[Traddad]

I'm chasing a hum/hiss down in my computer/DAC/amp system and wondering if a USB DAC with a discrete power sourse (not powered by the computer via the USB cable) would put the kibosh on the electrical noise. I might be dealing with a ground loop but so far I have not been able to locate it. I was thinking that a data only link (unpowered USB or Toslink) might sever the connection rather than trying to put a HumX on every component on the computer end of the system (monitor, computer, printer, etc). None of the plugs on the amp end have 3 prong (grounded) plugs and the Amp/CD or DVD or TV combinations have no noise. It's only when the computer/DAC is hooked in.


Some of what is happening to my system:

Computer + DAC on wall AC = Hum
Computer + DAC on battery = No Hum

 

[joe_cool]

Sadly the USB signal ground from the PC is connected to the chassis ground of the PC. This is part of the design and safety rules. This may be one of the factors.

The AC power supply for the DAC seems to be another factor. You may be able to replace or modify the power supply to get some improvement. Does the power supply have an AC or DC output?

 

[Traddad]

Quote:

Originally Posted by joe_cool /img/forum/go_quote.gif Sadly the USB signal ground from the PC is connected to the chassis ground of the PC. This is part of the design and safety rules. This may be one of the factors. The AC power supply for the DAC seems to be another factor. You may be able to replace or modify the power supply to get some improvement. Does the power supply have an AC or DC output?

I'll try this again (my last reply disappeared)

My present dac is powered by the computer through the USB cable. I was hoping that breaking the power link would stop the noise. Sadly, you answered my question (all USB cables are grounded to the computer).
Please tell me that a Toslink cable is non-metalic....please?

 

[joe_cool]

Yes, Toslink (Toshiba) cable is optical and made of glass or plastic.

 

[Traddad]

Quote:

Originally Posted by joe_cool /img/forum/go_quote.gif Yes, Toslink (Toshiba) cable is optical and made of glass or plastic.

What about SPDIF?

 

[joe_cool]

SPDIF is a data format.
WIKI

 

[BigTony]

use a USB/Optical Convertor. Then your decoupled from the PC hum etc.

 

[joe_cool]

I once had a USB-Coax SPDIF converter with this kind of problem. The coax output ground was connected to the USB ground (and therefore connected to the PC ground). When I disconnected the coax pulse transformer from the common ground the noise went away.

 

[mrarroyo]

Quote:

Originally Posted by joe_cool /img/forum/go_quote.gif I once had a USB-Coax SPDIF converter with this kind of problem. The coax output ground was connected to the USB ground (and therefore connected to the PC ground). When I disconnected the coax pulse transformer from the common ground the noise went away.

That is why BigTony recomended to connect from the PC using an USB cable to an USB/Optical converter then using an optical cable to the DAC.

 

[Ori]

Quote:

Originally Posted by Traddad /img/forum/go_quote.gif Some of what is happening to my system: Computer + DAC on wall AC = Hum Computer + DAC on battery = No Hum

Based on that observation, it's clear that you have a crappy wall supply. These are not grounded to the mains ground, so the noise must be just bad regulation or insufficient current capacity. The simplest approach is to replace the wall wart with a linear power supply.