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Mains noise in studio monitors

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#1
I have just moved to a new apartment and I'm getting electrical noise feeding back into my powered monitors (Adam A7X). This is high frequency noise bleeding in from some noisy dimmable lights, making the tweeters buzz. All the audio equipment is connected through a Furman PST-8D, but this doesn't seem to mitigate the noise at all. The connection from DAC->Monitors is balanced (and quite a short run), so I'm confident it's not line noise picked over the cable.

Additionally, and tangentially related, I have a small m-audio monitor connected in another room, and this was making a popping sound when the master bathroom fan was turned off (I am well aware that electric motors can act as a large inductor and feed current back into the mains when the field collapses after power off). Oddly, there was a monster power conditioner (HTFS500) already installed in the apartment on that socket, and it does much better at reducing/eliminating this issue (compared to the Furman).

I was wondering if something like a tripplite isobar would be effective at isolating the monitors from this sort of nose on the mains. If not, is there something that may be effective? I was surprised that the Monster unit outperformed the Furman, and now I'm wondering what my best options would be.

As a side note, the monster units are now discontinued, so trying another one of those is out of the question (the current unit is run in wall so I can't move it to test on the Adams).

Thanks for the help!
 

RayDunzl

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#2
Maybe it's not just you.

Except for some hiss, my little JBLs are quiet. So is the rest of the system.
 
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#3
Maybe it's not just you.

Except for some hiss, my little JBLs are quiet. So is the rest of the system.
I'm used to powered monitors having some noise, but this is directly correlated to having a specific set of lights on/off. The lights make the same sound, just louder, and then that seems to come through the tweeters. Since the noise from the lights is louder than the noise from the tweeters it's not a huge practical issue, but it's a bit irritating knowing it's happening. (The noise isn't identical, but seems to be modulated at the same rate, just higher pitch like a harmonic).
 

DonH56

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#4
It may be RFI straight into the speakers... Can you replace the dimmer (or get rid of it and use a regular switch instead?)
 
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#5
It may be RFI straight into the speakers... Can you replace the dimmer (or get rid of it and use a regular switch instead?)
I can't remove the lights (I'm a renter) but I'm going to add a lamp and stop using them. They are far noisier (audibly, not electrically) than the speakers. I can also test on a UPS to see if the noise is induced through the mains or RF, as running off a battery would remove the variable. I suspect the ballast is dumping current back into the mains at some harmonic of it's a switching frequency.

More concerning was the motor popping my other speakers, but the Monster Power unit actually seems to have mitigated it, which is a huge surprise to me from Monster of all companies.

I suppose it's a bit academic, as the lights themselves aren't really tolerable.
 

andreasmaaan

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#6
Coming at this with no knowledge of the electrical reasons why the light/dimmer is doing this, I have had the experience in a previous house of light bulbs run through a dimmer making a similar noise, which disappeared when I replaced the energy-saving (I think) LED bulbs with standard incandescent ones.

Perhaps someone who understands these things can tell me if I was imagining it (was a long time ago)....
 

DonH56

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Coming at this with no knowledge of the electrical reasons why the light/dimmer is doing this, I have had the experience in a previous house of light bulbs run through a dimmer making a similar noise, which disappeared when I replaced the energy-saving (I think) LED bulbs with standard incandescent ones.

Perhaps someone who understands these things can tell me if I was imagining it (was a long time ago)....
There are a few things I have found with dimmers and LEDs after swapping most of the standard and CFLs in the house with LEDs:
  1. LED quality varies fairly wildly. Some buzz, some flicker, some cause every AM radio in the house to buzz unbearably, and some just work. The "big boys" seem to be more consistent (Phillips etc.) Note they include a little switching supply inside and it can be a noise generator just like the dimmer itself.
  2. Not all LEDs are rated to be used on dimmers, and even those that are seem to have a smaller range of brightness than standard LEDs. And in one case I have to turn the light level up to nearly full before the LEDs cut on, then can dim normally. No idea if it is the LEDs or the dimmer at fault.
  3. LEDs are a light (no pun intended) load and several of our household dimmers would flicker sporadically (and annoyingly, especially the one in the family room where my wife lives). Replacing one LED with an incandescent bulb solved that problem. I have no idea if newer dimmers might tolerate the low-power load better but my boss has a new house and had to do the same thing (he actually gave me the idea).
FWIWFM - Don
 

DonH56

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I can't remove the lights (I'm a renter) but I'm going to add a lamp and stop using them. They are far noisier (audibly, not electrically) than the speakers. I can also test on a UPS to see if the noise is induced through the mains or RF, as running off a battery would remove the variable. I suspect the ballast is dumping current back into the mains at some harmonic of it's a switching frequency.

More concerning was the motor popping my other speakers, but the Monster Power unit actually seems to have mitigated it, which is a huge surprise to me from Monster of all companies.

I suppose it's a bit academic, as the lights themselves aren't really tolerable.
Not much you can do about the motor -- the usual fix is a capacitor across it but that's not a DIY fix unless you have a technical background and are willing and able to disassemble (and hopefully re-assemble ;) ) the fan.
 

RayDunzl

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#9
Move a portable AM radio around near your suspected noisemaker and see what it outputs.

Extra Credit: use it to check out your PC, laptop, DAC, TV, etc.
 
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#10
Not much you can do about the motor -- the usual fix is a capacitor across it but that's not a DIY fix unless you have a technical background and are willing and able to disassemble (and hopefully re-assemble ;) ) the fan.
It seemed like something to be addressed at the motor side of things of things. I'm a fan of the YouTuber AvE, and he discusses this very solution in a number of his videos. Unfortunately, I'm not qualified to work with mains power, and it's a rental property, so DIY is out. I was very thankful the Monster unit was that effective.
 
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#11
Move a portable AM radio around near your suspected noisemaker and see what it outputs.

Extra Credit: use it to check out your PC, laptop, DAC, TV, etc.
I'll be damned, you're right! I didn't have a radio on hand (still unpacking, also not sure I own one). Instead, I hooked up to an unplugged ups (running on battery only), and when I powered on the monitor, the noise had changed frequency, but seemed to have the same amplitude and modulation. Thank you so much, I love to learn new things, and this wasn't something I had considered! Its always fascinating to me how everything we connect together forms a radio and analog circuit, even if its a bunch of digital components. One less thing to nag at me :)
 

jsrtheta

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#12
There are a few things I have found with dimmers and LEDs after swapping most of the standard and CFLs in the house with LEDs:
  1. LED quality varies fairly wildly. Some buzz, some flicker, some cause every AM radio in the house to buzz unbearably, and some just work. The "big boys" seem to be more consistent (Phillips etc.) Note they include a little switching supply inside and it can be a noise generator just like the dimmer itself.
  2. Not all LEDs are rated to be used on dimmers, and even those that are seem to have a smaller range of brightness than standard LEDs. And in one case I have to turn the light level up to nearly full before the LEDs cut on, then can dim normally. No idea if it is the LEDs or the dimmer at fault.
  3. LEDs are a light (no pun intended) load and several of our household dimmers would flicker sporadically (and annoyingly, especially the one in the family room where my wife lives). Replacing one LED with an incandescent bulb solved that problem. I have no idea if newer dimmers might tolerate the low-power load better but my boss has a new house and had to do the same thing (he actually gave me the idea).
FWIWFM - Don
It seems to my ignorant self that the problem here is the dimmers. I have LEDs throughout the house, and no dimmers. Hence, no problem.
 

DonH56

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#13
It seems to my ignorant self that the problem here is the dimmers. I have LEDs throughout the house, and no dimmers. Hence, no problem.
Alas, that is not true in my case. We have some LED lights that cause every AM radio in the house to buzz loudly and they are not on dimmers. I am slowly working on swapping them out.
 
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#15
Dimming LED lamps isn’t as straightforward as it is made out to be, it’s still a technology that is still in its infancy and is improving all the time. There can be annoying compatibility issues, as highlighted in the above posts, most of these will be down to the dimmer rather than the lamps.

Most dimmers have a minimum and maximum rated wattage, changing to LED lamps can reduce the load to below the minimum rated wattage which can cause the flickering/strobing effect. Hence why replacing just just one LED lamp with a halogen lamp can rectify this.

Manufacturers also recommend down rating the stated maximum wattage by anywhere between 10-25% of its maximum rated wattage. So a 400W dimmer might only be suitable to dim 40W’s of LED lamps.

There are modern dimmers designed for LED lamps which are “programmable”. If they don’t cure the strobing they can be set to have minimum and maximum dimming level just before the strobing starts.

Throw in all the other issues slowly being addressed with LED lamps (lumen levels, beam angle, colour temperature, colour rendering index, 2 way switching problems) and you potentially have a real headache!
 

maty

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#16
You have RFI/EMI interferences at mains and in the air.

At mains, with the Furman PST-8D should be OK. But air?

The studio monitors are not RFI/EMI shielded. MDF, composite... and electronics are not inside metal box.
 
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#17
Yeah, dimmers have always ranged in quality. Even as a child, pre led and cfl, dimmers would frequently buzz or humm audibly. I understand now that a light bulb is (was at the time) a resistive load, and therefore you need some form of voltage regulation that doesn't just dump a ton of power into a pot in series (immagine dissipating a large portion of a 100W into a wall switch :eek:). So PWM and other technologies must be used, and any oscillator is a radio emmiter, so it all "makes sense."

Add in the various new bulb technologies and you have a really complex and challenging environment for sensitive equipment like amplifiers.
 

AnalogSteph

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#18
LED quality varies fairly wildly. Some buzz, some flicker, some cause every AM radio in the house to buzz unbearably, and some just work. The "big boys" seem to be more consistent (Phillips etc.) Note they include a little switching supply inside and it can be a noise generator just like the dimmer itself.
Usually the quiet ones tend to use conventional capacitor dropper supplies (a lightbulb base just doesn't provide enough space for a well-filtered SMPS); flickering is a result of no or inadequate smoothing capacitance, and the phosphors are another factor - ones with long decay time con cover up quite a bit of flickering since their contribution dominates our perception.
 

DonH56

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Usually the quiet ones tend to use conventional capacitor dropper supplies (a lightbulb base just doesn't provide enough space for a well-filtered SMPS); flickering is a result of no or inadequate smoothing capacitance, and the phosphors are another factor - ones with long decay time con cover up quite a bit of flickering since their contribution dominates our perception.
That is interesting, have to look into that, thanks. Most of the EE trade articles I have read show SMPS but also talk about the huge problems with heat dissipation. I suspect the articles were mostly about some vendor's new LED supply chip so I did not read about the more mundane (and quieter) solutions. This is nowhere close to anything I work with, just catch an article now and then. And a lot of buzzing in the house since I upgraded everything last year... The worst offenders are the ones with clear bulbs used in our bathrooms for the lights over the vanities.

Then there is the box of indoor floods I bought to provide brighter "daylight" for the kitchen. Was supposed to better show food colors and all that jazz. Wife hated them, so went back to the warmer temp lights, saving the bright ones for another project that I've never gotten around to...
 
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#20
That is interesting, have to look into that, thanks. Most of the EE trade articles I have read show SMPS but also talk about the huge problems with heat dissipation. I suspect the articles were mostly about some vendor's new LED supply chip so I did not read about the more mundane (and quieter) solutions. This is nowhere close to anything I work with, just catch an article now and then. And a lot of buzzing in the house since I upgraded everything last year... The worst offenders are the ones with clear bulbs used in our bathrooms for the lights over the vanities.

Then there is the box of indoor floods I bought to provide brighter "daylight" for the kitchen. Was supposed to better show food colors and all that jazz. Wife hated them, so went back to the warmer temp lights, saving the bright ones for another project that I've never gotten around to...
Check out some of BigClive's LED bulb teardowns on YouTube, lots of capacitive droppers in use. Along with heat dissipation, they have horrible power factors (.5 or below frequently), which is exactly what you'd expect I guess.
 

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