[youurayy]

Hi all / first post,
 
my main setup is a computer video card connected to a SONY STR-DN1030 receiver via a HDMI cable. This connection is perfect and noiseless, whether I output into 7.2 or into headphones directly from the receiver.
 
Recently I added a 2-channel tube amp with 2x RCA stereo input, which, when driven e.g. from iPad, also has no noise (besides the nice tube background hum.
 
Now, when I connect the receiver (from the headphone jack) to the tube amp (2x RCA), __and__ the computer is running (it must be on), there is a background noise in the connection.
 
When the computer is turned off (e.g. when playing a movie from a Blu Ray through the receiver), the noise is gone.
 
Another point -- the noise has diminished a lot when I replaced a: "6.35mm adapter -> 3.5mm headphone jack to 2x RCA cable" -- with -- "6.35mm jack to 2x RCA adapter -> 2x RCA line cable" -- but has not gone away entirely.
 
How to solve this?
 
I know a separate DAC will most likely solve this, but I'd like to be able to feed the tube amp directly from the receiver on occasion.
 
I don't really understand what's happening here, because even when the computer is on, the moment I disconnect the cable from the receiver, the noise is gone.
 
Let me just repeat -- when the computer is ON and I plug the headphones directly into the receiver -- there is no noise whatsoever -- zero. Only the the tube amp is susceptible to it, and only when connected into the headphone jack of the receiver, and only when the computer is on.
 
Help appreciated,
youurayy
 
EDIT: there's no other way to output a line from the STR-DN1030, the purpose of the only other audio-out (2x RCA) on the receiver is to connect it into another receiver in "party mode", and then it can only output the sounds it originates (e.g. playing from a USB key or radio).

 

[ProtegeManiac]

Try hooking up the tube amp to the Zone 1 Audio Out.

 

[kimvictor]

Amps can worsen noise issues, but you said that you've never heard the noise before...maybe it's poor shielding somewhere in the new chain?
 
One of my DACs used to pick up radio signals(I could hear people talking, so I assumed it was radio signal), and I could hear it on certain amps, and it drove me nuts.

 

[youurayy]

  Try hooking up the tube amp to the Zone 1 Audio Out.

My understanding is that I cannot use it with Zone 1 because it cannot output the HDMI input from my computer. Do you mean just to try it out to see if the interference is there?
 
 

  Amps can worsen noise issues, but you said that you've never heard the noise before...maybe it's poor shielding somewhere in the new chain?
 
One of my DACs used to pick up radio signals(I could hear people talking, so I assumed it was radio signal), and I could hear it on certain amps, and it drove me nuts.

Interesting, haha. What confuses me is that the amp only picks up the interference from the running computer when the cable is connected to the receiver (which is when it should be grounded on both sides). It's like the amp cuts off the connection / amplification circuit if the cable is not connected.
 
 
 
Reflecting on my first post --- if a better shielded cable has lowered the interference, maybe to get completely rid of it, I need to get a really-really well shielded cable...

 

[kimvictor]

  My understanding is that I cannot use it with Zone 1 because it cannot output the HDMI input from my computer. Do you mean just to try it out to see if the interference is there?
 
 
Interesting, haha. What confuses me is that the amp only picks up the interference from the running computer when the cable is connected to the receiver (which is when it should be grounded on both sides). It's like the amp cuts off the connection / amplification circuit if the cable is not connected.
 
 
 
Reflecting on my first post --- if a better shielded cable has lowered the interference, maybe to get completely rid of it, I need to get a really-really well shielded cable...

A simple trick to test if it's a shielding issue is to wrap all your gears with aluminum foil, or so I've heard. Never tried it myself, but I've heard that some people did that to test for shielding issues(I know it blocks RF, but not so sure about EMI). Worth a shot to see if it is actually an external noise or internal noise.

 

[ProtegeManiac]

  My understanding is that I cannot use it with Zone 1 because it cannot output the HDMI input from my computer. Do you mean just to try it out to see if the interference is there?

 

You're describing the Zone 2 (maroon box) output restrictions because Sony (and they got other manufacturers to go along with it) to disable that so people cannot pirate (primarily Sony-BMG, Sony Pictures) CDs, DVDs, and BluRays. What I meant was you try to hook up the graphics card output to HDMI Video 1 (blue box on top) and then hook up the headphone amp to the Video 1 (which is still Zone 1, ie, presumably not going to the patio) and see if 1) it can actually output a signal and somehow not restricted like Zone 2 outputs, and if it does, 2) if the noise is still there. If it does output sound this is a line out signal as opposed to running the signal through the Sony's headphone output circuit, which hardware wise is the likely source of the noise you're getting.

 

[youurayy]

  A simple trick to test if it's a shielding issue is to wrap all your gears with aluminum foil, or so I've heard. Never tried it myself, but I've heard that some people did that to test for shielding issues(I know it blocks RF, but not so sure about EMI). Worth a shot to see if it is actually an external noise or internal noise.

The receiver is directly above the PC, so this gives me an idea -- to put some sort of EM shielding between the two, something like a mat the receiver will stand on in the shelf. Thanks!
 
 

 

 

You're describing the Zone 2 (maroon box) output restrictions because Sony (and they got other manufacturers to go along with it) to disable that so people cannot pirate (primarily Sony-BMG, Sony Pictures) CDs, DVDs, and BluRays. What I meant was you try to hook up the graphics card output to HDMI Video 1 (blue box on top) and then hook up the headphone amp to the Video 1 (which is still Zone 1, ie, presumably not going to the patio) and see if 1) it can actually output a signal and somehow not restricted like Zone 2 outputs, and if it does, 2) if the noise is still there. If it does output sound this is a line out signal as opposed to running the signal through the Sony's headphone output circuit, which hardware wise is the likely source of the noise you're getting.
 

Tried it, but the Video Out is silent when card is in HDMI 1 (normally I have it in GAME, but no go there either). I guess it's for the same reason -- copy-protection for digital content. I'm planning to maybe upgrade the receiver soon, so I may get something with a decent audio RCA output.
Another path I discovered thanks to your suggestion is to set the Amp HDMI output to "TV+AMP", then mute the amp, and take the line from the TV's headphone jack --- no noise there, but I'm going with the TV's DAC (Bravia KDL-42W655) which probably is not as good as the one in the receiver.

 

[ProtegeManiac]

 
Tried it, but the Video Out is silent when card is in HDMI 1 (normally I have it in GAME, but no go there either). I guess it's for the same reason -- copy-protection for digital content. I'm planning to maybe upgrade the receiver soon, so I may get something with a decent audio RCA output.
Another path I discovered thanks to your suggestion is to set the Amp HDMI output to "TV+AMP", then mute the amp, and take the line from the TV's headphone jack --- no noise there, but I'm going with the TV's DAC (Bravia KDL-42W655) which probably is not as good as the one in the receiver.

 

The problem with sticking to an A/V receiver is that unless it's the preamp outputs, or you can test them in-store for that specific function, it won't output anything either. Or you're going to get an output that goes through its preamp stage which makes setting the volume problematic. If you can find a 7.x receiver however that allows for the extra two channels of amplification (and use only 5.1 for HT) to be used as Zone 2 then you can get a speaker output to headphone socket adapter, like the one HiFiMan sells, and just up the headphone to that one.

 

[youurayy]

 

 

The problem with sticking to an A/V receiver is that unless it's the preamp outputs, or you can test them in-store for that specific function, it won't output anything either. Or you're going to get an output that goes through its preamp stage which makes setting the volume problematic. If you can find a 7.x receiver however that allows for the extra two channels of amplification (and use only 5.1 for HT) to be used as Zone 2 then you can get a speaker output to headphone socket adapter, like the one HiFiMan sells, and just up the headphone to that one.

You're right, I did a little looking yesterday for new receivers -- and there's no new reason they should have a high-quality recordable output (copy protection again). I did noticed some with pre-amp outputs, but on a second thought, I do need to use the headphone output for a full fledged stereo-downmix (e.g. when watching a movie) -- Yamaha even has some special headphone programs for this.
 
I do use this chinese headphone adapter with the tube amp -- I may try the one from the HiFiMan, given the importance of that component in my chain!
 
Btw. this is the amp, and I use it with these tubes.

 

[youurayy]

Yeah so, after some more googling - this turns out to be a quite common problem when making connections between two ends with unmatched impedance -- that's when "receptive ground loop" is formed which acts as RF antena and picks up the noise -- in my case the noise of my PC.
 
The type of product to solve this is named "hum eliminator".
 
I'm thinking about this one: https://www.amazon.com/Behringer-HD400-BEHRINGER-MICROHD/dp/B000KUD2G4/
 
A guy on another forum measured it: http://forum.cockos.com/showpost.php?p=725271&postcount=14
 
Pretty clean, as a purist of course I hate to put a transformer in the signal path, but it should be fine for occasional use.
 
EDIT: Audiophile version: http://www.jensen-transformers.com/product/ci-2rr/

 

[youurayy]

Feel like I should update this.
 
I just have swapped the PSU in the computer, for a higher quality one -- my main motivation was to achieve a quieter PC, which was also acomplished (the new fan is basically silent).
 
The RF noise dropped to a very reasonable levels, only discernable when no sound is playing.
 
PSU that went out: Sharkoon SilentStorm SFX Gold 500W
 
PSU that went in: Corsair PSU 600W SF600W SFX