2. amps-preamps
  3. 173568-168155

USB Input causes noise across whole amplifier - Musical Fidelity M5si

Hi,
Has anyone experienced this:
 
If a computer is connected to the USB input, the noise level of the amplifier is raised across ALL INPUTS. This is not a 60hz hum. There is an upper mid-range whine/tone and some crackle. This is audible regardless of which input is active. IOW, when using any input, such as AUX2, this noise is present, until the USB cable is disconnected. Apparently there is bleed through the whole system.
 
I have tried different USB cables, USB2 and USB3, USB cable with an incorporated choke. The effect is the same. The noise comes on about 2-3 sec. after connecting the USB cable.
 
This is a new, recently purchased unit.
 
Thanks for any insights
photon_arts

Showing 2 responses by erik_squires

erik_squires
16,644 posts
 

@photon_arts You can find them from around $30 I think.  Just make sure it supports high speed 2.0.

It does stink, especially when I have seen some mega-buck DAC vendors sell this as a huge upsell. 

And it's also upsetting because 90% of the time there  is a USB ground loop problem it is NOT audible hum.  It's really bad jitter which listeners may never know about.  They'll hear it in lack of clarity, focus and harshness, but without a jitter analyzer they would not know they had an issue.

It is only a very small amount of USB ground loop issues which show up as audible humm. 

erik_squires
16,644 posts
 

Yes, I know exactly what this is.

Unfortunately, even today, DAC makers still don't universally use galvanically isolated USB inputs. << insert big sigh here>> and this is 100% what happens.  Especially when your PC and audio are on different AC circuits.

The solution is really simple and cheap though.  You need a USB isolator.  Make sure it supports the bandwidth you need.  Here is a good one.

This is a bad situation because there are a number of situations where a ground loop occurs and it's not this obvious.  Usually listeners "only" suffer from elevated jitter, but it is detrimental to the sound quality.

 

 

More to discover