Hum from Fiio Olympus E10K -- Ground Loop?

[ukplc]

Dear all,

First I want to say I have been lurking on these forums for a few months and found it really helpful to read people's opinions and advice, so thanks.

I have an issue with my Fiio E10K 'Olympus' USB-DAC and Headphone amp. Sorry that my description is long-winded, but I wanted to make sure to include all the relevant details.

I've recently noticed a low-pitched hum from the Fiio, only really noticeable in the quiet bits and gaps in the music. I have read around a bit and now suspect that I have a ground loop, but I'm not sure how to address it.

The Fiio has a USB input (this is its only input), from which it also draws power from the laptop. I am using the headphone output to in-ear headphones. It also has a line-out and coax output, but at present I don't have the kit to test these to see whether the hum would still be there.

Observations: if I pick up the Fiio and hold it in my hand, the hum goes away. If I put it down on any surface, the hum is there. The volume of the hum remains the same if I turn the Fiio's volume up or down; it also remains the same if I vary the input volume from the laptop. It also remains if the device is powered off but still connected by USB. The hum also goes away if I disconnect my laptop from the mains power and run it on its battery power. The laptop connects to a standard power adaptor, and from there straight to a mains outlet.

I only have one USB cable with the correct (Micro-B) connector, so I have not ruled out a different cable as a possible solution, but I would appreciate any thoughts on this. I saw a suggestion about a cable with a ferrite bead, but I looked this up and apparently this can deal with high frequency interference noise, rather than the low-frequency hum that I have. The only other thing I can think of is using some sort of power strip for plugging in the laptop that would somehow affect the way it is grounded. Is there anything in this area that might help?

Finally, I paid about £50 for the Fiio, so I'm looking for fairly low-cost solutions, if possible.

Many thanks for any advice you can offer.

 

[ukplc]

Thanks for your reply, Gray -- I had not thought to check that, but the answer is yes -- same hum, and it disappears when I go on to laptop battery power. I guess this means that it is nothing much to do with the Fiio or the connecting USB cable (although it does make it strange that picking up the Fiio stops the hum...)

Thanks again. Again, if this points you (or anyone else) towards possible solutions, I'd be very grateful for any suggestions!!

 

[Gray]

What happens when you plug headphones directly into the laptop (with USB plug removed)?

Can you still hear a hum that disappears when swapping from mains to battery power?

 

[Gray]

Probably not easy but it would be interesting to try another laptop PSU. (Though I think it unlikely that yours will actually be 'faulty')

In case of some localised mains noise, I'd just try it in other sockets - and even away at say a relatives house. (Though I would not expect any mains noise to still be present on the DC side of the PSU)

As always, it's a process of elimination. Good luck.

 

[ukplc]

I'll have a play around as much as I can to see if I can eliminate the mains socket and/or PSU.

Cheers