I have a dificult problem, Please help me!

I have a fault with my hifi setup and I don't know what causes it.

As I mentioned before I use my PC to decode DVD's and then send the decoded info to my preamp where the rest of my kit turns it into happy noise.

I had a problem recently where I was getting a hum through the speakers when the preamp was turned to the computer input.

When the CD was selected there was no hum meaning everything from that stage on must be ok.


Irrespective of which cable I use the hum is there so therefore the cable cannot be the problem.

The hum is there if the computer is on or off.

The hum goes if the cable is unplugged and return when it is reconnected.

I assumed that the card had a faulty connection on the back and sold it.

I then recconected the setup using the onboard soundcard...exactly the same problem returned!

Does anyone have any suggestions?

The only thing I can suggest (merely due to lack of knowledge on the subject as oposed to any rationialisation) is that the 3.5mm stereo jack combines the return path of both channels.

Would this be a problem?

Please help I have wasted £100s on this problem and cannot place it.

Is there anything else i should check?

 

It sounds like a ground loop forming through your computer. To test this theory, leave the cable in place between computer and preamp, and unplug computer from the mains. Plug the comptuer into a different spur/ringmain to the hifi, and it should solve itself. Might also help just by changing what's plugged in where on the same ringmain.

 

Is your sound card a PCI type or external?

I have noticed a hum with audio on my PC when copying audio from turntable to my PC, I found this out to be related to the relatively cheap quality and design of the plu-in PCI type Sound Blaster sound card.

I for one need to look at a much better audio contro, system for my PC as I spend a great deal of time copying vinyl for myself and others (personally, no dodgy sales going on here!).

 

I had a similar problem with a VCR once, it generated hum into the audio system (which we found after several hours of investigation), and ended up putting an earth stud on to my mains outlet socket (with a hard wired earth lead connected to the main earth for the ring), I then made up a dedicated earth 'strap' lead that was clamped on to the earth stud on the mains outlet socket then connected to the chasis of the VCR by one of the self-tapping chasis screws already in place at the rear of the VCR (make sure that any kind of insulation/chasis paint is removed driectly around the connection area).
This relsoved the hum immediately
Of course, any work on your electrical system should be checked with a qualified and authorized electrician.

 

It could be that you're interconnect is faulty and is not making the earth connection so you have floating signal leads. This can cause hum.

 

Thanks Isaac,

They are both plugged into the same surge protector. Do you suggest I run an extension lead and plug the PC into a different outlet?

 

Thanks Listening Ear,
Are you suggesting I manually earth the computer chassis?
Sound reasonable.

The card was origionally an Audigy 2 zs. Good card £200. I now use the crappy onboard.

 

Cute picture technobear,

I tried more than one lead. the second was handmade...I have double checked all the connections

 

Peter - it doesn't cost anything to try.

 

Ok I have now split the hifi and computer onto seperate sockets (other sides of the room)

The hum is still there....

If I earth the computer to my hifi would that fix the problem? If so which component should i do it too?

I am not suggesting anything major here, just use a bit of spare speaker wire connecting both/all my cases.

 

Ok i tried that...
Still got the hum.

I have a small flat so i think there is only one ringmain.
I have a high drain socket in the kitchen..that would be on a different ring.
Now why do they only put high drain sockets in the kitchen...my amp has a HUGE drain.

I will try that next

 

Huge is relative.

A kettle, for example, will draw more power than any amp this side of a very large and expensive krell. So will a steam iron. A cooker draws quite a bit more than the ringmain that your entire hifi, computer and all of that is connected to could provide.

In the scheme of things, a class AB amp doesn't actually draw much power assuming it has a sensible idle current (S300 owners take note).

 

...try the earth strap it's very cheap to do yourslef and at least you will have tried it.

Isaac mentioned various pieces of domestic applieance but the one I would like to pick up on is a steam iron. These are notorious for creating problems, we spoke to an electrician recently who always asks customers what brand of steam iron they use when visiting homes where there are problems with ring mains (mostly RCB tripping and neutral faults).

I need to replace our iron and I always get the wife to use it on the upstairs circuit.

Just a bit of trivial info...

 

Listening ear...
What do you mean by the earth strap?

and I am not really sure what an iron is either...i have heard them mentioned...but it means nothing!