USB Input causes noise across whole amplifier - Musical Fidelity M5si

Thanks.

I need flexible options right now, as I'm going through some component failures and repairs, changing of systems, and eventual moving house. I wanted the USB capability to provide one aspect of this flexibility.

I'm disappointed that the USB input is not at all isolated from the rest of the preamp, thus allowing the noise to bleed into all uses of this integrated (not in a good way here) amp.

You need a dedicated USB card with external power.

Matrix usb h via battery power takes all the motherboard noise out of the chain, USB is a dirty signal, and will cause noise issues up and down the entire frequency.

I have a picture of a modded card as my avatar ^^^^

Hi carlsbad,

Thanks for the suggestions.

The computer and integrated amp are on different areas of the room. The comp is on it's own surge protection; the amp is direct into the mains. I have tried reversing the amp power polarity.

I'll try running a line from the same socket to the comp to see if that has any affect.

Thanks.

@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. 

Hi erik_squires,

Thanks for the info and link.

Alas, for the $$ I'd like solutions inherent in the device, sigh.

I'll look at the isolator though.

Hi tony1954,

"From what is says in the manual, I would check that the driver your computer (either Mac or PC) is using is compatible "

My manual doesn't mention drivers, that I could find anyway. All USB devices are working, and those that require drivers are up to date.

I didn't mention but I also tried different USB busses.

The M5si is recognized, is set as default. And it works as expected.

It is only the noise, regardless of whether USB is selected as source.

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.

I have the Musical Fidelity M6si, so I assume the 5si is similar with regards to USB functionality.

From what is says in the manual, I would check that the driver your computer (either Mac or PC) is using is compatible and current and that the computer's settings are correct.

Or just contact Musical Fidelity. They are very helpful and quick to respond.

Yes,I know. Just leave the internal  DAC there,you have no way to use it.

Add external DAC if possible.

Thanks, but this integrated amp doesn't have an optical input.

If that is the case,do not use the internal DAC.

I have bad experience to use USB port in hifi system,so since then I never use USB port in hifi system again. Now I use optical port,the sound is very good.