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Old 2nd February 2008, 16:53   #1
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Default Using PC SMPS Unit As a Power Source for Creative Speakers

Hi,
I have Creative SBS 2.1 Speakers connected to my desktop PC. The AC power adapter has conked-off (primary coil of the transfer has blown). It's output was 2.9Amp @ 12V AC.
I was wondering whether it is possible to get an original replacement, and how much would it cost, when it struck me why not use a PC SMPS unit (its easy to get one in the market for 300-400 bucks). After all, it also has outputs at 12V and is capable of supplying several amperes.

Is it technically feasible, or is a plain old transformer-based power supply
better for an audio equipment?

Any views or suggestions?
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Old 2nd February 2008, 17:56   #2
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you will get a transformer with the same rating for about Rs 100-150... you only need to solder it back and it'll be done...
Audio equipment usually run of transformer based systems as it requires analog power output to run without any distortion in the sound it produces, SMPS is switched output , for digital equipment...s o stick to the old supply.
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Old 2nd February 2008, 18:08   #3
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Get the transformer repaired it will cost you Rs 100-200 only.
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Old 2nd February 2008, 18:21   #4
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smps has a lot of audible noise in the supply, and besides, most SMPS also have a minimum rated load. besides, they prefer having fairly constant loads. a 12V 3A power supply should cost about the same / if the transformer enclosure isnt moulded ( i think they are though :( ) getting it rewound should be cheap
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Old 2nd February 2008, 20:24   #5
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Anuragn,

The speakers required 12V 2.9A AC power as per your post.
The SMPS is putting out 12V DC power.

Also, im not so sure that the SMPS wattage would be suffiecient to power the speakers? (IF they required DC).

cya
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Old 2nd February 2008, 21:20   #6
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Rehaan .. the transformer is to step down the voltage from 240 to 12 or what ever is necessary in this case, there is a rectifier after that for conversion.
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Old 2nd February 2008, 21:37   #7
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Dinar,

The input to the subwoofer (which houses the amp) is 12V AC, so in other words, the rectifier will be housed within the subwoofer, probably as part of the IC, correct?
Which means that he will have to open the subwoofer and plug in beyond the rectifier if he intends to make this work... sounds like a lot of work.

cya
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Old 2nd February 2008, 21:43   #8
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Quote:
Originally Posted by Rehaan View Post
Dinar,

The input to the subwoofer (which houses the amp) is 12V AC, so in other words, the rectifier will be housed within the subwoofer, probably as part of the IC, correct?
Which means that he will have to open the subwoofer and plug in beyond the rectifier if he intends to make this work... sounds like a lot of work.
nope. not quite. if you plug in DC to an AC input, when you know that there is a rectifier downstream, its not an issue, in fact , now you dont even have to worry about which polarity you're plugging it in!


but still, getting a 12v 3A transformer is a better option now , as now you dont even have to bother with the rectification/filtering, so will work out about the same cost(with an enclosure) , or lesser

Last edited by greenhorn : 2nd February 2008 at 21:51.
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Old 3rd February 2008, 00:21   #9
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Hi greenhorn,

Thanks for explaining that! Makes sense.

Why is it that a SMPS will have more noise in the power supply than a wall-wart transformer ? If at all, i would have guessed the opposite...

cya
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Old 3rd February 2008, 14:52   #10
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Quote:
Originally Posted by Rehaan View Post
Anuragn,

The speakers required 12V 2.9A AC power as per your post.
The SMPS is putting out 12V DC power.

Also, im not so sure that the SMPS wattage would be suffiecient to power the speakers? (IF they required DC).

cya
R
It is a small 12 watts rms output set.

Creative SBS 2.1 350 - 2.1 computer speakers for your games, DVD's & MP3 music

He can easily run it through the PC SMPS supply without any problem. But the best bet is to get the Transformer rewinded from any local shop who makes CVT, Voltage Stabilizer.
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Old 3rd February 2008, 21:44   #11
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Thanks for all the advice.
The transformer is a sealed unit, so it has to be broken for rewinding.
I was also of the opinion that SMPS output would contain lots of audible noise, hence this query before trying out. But otherwise, inputing DC voltage where AC is required means a voltage drop of appx 1.4 V (i.e 2 diodes in series in a bridge rectifier). And the rectifier can be easily bypassed if DC power source is reqd to be used.
Now that getting a new transformer seems to be the best solution (I do not somehow feel comfortable getting an original one rewound....it would still not be same as new),
can somebody tell where can I get a good torroidal tansformer in Mumbai (apart from Lamington road), and how much would it cost compared to a conventional one?
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Old 3rd February 2008, 22:38   #12
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Quote:
Originally Posted by Rehaan View Post
Hi greenhorn,

Thanks for explaining that! Makes sense.

Why is it that a SMPS will have more noise in the power supply than a wall-wart transformer ? If at all, i would have guessed the opposite...

cya
R
in a linear PSU, the whole thing runs at 50hz. thats why they have the big transformer and the big filter capacitors. In an SMPS , they modulate the input wave at a very high frequency. this can then be stepped down using a much smaller transformer. While you CAN make SMPS with low noise output ( i believe thats what's used in most car amps) for a PC PSU maker, thats the least of his priorities. this, as well as other power line noises as well tend to make the DC a bit 'dirty' . but that, you can live with, because the retifier's filters should remove most of it

A bigger issue might be that some PC PSU's have voltage regulation only on one rail . IE the 5V may be regulated , and we assume the others bear a constant ratio. But if only the 12V is loaded , the results may not be predictable

Quote:
Originally Posted by low_bass_makker View Post
It is a small 12 watts rms output set.

Creative SBS 2.1 350 - 2.1 computer speakers for your games, DVD's & MP3 music

He can easily run it through the PC SMPS supply without any problem. But the best bet is to get the Transformer rewinded from any local shop who makes CVT, Voltage Stabilizer.

IIRC, the whole thing is in a moulded enclosure. You will have to destroy/ rip it apart to get to the transformer. thats why i recommended getting new

anyway, if the OP is feeling adventurous , and knows his circuits , i don't see any problem in this . it can be made to work. But if you're a noob to electronics , and just want to save a buck, then no, don't. the linear is the better (and correct , i might add) method

Last edited by greenhorn : 3rd February 2008 at 22:43.
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Old 3rd February 2008, 23:31   #13
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Thanks for the informative post but I think the current draw of the speaker set is quite low and the SMPS can easily handle it. And the noise level in the SMPS are quite in range and will not effect the output of the speakers
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Old 5th February 2008, 12:07   #14
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Thanks greenhorn for a nice explanation.
Latest update:
I found one old "speedking" battery eliminator lying in my DIY shack. It's output is 2 amp @12V, so thought let's give it a try.
Tapped 12V AC directly from the transformer and connected it to the speaker setup. Although the green power LED on Creative's wired remote lighted up, but there was no sound. So I guess the amp or something else has gone bad. Would have to find out now. So now the problem is a bad amplifier board.
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Old 5th February 2008, 15:02   #15
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You'll get a new 12V AC power adaptor for 200 bucks. Just go buy one.
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