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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
photon_arts OP
6 posts
 

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.

yuviarora's avatar
yuviarora
537 posts
 

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 ^^^^

photon_arts OP
6 posts
 

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.

 

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