[jexby]

  Hi all!
 
I recently purchased a Lyr + Bifrost (with USB Gen2 upgrade) combo along with a set of LCD-2's
 
Whilst the SQ is on a whole other level to anything I've owned before in the head-fi domain, there is a constant underlying hum in the output to the headphones.
 
I think this may be EM interference - the DAC/Amp are sitting directly behind my TV, above my main receiver, and next to a portable HDD on one side and my main speaker on the other - but haven't yet had the opportunity to shift the kit to test it.
 
Setup is Mac Mini -> Bifrost (via USB) -> Lyr (Stock Tubes) -> LCD-2
 
Any thoughts on what may be causing this IF it isn't EM?
 
Thanks in advance...

 
I won't speculate on your cause, only offer that after days/weeks of trying everything electrical wise, computer wise, USB cable swap outs, this was my fix:
 
post #3527

 

[tim79b]

  The Bifrost is sensitive to ground loops from other "things" on your house mains.
They can be very difficult to find.  Use the best power conditioner you can find.
I like Furman AC-215.  There's one for both 110 and 220.
There are other widgets as well.

I'll have to look into this...what are these worth?
 
 

  Sounds like a couple of things. Move all power bricks like portable HDD if it has one alway from audio equipment. Are you using cable for TV? If so you may have a ground loop from the cable ground that is different from the audio equipment ground. Even if the cable is directly connected to the TV or a cable box that ground loop can still exists even when the Schiit is connected to another unit like your Mac mini. Disconnect the cable from the wall and see if you still hear the hum when nothing is playing of course. If this does not change the hum disconnect the inputs on the Lyr and see if you still hear the hum. We have to narrow down the issue.

 
No power bricks near the units - closest one is a good 1.5m away.
 
No cable TV - I did unplug the aerial connection - no change.
 
Went through and progressively unplugged all other nearby electronics, no change.
 
No change with different inputs selected on the Bifrost

BUT - the hum does disappear when I unplug the inputs to the Lyr whether the bifrost is on or off...
 
I'm using a monster RCA cable as an interconnect - seems to be quite good quality, and moving the cable around doesn't make any difference, so I'm assuming it's not some sort of transient interference on the cable - Also lifted the Lyr out in front of the TV a bit and no change.
 
That ground loop through the power is sounding more and more likely...
 
 
 
Really frustrating...

 

[john57]

   

BUT - the hum does disappear when I unplug the inputs to the Lyr whether the bifrost is on or off...
 
I'm using a monster RCA cable as an interconnect - seems to be quite good quality, and moving the cable around doesn't make any difference, so I'm assuming it's not some sort of transient interference on the cable - Also lifted the Lyr out in front of the TV a bit and no change.
 
That ground loop through the power is sounding more and more likely...
 
 
 
Really frustrating...

I understand that. It does sounds more like a ground loop all right. Disconnect the power AC plug from the Mini and the DAC and leaving the Lyr with power and with the RCA cables, like the monster still connected , are you still hearing the hum?. If so disconnected the HDMI cable from the mini and the hard drive if connected. The hum should go away and if not check with any interconnected devices you have not listed. Let us know the results.

 

[tim79b]

  I understand that. It does sounds more like a ground loop all right. Disconnect the power AC plug from the Mini and the DAC and leaving the Lyr with power and with the RCA cables, like the monster still connected , are you still hearing the hum?. If so disconnected the HDMI cable from the mini and the hard drive if connected. The hum should go away and if not check with any interconnected devices you have not listed. Let us know the results.

Ok - if I remove the DAC from the wall plug the hum reduces, but is still there...
 
Shifted the DAC plug from the wall socket to a power board I have for my other stereo components and it stays at the reduced level.
 
Still annoying, but slightly less so...

 

[sceleratus]

Ground loops are very difficult to track down.
Whatever you do, don't clip your ground lead or use an adapter plug.
 
The HUM-X is specifically for ground loops.  The Furman doesn't state that but it the best power box hands down.
Here's the link to the Hum-X.  It has great Amazon reviews and has worked for several Head-Fi'ers with Ground Loop problems.

 

[sceleratus]

Ground loops is essentially a small amount of voltage that leaks from a device to ground.
If / when the Bifrost picks this up on the ground.... hmmmmmmm

 

[sceleratus]

This is a great description.  Best I've found so far.
The punch line is:   2 pieces of audio equipment are connected to different grounds.  (Points "C" and "D" in the illustration)  That is bad.
 
[size=medium]Unfortunately there are other causes....[/size]
 

Ground loops: how they work and how to deal with them.

 

A ground-loop is created whenever two or more pieces of mains-powered equipment are connected together, so that mains-derived AC flows through shields and ground conductors, degrading the noise floor of the system. The effect is worst when two or more units are connected through mains ground as well as audio cabling, and this situation is what is normally meant by the term "ground-loop". However, ground currents can also flow in systems that are not galvanically grounded; they are of lower magnitude but can still degrade the noise floor, so this scenario is also considered here.
The ground currents may either be inherent in the mains supply wiring (see "1: Mains grounding currents") or generated by one or more of the pieces of equipment that make up the audio system.(see "2: Transformer stray magnetic fields" and "3: Transformer stray capacitance")
Once flowing in the ground wiring, these currents will give rise to voltage-drops that introduce hum and buzzing noises. This may occur either in the audio interconnects, or inside the equipment itself if it is not well-designed. See Section 4.
Here I have used the word "ground" for conductors and so on, while "earth" is reserved for the damp crumbly stuff into which copper rods are thrust.
HUM INJECTION BY MAINS GROUNDING CURRENTS.
Fig 1 shows what happens when a so-called "technical ground" like a buried copper rod is attached to a grounding system which is already connected to "mains ground" at the power distribution board. The latter is mandatory both legally and technically, so one might as well accept this and denote as the reference ground. In many cases this "mains ground" is actually the neutral conductor, which is only grounded at the remote transformer substation. AB is the cable from substation to consumer, which serves many houses from connections tapped off along its length. There is substantial current flowing down the N+E conductor, so point B is often 1 Volts rms or more above earth. From B onwards, in the internal house wiring, neutral and ground are always separate. (In the UK, anyway)

Two pieces of audio equipment are connected to this mains wiring at C and D, and joined to each other through an unbalanced cable F-G. Then an ill-advised connection is made to earth at D; the 1V rms is now impressed on the path B-C-D, and substantial current is likely to flow through it, depending on the total resistance of this path. There will be a voltage-drop from C to D, its magnitude depending on what fraction of the total BCDE resistance is made up by the section C-D. The earth wire C-D will be of at least 1.5 sqmm cross-section, and so the extra connection FG down the audio cable is unlikely to reduce the intefering voltage much.
To get a feel for the magnitudes involved, take a plausible ground current of 1 Amp. The 1.5 sqmm ground conductor will have a resistance of 0.012 Ohms/metre, so if the mains sockets at C and D are one metre apart, the voltage C-D will be 12 mV rms. Almost all of this will appear between F and G, and will be indistinguishable from wanted signal to the input stage of Unit 2, so the hum will be severe, probably only 30 dB below the nominal signal level.
The best way to solve this problem is not to create it in the first place. If some ground current is unavoidable then the use of balanced inputs (or ground-cancel outputs- it is not necessary to use both) should give at least 40 dB of rejection at audio frequencies.
Fig 1 also shows a third earthing point, which fortunately does not complicate situation. Metal water pipes are bonded to the incoming mains ground for safety reasons, and since they are usually electrically connected to an incoming water supply current flows through B-W in the same way as it does through the copper rod link D-E. This water-pipe current does not however flow through C-D and cannot cause a ground-loop problem. It may however cause the pipes to generate an AC magnetic field which is picked up by other wiring.

 

[tim79b]

That's a lot of info, and I am honestly not sure I understand it all...

 
Do you think that a power conditioner will resolve the hum?  and...
 
Does anyone know where I can pick up a decent one in Sydney??
 
Thanks!

 

[john57]

 
Ok - if I remove the DAC from the wall plug the hum reduces, but is still there...
 
Shifted the DAC plug from the wall socket to a power board I have for my other stereo components and it stays at the reduced level.
 
Still annoying, but slightly less so...

One more thing. If I understand your layout disconnect the mini digital signal cable to the DAC, does the hum changes? Are you using optical or coaxial?

 

[tim79b]

I'm actually running the DAC through USB. If I change the input the hum doesnt change...

 

[sceleratus]

The #1 best thing is to find the source of the ground loop and fix it.
The Hum-X, etc are masks not fixes.

 

[bearFNF]

Agreed, find the source of the hum and fix it, if possible.  I found a ticking sound that came from my laptop charger of all things, but not much I can do about it, other than change sources, which I did for the most listening anyway.

 

[john57]

I'm actually running the DAC through USB. If I change the input the hum doesnt change...

I mean to physically disconnect the USB cable from the DAC. We have to get the Mini out of a another possible loop. Changing the input on the front pannel will not do it. Just a bit more troubleshooting may pointpoint the issue.

 

[sceleratus]

go with @john57.....

 

[gefski]

The #1 best thing is to find the source of the ground loop and fix it.
The Hum-X, etc are masks not fixes.

+1 on this.

Try free fixes first. Does hum diminish when you touch a component? If so, try a piece of wire between chassis and/or to an absolute ground.