The great news is, I finally have my studio completely set up, essentially for the first time ever, including a subwoofer that has sat idle for over two years. All of the important software is installed and I'm ready to go.

The issue is low-level static and a medium-pitched whine (not 60 Hz, but maybe an upper harmonic) in my main speakers. It's not apparent when music is playing at a conversational level, but is noticeable in a quiet room, and bothersome during quiet passages of music.

Except for incandescent replacements, there are no fluorescent lights or dimmers in the house. I have ruled out the cable modem and wireless router in the room, which can't be moved anyway.

All of the AC except the sub is plugged into a single surge suppressor, including the DAW, mixer, headphone amp, video monitors, speakers, and Roland VG-88. The only things running now are the DAW, dual monitors, and speakers. The sub is plugged into a separate surge suppressor on the same outlet pair as everything else.

My control, signal, and power lines are a rat's nest, and I know I need to work on that. What else, in your collective opinion, needs doing?

Thanks in advance,

Richard

Have you tried the most simple but most time-consuming test: unplug all cables?

First set: Have only power amp and speakers working? Is the whine still there?

If not, plug in one more cable. Continue and: When does it start? And then it still might not be that certain cable. It might be a combination of cables that only starts to induce said whine when the last one is connected.

If yes: The source of the whine is something that affects either amp, or speaker cables, or the speaker itself. Maybe it is only a bad connector.

No, I haven't done that yet. I should be able to today. The speaks and sub (Behringer TRUTH B2031A and JBL PSW-D110) are active, so there is no separate power amp.

I did D/C the PreSonus AudioBox USB line from the DAW and the noise completely stopped. Does that localize it to the PC? If so, what then?

You may be experiencing an earth loop through the signal chain.

USB is a current loop standard: 2 wires are 0 and +5V, the other two are the current loop signal path, if the 0V is also connected through to the signal path earth/ground connection (unbalanced -ve/earth or balanced shield) through the Presonus then simply disconnecting elsewhere in the signal path (lift the shield at one end of a balanced connection?) should eliminate the noise.

PC's are a dreadful source of noise... Of course there are a couple of assumptions here that may not be correct...

I can't see whether you said or not, but if the DAW is a notebook some models (as in my HP) have the earth from the mains connected through the charger into the ground plane of the PC. Disconnecting the charger from the PC (so it's running on battery) would eliminate the noise if that is the source.

Also, CFL lamp replacements are still Fluorescents (as I'm sure you know). I've found that LED's are far superior, but you usually need to shop around to find them at a resonable price, retailers are still price gougeing on them

My DAW is a full tower PC with a self contained power supply. It is shielded on all sides but the bottom.

I'll have to check on the type of ceiling light in my room. How do you do an earth/ground lift on a USB line?

There is a Cat 5 Ethernet line running through the rat's nest behind my studio desk. Could that be a source of interference?

ETA: There is a laptop in the room. It's on another outlet and surge suppressor, but presumably on the same breaker.

I'll assume it is a normal steel case so the bottom will also be shielded by the metal of the case which is grounded through the PSU


You don't, it would have to be done in a common signal path somewhere.


Anythng is posible, but I doubt it. You are talking RF signals of more than 10MHz. Actually it's probably at least 100MHz.

Something you might try:
leave the Presonus plugged in on the audio side, but UNplug the USB cable (I assume it doesn't use the USB cable for power?)

Hmm, thinking about a ground lift on USB, if the Presonus IS externally powered it might be possible to disconnect the power wires in the USB cable at one end. Only possible downside is if the USB interface itself needs to be powered by the USB cable...

The AudioBox receives both signal and power via USB.

Hmm, disappointing. Oh well, that just makes it a little harder. I would look for another place in the signal chain to do the ground lift.

I have the behringer 2030a just got secondhand a few months ago, I think you replies to a thread of mine on Here Ryszard, not too sure if I remember correctly but I have a vague recollection that you said that you had cables in an unbalanced configuration, maybe I remember wrong and it was somebody else.

Anyways I had the same type of hum on speakers, didn't get or felt it wouldn't help to get balanced cables from interface to monitors.

Tested an old cable that I had lying around and hey presto it seemed to cure it, so got the balanced cables on ebay for £15.

I would say hum and noise is gone now even when I turn speakers to full volume, maybe a little background static, which is probably normal enough.

Balanced cables seem to have solved my problem. Hope you can cure yours as easily.

Musiclover

"My control, signal, and power lines are a rat's nest, and I know I need to work on that."


I would start with that rat's nest. Disconnect and bundle like-wires together with cable ties - audio with audio, etc. Get any AC wiring away from audio cables. If you cannot keep AC wires completely separate from audio cabling, cross them at a 90 degree angle - do not run them parallel to audio cabling.

As Musiclover said, I would also invest in some quality balanced cabling. Good luck.


Regards,

Bob



p.s. I hope I'm not being condescending and telling you something that you already know.

Ryszard,

One of the reasons I got rid of my PreSonus Firebox (basically a firewire version of your Audiobox) is that there was two internal signal issues with it - which turned out to be somewhat common after perusing their support forums:

1. Signal bleed from headphone output (no mics being used) into the input channels. I never realized it was an issue until final mix-down of a song that I blew through in a day. Here's the song: https://soundcloud.com/rockstar_not/scott-lake-rest-ye-orion listen to the very tail end of the song. If you turn up the playback enough, you'll hear my click-track. No microphones were used in the recording process

2. The second issue was that there was a very high pitched whine on the input pre-amps, when turned up to the last 20% or so of gain. Again, an issue that I found out was common through the threads, but after my warranty period expired. I would estimate the frequency at 8kHz or above.

I no longer have that device - I sold it after my fire-wire equipped lappy went south permanently.

I hope that your situation is not the same and that you simply have some grounding issues to contend with.

Other sources of whine to be mindful of:

1. Some laptops LCD backlight is controlled by a pulse-width-modulated control circuit which can induce whine over the USB. We had some Thinkpad T-series laptops at work which exhibited this issue.

2. Other stuff on your USB - try to eliminate as much off of the USB as possible, including any powered ports. The power supplies on those are usually crappy switching jobs, and they can make headaches for noise on the supply of the USB, which depending on how well the audio interface is designed to reject incoming noise on the USB, may cause issues.

-Scott

Take the first simple step again: replace cables, It is cheaper to change a 5 dollar cable than a 100 dollar gadget. While there may be many sources for corrupting your signal, a bad connection might be a probable cause.

If it is not the cable, the next step that I would take is: take that box to a different location in the studio, even if it means longer cables for the test.

Eliminate the cheapest and easiest accesible sources of noise first. It is not always the most expensive part, Murphy's milage may vary.

Thank you all. I have several things to try now. Some are from checking the PreSonus site. It is not complete, and they are in no particular order.

1. Replace the USB cable.
2. Make sure it's not plugged into a USB 3 socket.
3. Isolate the PC. (I may try a ground lift there.)
4. Reroute control, power, and signal lines as appropriate.
5. Replace the sound card. (That would be kind of okay since I'd like to upgrade to one with a S/PDIF output so I could use the Focusrite(?) VRM speaker emulator with my headphones.)

There is more, but this will keep me busy for a while. I'll keep you posted.

R.

If the distance between our locations wouldn't be that long, I'd take a case of beer and come help. I like this kind of challenge.

R, ofttimes, cheap cabling can be a culprit. I think you're on the right trail, Tonto, now it's perseverance you'll need. Some noise problems would peeve Job (not Steven).

Best to you on finding a solution.

I'm sorely tempted to hire Guido, if only for the beer und shashlik. lol

Personally, I suspect a earth (ground) loop.

Maybe I've missed it, but do we know the hum frequency? That would help isolate PSU or mains. Does it sound like your Barber's clippers (mains) or a harmonic thereof (PSU)?

Come on down! I've got a case of Spaten Optimator in the fridge. We may not get it fixed, but we won't be feeling any pain!

Don, cabling is the first thing. I'll see whether I can find a more heavily shielded USB cable for the AudioBox. I also remembered that I have another sound card (TASCAM US-224) that I had used on my laptop. If the latest drivers (XP/Vista 64-bit from 2007) work I may have something.

The tone is definitely a musical note. I'll zero in on it and report that, too.

Thanks, guys!

For the most part this sound reasonable, BUT, I am very uncomfortable with #3. I hope you are not considering a MAINS ground lift. IMHO that is potentially a very dangerous thing.

FWIW I'm ALWAYS nervous when people start talking about lifting pretective earths from inside mains powered equipment. Double insulated is one thing, but your PC has a metallic case.

I appreciate the concern, Lawrie. How would you feel about this--a one-time test using a two-prong adapter to see whether that does it? If so, I could buy a proper isolator. If not, I remove the adapter and proceed with other steps. It's a quick, simple approach, if you approve. That's a question, so I look forward to hearing back from you.

In the US, our mains are 120v, 60 Hz, meaning that the first order harmonic is 120 Hz (2x 60 Hz), or roughly equivalent to key 27 on a standard 88 key piano. Musical indeed.

... like those -ator beers. I know about 15 different ones, but there are more. We could accompany the entire session

Spekulator - thinking about the problem
Animator - get busy
Operator - while we search the error
Triumphator - after we found the error,
Optimator - to enhance the system
Maximator - to make it even better
Multiplikator - telling others about our findings
Honorator - praising those who helped
Sympathor - if others have a similar problem
Celebrator - just for celebration
and finally
Poculator - after we emptied all the others (pocula is Latin for empty)

These beers are very famous in Bavaria during Lent and as you see their names support working. :-)

A technician's trick I've used countless times to see if a remote control was transmitting IR (Infra Red) was to operate it within a few inches of an AM radio. It should cause a static sound when buttons are pressed and it sure beats those little IR detector cards while providing audio feedback at the same time.

Try getting an AM radio near the suspect cabling.

In my case it was the PC and the two prong adapter fixed it. Our missing friend Mac told me all about it, there's no problem with using a ground lift when it's going into the surge protector. You know Mac, he went into his Electrical Engineer bag and explained it in great detail. If you're still not sure, I'll search my own posts, find his answer and post it.

This has been a while, maybe even last year and no problems and no noise either.

Bob

I have no problem with a one time test, but as a permanent solution, it's an easy way to die... That's why protective grounds exist in the first place.

Hi Bob,
I have great respect for Mac, even though we've disagreed in the past.

I would be most interested in that post as I do not see how a surge protector would make a ground lift any safer.

I know that you know your stuff as well Lawry and expected a question from you. Here's my old thread:

http://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=236913&Searchpage=2&Main=33793&Words=jazzmammal&Search=true#Post236913

What I forgot that Mac said was his last comment about you MUST have other equipment plugged into the same surge protector as the PC with the ground lift. That way it's still grounded through the other equipment. Remove everything but leave the PC plugged in and then you're at risk.

Bob

Bolding mine - yup - still, knowing human nature the way I do, little things like this can be forgotten. Or interfered with by someone who is ignorant of what's going on.

That's why I ALWAYS try to find a point in the AUDIO chain to lift the ground rather than at the mains. Doing my best to make things foolproof, but them fools is soooo inventive, it's a loosing battle

Removing grounds is never a good idea. They are there to keep the dangerous voltage potentials off the chassis and routed safely to ground.

To use a surge protector as protection against chassis voltages and depending on another device's ground for protection is foolish.

There's only one way this should even be considered and that is IF the circuit is GFCI protected.

A surge protector will not disconnect the circuit if 80ma of current flows from hot to ground. That's enough to cause cardiac arrest in healthy people...... but the GFCI will trip and shut the circuit off when it detects 7ma flowing to ground from hot.


I'm curious if you have tried the "divide and conquer" method of troubleshooting yet to try to isolate the whine. And if so, what the results were.

Hi Guitarhacker,
the surge protector approact RE lifting ground on the PC works like this:
ALL the devices plugged into the surge protector are part of the system. As there is a ground connection that goes via the AUDIO path between the devices should the PC (with a lifted ground) become faulty, the ground connection would still be in place via the AUDIO path and back out to the surge protector via the protective ground connection of one of the other devices. Actually, one could argue that as the protective grounds of the premises power outlets should all be bonded to the same earth stake you don't even need the surge protector. It just brings the common ground path closer and helps eliminate voltage differentials that may exist between grounds on different circuits.

HOWEVER, I DON"T like using this approach, not because it won't work, 'cos it will, but because the current carrying capacity of most audio grounds is well below that of the wiring that is supplying the power in the first place and could easily be burnt out thus removing that protection and potentially causing a fire. It'll get HOT in a fault condition. E.G. in my house in Australia, the power reticulation is done in 2.5 sq mm conductors and fused (actually I have circuit breakers) at 16 Amps - more modern houses use 20 Amps. The cabling itself will carry far more than 16 or 20 Amps before it would start to overheat and burn but the breaker/fuse would limit it to that. The gound wire in most of the audio chain would be unlikely to carry more than 2 Amps before starting to overheat AND if it's travelling ANYWHERE along it's patch via a printed circuit board path then you can pretty much drop that to the milli Amp range. It WILL burn out and go open circuit long before the breaker/fuse could do its job and then you would have a live and unprotected PC chassis to contend with.

Of course, while the fuses/circuit breakers should help protect against this, and Core Balance Relay Sets (Safety Switches, GFCI, RCD - all the same thing really) that should stop it in its tracks, but IMHO you can't be too careful. I personally prefer to rely on good, basic design rather than fancy gizmos that might fail at the crucial moment.

Every time this subject comes up either on this forum or on other forums I frequent it always descends into comments like these. You guys make it sound like if all the wiring and all the connections are not just absolutely perfect we're all gonna die.

Look, it wasn't until sometime in the 70's I think that houses were required to even have ground circuits in them. My friend lives in Manhattan Beach, California, a very expensive area in a house built around 1962 or so and some of her outlets have just two prongs, and some have three. Anybody here who's over 50 or so grew up in a house like that and guess what? We didn't die. We all had wire snippers and either cut the ground plug off an AC plug so we could plug it into a two prong outlet or we bought the adapters. Years ago I remember my dad had a drawer full of them. We're all still here.

You guys need to lighten up a bit about ultimate safety. Sure it's safer to have everything grounded, it's also safer to only drive a brand new car every year because after all, that model is safer than the previous year. How old are your vehicles? Don't you know that a nice 25 year old truck you drive every day is an unsafe piece of crap?

C'mon, put a little perspective on this.

Bob

Who or whom else remembers the screw-in fuses that Dad would substitute a copper penny as a temporary solution until the proper amperage fuses could be purchased? During War years, when fuses became scare, it was the only and permanent solution! I don't remember a noticeable rise in house fires during the war years.

Remember them, Don? I even HAVE a few left in my house for special circuits to the furnace and water pump. Disclosure: both my house and camp are over 100 years old...

Some would argue that replacing the burned-out fuse isn't a permanent solution; it's only temporary until the fire starts.

I'm not wading into this grounding question except to say I ran an electronics store in the mid 70s, and we kept wondering why all the audio equipment kept failing. We had the electric circuits tested and the entire wall of AC outlets were improperly grounded, setting up a floating ground through anything (or anyone) who 'connected' a chassis to ground. The current was just enough to blow equipment and give your teeth a little chatter, too.

Thanks for the trick about testing the remote with an AM radio.

Hi Bob,
hmm, perspective, here in Australia we've NEVER had power without a protective earth - but then we never used 110V either...

How often does equipment fail? Not very often at all, but if it does why not play it safe? You only get one life. Sure, I may be being over cautious for you, but then I've SEEN what can go wrong...

Ever seen a burnt house that was caused by an electrical fault? I have. I had to help in the clean up too. Ever seen an electrocuted body? I haven't but I know a guy who was so close to being electrocuted to death that his sphincters let go.

Add to that, in my formative years my parents owned an electrical fitting business and I got to see, and eventually repair, motors and other electrical goods that had failed.

You want to be cavalier about it? It's your life, go right ahead - I've seen the other side and I'll choose to be cautious thank you.

Simple, but easy to forget. Have you tried listening on earphones? Is it still there? I find if I turn my amp down, and the PC up I get better signal to noise

Z

A ground loop eliminator is placed between the PC/laptop out and amp/mixer. The AC power is still grounded, as well as the rest of the system. Search <ground loop eliminators>, in the forum lots of posts on this subject. Later, Ray

ZeroZero, it is in the phones as well. The powered satellite speakers are turned up to their max, which is 6 dB above line level. Everything (meaning software mixers) in the PC is set at max, so there's nowhere to go in terms of S/N. I hope that is responsive to your comment.

RE: Grounding: Y'all have put the fear of God in me as far as mucking about with that. I'll find another way.

To all: Remember I said the noise consisted of static and a whine? FWIW, the whine is pitched at B above E on the first string of my guitar. The static is affected by my Bluetooth mouse. I'll have to get a USB mouse to see whether that's it.

Meanwhile, Life Keeps Happening. I'll keep you posted.

Hi mate, for fault finding purposes go ahead and lift the ground: do a positive elimination test, just don't leave it that way. I mean, it isn't an instant death scenario...

If you prove that it is the ground, all you need to do then is identify a ground in the signal chain that you can open and all should be well.

Until you do the test you are groping in the dark.


I had a quick look at a frequency chart and it turns out that B1 is 62 Hz. That makes ALL B's a multiple of 62Hz which is VERY close to the 60Hz US power oscillates at. Reckon you've proven a mains connection for your noise mate.

The fact your mouse has an impact on the noise also suggests your PC is the most likely culprit - not surprising since there are sooo many sources of electrical noise inside a PC.

Rzyard, just read what Mac wrote last January, he knows what he's talking about but not to say Lawry doesn't, he knows too. Note Mac warns about making sure I don't forget and leave the PC ungrounded in the power strip after I've unplugged everything else for whatever reason.

If you read that entire thread you'll see my first choice was to buy a proper grounding device but the inexpensive ones are no longer available. I called around to several electronics supply places here and the cheapest one I found locally was over $150. I found one online for $75. The one I found a few years ago was only twenty bucks. Apparently few care about this or those would still be around.

This is yet another example of why we all need to be nerds when it comes to this stuff because PC's are not designed for our kind of work. We can't be a brain dead doofus walking around with our thumbs up our noses just doing stuff with no thought behind it. Those are the ones who keep winning the annual Darwin Awards.

Bob

Agreed on the use of grounds through the audio cables.... they will not safely carry the 15 or 20 amps..... actually much more than that during a hot to ground fault condition. They become heating elements pretty quickly and not fast enough to protect you.

This does NOT sound like a ground problem or a ground loop. A ground loop would have a 60hz hum.... like a guitar amp when you touch the tip of the guitar cord. It's approximately a low "B" in pitch.

You can try removing grounds with the adapters..... never cut the ground plug connector off. I doubt that you will solve the whine this way.

Whining sounds are mostly caused by interference. In another forum site, we get this kind of issue from folks using the wireless mice and other radio frequency devices around the audio gear.

You absolutely must find the source of the noise first before you can work on solving it.

Since many folks use unbalanced wiring and cheap cords, the first step here is to ID the offending device. Shut off the wireless devices (one at a time, but then leave them off if there are multiple devices... perhaps the source is not singular but from multiple sources) that are in use in the proximity to the computer/DAW. Did it go away?

Don't rule out the wi-fi gear nearby either. Turn off the wi-fi internet.

Shut down other computers as well.

Unplug the wires from the inputs to the speakers and with them turned on and up and nothing connected, do you still hear it?

Unplug any outboard gear from the system. Gone?

Leave no stone unturned in the search for this problem.

Guitarhacker,

The hum is a B over the E string on a guitar, so it is a harmonic of 60 Hz.

I'm looking for my two-prong adapter.

I have positively ruled out my cable modem and wireless router, unless they generate RFI when powered down. I do have a wireless mouse. That's the next thing I'm going to check. I have also turned off the Ethernet-connected laptop in the room.

The issue is not in the powered speaks and sub.

R.

Edited to add: It wasn't the mouse, nor was it the laptop.

Hey Ryszard,
I've just had an unpleasant thought...

To set the background, I have a time share ownership in a "luxury houseboat", and it is pretty good I must say.

...but there is a slight problem. Being a boat, there's no real ground one can tie the on board power to. Power on board is supplied by 12V batteries connected to an inverter. The batteries are charged by a 240V, 2000W Honda generator via a normal battery charger (actually, 2 fairly smart ones - there's 2 battery banks)

Anyhow, that's all to set the scene for my HP notebook and really BAD noise when connected to the inverters.

My particular model of notebook has the mains earth extended through the charger and into a 3rd wire in the connector to the notebook. I assume it's some protective arrangement.

I MUST disconnect from the charger to stop the noise, and I note it's REALLY bad.

I believe it's caused by the floating earth (pun not intended... Oh alright, it WAS intended ). If the boat's ground were properly earth staked I believe the problem would either not exist or be considerably reduced. By really bad I mean it almost totally drowns out the music!!!

This has made me wonder if the ground in your house might be resistive enough to be floating a little above 0V. It's not an uncommon thing you know. You might try locating your earth stake and pouring a bucket of water over it, paying particular attention to where it enters the ground - try to get that quite wet.

I love it: "floating ground" on a boat. That is indeed hard to get your head around.

Lawrie, good thought. If I can find the earth/ground stake that will be easy to test. On the other hand, wouldn't a good soaking rain accomplish the same thing?

Depends where the stake is. I have a garden bed under my bedroom window, small eave, that HAS to be watered - doesn't matter how much it rains the prevailing winds in my area are such that you can stand there in all but the worst downpours and stay dry.

Add to that I'm on very sandy soil - actually no soil, just sand

Fortunately, my earth stake is also bonded to the water pipes (legal requirement here in Oz) and the water pipes are metallic out to the street which in turn gives a much larger surface area on the effective earth stake to make it more effective. As well, we run M.E.N (Multiple Earth Neutral), I assume this is also done in the states?

M.E.N is where the Neutral is also bonded to the earth at every premises, so, for example, every house in my street has the Neutral bonded to the earth stake AND the water pipes. Even so, you can still get potential differences in the earth from house to house... Electrickery is a curious thing...

Yeah, I like it too...

A mate of mine actually built the boat and he and I and another mate who had shipwright experience discussed the grounding issue.

I thought it might be a good idea to have a metallic connection into the water as part of the boats ground but apparently that can cause some serious electrolysis problems so the idea was canned.

Guitarhacker makes some really good points here. Particularly:
A ground loop would have a 60hz hum.

The fact that the interference is a multi-octave harmonic suggests there's some "signal processing" going on. If it were, say approx 120Hz, I'd suspect a badly filtered bridge rectifier somewhere - but it seems to be above the 330Hz of the 1st E string - the B above that is nominally 493.9Hz - the nearest 60HZ multiple up there is 480Hz (3 octaves higher than mains 60Hz) - and maybe a quarter tone flat

Thus there is something processing it and while a simple earth loop may well be the original noise signal source, there's something else going on too.

Rzyard, my noise was exactly what you described. Mac said flat out it's the PC. I spent time checking every audio cable and all the connectors, unplugging the mixer, using headphones alone, using process of elimination, all that stuff. It's the PC. Just find a two prong adapter, follow his instructions and be done with it. If you're really paranoid buy that $75 thingy that truly eliminates the shock potential.

Bob

Bob, I'm ready. Here I am about to call an electrician to see whether neutral is really 0 volts. Really, now. If I can't find the adapter in my own staff I'll go to Ace tomorrow and get one. If that does it I'll check out true isolators and go from there. I'm tired of this.

Thanks,

R.

A note on inverters. Most of them, especially the cheap ones, do not have "true sine wave" output. (very similar to how our gear "samples" an analog signal and reproduces it as audio later) They use a method of creating an approximation of a sine wave that is basically square waves in steps. For most AC powered devices, this is not an issue. However, sensitive electronics can exhibit side effects from the simulated sine. Hand tools and heating devices are not bothered by it at all and run perfectly fine.

On the house electrical system ground. You can check for corrosion and loose connections. I've seen rods that looked perfectly fine be totally corroded in the ground due to acidic soil conditions. Sandy soil tends to have the higher resistance since it dries out so quickly and doesn't have good conductance period. If you are eliminating possibilities, certainly have an electrician with the proper equipment come and check the ground. An ohm meter is NOT the proper gear for checking a rod to ground connection. You need a ground resistance tester and the test needs to be done according to the instructions. Pouring water on it simply makes it wet unless the ground is totally dry, it will probably do very little to remedy the problem.

I don't believe you are going to find the problem in the electrical system of your house. If the hum was 60 hz, I might say it was possible, but the sound is higher in pitch and freq.

Since it's a tower computer, you can't run on battery to do this next test. But I think you will likely find the issue inside the computer. Since everything else you have done to eliminate the issue from outside, through the cables and the peripheral gear has not found the issue.... I'm starting to think you will need to dig in to the internal components, likely starting with a power supply swap. The switching power supply in the computer operates at a much higher frequency than the 60hz line..... and you mentioned that the freq was 300 something..... It's been a while since I looked at the specs on the switching power supply....

(pause) I went to google to see what I could find on switching power supply freqs..... not too much info on this topic but in one site I did see that some of the switching power supplies have a frequency of "several hundred hertz"...a little bit vague.....however, as I recall from my past studies, the freqs were in the 300 to 400 range in the supplies I was working with. Easiest thing would be to get a new supply and swap it out. Get one rated for more than the computer needs.

I guess I need to start posting system specs again instead of cutesy quotes. To be honest, though, I'm gonna resist digging around in the guts of this thing. It's a purpose-built heavy-duty machine specced by me for use as a DAW. The PS is a brand-name unit rated well over what I need. I'm just not ready to tear it unless I start smelling smoke. (If I'm wrong, I'll freely and publicly admit it.)

That said, I'll do the ground lift test today or tomorrow. If that doesn't do it I'll be more amenable to doing the computer mechanic thing.

Lawrie's description of the boat issue brought to mind a recent issue I had with trying to use a small portable speaker system designed for use with PCs, connected to my laptop (I've had this arrangement in use for many different incidents) but this time, I used them powered through a GFCI outlet in our home. Hum/buzz city.

I still strongly suspect that there might be some evil in your power signal chain that is not ground related but from some crummy switching power supply or pulse-width-modulated signal to give certain RMS power values. I've had way too many experiences with this to ignore it without peril. Again, I refer to T-series ThinkPad laptops - built to withstand a near nuclear attack, put a terrible PWM-related buzz/hum on the supposed 5V DC in the lappy's USB.

-Scott

That would suck.

Scott reminded me of another great noise source in homes - light dimmers. They are infamous sources of noise on your AC mains.

Just another possibility.

Given the results Ryszard has had, and the descriptions he's given, I'm inclined to agree that there's something within the PC that's the real cause.

The fact that the noise is apparently 8 times the mains frequency points to some kind of filtering issue as clearly there is some kind of unintended "signal processing" going on.

A temporary ground lift on the PC with a "2 prong" adaptor is a good test. It will at least prove whether breaking the earth loop somewhere will alleviate the problem.

I'll tell you later today.

Don, I don't think there are any in the house, but there may be a CFL in the studio. I need a ladder to check. Thanks for the thought.

R.

Bear in mind that I probably know the least of everyone posting here, but...

I don't understand your comment about turning up the speakers. do you mean their amps? Personally I would at least try with levels non maxed with everything.

As far as dimmers go just switch them off. Switch off everything, everything, even your fridge in the house, all things you can switch off, except the PC, then plug in earphones to the speaker outs or whatever you have, eliminate everything except for the PC.

Try also plugging some other music gear, does that have a hum?

Just brainstorming with my only remaining brain cell..

Z[/b]

Off topic tip: I have my sub running off a spate power supply and I switch it of when I ma not in the mood to rhumba

Another idea - I used this when my studio has an issue. I used a extension lead to run some power from somewhere else, not on the same circuit, to establish if it was the mains input.

Okay, I have several new data:

1. There was no fluorescent light in my room. The closest CFL is two rooms away.
2. There are no dimmers or "choppers" in the house.
3. My DAW froze briefly yesterday. During that time the static noise disappeared. Does this point to the VPU? (I hope not, I paid $200 for that sucker.)
4. And the biggie: I put in a 3/2-prong adapter, and Lo! both the hum and static have become barely audible. As in, I have to put my ear up to the drivers to hear it. The noise coming from the liquid-cooled PC is louder. The hum and static are barely audible from my normal listening position.

Onward.

1. & 2. - good.

3. - Probably not the CPU directly, but there may be poor onboard PSU filtering. (there are CPU power supply regulators on motherboards these days - have been for a long time) It's also possible the 5V filtering for the USB supply is not great.

4. - Excellent - now we know there is a definite correlation with an earth loop somewhere. Is there anywhere in the signal chain where an earth can be lifted that will always be part of the overall signal chain?

Perhaps you can describe where connections go from PC to speakers?

Also, given that the hum is only reduced and not completely eliminated there is still some tracing to do. That said, removing a signal earth somewhere rather than the PC's mains earth MAY do it.

Lawrie,

1. I should have spelled #3 above. I meant the video card (VPU), not CPU. IT's a Zotac 560 2-Gb card.

2. Signal goes from back panel USB port—which MAY be USB 3, I don't know how to tell—to PreSonus AudioBox (PAB) USB. Signal also comes from Behringer 16 x 2 mixer to PAB preamps. Signal comes out of the PAB to (a) Behry 4-ch. headphone amp, and (b) JBL PSW-D110 sub ins, and out of Xover to (c) Behry TRUTH B2031A active two-way monitors.

Note: It ain't the speaks. There is abso no noise when the PAB us D/Ced from USB. The mixer has also been positively ruled out as a source.

3. I have no idea how to lift ground in the signal chain. Please say more.

R.

The USB 3.0 ports on my machines all have a blue strip inside the connector. USB 2 has a white strip.

Ahh, I would have called that the GPU (Graphics Processor Unit).


OK, so the PAB is like the centre point of a star.

Grounded PC to USB I/O port on PAB, Possible double insulated mixer to audio I/P on PAB, OUTPUT of PAB to headphone, OUTPUT of PAB to SUB and thence Speaker system via X'over...


Hmm, if I am correct and the mixer is double insulated then I would open the ground wire in the audio cable between the PAB and the Sub.

If the mixer is NOT double insulated, AND the previous doesn't do the trick, then I would open the ground in the AUDIO cable(s) between the mixer and the PAB.

To open the ground:
Balanced cables - cut the shield wire at ONE END ONLY
UnBalanced cables - cut the -ve (normally shield wire, though the sheld and the -ve may be bonded together - possibly only at one end, in which case cut both) at ONE END ONLY.

As I am skilled with making cables I would just "do it" but if you're not then I would test with cables that are (old) on their way out, or which I have spares for, so as to not be too worried about the damaged/lost cables if it didn't work.

Remember, you are still testing at this stage.

Lawrie, you're absolutely right about the GPU. Minor brain fart there.

Yes, the AudioBox (PAB) is pretty much the heart of the system. Hadn't thought of it that way until you pointed it out.

I'm pretty good at making and repairing cables. I just bought some heavy-duty molded Hosa brand cables to go from the PAB to the sub and thence to the satellites (FL and FR). I'd really rather not hack into those.

Question is, how do I tell whether the mixer is double insulated? It's a Behringer Eurorack MX 2004A. The mains cord has two prongs, but goes thru an external transformer to a cord with a multipin connector into the mixer. I have no problem mucking about with the short (<1 m) audio cables with what look like Switchcraft 1/4" plugs running from the mixer to the PAB.

Final question for this session is, how risky is it to leave the PC plugged into the 3/2 adapter? I'm sure enjoying the noise-free thing here.

R.

It is more risky for the PC than for you.

Do you sometimes experience the little electric shock when you touch something after walking on a carpet? This little lightning might cause some parts in your PC to drift into the eternal sleep.

Hi Ryszard,
you've answered it yourself:
2 pin plug (from the manufacturer) = no earth = double insulated.

How risky..? How long is a piece of string?

If nothing fails there is no risk at all, but I would in no way advise you to do that.

I have, however, had a thought:

If you have, or acquire, a powered USB hub, you could connect the PC to the hub, and the hub to the PAB. With any luck the earth from the PC would be interrupted at the hub and there would still be no noise, but the PC would still have its earth connected.

Problem is I don't know if the earth would, in fact, be broken at the hub...

OK, just checked on I have and the earth is extended so power can be extended from the hub

However, you mentioned being skilled at making cables. Does that mean you'd be happy to have a hack at a cheap USB hub? If so, open it up, identify where the USB power comes in, make sure it isn't needed for the hub to be activated (external power should take care of that (I hope)) and break the tracks or whatever. Make sure you DON'T break them where power from the wall wart feeds USB devices plugged into the hub.

I do have a USB hub which is presently in use. Before performing experimental surgery on it, I'd like to revisit the idea of a power conditioner/isolator. What exactly do you recommend, and how likely is it to solve the problem? Would I need one for my entire outlet strip, or just for the PC?

Hi Ryszard,
given you've proven the problem into the earth connection, a power conditioner would do nothing as the ground would be extended through the conditioned untreated.

I would acquire a cheep USB hub to experiment on rather than use the live one...

Lawrie: I'm sorry; I confused the issue by mentioning power conditioners. I should have limited the question to an "isolator," which was brought up at some point during this multilogue. My system is somewhat finicky about USB port placement, so I'd rather explore other solutions than equipment modification.

Fair enough Ryszard, but I have nothing left to offer.

Should the unlikely happen and a fault occur in the PC that requires the safety ground to be in place, then the current carrying capacity of the USB and audio cables will be insufficient and they'll likely burn out, assuming you choose to continue with the 3 to 2 prong adapter.

Alright, Lawrie, a fair enough answer from you too. In that case, please tell me exactly where in the USB hub to interrupt the circuit. I believe I can do it if the directions are specific enough. And thank you for staying with me throughout this lengthy course.

Hi Ryszard,
hard to say without seeing the circuit...

The connection from the PC to the hub will most likely be a "B" connector - looks like a little house when seen end on.



You will need to follow the GND printed circuit track to a point where it can be broken BEFORE it joins the feed to the outputs of the hub.

One thing to be sure of is you must break the track BEFORE the feed from the wall wart too.

That's about the best I can describe without the actual hub in my hands.

I do stress, try this with cheepie hub first, it is still my best guess, not a guaranteed fix.

Ryzard, I told ya. Or actually Mac told me and I told you. Don't doubt the Macster.

Second thing just follow Mac's second piece of advice to me and make sure there are other grounded devices plugged into your power strip along with the PC. As long as that's the case and the PC is never plugged into that strip by itself you're good to go using the two prong adapter. Mac said this setup is UL approved, what more do you need?

Keep it simple and get back to work man. You already said things are nice and quiet.

Bob

Thank you, Bob. I'm still researching, but what you say is reassuring. There are several other three-prong devices plugged in.

Richard:

I am no expert in these things, but I just noticed this MF "No-Brainer." Reading the comments, it may be just what you need, and for #30, you can probably afford to take a flyer, and sell on eBay if it doesn't do anything.

http://www.musiciansfriend.com/accessories/musicians-gear-power-conditioner

Thanks, Brad. That looks quite interesting and is certainly a great value.

Richard

Except that's not solving the problem we're talking about here. Apples and oranges.

Bob

Hi Bob,
With respect to both you and Mac (who I suspect would agree with me in this instance), I still maintain that the current carrying capacity of the USB cable FROM the PC to the next device(s) is INSUFFICIENT to provide the protection that should be expected.

If the USB ground wire and latter PC board tracks were able to carry 30 or 40 Amps for a few seconds then I'd be happy with that, but that USB cable ground wire would be lucky to carry 5A for any length of time, and the PC board tracks even less I would guess (without having seen them of course).

I know people will continue to think I'm being over-conservative, but I have a very healthy respect for what electricity can do to the human body. It takes a mere 7mA (that's milli-Amps) across the heart muscle to initiate fibrillation. You can easily do that with a 9V battery if you can get it close enough to the heart! Of course, you'd need to have a hole in your chest

No, that's not what Mac said. Here is what he said:

"If you use the Grounded Surge strip and plug everything else into it along with the computer through the two prong adaptor, there will still be a path to AC Ground for the computer, it will just be going through the other stuff that's hooked up, one path instead of two.

This is legal in the US electrical code, that's why the adaptors are still UL listed, among other things."

The USB cable has nothing to do with this. Without rereading this whole thread, I believe you brought that up merely as one possibility for solving this. It's now been shown it's not necessary to worry about the USB cable, the other stuff plugged into the power strip is covering the AC ground.

Bob

Sorry Bob, but in THIS case the USB cable has EVERYTHING to do with it. It is the USB cable that is connecting to the next device (Presonus AudioBox (PAB)) AND PROVIDING THE SECOND GROUND PATH that needs to be eliminated.

IMHO a USB cable ground wire has insufficient current carrying capacity to truly provide protection.


Back panel USB port mentioned above is from the PC.

I'll freely admit I don't fully understand all of this but the bottom line was Rzyard used a two prong adapter and the noise stopped. I did the same thing and the noise stopped. My interface is a Sonic Cell with a USB connection. I have several other devices plugged into that power strip like my mixer, my 32" HD TV and a couple of other things that use a regular heavy three prong AC cable. As long as that remains the case Mac says that is fine, I'm protected so I don't see where the USB cable comes into this either with my setup or Rzyards's. There's still plenty of ground protection coming through the fully grounded 110v AC from the other devices.

Bob

Hmm, just read this in preview and I see I'm coming across as a bit testy and frustrated - I apologise if this offends anyone, but I stand by what I'm saying.


With the greatest of respect Bob, that's BULL****

Here's why:

Let me see if I can make this very simple:
The ground path for the PC (when using a 2 prong adapter) is provided via the groud connection FROM the PC to the next device in the audio chain.

Now, in this particular case, the ONLY connection to the next device (which is the PAB) is the USB connection.

This means that the ONLY ground connection is ALSO through the USB cable. Forget ALL the other devices plugged into the power strip for the moment because the ONLY connection for the PC's ground is via the USB cable to the PAB and only then to the next devices that finally have a ground connection (the PAB and the mixer connected to it are double insulated - they have NO ground connection to the power strip anyway).

Therefore the ground connection can ONLY be coming from:
(a) Behry 4-ch. headphone amp,
(b) JBL PSW-D110 sub ins, and out of Xover to,
or
(c) Behry TRUTH B2031A active two-way monitors.

Provided THEY are all in the same power strip and not double insulated. BUT, remember, the ground FROM the PC is via that USB cable and IMHO it CANNOT carry sufficient current.

Bluntly, if anyone reading this cannot follow the circuit paths I'm describing without a drawing, then you have too little understanding of electrical paths to have an opinion.

Now, a caveat: IF, and ONLY IF, the ground connection from the PC was via actual AUDIO cables with reasonable current capacity grounds I would totally and absolutely agree with Mac, BUT THIS IS NOT THE CASE HERE!

Decided a quick and dirty schematic wouldn't hurt:



A = Active
N = Neutral
E = Earth or Ground

The USB cable has 4 wires:
Data +
Data -
+5V
0V, which is connected to the motherboard ground plane which is connected to the PSU 0V which is connected to the EARTH via the case and the PSU.

I know the PAB and the Behringer mixer do not have an earth, I suspect the headphone amp (labelled HP) does not have an earth. These are OK as they are double insulated.

I know the PC does not have an earth when the 3 to 2 prong adaptor is used. This is the potential problem.

I don't know which of the other devices have earths, at least one of them must or there wouldn't be an earth loop problem in the first place. Those that do not are probably double insulated and therefore OK. (assuming they do not also have 3 to 2 prong adaptors.

If you follow the schematic you can easily see the ONLY earth connection for the PC is the USB cable if the 3 to 2 prong adaptor is used. This is unsafe. The USB cable will NOT have sufficient current carrying capacity in the event of a power to case type failure in the PC.

IMHO the best place to break the earth loop is in the USB connectivity, although the audio cable from the PAB to the Sub would also be a good spot PROVIDED NO OTHER OUTPUT DEVICES THAT HAVE GROUNDS GET CONNECTED.

Ryszard,

As an experiment, get a long heavy duty extension cord and use it to plug your monitors into a wall receptacle that is completely isolated from the rest of any circuits from the circuit breaker box to your other equipment. A "dedicated" circuit. Know what breaker controls that circuit and make sure everything else in the circuit is off: Ceiling lights, table lamps, phones, anything etc. If it works then at least you'll know where to start.

If you have part of your monitor system plugged into one circuit and the others to a different circuit that cold be an issue as well. Worth a shot. Helped me a few times.

Dan