Loud hiss on speaker system

[Harry Sherwood]

Hi!
Just thought i'd ask about a problem that's been on my nerves for a while now. I have a mixing desk plugged into my computer via a 3.5mm jack, which then after being pre-amped by the mixer gets sent to some 80w powered speakers and some 100w passive speakers driven by an amplifier.

whenever the system is up and running there is a loud, annoying hiss (frequency ~ 500-1000Hz) and an uneven crackle which changes based on what I do on the computer. For example, when I scroll using the mouse (which is wireless, if that is of any use) the crackle seems to change tone slightly. The cause is not the monitor or the mouse as I have unplugged both of them and the noise persists. also, when the computer is very active (searching on the disk or something) the noise also changes.

If it was quiet I wouldn't care but it's pretty loud (you need to turn up the volume quite loud to forget that it's there.) Also, turning up the volume does not change the volume of the hiss. Even when everything is muted it is still there.

I've read a bit about using isolating transformers, is this what you guys would recommend or is there another solution? If so, which brand/model should I buy? Thanks!

 

[smorizio]

Check where the onboard audio and cd-rom cables are if there flopped over the gpu you could be picking up fan noise. On your mb check if all the grounding standoffs were used and there no rubber or plastic screws used to hold the mb down causing a grounding issue. Look at your brand and wattage power supply. If it a cheap one it could be pumping noise into your system. I find the mb sound chipsets act as ariales on some pc picking up cell phone noise and speaker feedback. Sometime you have to use a longer audio cord to keep the pc from picking up noise. If the sound chip is the cause see if a friend has an older sound card to rule out the sound chipset.

 

[Harry Sherwood]

Check where the onboard audio and cd-rom cables are if there flopped over the gpu you could be picking up fan noise. On your mb check if all the grounding standoffs were used and there no rubber or plastic screws used to hold the mb down causing a grounding issue. Look at your brand and wattage power supply. If it a cheap one it could be pumping noise into your system. I find the mb sound chipsets act as ariales on some pc picking up cell phone noise and speaker feedback. Sometime you have to use a longer audio cord to keep the pc from picking up noise. If the sound chip is the cause see if a friend has an older sound card to rule out the sound chipset.

Thanks! I shall certainly have a look into that. One thing i did notice is that when plugged into an iPad or other device the hiss stops. when plugged into something like a laptop with a power supply, however, the hiss returns. I'm pretty sure the laptop is properly grounded etc. Do you know anything regarding isolation transformers?