Ground hum issue

[David Neel]

I have a mild ground hum issue with my Hakai. I've tried various things to eliminate it: powering Hakai from a socket far away from the rest of the system does not help, but disconnecting the USB to the Gigaport DAC does. Disconnecting Hakai also works. Is this likely to be related to the Nano PSU I'm using, or is it inherent in having a USB-powered DAC?

The hum has become apparent since I made two changes: replacing the 3160 motherboard with the 3050 board (can't see how that should affect things?), and installing Entity. There is an extra ground cable with Entity to be used in such cases, but I'd rather fix this at source.

Thanks in advance for any ideas - I'm happy to rebuild Hakai into a new case with a different PSU if that would change things.

[FairPlayMotty]

We've used the same boards and cases, no problems here so far.

[lejonklou]

Thank you David!

This is a very interesting field of improvement for any HiFi system and as you report a slight hum, it's a clear indication of a ground loop somewhere in the system.

Ground loops always decrease the performance of a system and it will often go unnoticed until there's an actual hum. But countless of times I've had one - usually due to the TV I often have connected to our living room system - and its detrimental impact is never obvious to me (it doesn't create any hum) until I've cut the loop by disconnecting the TV or moved it to a power strip without ground.

Entity has a very large gain of 71 dB, much more than most MC phono preamps, and therefore it will amplify the hum created by the ground loop. In this case, I suspect that the power supply of the HAKAI grounds the chassi and the main board and then transfers that ground to the Gigaport USB DAC. From there it enters your preamp.

I can't be certain of the solution until I've had a look at your entire system, but I do suspect that it's the power supply of your HAKAI that connects the USB ground to mains ground. And the solution is likely that the mains ground to HAKAI should only connect to its chassis but not to the main board. Not sure how to accomplish that, however, as I don't have an original HAKAI here, only variants with my own power supply, where the mains ground is not connected to the main circuit board.

It could also be another unit that connects mains ground to signal ground. It does take two such connections to create an actual loop.

[David Neel]

It's been an interesting evening. I know there is an extra ground cable supplied with Entity, but was reluctant to use it, as I presume it slightly reduces performance of Entity. So I've been looking for the root cause. The hum was only occurring when both Hakai and Entity were powered up. First attempt was to separate them, they were on the same shelf. No difference. Then I tried powering Hakai via a long extension lead plugged in at the other side of the room. No difference.

Then I switched Hakai off, again no difference, until I realised that the USB Gigaport DAC remained powered. Unplug Hakai completely so no power went through to the DAC, silence. Unplug the DAC, restart Hakai, also silence. Plug the DAC into my LSNAS (only to power it), silence. So the hypothesis became that it was not the DAC, but rather the interaction between it and the Hakai's Nano PSU.

Long story short, after an evening with screwdrivers, a spare case and motherboard, I now have a HakaiNAS, an LSHakai, and no hum! So it seems Fredrik is right on the money. An interesting side effect of this is how the sound has changed, with a 520W ATX PSU powering the Hakai.

[David Neel]

We've used the same boards and cases, no problems here so far.

Nor here, until Entity replaced my Urika.

[tokenbrit]

.. An interesting side effect of this is how the sound has changed, with a 520W ATX PSU powering the Hakai.

[better | worse | different]?

[David Neel]

[better | worse | different]?

Yes! Too many variables to be sure what's going on as yet...

[tokenbrit]

[better | worse | different]?

Yes! Too many variables to be sure what's going on as yet...

Be true to your signature :)

[David Neel]

Update: The hum is more accurately described as a whistling or rumbling, i.e. it pulses rather than stays absolutely steady. It is more pronounced when I use the 3050 motherboard, compared to the 3160 (i.e. the motherboard has some influence). It is only present when both Entity and Hakai are powered up. With both powered up, it can be removed by either disconnecting the DAC, or by disconnecting the LP12 inputs to Entity. I have re-dressed the power cables and interconnects, to no effect.
It is subtle enough that I did not notice it, after installing Entity, until I changed the Hakai motherboard from 3160 to 3050. I have experimented with a different PSU, which removes it. The problem is that the optimum configuration of Hakai is the Streacom case and Nano PSU, albeit with the 3160 board. My case and PSU substitution reduced the musicality, even if it did add some welly.
Any ideas? If it's relevant, amps are Sagatun Monos/Tundra Monos.

[lejonklou]

This is an interesting and completely new one to me, David.

What I would do is to methodically measure earth continuity in the system. Which chassis are grounded, which signal grounds are tied to chassis ground, how and where. In particular the HAKAI.

Very difficult to instruct or perform from a distance, I'm afraid. It's more of a hands on detective work. You've already made some interesting discoveries, now I suspect basic measurements would help the most.

[FairPlayMotty]

Update: The hum is more accurately described as a whistling or rumbling, i.e. it pulses rather than stays absolutely steady. It is more pronounced when I use the 3050 motherboard, compared to the 3160 (i.e. the motherboard has some influence). It is only present when both Entity and Hakai are powered up. With both powered up, it can be removed by either disconnecting the DAC, or by disconnecting the LP12 inputs to Entity. I have re-dressed the power cables and interconnects, to no effect.
It is subtle enough that I did not notice it, after installing Entity, until I changed the Hakai motherboard from 3160 to 3050. I have experimented with a different PSU, which removes it. The problem is that the optimum configuration of Hakai is the Streacom case and Nano PSU, albeit with the 3160 board. My case and PSU substitution reduced the musicality, even if it did add some welly.
Any ideas? If it's relevant, amps are Sagatun Monos/Tundra Monos.

David,

Are the Hakai motherboards in separate cases?

[FairPlayMotty]

My only experience of regular mains hum was between my MC phono amp and my turntable. To avoid it i had to stack a certain number of CD cases and place the phono amp on top. Now I've moved my turntable is in a cupboard. Death by Hakai.

[David Neel]

Are the Hakai motherboards in separate cases?

I've only the one Streacom case, so I've been swapping motherboards by using a screwdriver!

[FairPlayMotty]

Are the Hakai motherboards in separate cases?

I've only the one Streacom case, so I've been swapping motherboards by using a screwdriver!

The mismatch in motherboard effects is so odd - the boards are so similar in layout and content.

[David Neel]

Are the Hakai motherboards in separate cases?

I've only the one Streacom case, so I've been swapping motherboards by using a screwdriver!

The mismatch in motherboard effects is so odd - the boards are so similar in layout and content.

It's not the motherboard itself, I now think. I (unintentionally) replicated the effect by re-installing the SAME motherboard... so the act of re-installing is changing something else. Maybe I need to be careful in routing the cables? Or how tight the motherboard is screwed down? Or the phase of the moon? It's been a full moon this weekend...

[David Neel]

Problem sorted. Immense thanks to Fredrik for his diagnostic help. I am now using a two-wire (rather than three) lead to power the AC adapter for the Nano PSU. I felt a lot of resistance to doing this, but now I'm grounded, even if the power lead isn't.