Computer to Amp Buzz

[Funky971]

Hi, I got my QED A240CD working today (finally!). The amp sounds great but when plugging it into my PC I get a buzz no matter which input is selected. I didn't have this problem with my previous amp. The problem only occours when the PC is plugged into the amp, when it is unplugged it sounds fine.

Today I also got a new case for my pc which had a zip drive, tape drive and SCSI card which i have connected but I don't suppose that would be the cause of the problem although I thought it would be worth including.

My research suggests this being a ground loop problem. How would I go about solving it?!?

[Zen Mod]

you need ground breaker between PC tone output and amp tone input;

either via isolation tone xformers , or put caps in both lines - hot and gnd (meaning - for both channels)

[Funky971]

I've read a bit about these ground breakers. Do they reduce sound quality at all?

[Zen Mod]

Originally posted by Funky971
I've read a bit about these ground breakers. Do they reduce sound quality at all?

sound quality ........ straight from PC ?

[jaycee]

Check that your PC and monitor (if its a CRT) are earthed correctly. It may be worth disconnecting any external peripherals if they have their own power supplies, to verify that the buzz is not getting in through any of them.

You mention a new case. Does this include a new PSU? Check there is earth continuity to the case. Also check that there is continuity between the earth pin, and one of the 0V (black) lines from the PSU.

Do you get the buzzing even if the PC is turned off ?

A ground breaker transformer should be the LAST resort. Yes, they reduce quality, and they are usually used in car audio. Find out where the buzz is coming from first.

[sakis]

1- one thing you can do is try to supply your stereo system from the same socket that your pc is powered
2- the trafo of course is a solution but yes reduces quality
3- another NOT SAFE solution is to remove totally the ground from your amplifier power cord ( not recomended but possible to work )


and here is the best !!!!!!!!!!!!!!!!!

is you sound card have a line out ???? if your answer is yes then i will tell you that you need to re verify that !!!!! how ??? by simply connecting a pair of headphones in the so called line out !!!! if the head phones play normally and with a quiet good ammount of level then this is not a line out !!!!!!!

it is probably after the D/A some small smd chip probably a 4558 op amp configured as a small amplifier with power enough to drive a pair of headphones or cooperate with the input of some desktop speakers

the quality of your signal and also all earth issues are related to this chip ....the remark about the quality is the most importand actually cause your D/A converter may be support a crosstalk for example between the 2 chanels L+R that is amazinglly good BUT THE 4558 CANNOT !!!!!

also the same with frequency response !!!!!! ALL OF IT DEPENDS ON THE QUALITY OF THIS CHIP !!!!!

dont have to remind that old audio cards had jumpers inside to isolate all that ...... between real line out and locall op amp or biger amp existing in the card

your solution is to find the inputs of this chip isolate them from the chip and then 10 cm of audio cable goes to a pair of isolated phono plugs fited on an emty slot of your pc and you are done !!!!!!

you will notice that the real line out has less drive ability but amazing sound noise free ....

in normal sound cards chip exists just behind the 3.5 mm headphone/line out jack

if your card is on board card then you are in more trouble

try it and have fun !!!!!!!!!!!!!!!!

[burbeck]

hi Funky
most likely ground loop, this is a solution transformers cheap and stereo worth a try for a tenna, does degrade signal but fine for most computers

http://www.maplin.co.uk/Module.aspx?ModuleNo=33172

[Funky971]

Hi, I am using the same power supply for my new case as for my old one.

The 'line out' from my pc is powerful enough to power a pair of headphones (and give them a fair amount of volume!) and the sound is onboard. I have tried using an older PCI soundcard and had the same issue. Also the buzzing happenes when the PC is switched off.

Also I didn't have this problem with my old amp. If it will help I can open up my pc and disconnect the new devices (SCSI card, SCSI tape drive and IDE zip drive) to see if that helps. However considering that it still buzzes with the PC powered off I cannot see this being the problem but will check if it could be the problem.

[sakis]

of this pc output is exactly like that

you have a 4558 or other simular chip that is probably single supply has a capacitor in the output to prevent any DC going to speakers or hedphones or line in and then the ground terminal is connected to the box of your pc

probably your new amp do not or does have simular configuration

for examle there is amplifiers that the signal ground is the one and same thing with the sassi ground ( to my understanding this is wrong ) removing this might be a solution

IE do not destroy the safety earth that exists in your amp ( i presume that your amp has a 3 pin power plug ) but remove the connection to signal ground ( what normally a ground lift switch will do )

i presume that all these things we talk here you understand because if not then all this is academic .....

removing periferals suggestion has nothing to do with things existing inside the box ......but it has some to do with peripherals like printers scanners and stuff like that ( anything else that is connected to power except your pc )

[Frank Berry]

I had the same problem between my computer and preamp.
I solved the problem by using a pair of good quality (Jensen) 1:1 audio isolation transformers.
The audio quality is very good (after all, the source is a PC).