external speaker power supply question

markyb · Post by **markyb** » Sat Aug 08, 2009 3:55 am

Hi folks.. Bit of a weird one this. as its not directly linked to silencing. But still after advice on how to approach it best. At the moment my current pc *packard bell* has a external plug supply for the speakers.. Ive took a pic for you to give you a better idea what i mean..

Anyhow. Id love to encorporate these speakers into my new rig. mainly due to the Sound quality they have producted.. *they are packard bell speakers but producted by Diamond Audio which are known in the car audio circles as being a great quality producer* So i find it hard to ditch them to buy new.

http://support.packardbell.com/uk/item/ ... P700401801

The problem im having is that i cant find any external power supplies that will plug into the speakers.. *what i need really is the female adapter to beable to use the speakers*

anyone got any ideas before i have to go and fork out for another set?

thanks

sonic6k · Post by **sonic6k** » Sat Aug 08, 2009 8:32 am

Since it is DC 12V, it's going to be very easy. I've done this million times!

What you need is an adapter, which converts for example a Molex connector to the DC connector you need for your speakers. If you can't find the proper adapter, get any unused fan with a Molex female connector and cut it off (along with some wire of course, not only the connector!). Wire a DC female jack* to the yellow and black wire of the Molex connector. No need to have a soldering iron, just strip the wire ends and twist them with their counterparts of the DC female jack. Finally you can use some electric tape if you want to make it look more tidy or glue to keep it in place.

* To get the proper type of DC female jack, if you're willing to sacrifice your current PSU then disassemble the PSU and take out the connector, make sure you cut enough of the wire connected to the DC female jack. If you are not willing to do this, get any compatible DC jack from any trashed electronics or if you're adventurous, cut off the DC connector itself and connect your speakers directly to the Molex.

Finally, if you're not into case modding, get something like this to get the connector outside: http://linitx.com/viewproduct.php?prodid=11293

I'll make a picture if this sounds confusing.

markyb · Post by **markyb** » Sat Aug 08, 2009 9:36 am

i might be picking your brain abit more during the week mate

even though i searched CPC farnell *only 5 miles away from them!" and Maplin i couldnt find anything of the sort. But had another look ive found this on maplins site..

http://www.maplin.co.uk/Module.aspx?moduleno=1407

I go past a maplin store so i'll bob in on monday night on my way home from work.. Guessing this should be ok? I have a PCI blanking plate so i can easily drill a hole into this or as you say drill a hole into the case. But i am undertaking some case mods as we speak

thanks for the reassurance.

sonic6k · Post by **sonic6k** » Sat Aug 08, 2009 11:51 am

markyb wrote:i might be picking your brain abit more during the week mate

even though i searched CPC farnell *only 5 miles away from them!" and Maplin i couldnt find anything of the sort. But had another look ive found this on maplins site..

http://www.maplin.co.uk/Module.aspx?moduleno=1407

I go past a maplin store so i'll bob in on monday night on my way home from work.. Guessing this should be ok? I have a PCI blanking plate so i can easily drill a hole into this or as you say drill a hole into the case. But i am undertaking some case mods as we speak

thanks for the reassurance.

That could work, but you'll need a soldering iron and some solder of course! Connecting wires directly to the metal contacts of a connector requires the final result to be solid as a rock, because should for example the ground wire "get off" and interfere with the audio signal, you'll get massive problems. I killed a monitor speaker this way, because my "DIY audio switcher" had a ground wire give up too early, which started making interference in the power supply and audio signal and of course made the problem from a simple ground loop to a fight of signals and while I was a metre away sitting in my comfy chair listening to the music, I didn't notice much of the "electrical buzzing" till the speakers made a high "kiippuuumm". I did get a replacement unit under warranty though, said that the problem "happened on its own" while I was "not in the reach of the speakers" and that I had a "power outage" as well

markyb · Post by **markyb** » Sat Aug 08, 2009 12:01 pm

im ok with a soldering iron and i have done a few projects which has worked. i might get another just incase

Also my mum used to work at a phone circuit board company (was marconi) along time ago before robots did pcbs etc.. I'll get her in on the job

You tell liar.. fair play for getting away with it tho

thanks again for your help so far

sonic6k · Post by **sonic6k** » Sat Aug 08, 2009 12:05 pm

markyb wrote:You tell liar.. fair play for getting away with it tho

I can NOT hear you, the replacement unit is SO loud

Mr Evil · Post by **Mr Evil** » Sun Aug 09, 2009 12:43 pm

Check the polarity of the plug. Usually the outside is ground, which is fine, but in rare examples the outside is positive, in which case you won't be able to use that metal socket in a metal case, because it will short positive to the grounded case.

markyb · Post by **markyb** » Mon Aug 10, 2009 10:55 am

Well spotted. Thanks for that Mr Evil

I drilled a hole in the case as i assumed that it would look neater and also bearing in mind it should be a permanent thing *unless the speakers go pop!*

Okies. i have got one this afternoon and wired it up to what i think is correct which is as you say Mr Evil.. Postive centre pin, ground external. I belled these out with a multimeter.. Ive put some cable to it so then i can attach it to a molex once i get the cables out the way behind the case.. One other question.. and bearing in mind im not electrically minded

The speakers are 12v 1A. will the PSU molex connection be too much for that @ 1Amp? or is that the current drawn so will make no odds at all as long as its getting 12v dc.

Thanks for everyones help so far

Mr Evil · Post by **Mr Evil** » Mon Aug 10, 2009 11:28 am

markyb wrote:...The speakers are 12v 1A. will the PSU molex connection be too much for that @ 1Amp? or is that the current drawn so will make no odds at all as long as its getting 12v dc.

The PSU will supply however much current is needed. 1A is not a lot, so it will work fine.

markyb · Post by **markyb** » Wed Aug 26, 2009 1:43 pm

Worked a treat thanks

But a quick update.. Im getting some electrical interference in a way of buzzing through the speakers. Not alot but when the pc is pretty quiet now, its getting annoying already lol. Can you think of any ways to stop this at all? Alittle like suppressors on car radios for interference? I was thinking it could be to do with me using the wire i have? ie Not sheilded? And running the cables close to the power connection.. *in car audio which im more familar i would have run the power and signal cables down either side of the car to prevent.minimal interference but its not as simple in a pc case!*

Any help would be fantastic.. If not i might have to change them after all

markyb · Post by **markyb** » Wed Aug 26, 2009 2:52 pm

Another thing as well, although im fairly confident its not related. i have a beep through the speakers every 10 seconds without fail and it seems to be linked in someway to the Hdd light, as when it beeps the LED flashes bright into life then dims as normal as a hdd light does.. Im going to update the lot soon, drivers etc see if it might be firmware related. i hope so

This isnt a beep from the motherboard, its coming thro the speakers. And seems to be not volume related. Master vol at 0 but if i turn the speaker vol up *along with the buzzing* the beep is audioable. Will get the video camera out to record.

markyb · Post by **markyb** » Fri Aug 28, 2009 11:02 am

OK after going thro and disconnecting all the componets i could, I now know its the cable itself. *tested on my other pc which i also get the hard drive interference*

So is there any way of eliminating this? Sheilded cable? Im guessing this didnt happen before because it wasnt hooked up thro the sound like it is now. Im also using a molex connection from a cheap old fan.. Will this have a bearing on this? Ie cheap wire?

Zeroignite · Post by **Zeroignite** » Fri Aug 28, 2009 11:34 am

Does the buzzing/electrical noise seem sound to be at a constant 60 Hz? If so, you've got a problem with either a dirty power supply or a bad ground.

markyb · Post by **markyb** » Fri Aug 28, 2009 12:26 pm

Not 100% sure on the 60hz to be honest. but i have uploaded a video.

This is on the old pc which is the same noise i get. Please note that the volume is at MAX so i would expect abit of noise, as i cant hear myself think at a 1/4. But it proves that its something to do with the cable not the PSU or other components of the new pc..

http://smg.photobucket.com/albums/v112/ ... I_0294.flv

Mr Evil · Post by **Mr Evil** » Fri Aug 28, 2009 12:28 pm

The interference is almost certainly conducted through the cable, so shielding it will do nothing. Hopefully you will be able to filter out the noise without too much trouble by getting hold of a ferrite toroid (the doughnut-shaped things with wire wrapped around them on the Wikipedia page on toroidal inductors) and wrapping the cable around it a few times just before or just after it exits the case. This will form an inductor which will block high frequency interference.

You can find such toroids in old electronic equipment, often with the mains cable wrapped around them.

If that doesn't work, you could additionally try adding a capacitor in parallel with the cable. The mos convenient place would probably be inside the speakers themselves where the power cable attaches. It will need a voltage rating of 16V or more, and a capacitance of about 100-1000uF.

Again, you can find hundreds of these in old electronic equipment which can be removed with a soldering iron.

markyb · Post by **markyb** » Sat Aug 29, 2009 8:59 am

Hi Mr Evil, thanks for your thoughts.

I have a ferrite Clip on which i got with a USB cable, i tried that before posting to be honest but didnt know where to use it. on the power cable or stereo jack itself. Tried both a got very little difference. Im guessing its very similar to what ive already tried. do you think the other ferrite toroid will have a stronger effect at all? As i dont know the strength of the one i got.
Apart from that.. it really only leaves soldering in a capacitor, which is alittle over the top of me if im honest! but the annoyance is getting me already even at low volumes!
if i decide to have a go this will go in line of the + ? also struggling finding a 100-1000 rated one. They seem to be fixed only?

thanks

Mr Evil · Post by **Mr Evil** » Sat Aug 29, 2009 10:19 am

A toroid will have more effect than a clip-on one. It should go on the power cable, since that's the most likely way that the noise is coming in (if it was coming through the audio cable it would vary if you change the speaker's volume).

It's not hard to add a capacitor, since you know how to solder. When I say 100-1000uF I mean any value between 100 and 1000 will do. It will have two leads, and one will be marked with a minus sign. That lead should be soldered to ground, and the other to 12V. It needs to be placed somewhere between the toroid and the speakers.

It could also be a ground loop, as Zeroignite suggested. You can fix that by disconnecting the ground connection from the audio cable, so the speakers are only grounded through the power cable. That might be a bit hard to do without making a cable or adapter though.

markyb · Post by **markyb** » Wed Sep 02, 2009 12:26 pm

Sorry for the stupid question time again Mr Evil

Ive found a website which might be of some interest. Im going to call in maplins tomorrow and see if i can get a Ferrite Toroid but at the same time get a Capacitor as for the price.. it saves the journey again.. The website is using a Car suppressor but im guessing the capacitor is just the same in theory?
Is that diagram correct to how i need to solder this capacitor to the power lead? I always thought that electricity took the easy route and had to "pass through the capacitor" for it to work? Is that just me and being wrongly informed?
http://www.vlf.it/noisesuppressor/PCno ... essor.html

I'll grab one of each tomorrow if they have them in stock.. I might just have done with it and see if the capacitor can be done. hopefully that will cure it once and for all!

Again thanks for your info with something totally out of my league!

Mr Evil · Post by **Mr Evil** » Wed Sep 02, 2009 12:52 pm

Yes, that suppressor is in principle exactly the same - there is an inductor in series with 12V (the wire becomes and inductor just by wrapping it around the toroid) and a capacitor in parallel after it.

You're right that electricity does take the "easy route", but what is easy depends on the frequency. For DC, it can easily pass straight through the inductor, but cannot pass through the capacitor, so it behaves exactly the same as if those components weren't there at all. At high frequencies (i.e. noise), the inductor is hard to pass through, but the capacitor presents a very low resistance, so it passes through the capacitor instead of into your speakers.

One possible problem with the "make your own" part on that page: It suggests a 2-10mH inductor. This is a much larger value than the toroid will give you, so it will block noise better, but most inductors of that value that you can buy will not be able to handle much current. Ones that are designed for higher currents tend to be rather big.

markyb · Post by **markyb** » Thu Sep 03, 2009 12:50 pm

I have a sneeky feeling that you have subscribed to this thread Mr evil due to the extremely quick replies.. Again thanks for that.

Well i took a trip to maplins and got myself a toroid and some capacitors to try all over 16v and was a 220, 470 and a 1000 uf ones.

This is the cable made up.

Tried it and guess what... No change! I used the 220 uf and i also tried the 1000 one. I guessed id see the both extremes at that. Im sure it must be me thats doing something wrong and why i have posted a pic of the cable. I then unsoldered all the lot and tried to fault find if it was the punnie cable on the molex. no change. There is a difference when i plug it in the 5v instead of the 12v molex live. cant understand it. I dont know how to test if its a ground loop, but both old and new pc's suffer from the interference. So i can assume its not the case.

I just dont know where to go from here apart from buying new speakers which is the whole point of the project. Any thoughts?

As always. many thanks

Mr Evil · Post by **Mr Evil** » Thu Sep 03, 2009 2:59 pm

Everything in the photo looks correct (but wrap some insulating tape around those wires before you put it in the case!). If it has no effect at all then that means the noise isn't getting in that way after all.

I just noticed something in a previous post that I should have payed attention to before:

markyb wrote:...Master vol at 0 but if i turn the speaker vol up *along with the buzzing* the beep is audioable...

So does the noise vary when you turn the volume control on the speakers themselves? If so, that makes the likely source the sound card itself. I can't see any mention of what sound card you are using, is it the same one for both computers? On-board sound in particular can sometimes be terribly noisy. You can help reduce it by turning the software volume control up as loud as it will go and turning the volume control on the speakers down to compensate. Otherwise there is not much you can do about that other than use a better sound card.

And yes, I have my preferences set to subscribe to every thread I post to.

markyb · Post by **markyb** » Fri Sep 04, 2009 10:02 am

Im in fact using the on board sound on both pc's, So 2 separate mobo sound cards. The New pc has the P5Q deluxe in it and is alot more advanced then the one on the old 8 year old one and also boasts alsorts of HD quality sound and such. but seeing its on both pcs. I dont know..

The volume does alter the interference noise level on the speakers and the software volume is up at Max (the way i always have it). Although there is that constant buzzing at the same level up to around half and then gets louder with the volume control on the speakers. If i plug headphones into the speaker headphone jack, same electrical buzz.. The volume control is at min with the buzzing, but i also still get the 10 Second cherp which seems to be linked to the Hard drives in someway. In essences, its lookin like new speakers with a proper external power as im sure this is the cause of it. I never had this problem on the old pc with the dc connection built into the PSU.

do you think anything could be gained in taking the old PSU apart? Obviously a drawing or schematic would be great but somehow i dont think thats going to be available

Or how about cutting off the male connection off the speaker side, put the female connection i have and buy a cheap 12vdc external supply via a 3 pin plug?

Again thoughts are greatly appreciated.

Edit: Dont know if this also eliminates anything further but i have connected a toslink cable from the sound card on the new pc to an external home cinema system with no interference at all.

Mr Evil · Post by **Mr Evil** » Fri Sep 04, 2009 2:28 pm

Do you have a discrete sound card at all? Any one would do just for testing.

Even if the on-board sound uses good hardware, there is huge variability in how well each motherboard implements it e.g. using sufficient filtering (like in the cable you made, but on the motherboard). It's only the analogue part which is prone to noise, which is why the digital TOSLINK is fine. The actual source of the noise will be elsewhere though, so you might be able to improve the situation by moving cables and PCI cards around, or even using a different (possibly less noisy) PSU. Or just use another sound card.

Since the noise doesn't seem to be getting in through the power supply connection, you won't learn anything by looking at the old PSU. You could try using an external 12V supply if you want to completely rule out power supply noise (and it would rule out a ground loop if it's a power supply that isn't earthed).

markyb · Post by **markyb** » Fri Sep 04, 2009 4:27 pm

Hi, no i dont own a standalone sound card if thats what you mean. Something ive thought bout getting but never did get around to buying one.

It seems i might have made a bit of head way here..

I have a 240vac to dc adapter that i used to frequently use for powering devices such as mp3 speakers etc.. ive basically reversed the set up i have for the cable using the adapter plugged into the cable (female) and for a moment have had the exposed molex pins touching the male connection to the speakers. Completly by passing the power supply from the PC. The beep has gone completly and the interference has all but nearly gone. (its at least 50% better)

So is it safe to say. its the PSU thats causing my problem of the interference? and if so is there anything that can be done? Or im i stuck with it?

Mr Evil · Post by **Mr Evil** » Mon Sep 07, 2009 9:40 am

This is a more difficult problem than I had expected. If the DC adapter reduces the noise, then it could be that the noise is coming from the PC's PSU but it's too low a frequency for your DIY filter to block. You can build a better filter, but it would require a large inductor. A stand-alone sound card would likely fix it too.

Alternatively it could be a ground loop. You can test that by connecting it back to the PC's PSU, but only connecting the 12V wire, leaving the ground unconnected so the only ground connection is through the audio cable. Don't leave it like that very long though, and don't turn the volume up because the ground through the audio cable might not be able to handle much current. If that is the problem, then you can fix it more permanently by making an audio cable with no ground connection (and reconnecting the power cable's ground).

markyb · Post by **markyb** » Fri Sep 11, 2009 11:01 am

Well, im pleased to say that the annoying buzzing has now gone!

but i am annoyed at the same time. Firstly, I went a bought a 12vcd 1 amp transformer from CPC farnell Which was alot better then the plug in type external one i had it plugged in before. But ive also arranged some cables at the back of the pc around. After try the older power supply again, the buzzing was faint but not all together gone. So it seems half and half so far. Totally happy now with no nasty interference! Next step im going to try is rewiring it back up as we had it before from the PSU on a molex connection and see if i get the same interference again. As im not totally conviced it was the transformer or Power supply that was giving me the problem. If all is well with that.. I'll obviously sell the 12vdc PSU to recoup some of the loss. Which is only Â£6 plus the other bits like capacitors/ferrite etc Altho i still have the ferrites fitted to the power supplies anyway. (cant hurt!)

All in all, sounds promising. Massive thanks for your input over the course of the thread mate.. I might not have totally finished yet. So i'll post up my findings tomorrow when i try the first way again.

markyb · Post by **markyb** » Tue Sep 15, 2009 1:15 pm

Well as i thought. The problem came back when i plug it back into the Molex 12v. The noise wasnt as bad, but i still could hear the hard drive clicking and such through the speakers.. The external 12v dc adapter was buzzing till i connected it to the speakers which then became silent. So everything is great. Altho, i have had to cut the plug off the adapter and put a switchable plug on it to turn the power off the speakers now. No major one.

Huge thanks mate

Still slightly annoyed i couldnt get it to work the way i wanted thro the molex but hey.. more important things to worry about in life

Mr Evil · Post by **Mr Evil** » Tue Sep 15, 2009 2:09 pm

Sorry I couldn't have been more helpful, but I'm glad you have it working ok now.

barefootzero · Post by **barefootzero** » Tue Sep 15, 2009 2:33 pm

Having read the whole thread I feel confident the PSU is the problem. I noticed Mr Evil did not tell you how to calculate the frequency of your filter.

Also your filter is missing a key component.

Take a look at this. It will explain what a RC low pass filter is and how to wire it. http://en.wikipedia.org/wiki/Low-pass_filter

There are two components to an RC filter. As the name implies one is a resistor and one is a capacitor. In your case the wire and maybe a few components in the speaker are acting as the resistor and might not be doing a very good job of it. The cut off frequency for a low pass fileter will be 1/(2*pi*R*C) (often approximated as 1/RC).

You would be better off using a separate resistor. Maybe .1 ohm. At 1 Amp that would use .1 watts. If you wanted your filter to filter out any noise above 5 HZ then you would need a capacitor that is ~0.3 Farads (That is alot of capacitance).

If you got a 1 ohm resistor you would need .03 Farads and it would use 1 Watt. Typical small resistors are only 0.25 watts so you would have to get something a little bigger. or you could use 4 .25 ohm .25 watt resistors in series.

If you think your noise is above 50 Hz then you could use a 1 ohm resister with a .003 Farad (3000 ÂµF) Cap or a .03 Cap with a .1 ohm resistor.

The problem with a ferrite core is that inductors filter current so if you wanted a constant current that would be the thing to get. Unfortunate you want constant voltage so you need a filter that filters voltage like the RC filter I described. .

There are more energy efficient ways to filter but this is the cheapest and easiest option.

Sorry I did not reply earlier. If you are happy with the external supply then more power to you.

Mr Evil · Post by **Mr Evil** » Tue Sep 15, 2009 3:51 pm

I didn't mention the cutoff frequency because that requires knowing what frequency the noise is, which is hard without an oscilloscope. Inside a PC it's probably hundreds of kHz or MHz. A ferrite toroid is easy to use and effective at MHz frequencies, so I thought that a good place to start.

Using an RC filter is inefficient compared to an LC filter because it has a shallower slope i.e. it attenuates high frequencies by a lesser amount. And it wastes power; a resistor large enough to be effective would significantly reduce the power output of the speakers.

Inductors do resist change in current, but it only has an effect at higher frequencies (above audio) where that doesn't matter. Also, that's why the capacitor follows it; the capacitor will supply high currents very quickly if needed.