Dan's Data letters #116Publication date: 13 July 2004.
Last modified 23-Aug-2012.
I'm pondering investing in a Jens of Sweden mp3 player. They have 3 different types with the FM tuner and the 256Mb of RAM I require.
The players apparently range from 2x7mW -2x13mW headphone output (I don't know if these figures makes any sense). Would the cheapest player be enough to drive my Sennheiser HD 457 headphones, or would the 2x7mW be too weak and make the bass sound like farting noises?
How many mW should an amp put out to work well with real headphones?
The output power spec does give you a rough idea of the amp power of the player, but if you don't know what its maximum output voltage is or the impedance it needs to be driving to achieve the quoted output power, then the figure by itself isn't very useful. If you're trying to drive high impedance headphones, you need an amp that can output more volts than if you're trying to drive low impedance 'phones, to get the same volume. This assumes that both pairs of headphones have the same efficiency (loudness per milliwatt), which they won't, but efficiency isn't a problem for most consumer headphones; they're generally all pretty good.
Your HD 457s, like many cheap-ish headphones ($US34.95 ex delivery in the USA; Australians can get them for $AU100.10 delivered, and can click here to order them from Aus PC Market, plug plug), have an impedance of only 32 ohms. So any old amp should be able to drive them as well as it can drive any pair of headphones. They'll work OK with the Jenns players, but you shouldn't expect them to sound very good at more than low volume, because even 13mW-per-side isn't much (though you won't necessarily be able to tell, if there's enough background noise). As I've discussed before, this problem is normal for portable players of all kinds, and especially for tiny portables, and there's not much you can do about it but use an add-on amp.
The 13+13mW output figure for the MP-130, by the way, is specified as only being for 16 ohm headphones. Quality 16 ohm 'phones are pretty rare, but the Shure E2C canalphones that Jenns recommend (and sell as optional extras) qualify. They have high efficiency, too, because they're plugged right into the ear canal and waste very little sound. Into 32 ohms, the MP-130 can probably only manage about the same power as the other Jenns players; I wouldn't be surprised if they all actually have the same output chip.
You can read a lot about the voltage, current and resultant power needed to drive different kinds of headphones here.
In a box of PSUs I recently bought on eBay came a couple of (to me) strange devices; a BPS power supply, Model BPS-270RD.
I Googled them and they're the singular of a "dual hot swap" PSU. Unfortunately I don't have the rest of it. But I'd like to solder (observing the proper "don't nuke yourself" precautions) an ATX power cable onto the circuit board which hangs out of the side of the thing. Problem is I cannot seem to find a pinout for the card edge.
I've seen the "white papers" you seem to be able to find for everything - I'm hoping maybe you'd be able to send me in the right direction?
Judging by a (similarly Googled) page, I think this thing's an AT, not ATX, PSU, so what you want to do is unlikely to be possible. AT PSUs have no +3.3V or +5VSB outputs, which you need on an ATX PSU. I can't find a proper datasheet for the BPS supply, though; I don't even know where the manufacturer's Web site is. I'm guessing it's not BPS Engineering.
After I put this page up, a correspondent who'd bought a complete surplus BPS-270RD kindly sent in pictures of its spec sticker:
...and the interior of the mounting chassis for the two modules:
As you can see, there's rather more in there than a mere backplane. Perhaps all of the chassis circuitry just handles the redundant PSU failover and hot-swap functions, but I wouldn't bet on it. And the spec sticker confirms that this ain't no ATX PSU.
Many of my friends, and myself, use "AS-830" headphones from Aussie Sound. Here's a link - the only one I could find in Google. I got them for 29 bucks at a swap meet in Melbourne. To me, they sound awesome.
Have I just got uneducated ears?
Will the 100 dollar PX 100 sound better? (I know "better" is a bit hard to define).
My initial interest is due to a desire to get myself one of those cool MP3 flash players. I don't think my large AS-830 headphones would be practical. The wrap-around-the-back-of-your-neck style headphones seem to be the current in thing, so I'm tempted to just get the most-expensive-under-100-bucks Sony version. Should I? Are the AS-830s that I've got any good?
Ah, international mega-brand Aussie Sound!
Yes, it's quite possible that you've never actually heard good headphones. There's really no such thing as a good-sounding set of $AU29 headphones, and if there's a boom mic as well for that money (as there is, with the AS-830) then the headphone components obviously have to take another quality hit.
There certainly are good value cheap headphones and headsets, though. And for the kinds of things people do with headsets, dirt cheap ones are often perfectly adequate. For things like LAN parties and Internet cafes where there's tons of background noise and a serious chance that your headphones will get lost, smashed or stolen, there's a lot to be said for bargain-basement units.
A set of PX 100s will, very probably, sound considerably better than what you've got. You'll certainly look less of a dork if you use them with your MP3 player, in public.
I'd be willing to bet that, compared with lots of rather more expensive brand name 'phones, the Aussie Sound units sound pretty lousy. However, I've never listened to the AS-830s myself, so for all I know they sound quite OK. The big brands are perfectly capable of making expensive headphones that sound no better than much cheaper ones (coughHD 270cough), and it's also quite possible for cheap 'phones to, occasionally, sound a lot better than you'd expect.
The PX 100s are hard to beat if you're looking for a pair of lightweight, slimline, highly portable, bassy, pretty cheap headphones, though.
In letters #115, you say about iiNet: "If you manage to exceed the limit they just reduce the connection speed to a mere twice that of a dial-up modem; you don't pay any more. That's the way civilised ISPs do it."
Man, that really bites. I know Australia's a bit far off from the major Internet backbones, Telstra's having a hard time convincing itself that gouging customers isn't a way of doing business, and I've witnessed the awe of an Aussie geek the first time he did an APT-get from ftp.fr.debian.org with himself connected on the same continent, but really, are download caps that frequent a practice down there? I thought that real civilised ISPs just offered a flat rate and that was the end of it... ;-)
Since Telstra's customers include every DSL provider in this country, I can see why... firm business practices still look like a good business plan to them.
But anyway - yes, download caps are a fact of life for most Australian Net users. When consumer broadband first became available in Australia (cable Internet, a bit more than five years ago), it was an uncapped wonderland that lasted until it actually started getting popular. Then really tight caps were imposed - 3Gb a month, followed by throttling to 32 kilobits per second if you were lucky, even on cable.
That lasted a couple of years, and then loosened up again. Over the last year or so, we've been seeing lots of plans with big download limits, and now even some worthwhile unlimited plans - as opposed to "unlimited*" plans....
That second kind of "unlimited" plan, with an asterisk and a bunch of small print, is actually the norm in most countries where download caps aren't normal. In that Small Print Nobody Reads there's usually an anti-super-leech clause. There has to be, since consumer Internet services are always sufficiently oversubscribed that a few leeches genuinely can fill the whole pipe; if they do that all the time, an ISP can either watch its customers leaving for faster services, or it can perform expensive upgrades (which the leeches' activities will swiftly expand to fill, of course), or it can kick the leeches (or get tricky...).
Take Comcast, for instance. Their AUP's "Network, Bandwidth, Data Storage and Other Limitations" section says you're not allowed to "represent (in the sole judgment of Comcast) an unusually large burden on the network". Overdo it and you'll get a nastygram; keep it up and they will Cut Yo' Ass Off.
It's not just the popular-but-not-so-great ISPs, either; Speakeasy's Terms of Service also specify that you mustn't "utilize any of your Speakeasy services in a manner which consumes excessive bandwidth". I doubt you'll find a consumer broadband ISP anywhere that doesn't have a similar clause; they only differ in their enforcement policies.
Now, these "unlimited" plans may indeed give a much larger real download allowance than the best of the plans available in Australia - but then again, they may not. It's rumoured that Comcast's current secret limit is about 1.5Gb a day. That's good by Australian standards, but not too hard to exceed if you're really trying. I quite like having a large cap - especially one that just throttles your link if you exceed it - rather than a limit that you don't even know about until you hit it.
Cyrille, who's in France, got back to me to point out that his current ISP (PDF terms of service here) or the one he'll be moving to soon don't impose such limitations on their users. I've kinda got to take his word for it, there, unless I turn to machine translation, happy the not sense making over purple me will help.
Nerim apparently has a genuine all-you-can-download policy, provided you're not violating copyright. Which, of course, rules out all of the super-leeches in the first place.
If a bunch of people sign up and all start maxing out Nerim's pipe all day with legal material, though (hey, it could happen... imagine a video version of AllOFMP3 for instance), I'll bet there'll be a change to the policy. There's just no way around it; you can put an apparently-permissive Acceptable Use Policy cushion between the users and the hard facts of oversubscribed connections, but you can't change those facts. If more than a few people take full advantage of their "unlimited" connection, you've got to stop them.
Cyrille also pointed out that one of the abovementioned ISPs is delivering TV over DSL at the moment as well, which would appear to be a bit of a bandwidth monster. I think most, if not all, TV over DSL comes from servers hosted by the ISP, though. It doesn't actually take up any of their external bandwidth. I think the usual deal is to set up a bunch of MPEG encoders, one for each channel the ISP wants to provide, and feed them each from a single regular video source - satellite, cable, whatever.
It's not completely ridiculous to distribute TV over IP between ISPs, but you'll need a DS3 line for 30 1.5 megabit per second channels. If that's a cheap trunk line to a TV-company-affiliated distribution centre or something then it's acceptable, but if it's a full-function, full-price link then the ISP would probably rather use it to serve another one or two thousand customers.
I'd love for you to get your hands on one and give the magnet array a once-over.
Since the Perendev magnetic motor is a perpetual-motion device, it is about as certain to be fraudulent as the sun is certain to come up tomorrow. No review units will ever be available to anyone, and no demonstrations supervised by independent authorities will ever be performed. There've been many "magnetic motors" before this one, and there will be many more after it.
So far, the sum total actual evidence for the claims presented on the Perendev Power site appears to be one video clip (get it here), which is very pretty, and all, but could have been rigged in about a thousand ways.
The basic question for all of these devices is not "how does the motor work?", because it never does, but "how does the scam work?" Are they selling plans, distributorships, shares of stock...?
In Mike Brady's case, perhaps the press release you linked to indicates that he is now selling worthless distributorships to well-heeled suckers around the world. That's the way to quickly pile up enough money to keep you living comfortably after the International Conspiracy To Enforce the Laws of Physics forces you to fold your tent and steal away to somewhere with few extradition treaties.
Or perhaps Brady's just taking deposits from people:
And what do you know; Mike's in the magnetic water business, too!
It'd be a tremendous boon for the world if a magnetic motor, or any other kind of over-unity device, worked. But different designs for the things come and go like mushrooms all the time. They occasionally get some press from gullible, corrupt or severely underworked media outlets (have you noticed that the still-unseen Kohei Minato magnetic motor continues to be front page news on japan.com? It's probably the only "technology" story that site's ever had, since the most recent of the numerous times the domain's changed hands), but then they fade away, like every other dream.
Another lost soul
[sent to me and 15 other semi-randomly-chosen people, all in the To: field]
I visited your site, today, and really like it.
I run a site similar to yours, and was wondering if you would like to trade links with me?
You can see my site at http://www.geocities.com/amaltheainc/. I would give your site a prominent listing on my page at http://www.geocities.com/amaltheainc/links.htm, if you would be willing to do the same.
Please let me know if you have any questions or comments.
I'm not going to give all you cruel, cruel people a mailto: link for Mercedes, or Mercedez, or whatever; you can dig it up from that Geocities site if you like. I can see how she'd have thought my site was similar to hers, though; I'm sure I've had something to say about "Astrology, Feng Shui, Personal Tarot Readings, Crystal Therapy, Balance of Chackras [sic], Reiki" and the various other things with which she occupies her time, over the years.
So: Sure, Mercedes! Here's your link!