Icon Audio HP8 MKII: annoying noise coming from PC captured by left channel RCA input

[DeBilbao]

I'm really satisfied with my Icon Audio HP8 MKII headphone amplifier, but I'm experience a weird problem that is driving me crazy.

 

Until recently, I've been using different solid state headphone amplifiers and have been a great Burson Audio fan, but even the Burson Conductor can compare with the musical experience I'm getting from this great tube amplifier. My current setup includes two Shu Guang CV181-Z 50 Years Treasures drive tubes and one PSvane 12AX7 preamp tube.

 

 

But I'm having a problem that's driving me nuts. The HP8 MKII is "capturing" noise from my desktop Windows 8.1 Pro PC through the left channel RCA input. It's not a continuous hiss but instead is some kind of sizzling noise.

 

My current audio route is the following: Windows PC Windows > Audioquest Pearl USB A-B cable > iFi iDSD micro > 2x RCA Audioquest G-Snake cable > Icon Audio HP8 MK II > Sennheiser HD 650 and I've made the following tests:

 

• Disconnecting the left channel RCA cable, noise dissapears.
  
• Rotating the left channel RCA cable conector, noise changes and there's a point where it is less noticeable but I want it out.
  
• Interchanging left and right RCA cables or crossing them, noise persists.
  
• Reversing the direction of the RCA cables, noise persists.
  
• Changing the RCA cables with another Wireworld Solstice pair I have, noise persists.
  
• Unplugging the USB cable from the PC and plugging it to a MacBook, noise is still present if the PC is turned on.
  
• Shutting down the PC, noise persists.
  
• Using another source component via RCA input, noise dissapears.
  
• Connecting the headphones to the iFi iDSD micro as an amplifier, and the noise is absolutely absent.
  

 

Any suggestions? I'm really close to sound heaven, but this noise is driving me crazy.

 

Thanks in advance,

[pooger]

I can see why this would be vexing! You've really trouble-shooter this correctly. The fact that the sound stays in the left, even when you reverse input leads, etc. would point to the problem being in the amp itself. But then, it is silent with other sources... Here's what I think.

 

first, try using your Etymotics with another source hooked up. I know you'll have the volume way down on the amp, but I'm wondering if you might still hear noise through more sensitive phones. There is probably a poor solder joint, or maybe a resistor having a problem, on the left channel input section. The ifi may not have a low enough output impedance (which strikes me as odd for such a modern piece) and this is interacting with the input requirements—well, with the not quite as they are supposed to be in the left channel input impedance. Or, if not an impedance mismatch, there is enough of a ground noise coming from the line out of the ifi (both channels, as you've tested), so that a slightly sub par ground connection on the left side of the amp is acting up. "Sizzling" doesn't strike me as a grounding issue, but it could be.

 

even if you don't know which end of a soldering iron is hot, you could do a visual inspection of the wiring in the amp. I don't know if that amp uses circuit boards, or is point to point (wires going directly to components). first look at the left input RCA connector. Is it really tight? (The twisting interconnect changing the sound makes looseness suspect!) Are there resistors or capacitors soldered right on the connector?

 

Next, look at all the connections from the right input—the side that is working well. All will be shiny, and if inspected with a magnifying glass, will have smooth fillets at all edges of the solder blobs. Any dullness, or edge that doesn't look like it just melted into whatever was being soldered is suspect.

 

the other possibility may be tube related. Have you tried swapping tubes? I know that the sound goes away with another source, but again, I think that since it's present from either side of the ifi, but not from another source, that the problem is a low level one in the amp, and that perhaps a stronger signal, or a more robust grounding scheme than the ifi has, is taking care of it. First of course, try switching power tubes. But also, try a different 12ax7. One side of that tube (it's a dual triode, and in this case is being used for both channels, one on each "circuit") may be slightly noisy, and again, the ifi input is not masking that noise, while the other source input is (or if not masking it, then, as suggested above, has more robust grounding that is working better). Certainly sizzling sounds more like a tube noise situation to me.

 

Report back. If you have a camera that does good macro, you could post close ups of the interior.

[DeBilbao]

pooger, thank you very much for such a detailed answer.

 

I've noticed that my signature wasn't updated and I can try your first suggestion with my Bowers & Wilkins P7, much more sensitive than the Sennheiser HD 650, or even with the planar-magnetic HiFiMAN HE-400i. I'll try with my Etymotics but the HP8 MKII is really powerful. I can't go further than a quarter of the ALPS knob.

 

I will definately try swapping the Shu Guang CV181-Z 50 Years Treasures power tubes. If the problem goes from left to right channel, they can be the culprit. I also have a pair of Tung-SOL tubes that I can use in the power section.

 

Regarding the pre-amp tube, I also own a JJ Electronics ECC83 (12AX7 equivalent) and I can try swaping them and see the result.

 

I'll try my best and report back as soon as possible with some pictures to share.

[esldude]

Sounds to me like the iFi Micro is the source of the noise.

 

You eliminated both computers (Mac and Win), and USB as a source of the noise.

 

You eliminated the RCA analog wires.

 

You eliminated the Micro if used as an amp itself.

 

By using other sources and feeding the Icon amp you have eliminated it as a source of noise.

 

However, you get the noise when using both the Micro and the Icon.

 

The noise I don't think is coming directly from the Micro's analog outs or you would hear it when using the Micro only. Or as suggested, perhaps the Micro has it at a very low level and the Icon amplifies the noise making it more noticeable.

 

My guess, would be the digital circuitry in the Micro is leaking into the Icon amp. It could be the noise is drained away when powering low impedance devices like headphones, but when the Micro is powering a high impedance like the Icon input the noise is present. It also could be EMI form the Micro leaking into the Icon. Tubes have very high impedances and are more susceptible to this.

 

It might sound weird, but first I would try connecting a 2nd set of headphones to the headphone out on the Micro with everything connected as you have it. And see if the noise disappears in the Icon. It is possible though I am betting it won't do the trick.

 

So I would next try to physically move the Micro and Icon apart and see if the noise diminishes. If so, you have some EMI. You can see if you get them far enough apart to get rid of it. Temporary things to try if you get lower noise with separation is taping some aluminium to a piece of cardboard. Tape a bare wire to the foil and ground the wire. Then put this board of foil between the two devices to see if it shields the Icon from the noise of the Micro. Not a permanent solution, but I have seen that eliminate problems like yours.

 

In any case, neither the Micro nor the Icon seem to be malfunctioning. It is an interaction between those two.

[DeBilbao]

Thanks for your answer, esldude. I'll share with you my advances on this annoying issue:

 

Yesterday night I performed a test that in my opinion offer a definitive diagnostic: noise is generated by my Windows PC and captured by the amplifier by some kind of induction.

 

The test couldn't be easier, power off and disconnect the iFi iDSD micro from the line input of the Icon Audio HP8 MKII amplifier and connect to it my Denon DVD-2910 multiformat player. This is what I got:

 

• With the PC turned on, noise is present.
  
• With the PC turned off, absolute silence, even with the pot at 100%.
  

 

After this conclusive test, I performed another and took the Icon Audio HP8 MKII amplifier and the iFi iDSD micro DAC to another room in the house, but instead of connecting it to the Windows PC, I plugged the DAC to my MacBook with the same Audioquest Pearl USB A/B cable. This is what I got:

 

• Absolute silence, even with the pot at 100%.
  

 

I must point out that I performed the same test yesterday, but with the MacBook in the same room than the Windows PC, and in this case I heard the noise.

 

So being the Windows PC the culprit, I tried opened it and tried to identify if any position change affected the noise, or if touching any cable using myself as a ground the noise was altered in any form. I also decided to deep clean the computer, removing every piece of dust with a vacuum cleaner and make a general revision of the cabling.

 

The result? I'm still experiencing noise, but at a much lower level. So low that at quarter of the pot I barerly notice it and this is the maximum SPL I can listen at with normal recordings. But if the passage is near silent and I try finding it, I can still identify it as a sound associated with the activity of the computer.

 

Another disconcerting news is the fact that now noise isn't associated to a single channel. If I disconnect the RCA cable either from the right or left channel, noise is present. A bit baffled with this change.

 

One more observation is that if I shutdown my Windows PC and put on my headphones with the pot at 100%, noise doesn't come out until the Windows logo appears on screen. During POST BIOS processing noise isn't audible. I've tried booting the computer from a Linux USB stick and noise is still present, so I discarded Windows as the faulty componente, but this also baffled me again.

 

It seems that only when hard drives begin with their activity noise appears, and the noise seem shaped with hard drive activity.

 

With this new discovering, I opened the computer again and started disconnecting the hard drives one at a time until only the system hard drive was present, but noise was present. I didn't try without the system hard drive or changing the SATA port because it's an SSD unit without mechanical parts.

 

Yesterday I was really tired and went no further. Tonight I'll try changing tubes in the amplifier and follow some of your advices. I'll keep you updated.

 

It's a long run but with your help I'm sure I'll fix it.

[Audio_ELF]

If I read your message right - you have come to a conclusion that the Windows PC is emanating some form of interference through the air the Icon Audio is picking up?

[DeBilbao]

If I read your message right - you have come to a conclusion that the Windows PC is emanating some form of interference through the air the Icon Audio is picking up?

 

That's exacty what I'm saying and trying to resolve.

[esldude]

So your description of results has changes somewhat. And your reply to Audio_Elf (Eloise) indicates you get this thru the air using the Mac without physical connection to the Win PC, is this correct? If so, then distance will diminish it.

 

There is a good chance the aluminium foil shield I mentioned would as well. Or you can use a cookie tin as well. Ground it with a wire and place it very near the PC. Or place it very near the Icon itself. Perhaps those tubes need a faraday cage around them. Obviously the shield I describe is a diagnostic aid and not permanent solution. But you might learn what needs shielding for a permanent fix.

 

I guess the next question is can you use the Mac and put the PC in another room?

 

One other thought, do you get more or less noise when using different USB ports on the PC? You describe moving around internal wiring and the noise being less, but in both channels now. So wondering if some sort of shielding or positioning of internal wires would get rid of the noise. And yet one more question. If you happen to have an external USB hub, if you put the hub between the PC USB and your Micro does it help at all with the noise?

[DeBilbao]

After a long time away from my Icon Audio HP8 MK II, I've come from holidays and realized that the weird noise problem hasn't gone away.

 

But during holidays I've read quite a few articles about electrical noise and my conclusion has been that the inducted noise is being "captured" by the RCA interconnect cables that act as antennas.

 

So with this diagnosis in mind, I've come to my usual electrical shop and asked for a filter to resolve the issue. This cheap MONACOR FGA-40MF has removed all the noise and now the background is completely silent.

 

It doesn't seem to be an audiophile choice, but it does the work.

 

http://www.monacor.de/index.php?id=4343793&L=3

 

 

Now I'm enjoying the fabulous Icon Audio HP8 MKII, with Jupiter Yellow Capacitors, the powerful and mellow Shu Guang CV181-Z 50 Years Treasures and the extraordinary PSvane 12AX7. I'm loving the combination with the Sennheiser HD 650 headphones.

 

 

Now the problem origin is located, I think it's time not only to begin enjoying music, but to try resolving the problem. My guess is that the power supply unit is coming to its end of life cycle. It's been working faultlessly since 2007 and maybe it's time to switch to another one.

 

 

My actual PSU is a modular Seasonic M12 (500W) and I'm thinking about the same brand but a more modern model like the X-650 that can can control the fan and use it only when real power is needed.

 

I will try to change and reorganize the internal cabling, maybe this helps too.

 

 

Any suggestions on a good quality PSU for a Windows PC that minimize audio interferences?