A friend recently gave me his old speakers and subwoofer from his mac (I assume there are no compatibility issues in using these for a PC, except aesthetically of course) but neglected to include the power adapter. Looking on the back of the subwoofer by the power adapter port it says “15V”, which I assume means I need a 15 Volt power adapter.
But searching on the web has been more difficult than I’d imagined. First I tried Staples (I can get a discount with them through my work account) where I did find this, but that only shows power capabilities in terms of Watts, and at $80 seemed more expensive than I imagined.
But I was sure I’d find one on the Best Buy website. I found: this - nothing about volts or watts, seems specific to digital cameras, and $113 this - only rated for 4.5 volts (but hey, at least were talkin’ volts)
and probably the closest: this - output 12V DC, but specifically for Yamaha keyboards.
My questions:
Since I found many products rated up to, but not beyond 12V, does 15V sound right for computer speakers/subwoofer? would 12V even work? cause damage?
Why are some adapters in terms of watts, while others in terms of volts?
Why do some specify the types of devices they are to be used with? Wouldn’t a 12V adapter be fine with any device that requires a 12V adapter. Why would one be specifically for a Yamaha keyboard, and others for digital cameras?
I haven’t really looked elsewhere for it yet (well, I found nothing in the way of power adapters at all on the mac site), but the very fact that I couldn’t find it at Best Buy made me curious. Is this really as difficult to find as it seems to be to me?
Ok, let me just say that I’m still wholeheartedly against the google ads,
BUT…
to be fair, they did just lead me to here which, at a quick glance does seem to have many adapters 12V and beyond, including one for 15V at only eight bucks and change.
Some new questions to add to (and NOT replace) the old:
What’s up with mA? Amps I presume? going from 400 mA to 1000 mA adds 11 bucks. What do I need to know about that?
When I submit this, will I get a google ad link to a FAQ on Amps?
Will google ads eventually become so intelligent as to completely replace the need for GQ?
(please disregard the last 2, lest I irritate the mods by not obeying forum rules).
Allow me to also add you need to find an adapter with the correct voltage, current and connector. It also must have the correct wiring on the connector. Most power connectors are round with a center conductor. On some the center is + and on others the center is -.
You may want to check with Apple. They generally sell spare power adapters. The price will be high, but at least you’ll have the correct one.
To properly spec out a power supply, you need to know the following about the amplifier:
Nominal input voltage.
Acceptable input voltage range.
Maximum input current draw.
The problem is that you only have the answer to #1 (15 VDC).
If #2 is fairly wide (e.g. 12 V to 18 V), then you can probably get by with an unregulated power supply. Otherwise you’ll need a regulated supply.
As far as #3 goes, you can only go wrong if you choose a power supply that can source too little current. So if you don’t know the maximum draw, then to be safe you should choose a supply that can produce quite a bit of current. But too high of a current rating also has a drawback, albeit a minor one: the supply will be bigger, heavier, and more expensive than it needs to be. Not to mention it may be less efficient from an electrical POV. One approach is to simply take the maximum output power, and assume 40% efficiency.
So here’s the upshot: If the only information you have is “15 V,” then your only choice is to be conservative, and you should select a regulated supply that can supply quite a bit of current (e.g. 2 A or more).
Thanks CM. I did look for a model number or name or anything I could find that might help me identify it last night but couldn’t find anything.
Just a comment: You suggest, as a conservative estimate, at least 2 A. But the Radio Shack link and my google ad link seem at a glance to max out at 1.5 A.
Anyway, I’ll respond again in a few hours when I have it in front of me to see if I can find any info on the other variables.
You say it’s a subwoofer and a pair of speakers. How many continuous & average watts do you think it can pump to the speakers at full volume?
If you use a 15 VDC/1.5 A power supply, and if we assume the amplifier is 40% efficient when operated at maximum volume (which may be a very poor assumption), then it will only be able to source 9 W (continuous & average power) into all the speakers. Is that how many continuous & average watts these types of amplifiers produce at full volume? I have no idea.
Also look at the speakers. Do they say what the maximum power level is?
Another idea is to pop open the case and see if you can fine a fuse on the +15 V input. If you see a fuse, try to read what the current rating is, and then get back with us.
But if you can, try to find a model number or something on the subwoofer.
BTW: I have no idea where I came up with that 40% efficiency figure. Let’s assume it’s a class AB amp with a maximum efficiency of 75% at full volume. So if you use a 15 VDC/1.5 A power supply, and if we assume the amplifier is 75% efficient when operated at maximum volume, then it will be able to source 17 W (continuous & average power) into all the speakers. Still not much, IMO. But maybe that’s all these types of amps produce.
I didn’t make it home last night, and my eyes are nearly closed at the moment, but I wanted to see what info I could post here before the day ended (i.e. with my going to sleep).
Unfortunately I can’t find much info.
Taking off the casing from the small speakers it looks like a serial code might be engraved into the metal bell-like piece but it’s obscurred by some tube sticking out. Best I can make out, it says “FIC” on top and then, under that, with the tube dead in the middle it seems to say “2 (tube) horseshoe”
It’s also got stickers on it saying Q.C passed 141, and another 151. (quality control I presume?)
The subwoofer has no real discernable marks of ID. It was made in China.
The power adapter port says “DC 15V” and then underneath “+@-” (the @ was the closest thing I could find but it’s more like a sperm that just penetrated a C.
If I read your diagram correctly that seems to indicate that the outside of the plug is positive, and the inside is negative.
Your best bet is to take it to Radio Shack. They sell power adapters and IIRC “adapt-a-plugs” that you select to fit the device. You buy the 15vdc adapter and you IIRC get the correct plug with it.