(EDIT: For the latest info, check later posts) UPDATE 1: 21/07/08 I thought this was worth a new thread: How do you power a set of speakers? Would it be possible to wire a set of PC desktop speakers to a DC source (such as a battery) and then plug the jack into an audio source and play? Or do you need an AC source (in which case a kit would be needed)?
It depends. If you have a separate AC-AC or AC-DC adaptor with just two wires from it to the power input on the speakers, chances are it's a single-rail DC supply inside and fitting a battery supply would be fairly easy. If a mains wire disappears into the sub it could be a split-rail DC supply, and you'd need 2 batteries.
Thanks for the reply, I'll just need a second to digest that So if, on the back of the speaker, where the power socket goes in, it says '13.5V DC', I can safely assume that the speaker runs off DC, and a battery could easily be connected. If it says '13.5V AC', I can't run them off a battery, without something in between to make it to AC. (Right...?) The speakers I want to tinker with are these: Which, I assume, have no sub, and thus, must be single rail. Does anyone have any recently purchased Logitech/other desktop speakers? Recent models I have seen seem to all run off DC, but my old-skool Harman Kardon run off AC, so I'm having second thoughts...
No, in the first case there's a rectifier and smoothing inside the adaptor to convert AC to DC, in the second there's a rectifier and smoothing inside the speaker case to do the same job. The amplifier itself runs off DC. If the speakers take an AC supply, you can either supply them with DC to the same power socket, which will waste about 1.5V from the DC supply but is safe and easy, or open up the case and bypass the internal rectifier.
Open up the main speaker, as in the speaker that accepts the power, and take a couple of good clear & close pics. We can whack a couple of arrows on the pics to show ya where to connect the battery leads to.
like was said you can bypass the bridge rectifier and solder in some cables directly. the bridge rectifier on these are usually four diodes like this arranged like this <>, somewhere after where the ac comes into the board.
Ooh, forgot I had this thread up. Thansk for the feedback lads. I'll have some pics up a.s.a.p., probably in my other thread (the project one). Now here's a question: Do you think I'll be able to power these speakers: With this battery pack: The speakers are 15W rms, so 7.5W to each. They take a wall socket, not an adapter, so I assume there is mechanical wizardry inside which provides a fairly small, steady DC voltage to the drivers. The battery outputs 12.6V DC - 10.8 V DC, and claims 1800mAh. Should it work? Or do I need something considerably smaller, like my previous choice of speaker. Any help is GREATLY appreciated, and will be rewarded with an e-cookie
From the size of it, I should think you'd need some thing much more substantial. That battery pack might work but it might run hot, and probably wouldn't last too long - depends what kind of current the speakers need (1.5A-2A isn't unreasonable).
Your cookie as promised: Thats what I'm thinking. Perhaps something larger, there are rechargeable batteries available which represent car batteries. This battery then, will go towards my current project...
Lead acid (Pb Acid) cells from UPS' might be worth a shot. Two of them in parallel would have enough clout to run them for years I'd expect... and if not, they're rechargable. Naturally they're also pretty heavy (what with being full of lead, and all)
SLA (sealed lead acid) is the battery type you're looking for, can be mounted at any angle and spill-proof. A 7Ah is about the sweet spot in bang for buck and weighs in at 3kg, a bit less than a house brick, but there's a wide range. Lighter in weight would be a bank of NiMH cells, say 'C' or 'D' size, but they're a bit more tricky to charge.
Sealed Lead Acid batteries. Thats brilliant! Found some very cheaply by simply Googling it: http://www.screwfix.com/prods/38315...ed Lead-Acid Battery 12V 7Ah 100 x 65 x 151mm Well thats definitely worth a shot. And the 7Ah does look like the best deal available since it doesn't cost must more, yet packs a lot of power. As promised, some more cookies:
£14 for a no-name is no bargain. Cheaper here at £10.52 or a top brand Yuasa for £15.20, delivery is about the same.
Aah. Thanks dude. I know of Yuasa, and I suppose with things like batteries, its better to go for a nice good brand - an assurance of quality. Tired of cookies? I'm not: On a rather random side note, can anyone recommend a nice, well priced motherboard which runs on 12V DC? - Is the output of a battery consistent enough to run a PC? Or can all mini-itx motherboards be powered off 12V DC?
Just to note down my thoughts in HTML, I have noted the SLA Batteries, and have realised they are perfect for the large, bassy set up that is required to build a real boom box. However, I have neither the money, nor the expertise to try that just yet. Maybe a few months down the line I can look into it better. And then, I'll do the job properly, with an amp kit, a pair of crossovers, and some decent, spensive drivers. However in the mean time, I do have this battery, which I could use to power some speakers which are somewhat smaller, which can give me some experience, and leave me with a fun little product at the end. So my calculations at the moment: 12.6V DC available. Speakers: 5W RMS. V = P / I Assuming a 1.1A current usage... V = 5 / 1.1 = 4.54 V 8.06V left over to play around with. I can use this to run a 2.5" HDD caddy at 7.5V, and I have a bit left over to power a few LED's.
UPDATE 1 Well, back on the topic again, I'm still gathering the intel on this little project of mine. So far, the plan is: 1 - Chassis - retro styled - made of MDF/Plywood. Sealed up with fibreglass. 2 - Battery - SLA battery, 7000mAh 3 - Amplifier. The only one I can seem to be able to find in the UK is: Available at Maplin and Rapid, and made by Velleman. Here are the specs: The only problem I see is that it wants 12V AC. And I don't know how to provide 12V AC from a portable source Here is the circuit diagram: http://www.velleman.be/downloads/0/infosheet_k4003_connection.pdf The only solution I see is to look for another one. Can anyone recommend a kit or suggest whether a 12V DC supply would work here or not? Thanks
Tricky, as the board wants a 2 x 12VAC supply from a centre-tap or dual-secondary transformer, to give a split rail DC supply, +12V, 0V and -12V. For portable, that would need two 12V batteries in series with the centre junction to ground. Another source of similar amps is Quasar, and if you don't want headphone use, a pair of these BTL ones would fit the bill for 12V single rail operation, also suit MP3 player input.
Aah. That BTL looks like it'll do the trick! I only see one output... I trust that we could quite easily make that into two? The pricing looks pretty good as well. The only alternative I saw was to order one over from a European company called 41Hz. Its called the AMP6 BASIC and we see some pics of it here: http://metku.net/index.html?path=mods/ghettoblaster/index_eng2 This'll manage 25W into two channels, so I'll be able to run 2 x 4 ohm speaker set ups and it'll quite happily run off 12V DC. The price however, including shipping would be around £45. Any opinions on which would be the best value for the job it'll do? I also managed to pick up a pair of speakers for a good price (£7 at a local market!!) Made by Sanyo, and in excellent condition,they have a 4 ohm impedance, and a max 40W output. They sounded beasty and clear on my Technics stereo and I'm sure would sound just as good on a boom box. Having opened them up, I find that the drivers are simply wired to each other. Would not having crossovers create any problems in the future?
I doubt if it would cause any problems as long as you have a decent wattage amp in the boombox, but I bet sound suffers quite a bit right now without any crossovers.
