Frustrating Grounding Problem (HISS/BUZZ/NOISE)

James,

My speakers have balanced inputs. I have the option of using an XLR or TRS cable. I’m using a TRS. 

I don’t know much about this topic, but your suggestion sounds promising. I will try it when I go home.

However, are there any risks involved with doing this? Any negative consequences? Why did the manufacture design balanced inputs? Should I really be trying to circumvent the design?

What do others think of this?

What do others think of this?

If you are running from an unbalanced output, it might alter the noise, but the chances of eliminating it this way? Not good at all. You could even end up with it getting worse. Part of the problem is that the Behringers use an electronically balanced input, so you haven't lost the ground loop at all - unless you feed them from a truly isolated transformer. But because you've also potentially injected the noise back between neutral and ground in the power supply, it may well be there regardless, because the link still is...

The way to estimate how much of a fundamental problem you've really got is to disconnect the laptop from the monitors and listen carefully to them when you unplug the power supply. If, as is often the case, you hear a difference in the background noise then the power supply is also injecting it back into the ground system via its own mains lead - this is not unknown at all. And if this is the case, then you have one of those situations that's really hard to fix.

But hey, you may be lucky. Just don't count your chickens...

Must know,

I don't know whether you were serious or exaggerating when you said that you spent $500 on the monitors.  If that's really what you spent, you should return them to the retailer you purchased them from.  Street price on those should be between $260 (b-stock) and $340 per pair.  If you overpaid, you can return them and re-order them from another retailer and still have plenty of cash left over to buy some gizmos...Or you can use the $500 to buy a set of KRK Rockit, Alesis M1Active, M-Audio, etc.

Emmett

If you are running from an unbalanced output, it might alter the noise, but the chances of eliminating it this way? Not good at all.

Well that wiring scheme worked for me and I was listening carefully for noise in a properly soundproofed studio. The laptop audio noise floor sounded the same on batteries as it was on mains with this wiring scheme.

Cheers

James.

Well that wiring scheme worked for me and I was listening carefully for noise in a properly soundproofed studio. The laptop audio noise floor sounded the same on batteries as it was on mains with this wiring scheme.

I'm not saying it won't work - just that on the basis of both Wildduck and I hearing about and looking at different instances of this in different installations, and discovering a) no universal panacea, and b) some extremely stubborn cases, you were, quite frankly, lucky.

All laptop power supplies are different - as are all grounding systems. If you have a system that manages to prevent hash being coupled back into the common ground, then with a laptop I'd hazard a guess that there's a substantial mains filter somewhere in your system. This, if it's the correct form of filter, can sometimes help quite a lot, certainly with the path back through the power supply mains lead. But most filters don't manage to filter out enough hash at all frequencies, so it's still sitting effectively between the power supply negative connection and everything else's ground. That's the point at which it is very difficult to keep it out of everything as a common-mode signal.

As Wildduck has alluded, prevention is better than cure, but this can sometimes seem somewhat OTT - a linear 19v power supply delivering around 7A isn't either as small or cheap as a laptop switch-mode one. But since these generate no hash at all, they probably are the absolute solution, really.

Must know,

I don't know whether you were serious or exaggerating when you said that you spent $500 on the monitors.  If that's really what you spent, you should return them to the retailer you purchased them from.  Street price on those should be between $260 (b-stock) and $340 per pair.  If you overpaid, you can return them and re-order them from another retailer and still have plenty of cash left over to buy some gizmos...Or you can use the $500 to buy a set of KRK Rockit, Alesis M1Active, M-Audio, etc.

Emmett

Emmett,

I was slightly exaggerating. I paid 430 dollars Canadian for the speakers and with taxes and cables it came to 505 dollars. I want to return them, but the store I bought them from has an "exchange only" policy. I'm quite annoyed about that.

The Alesis M1 Active are going for about the same price. Are they significatly better than the Truths?

Ahhh...Canadian dollars.  I guess that would explain the larger amount!

I would say yes they're probably better than the Behringers, but I may be biased as they're what I use.  They have EQ switches to help them suit the room, just like the Behringers.  They should be considerably less "boomy" as well, since they only have 6.5" woofers.  When I was shopping, I had pretty much narrowed down my search to these and the KRK Rockit RP-6.  Although my retailer was heavily promoting the KRK's at the time, he was pretty confident that the Alesis would perform a little better, and they were the same price...I have the 620's, by the way.  They were a little bright at first, but I simply flipped the Hi EQ switch down a notch and that made them sound a lot more like I thought they should.  The SOS review is here: http://www.soundonsound.com/sos/aug06/articles/alesism1.htm.  Worth a look!

I had seriously considered the Alesis prior to purchasing the Behringers, but ended up purchasing the latter even though they seemed evenly matched.  The salesman was really pushing the KRKs on me (I wonder why).

Now that I've used the Behringers I can easily hear the "boominess" you refer to so I'm second-guessing my decision. Though as I've mentioned before, I need to install some bass traps in my room. Steve had mentioned various other factors that contribute to my mis-perception regarding the bass frequencies. I also need to mix a song in full and figure things out from there. I'll review the Behringers again once I've done this. Unfortunately, the grounding problem has been slowing me down.   

The way to estimate how much of a fundamental problem you've really got is to disconnect the laptop from the monitors and listen carefully to them when you unplug the power supply. If, as is often the case, you hear a difference in the background noise then the power supply is also injecting it back into the ground system via its own mains lead - this is not unknown at all. And if this is the case, then you have one of those situations that's really hard to fix.

But hey, you may be lucky. Just don't count your chickens...

I tried doing this. I found no difference whatsoever in the background noise.  What I've also tried is simply unplugging my laptop from its adapter and letting it run on batteries as mentioned before - now THAT makes a big difference. But this test is different from the one you suggest. 

I tried doing this. I found no difference whatsoever in the background noise.  What I've also tried is simply unplugging my laptop from its adapter and letting it run on batteries as mentioned before - now THAT makes a big difference. But this test is different from the one you suggest. 

There's no one test - you end up trying a lot of things, inevitably. But at least you've not got the worst problem you could have had. Is the laptop PSU plugged into the same distribution as the monitors? And are we talking about a 3-core mains lead or a 2-core one?

It's true...there is no 'one' test. I've had to try a number of things and I've already learned almost more than I care to (I'd rather just play music instead of fiddle around with wiring, etc.).  I thank everyone for their suggestions thus far.

Is the laptop PSU plugged into the same distribution as the monitors? And are we talking about a 3-core mains lead or a 2-core one?

I am not certain that I understand your question, mostly because I am unfamiliar with the terminology (in particular "distribution" and "core").  However, I will attempt to answer it.  My laptop PSU is connected to a power-bar, which in turn is connected to a three-hole plug in the wall.  The monitors are also connected to the same power-bar.  I've tried powering my laptop through another plug, vice versa, and various other combinations thereof. 

Do your monitors have balanced inputs? If so then you can probably get rid of the noise by simply changing your cable wiring rather than by adding any more gizmos. Wire the signal to pin 2 or the tip of the balanced input and connect the screen to pin 3 or the ring of the balanced input while leaving pin 1 or sleeve of the balanced input disconnected. This wiriing configuration will break the ground loop and works well with my Acer laptop.

Cheers

James.

About this rewiring idea. I intended on trying this. Unfortunately, the TRS cables that I have cannot be taken apart (I realize that some cables can be unscrewed, thereby exposing the wiring, tip, internal sleeve, etc. However, this is not one of those cables).  I am considering purchasing the right cables.

The next immediate test I'd like to perform, however, is that of using an external sound card that is powered by a separate adapter. I realize it's a long-shot, but I think there is a chance that this may solve the problem. Furthermore, it can also act as a crude "Mackie Big Knob" -- thus two birds with one stone.  Believe it or not the problem is in finding an external sound card. I've gone to at least 6 major computer stores in my area and not a single one sells them, which is quite strange. Is there anyone out there in the Toronto area who knows where I can purchase a simple external sound card?

The next immediate test I'd like to perform, however, is that of using an external sound card that is powered by a separate adapter. I realize it's a long-shot, but I think there is a chance that this may solve the problem.

There is a better chance that it could make things worse - that's certainly what happens here. You don't break any ground links, and you add an extra power source into the equation.

I've tried powering my laptop through another plug, vice versa, and various other combinations thereof. 

Did that alter the extent of this, or did it make any difference at all?

hmm...I can't quite recall whether the extent of the noise was altered.  I should have paid attention to that but I didn't.  All I know is that the noise remained.  I will try various plugging combinations again tonight and this time I'll pay closer attention to whether there are differences in the extent of the noise.

My thought regarding the sound card was that the power supply (the adapter) would not participate in the ground loop because there is no ground prong on the adapter, though I realize that it is possible for the noise to be carried into the card via the USB cable attached to the laptop.  I also realize that these assumptions and/or deductions may be flawed.     

My thought regarding the sound card was that the power supply (the adapter) would not participate in the ground loop because there is no ground prong on the adapter, though I realize that it is possible for the noise to be carried into the card via the USB cable attached to the laptop.  I also realize that these assumptions and/or deductions may be flawed. 

It's not a straightforward ground loop - a major part of this is capacitive coupling of hash, and the chances are that an ungrounded adaptor (unless it's a small linear one) will add to the noise. And yes, the ground connection will carry through the external adaptor.

[An Update]

An Update

I thank everyone for their suggestions. Here's what I've done to solve the various problems I mentioned at the outset:

1) Ground Loop Problem

      I got a backup power supply for 70 bucks. I'm using it to power my laptop. It works like a charm. I also used it to boost
      my car the other day (Canadian weather is taking it's toll).

2) No Volume Knob on Monitors

      This is more of an inconvenience than a problem, but I wanted to do something about it. I purchased and external sound
     card. It's got a remote control and a convenient volume knob. (though it's causing me other problems, which I mention
     in a new topic titled "New External Sound card - Synchronization Problem").

     I had considered the remote possibility that an external sound card that is powered via an adaptor without a ground
     prong might eliminate my grounding problems as well. Steve suspected this would not work...well...he was right - no
     surprise there. 

3) Boomy Monitors (Truth b2030a)

     I played around with the EQ settings on the back of the monitors and more importantly, I installed BASS TRAPS!! those 
     really did the trick! I'm almost shocked at the extent to which they alleviated the boominess.