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RFI and hum with Schiit Mjolinir and AK240 Balanced

post #1 of 5
Thread Starter 

I recently purchased an AK240 and a Schlit Mjolnir amp that are connected via Moon Audio balanced cables (2.5mm TRRS to dual XLRs) and auditioned via Audeze LCD-3 (Moon V3 cables).  I immediately became aware of RFI and what appeared to be a ground hum when the volume control was advanced beyond the 12:00 position.  I then connected the amp's power cord to a Furman Elite 15 PFi which eliminated the RFI but the hum has persisted.   I suspect that there is some persistent  "antenna" effect, since moving the AK240's balanced cable produces some crackling and, depending upon the position of the cable, variance in the intensity of the hum.  Is this the result of connecting a grounded device—Mjolinir—to an ungrounded device—AK240?  And if so, is there a solution, short of replacing the amp with a portable device? Has anyone had experience with the EBtech HE-2-XLR Hum Eliminator?

Thank you in advance.


Edited by roscoe9915 - 6/5/14 at 7:52am
post #2 of 5

Apparently, this is a known issue with the amp.  Email Schiit directly and they can offer some ideas for how to rid your system of this problem.  IIRC, the easiest way is a Tripp Lite isolation transformer.

post #3 of 5
Thread Starter 

Hello and thank you for your reply.

 

I spoke to Schiit regarding this issue and they felt that it was a cable to amp issue, since the amp is quiet without the cable attached.  I have also spoken to the creator of the cable, and it was felt that the issue is related to the absence of a ground connection in the AK240's balanced connector.  The cable is in the process of being modified to accommodate that absence.

 

Interesting that you note "Apparently, this is a known issue with the amp," as I have searched the Net and have not found any posts to that effect.  Had that been the case, I would not have purchased the unit.  By the way, with the cable in question removed from the amp, the Mjolnir is silent at max volume/ minimum attenuation.

 

I should have the cable back during the week and will determine whether it has achieved resolution.  If not, I will either return the amp and find something else, or obtain the isolation transformer suggested in your post,


Edited by roscoe9915 - 6/7/14 at 2:18pm
post #4 of 5

Glad you have a possible solution.

 

The hum has been talked about quite a bit around here.

 

http://www.head-fi.org/t/603218/schiit-mjolnir-headphone-amplifier/1890#post_8881501

 

http://www.head-fi.org/t/603218/schiit-mjolnir-headphone-amplifier/3165#post_10486394

 

For starters.  Particularly, read the second link and the posts that follow.

post #5 of 5
Thread Starter 

Thank you for the links.

The issues described in those posts seem to be power related (clicks, pops and buzz).  My experience is somewhat different in that it was dominated by a typical ground hum.  Admittedly, there were some microphonics as well, but they were eliminated with a Furman Elite 15 Dpi. However, it does appear that others have experienced Mjolnir/power related issues that would tend to suggest the need for better internal isolation in re the amp's design.  That said, I would be loathe to see it go, since the Audeze LCD-3/Mjolnir combo is magical.  

 

Update: I am still awaiting the grounded balanced cable for the AK240/Mjolnir, however, I had occasion to connect the AK240 to the Mjolnir in unbalanced mode and found the amp to be dead quiet at max volume/min attenuation.  There was no RFI, microphonics, hum, clicks, pops or other evidence for power contamination, suggesting that the problem is likely the missing ground in the AK240's balanced connector.

 

Latest Update:  The modified cable—grounded on AK240 balanced side via a 2nd connection to its 3.5mm socket—has arrived and has completely eliminated the RFI, hum and all other associated noises.  This corroborates the initial impression that the noise was not the fault of Mjolnir.  That said, I have since replaced the Mjolnir with a Bryston HBA-1 which is equally as quiet with the new, grounded, balanced cable.


Edited by roscoe9915 - 6/16/14 at 6:48am
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