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Headphone Amp - Ground Loop (Buzz/hum) A Fix?

post #1 of 19
Thread Starter 
Hey guys. I recently ordered the ibasso P2. (Products) The device works great, although I've got one rather major issue with it.

One reason I bought the P2 was because it came with the AC adapter to plug it into the wall. I don't want to use it as a portable device, and just want it to sit at my computer.



Hooked up to my PC's sound card is a set of Logitech Z5500 speakers. These have a headphone port on the control center. I simply plug the P2 into that headphone port, plug the AC into the wall, and then plug my headphones into the P2. Seems like it should work and be great. Cuts power to the speakers, sends it to the headphones, and this works.

The catch here is something I never knew about; ground loop. Apparently, because the speakers/computer/P2 are all plugged into the same power grounding, it creates some crazy electrical loop and this loop creates something called mains hum. This hum/buzz can be heard clearly in my headphones when using this setup. To solve this, unplug the AC adapter to the P2, and boom, gone.

Now, this in turn means, it works fine with portable devices, like you'd think. iPod, PSP, DS, they all work fine without this issue. But I bought this for my desktop. Yes, sure, I could just charge it, use it, and then charge it again, but I did not pay $157 for an amp to have an inconvenience like that. I want to plug it into the wall, and not have to worry about that. Not to mention charging it like that all the time wears out the battery so it won't be any good for when I do want to use it portably.

So, in the end, I am looking for a fix. I know I can buy some $80-100 power strips that create their own ground. Don't want to spend that much. Yes, I know there are devices like the following:

PAC SNI-1/3.5 Noise Filter Helps eliminate ground loop noise from your portable music player! (3.5mm plugs) at Crutchfield.com

Although, I fear that could alter sound quality, and again is nearly $30 shipped.

I figure that you guys, with all your experience with this stuff have found ways to solve this. Any way to power the amp over USB? (It is a 12V DC Adapter)

Thank you to anyone that can provide some incite.

Various Info:

- P2 uses a built-in 8.4V 470mAh Li-polymer Batteries or external power
- External power supply: 12V DC
- Battery Life: 11 hours
- Battery Charge time: 3 hours
- Both the Z5500 and the Headphone amp use a two-prong power adapter, so there are no grounding rods involved
- The same thing happens when I plug my P2 directly into my computer, maybe it is the original source of the buzz/hum?
post #2 of 19
Seems to me that you are amping aan amped headphone output from the Logitech speakers, not a line level output. I am not sure you have the D2 connected in an optimal way. Plug the D2 into the USB of your computer. Does that work better?
post #3 of 19
Thread Starter 
Quote:
Originally Posted by breakfastchef View Post
Seems to me that you are amping aan amped headphone output from the Logitech speakers, not a line level output. I am not sure you have the D2 connected in an optimal way. Plug the D2 into the USB of your computer. Does that work better?
Correction: It is a P2. Therefor, no USB adapter. Also, when you plug in the headphones, all power to the speakers is killed and it is a direct connection to the computer.

Since when I plug the P2 directly into the computer, I figure that the computer/soundcard might be the original source of the issue and that the Logitech speakers have nothing to do with it. Just a hunch though.
post #4 of 19
If you get no noise when using only batteries, but get a hum when using:

Computer Line Out + AC Adapter
Speaker Line Out + AC Adapter ...

Then perhaps there is an issue with your power supply?
post #5 of 19
Have you tried asking the amp manufacturer? They can usually tell you what to do to fix ground loops, which is what you describe.

TSC Tech Talk | Grounding

The filter you mentioned may not help with the problem you describe.

How about pics of the power supplies for both the amp and Logitech stuff.
post #6 of 19
I have my computer plugged into a surge strip (one of those under-the-monitor types) and if I plug the guitar amp into the wall outlet (different outlet than the one the surge strip is plugged into) I will get some nasty hum from the ground loop of the house wiring. If I have the amp plugged into the surge strip, the hum is a ton less.

Make sure it is plugged into the same outlet or same surge strip if you are using one.
post #7 of 19
Assuming the AC adapter for the headphone amp doesn't have a polarized plug, I'd try reversing its orientation to see if it makes any difference. I'd do the same with the powered speakers if possible.
post #8 of 19
Thread Starter 
Quote:
Originally Posted by Budgie View Post
Have you tried asking the amp manufacturer? They can usually tell you what to do to fix ground loops, which is what you describe.

TSC Tech Talk | Grounding

The filter you mentioned may not help with the problem you describe.

How about pics of the power supplies for both the amp and Logitech stuff.
Hmmm, thanks for the help. The logitech speakers really don't have a PSU. It is only a cord coming from the subwoofer.

Picasa Web Albums - GCTonyHawk7 - ibasso P2

There you can see what the P2 power supply looks like, not sure if that helps. It says on the bottom of it that it's 12V.

-----------------

To others; I did contact ibasso, and all they said is that this is normal and that my P2 is not defective. In funny engrish at that.

And reversing the plug on the P2 does nothing. I'll have to try plugging it into the same surge strip, it'd be cool if that helped. I'll let you guys know if anything changes.

Thanks for the help.
post #9 of 19
Quote:
Originally Posted by GCTonyHawk7 View Post
Also, when you plug in the headphones, all power to the speakers is killed and it is a direct connection to the computer.
Yes, you cut power to the speakers, but I'm quite sure that Logitech products do some degree of headphone amplification. You might find that changing the volume on the Logitech changes the volume through the iBasso. Though considering that you have problems even with direct connections, this may not be the whole problem.

Nobody has asked yet...... What sort of soundcard is it? If it is integrated sound or a really cheap discrete card, it may just be a bad/noisy source. You can hear it through headphones, but not speakers, because of the higher sensitivity.
post #10 of 19
Thread Starter 
Quote:
Originally Posted by Beefy View Post
Yes, you cut power to the speakers, but I'm quite sure that Logitech products do some degree of headphone amplification. You might find that changing the volume on the Logitech changes the volume through the iBasso. Though considering that you have problems even with direct connections, this may not be the whole problem.

Nobody has asked yet...... What sort of soundcard is it? If it is integrated sound or a really cheap discrete card, it may just be a bad/noisy source. You can hear it through headphones, but not speakers, because of the higher sensitivity.
You're right, the volume dial on the Logitech speakers does directly control the volume to the P2. But ya, since it does the same thing when plugged in directly, not thinking that is the issue.

It is the integrated sound card. Realtek HD, on an MSI p6N motherboard. Honestly, I would buy a sound card if I thought I needed one.... but this has all the options and outputs I feel I need, so ehh.

As far as it just being the sound card, that wouldn't be it at all. Since, as stated, the noise goes away completely when I unplug the DC adapter.

Thanks for the suggestions.
post #11 of 19
JackH suggestion in the first thing to try. Also, as Paragon suggests, the hum will be the lowest if the Logitech and the amp are plugged into the same outlet or power strip.
post #12 of 19
Quote:
Originally Posted by GCTonyHawk7 View Post
You're right, the volume dial on the Logitech speakers does directly control the volume to the P2. But ya, since it does the same thing when plugged in directly, not thinking that is the issue.
It will still degrade sound quality though.

Quote:
but this has all the options and outputs I feel I need, so ehh.
Long term, you should invest in a decent sound card. It will make a marked improvement.

Quote:
Since, as stated, the noise goes away completely when I unplug the DC adapter.
Thing is, the DC adapter shouldn't be making a ground loop - it should be isolated from the chassis and signal ground. Only the chassis should be connected to the signal ground for shielding purposes.

I wonder if it is the charging circuit or the DC adapter itself that is causing the noise? That might fit with all of your observations. To test..... are you able to connect the amp to a battery powered source, such as an MP3 player? Then try listening with and without the DC adapter plugged in to mains.
[EDIT] I just realised that you have tried it with battery powered sources...... but have you done these specifically with the DC adapter plugged in?
post #13 of 19
Thread Starter 
Quote:
Originally Posted by Beefy View Post
It will still degrade sound quality though.



Long term, you should invest in a decent sound card. It will make a marked improvement.



Thing is, the DC adapter shouldn't be making a ground loop - it should be isolated from the chassis and signal ground. Only the chassis should be connected to the signal ground for shielding purposes.

I wonder if it is the charging circuit or the DC adapter itself that is causing the noise? That might fit with all of your observations. To test..... are you able to connect the amp to a battery powered source, such as an MP3 player? Then try listening with and without the DC adapter plugged in to mains.
[EDIT] I just realised that you have tried it with battery powered sources...... but have you done these specifically with the DC adapter plugged in?
Yup, I have tried it with the DC plugged in, and the ground loop is gone. So, the noise is caused by the loop, not the DC adapter.
post #14 of 19
Thread Starter 
Ok, still an issue, and I decided to do some more extensive testing today. I figured the following have been consistent through all the tests.

- Computer running, plugged into same place
- Same headphones
- Various other things plugged in.

So, I decided to first see what would happen if I the computer completely off. Set up the loop with my speakers, shut her down while listening, and still heard the loop, never dipped or anything. Flipped computer off, same, unplugged it... same.

So, the computer being on the circuit didn't effect anything. (That being when it is plugged into the speakers. Did the same test only had the P2 plugged into the back of the PC, and oddly, same exact thing.

So, the ground loop is still there whether or not the things it is using for input are even connected to power. This strikes me as odd. I actually tried completely unplugging the Z5500 and the control until so the control unit was essentially wireless, and guess what... ground loop sound; although it did seem a bit less noisy. Got me thinking... unplug it from anything, and yes, there is a minor buzz, but not like the ground loop buzz. (This is just the interference from the input, gets louder and stuff if I move the cord around.

So, now I am thinking in a different fashion. It is not what is causing the noise... but more so what solves it. It seems to only go away when connected to a battery-powered wireless source; Nintendo DS, PSP, iPod, and it gets worse when connected to audioless and plugged in devices.

One other case that makes this interesting is that it goes away when plugged into those portable devices even when they are off.

I am obviously far from an expert here, but really need some help. This is bugging the hell out of me, and there has to be a solution.
post #15 of 19
Quote:
Originally Posted by GCTonyHawk7 View Post
This is bugging the hell out of me, and there has to be a solution.
Sorry mate, its out of my league now too
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