intervening components -- an active crossover and a preamp, both tube-based) undamaged. The amp's designer says he's never heard of such a thing, but since I subsequently found evidence (the audibility of loose components rattling around in the case) that the amp may have been damaged in shipment, it's going back to the manufacturer for repair (the seller has generously agreed to reimburse me for the cost -- there was no obvious external damage, so I doubt I'd have a claim against the shipper).

My best (barely educated) guess is that the ultrasonic switching signal from the (undoubtedly malfunctioning) amp leaked out through its **inputs** back through the crossover and the preamp (leaving them unaffected, possibly because they're tube units) and into the **outputs** of the D/A converter(s), frying some or all of their (solid state) circuitry. The power supplies in the DACs seem OK (the front-panel LEDs come on, and the line fuses didn't blow). Neither DAC will sync to an incoming S/PDIF signal, so at least the S/PDIF receiver chips are likely blown. How much of the rest of the digital and/or analog circuitry is also blown I do not know. **Both** DACs had that exquisite smell of cooked electronics after the adventure.

Electromagnetic interference, indeed! It's gonna cost me to have those two DACs fixed. I'm just lucky nothing else was fried (including the speakers and subwoofer). The system continues to play, using an older (Tripath) Class D amp, and a third D/A converter ahead of the preamp and crossover.

Fascinating post! So given what you know about EMC...

2011-02-18T01:29:44.035-08:00
Fascinating post! So given what you know about EMC, do you think it is possible that cell phones on planes can interfere with the plane's electronics? My take has always been that if there really truly was any evidence that they could, there would be a much more stringent procedure for ensuring phones are off than just telling people to turn them off.

Oh and I forgot to sign my comment. It's H.

2011-02-18T00:53:08.778-08:00
Oh and I forgot to sign my comment. It's H.

Isn't that illegal? Because electronics all sa...

2011-02-18T00:52:34.415-08:00
Isn't that illegal? Because electronics all say they have to accept all interference no matter what. Isn't it illegal, then, to make them so they don't?

Comments on Existence is Wonderful: EMC Engineering: What Does It Mean?

So, I take it you would consider it rude behavior ...

I have read of people making aluminum foil beanies...

(reply to jimf, part 2): ...**Both** DACs had ...

(reply to jimf, part I): jimf wrote: I purcha...

CPP: Regarding cell phone interference, as far as ...

H., it is not ALL electronics that need to accept ...

> To prevent electrical/electronic > devices...

Fascinating post! So given what you know about EMC...

Oh and I forgot to sign my comment. It's H.

Isn't that illegal? Because electronics all sa...

(reply to jimf, part 2): ...Both DACs had ...