The All Purpose Advice Thread - Part 2

Discussion in 'Advice Threads' started by shotgunshane, Mar 27, 2022.

  1. atomicbob

    atomicbob dScope Yoda

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    Several things to investigate:

    1) does the space heater have variable heat levels?
    If so, it may be using an SCR (think dimmer switch) which are notoriously prone to EMI / RFI emissions as well as conducted through the power

    2) does the space heater have variable speeds for the fan?
    Possibly SCR controlled, see 1 above.

    3) is the fan motor brushed DC rather than a brushless AC?
    DC motors also are notorious for EMI / RFI emissions and conducted noise
     
  2. rhythmdevils

    rhythmdevils MOT: rhythmdevils audio

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    Yes to the first 2, I don't know about the 3rd.

    This is the heater I'm using. Their website is super scammy looking but the heater is legit, I can't not use it now that I've had it. I have a lot of body temperature regulation issues from ME/CFS and with this heater, I can control the temperature in my bed and the temperature in the room separately. it also heats my feet the most, which get very cold, while not heating my head, which I need to keep cold or I feel worse.

    https://bedjet.com/

    One thing I'm considering is if this unit is defective. But that's hard to test.

    But there must be a product on the market designed to stop appliances like this from injecting noise/DC into your mains right?
     
  3. atomicbob

    atomicbob dScope Yoda

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    If the control system uses any kind of switching method, such as Pulse Width Modulation (PWM) and SCRs or other semiconductor devices to control the heat and fan speed, then the EMI / RFI will be considerable.

    In EMI / RFI screen rooms and high end studios such types of systems are not allowed. Lighting dimmers must be variac controlled rather the the cheap dimmer switches, for example. Motor control likewise must utilize non-switching methods to control the fan speed.

    One of the big advantages of balanced star quad cables is to reduce noise in microphone cables when they need to run near megawatt lighting dimmer packs in the stage cable raceways or catwalks. There is no easy way to keep the dimmer packs from emitting EMI / RFI.

    to prove the susceptibility to EMI / RFI I typically use something similar to:
    https://www.amazon.com/DEWENWILS-Dimmable-Incandescent-Halogen-Extension/dp/B08DCQ2166?th=1
    When designing our systems for medical devices I used this to demonstrate if the system had been designed with sufficient shielding robustness to endure such egregious sources of EMI / RFI.
     
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  4. rhythmdevils

    rhythmdevils MOT: rhythmdevils audio

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    I have some copper mesh cloth I can cover my ZDS with to rule out EMF/RMI very easily. it's designed to block it. Or I could try covering the heater with it. Because the vent comes out of a tube, so the unit could easily be covered in the mesh cloth. Unless I'm misunderstanding you.

    If the BedJet is injecting DC into the mains, do you think the Emotive CMX-2 is robust enough to have a heater plugged into it'? I have one here and could plug the BedJet into the CMX-2 and then into the balanced isolation power transformer.

    From memory, the BedJet pulls 1500 Watts. which is why I got the 2000W balanced isolation transformer. And I know that transformer is not defective, because I tried plugging the BedJet into my Equi=Core and it made the same noise and didn't fix the issue.

    Interestingly, this wasn't an issue when I first setup the ZDS 2 weeks ago. But the BedJet got unplugged from the extension cord that runs it into the hallway and when I plugged it back in, I heard the buzz, which I've heard before but thought this ZDS was immune to it.

    The DNA Starlett, Stratus and Stellaris are all immune to whatever the heater is putting into the system. @Donald North knows how to make quiet amps!
     
  5. zottel

    zottel Friend

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    Might be making a fool out of myself as I’m talking out of total ignorance, but the PA guys in a youth choir I sang in three decades ago used to solve mains hum problems by turning around the mains plugs of various gear so that the phase was on the other prong.

    But I guess that isn’t easily possible, anyway, with American three-pronged plugs?
     
  6. dasman66

    dasman66 Self proclaimed lazy ass - friend

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    I can't speak to much of the post, but the CMX-2 I have is rated for 15amps. I assume the heater plugs into a "normal" 15 amp circuit and doesn't need a 20 amp circuit?
     
  7. crenca

    crenca Friend

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    The bedjet is 'medical grade' (Medicare will pay for it)? I can get you a list of equivalent devices that are if you need it, if you decide to move on from it. Perhaps another brand address's this issue (scr switching, EMI, etc.)
     
  8. atomicbob

    atomicbob dScope Yoda

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    This is likely a radiated RFI problem rather than a conducted EMI issue. Depending on the frequency of the RFI shielding could range from challenging to very difficult. It usually isn't sufficient to drape copper mesh over the susceptible device. It often must completely envelope the receiver without gaps and the mesh must be grounded. Here are some visualizations from two resources for further information listed below:

    emi-rfi-shielding.jpg
    https://www.iqsdirectory.com/articles/emi-shielding.html

    EMI-RFI-diagram.jpg
    https://www.kebamerica.com/blog/electromagnetic-interference-vfds/

    Both resources have additional information and graphics which should prove useful.
     
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  9. bixby

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    Agree with @atomicbob , copper mesh will be ineffective if the buzz is comprised mainly of lower frequencies. For that you need a thick metal case. Maybe you can try a stainless steel stock pot placed over the suspect noise receiving component?
     
  10. fraggler

    fraggler A Happy & Busy Life

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    Any recommendations for power strip with surge/filtering for under $75? The old Isobar I was using lost at least one protected outlet (not sure when since everything still worked I think) to a surge at some point (MOV popped). Since it is ancient and the prices have doubled since I got it, I was looking for a decent replacement. I'd like at least 4 outlets. I have an Emotiva CX-2, which would be fine for my main components, but I'd like to plug a few other things in for comparisons and convenience.
     
  11. dBel84

    dBel84 Friend

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    @fraggler have you considered just replacing the surge / filter elements. This would be an easy thing for you and cost less than replacing the unit. Happy to discuss the "how", just ping me
     
  12. dasman66

    dasman66 Self proclaimed lazy ass - friend

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    FWIW, I would consider any MOV based protection to have lost effectiveness after about 5 yrs. Faster if you have bad power like we have in our area. I went with zerosurge products about 5 yrs ago... expensive, but they never need replaced and provide peace of mind.

    Or replace the movs on a regular basis...
     
    Last edited: Feb 19, 2024
  13. artur9

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    Running into the same question I decided to try out the Black Lion PG-P new from ebay for $69.

    Haven't gotten them yet. I liked the filtering, the wide socket placement. Don't like the attached cord.
     
  14. fraggler

    fraggler A Happy & Busy Life

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    I normally would go straight to doing the repair myself, but we just finished a renovation and are rearranging the house, so no time or energy for it at the moment. I will likely buy a replacement device so I can use my system sooner, but will absolutely reach out to get this back in service.
     
  15. rhythmdevils

    rhythmdevils MOT: rhythmdevils audio

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    I think the ZeroSurge devices are worth the investment. Also so you don't have MOV's in your audio chain which people have expressed concern about. And then you never have to replace them again. And they have isolated duplexes if you get the right model, which is a good thing for cheaper stuff that have smps.
     
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  16. artur9

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    The ZeroSurge are the ones that come under a variety of product names? Like BrickWall?

    I had one that tripped a GFCI breaker constantly; an electrician said not to use it. I didn't use it there since it didn't work but I did use it other places because I didn't trust him.
     
  17. dasman66

    dasman66 Self proclaimed lazy ass - friend

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    The do look alot alike... would be interesting to see the internals of both. I know zerosurge holds (held) the patent on the tech, so any similar products could be licensed as well. At this point, I have (3) 8 outlet isolated units and (2) 2 outlet units with zero problems (oldest is about 5 yrs old). Anecdotal, but that's all I can offer at this point.

    Was looking at picking up another unit recently and left it in my cart for the time being... probably next month.
     
  18. Ardacer

    Ardacer Friend

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    So a friend of mine decided to become a pilot as a hobby. He's buying gear now, and apparently bose a30 is one of the best headsets for cockpits. It costs an arm and a leg. Something like senn 260(pro) or beyer dt770m have passive noise isolation from 32-35 dB, and costs less than 1/10th of the price. A30 does have ANC, which might add like 20-25 db over whatever the isolation is (no info anywhere). He'd need a mic too, but that's probably easier to settle. Anyone has any idea of a robust, comfy, noise isolating headset or headphone with ANC? I'm guessing the problem is that most anc heasets are wireless (wire is probably necessary), there's no (easy) way to convert a non anc heaphone to one with anc, and possibly the mic has to digest 90+db all the time. Any ideas? A30 is like 1400 eur/usd, that's really quite high. Other headsets are also 1k+. (there are some in 200-300 range, but "the guys" told him these suck, probably no anc)
     
  19. yotacowboy

    yotacowboy McRibs Kind of Guy

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    Do not buy cheap airplane parts. They're harder to return after you've bought the farm.

    (just an observation from someone with 3 family members in, or retired from, the industry).
     
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  20. Velomane

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