Welder
09-11-2010, 01:04
Until recently I’ve been using an HRT Pro connected to my laptop. Between the HRT Pro and the laptop I’ve been using an adapted mains powered USB which has a galvanic isolator between the Dac and the Hub.
I sold the HRT Pro along with the powered hub and returned to the HRT 11+ and I’ve been running it off USB power until I get around to building another isolated mains powered USB hub.
Through my amp and speakers all seems fine, but when I connect it up through my headphone amp I get a noticeable hum in one channel akin to a grounding loop problem. If I earth the Dac by touching it the noise goes. If I stand directly in front of the laptop the hum decreases.
It may also be relevant that I use semi balanced interconnects (shield not connected at amp end, only at source)
So, I set about trying to see what could be done to ground the path from the laptop to Dac.
Like most laptops I imagine (?) it doesn’t have a ground lead from power mains plug to transformer to laptop power input.
If I leave an Ethernet cable plugged in (which carries a ground) even if the router is switched off the hum goes.
This would seem to suggest that the laptop could do with grounding.
I find it hard to believe it is just the combination of my headphone amp, Dac and cables causing this problem and wonder if all laptops using a USB only powered Dac have this problem :scratch:
Has anyone else experienced this problem and does anyone know of a way of grounding a laptop under mains power?
I sold the HRT Pro along with the powered hub and returned to the HRT 11+ and I’ve been running it off USB power until I get around to building another isolated mains powered USB hub.
Through my amp and speakers all seems fine, but when I connect it up through my headphone amp I get a noticeable hum in one channel akin to a grounding loop problem. If I earth the Dac by touching it the noise goes. If I stand directly in front of the laptop the hum decreases.
It may also be relevant that I use semi balanced interconnects (shield not connected at amp end, only at source)
So, I set about trying to see what could be done to ground the path from the laptop to Dac.
Like most laptops I imagine (?) it doesn’t have a ground lead from power mains plug to transformer to laptop power input.
If I leave an Ethernet cable plugged in (which carries a ground) even if the router is switched off the hum goes.
This would seem to suggest that the laptop could do with grounding.
I find it hard to believe it is just the combination of my headphone amp, Dac and cables causing this problem and wonder if all laptops using a USB only powered Dac have this problem :scratch:
Has anyone else experienced this problem and does anyone know of a way of grounding a laptop under mains power?