Topic: Ground loop hum
I had my brand new VPC1 and PTQ hooked up for the first time yesterday, and had a whole lot of trouble with an extremely annoying and loud hum through my Behringer keyboard amp/speaker, and crackling through any speaker (although not noticeable with headphones). The amp may not be the best choice for a powered speaker, but I can't afford to replace it right now. Pretty sure the loud hum was ground loop noise. Using a Behringer PCA202 audio interface. Laptop running Intel Dual Core, so it's halfway decent. What solved it was a combination of reducing the sample rate from 512 to 256 and inserting a Behringer hum destroyer (MicroHD HD400, about $25) after the audio interface. Now I can play even at high volume with neither hum nor crackle, and I can't say I've noticed any degradation of the sound quality.
Any comment on this would be welcome... this was an ad hoc "Trial and error" solution on my part.