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Hey experts,

I recently installed a Trendnet powerline network kit to get my network to a computer in a far bedroom (poor wifi reception). The network works great!! Very easy to setup and no problems.

But, now there is a low frequency buzz/hum coming out of my main destop speakers (good old Cambridge Soundworks speakers) that goes away as soon as I unplug the powerline network. The hum is even present during the low power 'standby' mode when the speakers aren't active. It's a very irritating noise, since the speakers are sitting right there below my monitor only a couple feet from my ears.

I've tried plugging the speakers' power cord into several different sockets (different circuits/breakers),to no effect. They are currently plugged into a medium level APC powerbar which has surgeprotection and (I believe) some powerline noise filtering capabilities. Is there something else I can do to get rid of the buzzing? Other noise filtering options?

thanks for any advice,

dave

Something like this (http://www.newegg.com/Product/Product.a ... 6842101349) would get the job done.

What you're looking for is something called a "power conditioner." The reason that the hum happens (and it's especially noticeable in speakers) is the power that is coming into the device isn't "clean." Have you ever read a power supply review where they talk about ripple and noise? It's the same thing. The amplifier in the speaker is picking up the extra noise that's being introduced into that circuit and doing what amplifiers do. Making it louder.

The battery backup part of the power conditioner is not really necessary for you to get rid of your noise issue. However, if you're going to spend the money to solve this problem it's a good idea to get a battery backup in the same unit (they are good to have anyway). The APC unit will give you nice and consistent power to both your speakers and to your PC. They can also be setup to shut your computer down if it detects that you have a power outage, and will give you the added protection against those quick brown-outs that can really damage electronics.

If nothing else do a search for power conditioners and read up on them. It's a good place to start.

Sounds like a ground loop to me. I have a similar issue and I'm having a heck of a time getting rid of it.

If the power adapter for the speakers has a non-polarized AC plug, try reversing it in the outlet. If it is detachable, you could also try replacing it with a switching adapter of the same voltage and similar wattage; switching adapters should be more immune to power line noise than "old school" linear ones.

If you plug everything in the audio power chain into a UPS that should isolate the circuit. Or, just start with the amplifier power and add from there.

Thanks for all the advice. I don't have access to it right now, but I'll try flipping the plug around when I get back. Also, I'll check the model of my APC powerbar to see if it has more than the basic for powerline conditioning. I'll post what I find out tomorrow morning. Maybe I'll be looking for a UPS like the one suggested.

Which Trendnet unit is it? Looking at what they show on their web page, it appears that the only connection between the powerline adapter and the computer is a cat-5 cable, correct? And if you unplug that network cable, does the hum go away? The behavior sounds quite similar to a ground loop, but since there are no grounds involved here.... My thought is that 60Hz AC hum is being imparted on the network cable through some sort of coupling in the powerline adapter and then being injected into the PC power rails. Now, how to go about fixing it? That I am not sure of right now.

--SS

SecretSquirrel wrote:

The behavior sounds quite similar to a ground loop, but since there are no grounds involved here....

That just made me think of something. While you are indeed correct that there should be no ground loop (since Ethernet normally uses a high-frequency pulse transformer for coupling with no common ground), a ground loop could still exist if shielded Ethernet cable is being used. Ethernet cables are typically unshielded, but shielded ones do exist, and if used could create a common ground path between the two connected devices.

You can tell you've got a shielded Ethernet cable by the metal shell around the connector, like in this Monoprice pic (click the bottom thumbnail on the left for a close-up view): http://www.monoprice.com/products/produ ... largeimage

LaChupacabra wrote:

Something like this (http://www.newegg.com/Product/Product.a ... 6842101349) would get the job done.

Disco wrote:

But, now there is a low frequency buzz/hum coming out of my main desktop speakers (good old Cambridge Soundworks speakers) that goes away as soon as I unplug the powerline network.

I'm going to take what I said back. I didn't read your original post throughly the first time through. What SecretSquirrel and just brew it! are saying sounds like the most likely cause. It's a weird problem for sure.

I've tried plugging in the speaker power different ways to no effect. The ethernet cable is not shielded (clear plastic head). The power brick I'm currently using is:
http://www.amazon.com/APC-PH8T3-8-Outle ... B00009KYCP

Would there be any point to upgrading this for better line 'conditioning'?

The model of Trendnet device is TPL-401E. The hum usually does go away after awhile (~15 min?). Also, if I unplug the powerline network the hum stops immediately, and then when I plug it back in the hum doesn't always come back. I'm not sure how strongly it is related to actual powerline network activity. The kids are only on that computer once in a while, but the hum can happen even when no activity.

Is the power to the speakers a separate brick, or is its power supply permanently wired (or internal) to the speakers?

Couldn't it be the inductive current or something?

The speakers usually go nuts when cell phone is about to ring or during the call, and there are no grounds or wires involved.

You may be interested in some of the resources on grounding and RF interference here:

http://www.rane.com/library.html
http://www.audiosystemsgroup.com/publish.htm
http://www.svconline.com/mag/avinstall_ ... olling_rf/

Madman wrote:

Couldn't it be the inductive current or something?

The speakers usually go nuts when cell phone is about to ring or during the call, and there are no grounds or wires involved.

Yeah, the speakers are presumably plugged into the same circuit as the powerline network tap; it's possible the amp in the speakers is picking up and passing along something from the power side to the signal side. I wonder if just a choke on the speaker power cord would make a difference? I guess the question is: what is the source of the hum: the speaker wires, something else in the signal path, or the speaker power source?

If it's 60Hz hum a choke isn't going to do squat.

What bothers me about the entire scenario is the fact that the problem can disappear on its own after equipment warms up. That almost sounds like a flaky ground connection somewhere in the system, for example a loose connection at the computer's speaker output jack. It's quite common for speakers and headphones to inject and then reproduce hum and buzz in the amplifier circuit if the jack is not fully inserted, or is making a complete connection due to a faulty plug or wire.

It's possible the problem has been there all along, and the electrical disturbance created by adding the new network wiring simply brought it to light.

I've checked all the jacks, and everything appears to be plugged in nice and tight.

The speakers have a separate, fairly large, power brick. In the system I have, the power goes to a central subwoofer, which has outputs to 2 front and 2 rear speakers. I never have the rear speakers plugged in.

Sometimes there is some static when I adjust the volume knob (separate from speakers - wired into subwoofer), but that doesn't appear to impact the hum when it occurs.

As you all may have guessed, I am no electrical engineer! What is a 'choke'?

Just star ground the lot. Ground loops .... grrrr.

Star Ground: Ground everything to the same ground point. With plastic everywhere these days a screw somewhere on the device will often work.

ludi wrote:

What bothers me about the entire scenario is the fact that the problem can disappear on its own after equipment warms up. That almost sounds like a flaky ground connection somewhere in the system...

Or heat. Any number of things could change with heat, both on the computer and on the power line adapter.

Disco,

Do you by chance have a network switch that you could plug both the computer and the powerline adapter into? I suspect the problem would go away, or at least be significantly reduced. You might consider a cheap ($10-$15) four port switch if you don't have something already. Yeah, kinda silly, but hey, if I fixes the problem...

--SS

just brew it! wrote:

If it's 60Hz hum a choke isn't going to do squat.

Are we sure that's what it is, though? Until we know what is picking up the hum and/or where it is originating, I'm not sure we can rule anything out.

Yeah, a UPS or a power conditioner would more then likely fix this as the second post proposed. A power bar isn't the same as a power conditioner. Power conditioners are around the same price as a UPS as well.

A good power supply or speaker system would filter out such noise. My Soundworks exploded roughly two years ago. They were definitely great for what they were, but I wouldn't put it past the system not filtering properly.

UberGerbil wrote:

just brew it! wrote:

If it's 60Hz hum a choke isn't going to do squat.

Are we sure that's what it is, though? Until we know what is picking up the hum and/or where it is originating, I'm not sure we can rule anything out.

No, we don't know that for certain; but he did refer to it as a "low frequency hum/buzz".

Disco wrote:

I've checked all the jacks, and everything appears to be plugged in nice and tight.

That doesn't mean the jack itself doesn't have a cracked solder connection. Can you modify the hum by gently wiggling the speaker jack in place?

Also try unplugging a front-panel audio jack from the motherboard, if your have one installed, and make sure your soundcard microphone inputs are muted if you're not using them (i.e. nothing plugged in). I believe newer versions of Windows now do this by default but it's worth a check.

UberGerbil wrote:

just brew it! wrote:

If it's 60Hz hum a choke isn't going to do squat.

Are we sure that's what it is, though? Until we know what is picking up the hum and/or where it is originating, I'm not sure we can rule anything out.

A turn or two through a ferrite choke will only clamp noise in the RF range. It won't do anything for the 100 or 120Hz audible hum that is induced by a 50 or 60Hz mains waveform.

I've rechecked the various jacks, and found no problems. As I mentioned, it's not a continuous hum. It usually lasts for 15-20 minutes after the speakers have been 'woken' from the inactive state. Sometimes it's a solid 'hum', and other times (yesterday) it was more of a cyclic pulsing buzz ~100 beats/min.

I think what I will do is purchase a UPS such as the Cyberpower CP1350, which seems to emphasize its ability to improve power quality, has a nice lcd screen, has enough juice to let me wrap up work in the event of a power outage, and has easily replaceable generic batteries.

Link: http://www.ncix.com/products/index.php?sku=23573

I'll let you know if it improves the situation. Regardless, it's probably a long overdue upgrade to my system. Hopefully I'll have some positive results to report back by early next week.

thanks for all your assistance and advice.

dave

Disco wrote:

I've rechecked the various jacks, and found no problems. As I mentioned, it's not a continuous hum. It usually lasts for 15-20 minutes after the speakers have been 'woken' from the inactive state. Sometimes it's a solid 'hum', and other times (yesterday) it was more of a cyclic pulsing buzz ~100 beats/min.

Good grief what a misread i just did. I thought you were currently using a UPS and so I ascribed the noise to a battery charging circuit. If you're not using a UPS now and the problem is most closely associated with the powerline network, then I'd have to suspect the powerline device. It's designed to inject a signal onto the mains, and if that signal is modulated (either intentionally or unintentionally) onto some carrier, or is rectified somehow, then the signal could show up in the audio band. There are strong regulations that govern this sort of fault, and you should be able to return the device for a new unit.

OK. So, I've now got a UPS installed with better power conditioning. I have heard the hum (more of a pulse), but it didn't last very long and wasn't quite as loud/annoying. Even though it means that there will be more network cable laying around, I'm going to try putting the powerline network device into a socket that is further away from the computer/speakers and see if that helps.

I'll let you know if anything changes.

dave

Sounds like there's an RF interference from that Trendnet device which is being picked up by your speaker's amp... I have old Klipsch ProMedia speaker setup which can "pick up" the CB radio (or some similar type of portable radio device) if some truck (or some commercial vehicle) is using it near our house (I can actually hear everything and can "amplify" the sound by using volume knob on speakers), maybe something similar is happening with your speakers...

JohnC wrote:

Sounds like there's an RF interference from that Trendnet device which is being picked up by your speaker's amp... I have old Klipsch ProMedia speaker setup which can "pick up" the CB radio (or some similar type of portable radio device) if some truck (or some commercial vehicle) is using it near our house (I can actually hear everything and can "amplify" the sound by using volume knob on speakers), maybe something similar is happening with your speakers...

That's typically caused by a diode rectification effect in the preamp or amplifier input stage. It's more likely to happen with AM-band radio reception but any AM-type radio signal could theoretically be picked up. Once half of the carrier is chopped off, the residual signal looks approximately like an audio-frequency signal riding on a DC offset. An AM receiver would perform this step intentionally, but any audio circuit with a BJT transistor can approximate it, and under certain conditions the audio portion of the signal can be passed into the amplifier.

What's happening here is very likely an ordinary ground loop, but those can be notoriously difficult to chase out. Browse any DIY audio forum, and even the veterans will be posting for advice periodically.

Well... it's been a few days using a different plug for the Powerline network connection. So far I haven't heard any strange noises from the speakers, so I guess that's all that was needed. Although the UPS did seem to help somewhat prior to moving the plug (better line conditioning?).

I guess problem solved! Thanks for all the in-depth advice. I appreciate your help.

dave

Different plug, or a different socket?