Hi - I am not au-fait with anything electronic so please bear with me.
I am also slightly bonkers.
My project is to fit powered speakers inside a PC case to cut down on desk clutter,and also have the speakers automatically on and off with the PC.
It has to be done cheaply and simply preferably using junk as I am fanatical about recycling (aka tight-fisted)
The desktop speakers have been dismantled and the components fitted inside the case.
Their power supply was a plug in 240v-to- 9v dc transformer.
The PCs internal power is 12v or 5v (or a "blend" of 7v between these two")
I chose the 12v wires and put two IN4001 diodes on the +12v and three on the -12v.
It all works really well and does exactly what I want.
However ,while the sound quality doesnt really have to be super fantastic it does suffer from interference when the hard drive and dvd drive are active,giving out bleeping, wheezing and scraping sounds (its not my sons rap music-Ive already checked!)
How can I minimise this?
I have some ferrite rings-would these help?
audio
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Simon (Webmaster)
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Re: audio
Hi
PC power supplies can give a pretty dirty output as well as interferance from other components - I often have problems with hum or hard disk noise on the soundcard outputs when connected to large PA systems.
You mention you have 2 diodes in the 12V supply and 3 in the -12V connection - I take it you mean the ground (0V) - the black wire in power connectors. The negative lead from the speakers should be connected directly to 0V from the power supply, with no diodes. If you need the diodes (I presume to drop the voltage) put them all in series with the +12V connection. Lifting the ground via diodes probably will make the noise worse. In fact the diodes may be shorted out, as the ground wire in the audio connection to the soundcard will be connected to both the power supply ground via the soundcard and the ground in the speakers power connection.
Suggestions:
1: Connect the ground connection (-12V as you labelled it) directly to the power supply 0V black wire without the 3 diodes. Move these diodes to the positive connection, i.e. 5 diodes in series.
2: Try disconnecting the ground wire in the audio cable connected to the soundcard. Since this connection will already be made via the power supply this could create a 'ground loop', creating hum.
3: If all this fails try filtering the power supply. You could try the ferrite ring first, otherwise try filtering with capacitors. You could replace the diodes with a voltage regulator such as a LM7809 and appropriate capacitors as shown in the datasheet for the regulator.
Hope this helps. Let us know how you get on.
PC power supplies can give a pretty dirty output as well as interferance from other components - I often have problems with hum or hard disk noise on the soundcard outputs when connected to large PA systems.
You mention you have 2 diodes in the 12V supply and 3 in the -12V connection - I take it you mean the ground (0V) - the black wire in power connectors. The negative lead from the speakers should be connected directly to 0V from the power supply, with no diodes. If you need the diodes (I presume to drop the voltage) put them all in series with the +12V connection. Lifting the ground via diodes probably will make the noise worse. In fact the diodes may be shorted out, as the ground wire in the audio connection to the soundcard will be connected to both the power supply ground via the soundcard and the ground in the speakers power connection.
Suggestions:
1: Connect the ground connection (-12V as you labelled it) directly to the power supply 0V black wire without the 3 diodes. Move these diodes to the positive connection, i.e. 5 diodes in series.
2: Try disconnecting the ground wire in the audio cable connected to the soundcard. Since this connection will already be made via the power supply this could create a 'ground loop', creating hum.
3: If all this fails try filtering the power supply. You could try the ferrite ring first, otherwise try filtering with capacitors. You could replace the diodes with a voltage regulator such as a LM7809 and appropriate capacitors as shown in the datasheet for the regulator.
Hope this helps. Let us know how you get on.
Re: audio
Thanks Simon-some good tips.
I will return with the results.
I put diodes on both sides simply because I thought its was the right thing to do.
The "7 Volt Trick " website chap shows the method to cut down the speed of a noisy cooling fan -so is this a potential problem too?:shock:
Ive made a start this evening and twisted the pairs of wires as you would find in network cables.
Is there a pair I should not put ferrites on?-I have a boxful of them taken out of old CRT monitors(they do have a use after all!)
Thanks for your time
Martin
I will return with the results.
I put diodes on both sides simply because I thought its was the right thing to do.
The "7 Volt Trick " website chap shows the method to cut down the speed of a noisy cooling fan -so is this a potential problem too?:shock:
Ive made a start this evening and twisted the pairs of wires as you would find in network cables.
Is there a pair I should not put ferrites on?-I have a boxful of them taken out of old CRT monitors(they do have a use after all!)
Thanks for your time
Martin
-
Simon (Webmaster)
- Site Admin
- Posts: 173
- Joined: Tue Jan 29, 2008 7:05 pm
- Location: Nottingham, UK
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Re: audio
The 7V trick will be fine for a fan since it has no other connection to ground - both connections are 'floating' with respect to the power supply ground (black wires). The problem with doing this with the speakers is that the negative power connection will also be connected to the ground in the audio cable, and hence to the power supply ground via the soundcard.
You can try the ferrite cores on any of the cables - it won't do any harm. Obviously try on on the power and audio cables to the speakers (or at least what is left of the speakers
), but not both through the same core. Also try on the power supply to the hard disk and optical drive, although depending on the diameter of the core you might have trouble getting the connector trough. Try a few turns of the cable around each core.
You can try the ferrite cores on any of the cables - it won't do any harm. Obviously try on on the power and audio cables to the speakers (or at least what is left of the speakers
), but not both through the same core. Also try on the power supply to the hard disk and optical drive, although depending on the diameter of the core you might have trouble getting the connector trough. Try a few turns of the cable around each core.Re: audio
Thanks for all the advice Simon.
Got it all back together this afternoon.
I made use of all the pointers however I made the classic mistake of doing it all at once so I dont know which of them actually made the most difference.
There is still the same noise interference, but at a much lower level.
Once the side panel was back on and the base unit stowed under the desk, its barely noticable.
As you said the ground from the soundcard was unnecessary.
Putting all the diodes together in series was also done -the led doesnt seem so bright now(?)
Theres ferrites on every run of wires.
The molex connectors to the drives wern't an issue as I already knew I could carefully press in the little tangs and release the individual pins,allowing me to pass all the wires through a small diameter ring.
Its been worthwhile,the whole thing is neatly self contained.
The speakers are mounted on an oak 'beam' which runs from front to back behind the side panel .
The circuit board,extracted wholesale from the speaker casing, is fitted to the back panel of the pC case with the Balance,Volume/on-off knobs and the led protruding through to the outside.
I originally found that it would fit nicely within an old floppy drive casing and therefore could have been front mounted in a spare drive bay.
But then I found that the knobs would have fouled the sliding cover so I abandoned that idea.
In hindsight I could have fitted it to an old expansion card backplate and put it at the bottom over a redundant AMR slot,rather than drilling the case itself.
I would like to do this with another machine,and have another set of old speakers,but the transformer is marked 12VAC-How do I get round this?
Thanks for your time
Martin
Got it all back together this afternoon.
I made use of all the pointers however I made the classic mistake of doing it all at once so I dont know which of them actually made the most difference.
There is still the same noise interference, but at a much lower level.
Once the side panel was back on and the base unit stowed under the desk, its barely noticable.
As you said the ground from the soundcard was unnecessary.
Putting all the diodes together in series was also done -the led doesnt seem so bright now(?)
Theres ferrites on every run of wires.
The molex connectors to the drives wern't an issue as I already knew I could carefully press in the little tangs and release the individual pins,allowing me to pass all the wires through a small diameter ring.
Its been worthwhile,the whole thing is neatly self contained.
The speakers are mounted on an oak 'beam' which runs from front to back behind the side panel .
The circuit board,extracted wholesale from the speaker casing, is fitted to the back panel of the pC case with the Balance,Volume/on-off knobs and the led protruding through to the outside.
I originally found that it would fit nicely within an old floppy drive casing and therefore could have been front mounted in a spare drive bay.
But then I found that the knobs would have fouled the sliding cover so I abandoned that idea.
In hindsight I could have fitted it to an old expansion card backplate and put it at the bottom over a redundant AMR slot,rather than drilling the case itself.
I would like to do this with another machine,and have another set of old speakers,but the transformer is marked 12VAC-How do I get round this?
Thanks for your time
Martin
-
Simon (Webmaster)
- Site Admin
- Posts: 173
- Joined: Tue Jan 29, 2008 7:05 pm
- Location: Nottingham, UK
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Re: audio
Hi
Good to hear it worked. I suspect sorting out the grounding probably made the most difference. The LED being dimmer makes sense, as before the diodes in the ground connection would have been shorted out by the ground connection via the soundcard, effectively making them useless. With all the diodes in the the positive connection the voltage drop would be higher.
You should simply be able to connect the other speakers needing 12V AC directly to the 12V DC supply - they will have a rectifier in so it doesn't matter which way around you connect the wires. You might, however, need to conect the ground to the soundcard on this one for it to work (try it without first to check). There is also the slight possibility the the voltage will be too low, as 12V rectified to DC is 12 * 1.414 = 17V. However I suspect the speakers will have a voltage regulator in, so it may not be a problem.
Good to hear it worked. I suspect sorting out the grounding probably made the most difference. The LED being dimmer makes sense, as before the diodes in the ground connection would have been shorted out by the ground connection via the soundcard, effectively making them useless. With all the diodes in the the positive connection the voltage drop would be higher.
You should simply be able to connect the other speakers needing 12V AC directly to the 12V DC supply - they will have a rectifier in so it doesn't matter which way around you connect the wires. You might, however, need to conect the ground to the soundcard on this one for it to work (try it without first to check). There is also the slight possibility the the voltage will be too low, as 12V rectified to DC is 12 * 1.414 = 17V. However I suspect the speakers will have a voltage regulator in, so it may not be a problem.