Contaminated AC line - Buzzing/RFI in my monitors

[RMcFarland]

I am seriously pulling my hair out. My monitors are buzzing like crazy! It is driving me up a wall!

I tried a fancy power conditioner - this had zero improvement. I tried different cables - nothing. I replaced the light dimmer with a standard switch - zilch. I don't know what to do...

Any ideas?

I should also add that the noise is present whether the input cables are plugged in or not. I also show that the outlet is properly grounded.

[AmplitudeAudio]

Do you have an LCD monitor for your computer? (if you even have a computer) I had a monitor power supply that caused a similar problem. I accidentally discovered it was the culprit when I turned off the monitor with the rest of the studio still on, the hum went away, turn the monitor back on, the hum was back. I was able to find a different power supply which corrected the problem. You may also want to try unplugging anything in your studio that uses a wall-wart type power supply.

Good luck,
Charlie

[RMcFarland]

I tried all of that. It happens if I just plug powered monitor into the wall with no other connections.

[AmplitudeAudio]

It could be a bad cap in the power supply, does it do it both monitors or just this one?

[RMcFarland]

both speakers

[Kiwiburger]

Maybe it's your monitors self noise (ripple) - are they quieter anywhere else? (Not just in a noisey shop?). Basically, the PSU in an amp has to turn AC into DC - and a cheap or faulty PSU can have "ripple" in the DC, which moves your speakers.

It could also be ground noise, being amplified. Do you have any measurable voltage between neutral and earth? If so, some amps (not all) end up with ground loop hum. I guess this depends on whether their circuits provide a return path between neutral and earth, allowing current to flow. I've noticed that often this doesn't become an issue until both input cables are connected - but your amp may reference both earth and neutral internally, causing this hum if you have a potential difference to start with.

An isolation transformer, floating on the primary, with a new groundspike connected to neutral on the primary side should give you a perfect earth with 0V difference. Check the legality.

Or - a battery & inverter, for true recycled isolation, with a new ground spike.

[tINY]

First thing I'd do is take them to your friends' houses and plug them in. Make sure that the problem is different when you change venues.

If not, then the monitors are at fault.





-tINY

[RMcFarland]

Do you mean an isolation transformer like this?

Tripp Lite | Isolation Transformers | IS250HG

[-Noodles-]

It may infact be a problem with the transformer.. I had a similar problem with mine, and it could've been a capacitor problem.

Phone the company that makes them?

[Omega Arts]

balanced power supply. wouldn't set up a room without it.

[RMcFarland]

What exactly is a balanced power supply? How does it help with the buzzzzzz?

[Omega Arts]

Balanced power eliminates the cold side and splits 120 into 2X60 with an earth ground. No way for a ground loop. It has also lowered the general noise floor of my room.

here FurmanSound.com - Pro A/V Product - IT-20 II

here FAQ's About Balanced Power

Larry

[Kiwiburger]

250W is probably too small for an isolation transformer - probably wouldn't run a decent PC. What are you running? I have a 5KVA one, but that's probably overkill.

Get an electrician - but find one who understands audio. A hifi shop *might* be able to recommend one, but I wouldn't hold my breath. They are few and far between.

All good electricians at least understand safety, and legal issues. That's a good start. But often the problem for audio isn't a safety or legal issue. Millivolts of AC can be a royal pain in the ass, but nothing unsafe or illegal.

Grounding is absolutely essential - be prepared to put in a dedicated ground spike. A very long stainless steel rod, hammered into moist soil which is kept moist, is a good start. Simply adding this to an existing earth system might make the problem worse - you can end up having the best ground in the neighborhood, and attract a lot more crap your way. I've seen this in action.

Balanced power is two phase power, with each phase 180 degrees apart. (This is very different from simply taking 2 of the available 3 phases, which are 120 degrees). This is achieved with a centre tapped isolation transformer, and the centre tap becomes your new earth. You would attach your ground spike to this new technical earth. In my experience, and in the opinion of others who I respect, most of the benfits of balanced power come from the simple benefits of an isolation transformer, and a new clean earth system.

In theory, any noise that enters a 2 phase balanced power line is cancelled out, just like balanced audio cables. Things like fluorescents and switching PSU and digital stuff dump a lot of crap into the AC, and in theory 2 phase power means this stuff nulls to zero.

But even balanced power and a perfect ground won't remove hum that is the result of power or faulty power supplies. AC is AC - no matter how clean it is.

[dbbubba]

Make sure that something isn't wrong with your AC.
Plug them in w/o anything connected at an AC source that you trust.
If the hum isn't there on a "good" AC system then the problem is with your AC.

There are only three wire and basically only two circuits at a standard edison AC outlet.
The 120V HOT, the NEUTRAL and the ground which is a SAFETY NEUTRAL.
Both the NEUTRAL and GROUND are at the same potential which is EARTH.
They are tied together at some point.

It probably IS NOT your AC causing this problem.

If the hum remains then there is something amiss with the power supply in your monitors. Bad cap(s) can cause this, but a transformer really won't.
A transformer either works or doesn't, but they can physically buzz because of loose windings. This is rare, but I had to switch one out in a Kurzweill K2000R.

As far as a balanced AC system room goes...
I have been in multi-million dollar facilities and too many other studios to count.
I have been "intimate" with some HUGE live sound rigs as well.
I have never seen anyone use balanced power.

I have heard people talk about it, but in my thirty-two years plus of pro audio, I have never seen it used.

It isn't neccesary if you have a standard AC system wired correctly.

I have seen countless people say that they had "bad power" and that it was causing their troubles.
I have never encountered "bad power" that I couldn't fix with proper AC practices.

[Kiwiburger]

Both the NEUTRAL and GROUND are at the same potential which is EARTH.
They are tied together at some point.

In an ideal world.

Earth & Ground mean the same - but not all electrical or technical earths are at the same potential with reference to actual earth (a spike in the ground).

In a less than ideal world, you can get small voltage drop between Neutral and Ground - which may be safe and legal, but some gear will hum.

Your audio shields are connected to ground. Or neutral, if your gear doesn't have a ground (plenty of 2 pin wallwarts there days). In theory, they should be the same. But what if they aren't?

If there is a potential difference between Neutral & Earth/Ground AND there is a physical connection - current will flow. Your audio shields are no longer shielding your cables - they are radiating EMI into them.

In some cases an Ebtech Hum Eliminator might be a solution. A lot of modern "balanced" gear isn't really offering proper balanced Common Mode Rejection - which is a bit of a rip off.