Build humbugging transformer

Ground loop elimination in video systems does not always ask for a complete isolation of the grounds. There are passive hum suppressor transformers that will very effectively remove the hum from the video signal, but do not affect the video signal otherwise. Those special transformers act like a common mode coils, which stop the annoying ground loop currents on the shield of the coaxial cable, but provide a straight path for the signal inside the cable. This type of device is capable of passing the signals from DC to tens of MHz without problems. The hum suppressor transformer both reduces the current flowing on the cable shield and compensated the voltage differences that would otherwise be between cable ends and eventually get to the signal.

The humbugging transformer/coil consists just of many (tens to hundreds) turns of 75-ohm miniature video coaxial cable wind on a suitable transformer core. The aim is to have a coil that has high enough inductance to keep the cable shield current low and still withstand the voltages/currents it gets exposed to in typical applications without saturation. This kind of hum reduction coil works by mutual inductance. The coax cable is wound around a transformer core so that both the inner and shield of the cable become inductors. The tight coupling ensures that any voltages/currents flowing on the cable shield, caused by variations in earth potential differences, are transformed into the inner conductor. This type of transformer is typically constructed to a specially selected toroid transformer core.

This type of hum suppression transformer has found it’s way to the professional video application (rental companies) and computer video applications (computer to video projector connections). The transformers of this type are usually called “hum bug transformers”, “hum-bucking transformers”, “anti-hum video transformers”, “hum suppressor transformers” or “video isolation chokes”. T The humbugging transformer presents a simple transmission line to the signal, so that its signal amplitude capability is essentially unlimited, and its bandwidth extends from DC to that frequency where line losses become excessive. Isolation increases with increasing noise frequency. The choke provides protection against moderate levels of 60 Hz hum, and protection against very high levels of RF noise. ypical performance figures are 30-40 dB hum level reduction up to 2-10V volt voltage differences at mains voltage frequency (50 Hz or 60 Hz). The maximum voltage the humbugging transformer can handle at low frequencies depends on the transformer specifications, usually limited by transformer core saturation. The humbugging transformer choke is primarily used in Broadcast TV because it passes the DC component of the signal. It is used in studio, and in remote ENG.

Humbugging transformer

This picture shows the inside a commercially sold “video hum bug transformer” sold by Finnish company RGB. The price range of this kind of commercial device is usually 100-200 US dollars range. I had to open this unit to change the BNC connector that was broken on a field use. This device consists of a toroid shape transformer core and around 50 turns of very thin 75-ohm video coaxial cable wrapped around it. You can make your own working similar device by taking he core from a 100-400W toroidal mains power transformer and winding 30-50 turns of thin 75-ohm coaxial cable around it. This will work well but is somewhat larger and heavier than the commercial devices like this. It is possible to optimize the size with careful selection of suitable core material and number of turns.

Here is an inside views of some humbugging video transformer products that I have made. They have performed very well on many video systems to solve ground loop problems.

humstop1

humstop5

71 Comments

  1. Casey Swarat says:

    You may need to really control the remarks on this page

    Reply
  2. Shawn says:

    Great content and thanks for sharing we have share via facebook and twitter.

    Once again thanks

    Reply
  3. Styrofoam cutting says:

    Fascinating column , I am going to spend more time reading about this subject

    Reply
  4. Gary Mandonado says:

    One additional method for promoting your blog is posting comments on unique sites with your weblog link.

    Reply
  5. tours to israel says:

    Hi there! This post couldn’t be written much better! Reading through this post reminds me of my previous roommate! He constantly kept preaching about this. I most certainly will send this post to him. Fairly certain he will have a good read. Thanks for sharing!

    Reply
  6. Georgetta says:

    I do not even know the way I stopped up here, however I believed this put up was good.
    I don’t understand who you’re however definitely you’re going to a famous blogger when you are not already. Cheers!

    Reply
  7. kayan yazı says:

    ARZ LED olarak sizlere ithalat’dan KAYAN YAZI ,LED, Led Ekran, Led Kayan Yazı, Grafik Ekran, SMD, Mobil Led Ekranlar sunuyoruz

    Reply
  8. Video over UTP « Tomi Engdahl’s ePanorama blog says:

    [...] applications you can see some details of possible construction for video current mode balun at my Build humbugging transformer, although for this application the design could be optimized (can be built using much smaller [...]

    Reply
  9. raspberry ketones drops says:

    First-class addition! Yet I’m more interested in the grand theme you’re using, mind sharing it’s name?

    Reply
  10. Ulysses Yacoub says:

    I precisely wanted to thank you very much once again. I am not sure what I would have made to happen in the absence of these recommendations revealed by you directly on that industry. Entirely was a horrifying situation in my position, however , taking note of a new expert technique you processed it forced me to leap over contentment. Now i am happy for your assistance and thus believe you know what a powerful job you are getting into instructing people today by way of a web site. I’m certain you haven’t met any of us.

    Reply
  11. June says:

    hi my name is June. I dont know any electronic knowledge. but i wanna learn this transformer. if u can teach me step by step. for example 1. 75om cable 2. …. core material.. ….. i dont know to try first. pls help me. thank u

    Reply
  12. mejor ordenador portatil says:

    Excellent post! We are linking to this great article on our site.
    Keep up the good writing.

    Reply
  13. Tomi Engdahl says:

    Home> Analog Design Center > Design Idea
    Actively driven ferrite core inductively cancels common-mode voltage
    http://www.edn.com/design/analog/4327929/Actively-driven-ferrite-core-inductively-cancels-common-mode-voltage?_mc=NL_EDN_EDT_EDN_designideas_20160216&cid=NL_EDN_EDT_EDN_designideas_20160216&elqTrackId=2f863376557c41c1adf36f5681b0c0bb&elq=1778c7b52b0f4ad695d86c4926d68aa6&elqaid=30825&elqat=1&elqCampaignId=26966

    An earlier Design Idea illustrated one approach to that traditional headache for the analog designer: the dreaded ground loop (Reference 1). That Design Idea described a simple and efficient multichannel circuit. But it’s an asymmetrical CMV (common-mode-voltage) approach in that it works only at the receiving end of a cable. It therefore applies only to signal inputs and does nothing for outputs. However, in cases in which CMV consists of purely ac noise, a different CMV-remediation method—active inductive cancellation—works bidirectionally and therefore cancels CMV-error components in both input and output signals.

    Engineers have for many years used passive-CMV inductive cancellation (Figure 1). Sometimes called a “humbucker transformer” because the power mains’ 60-Hz “hum” is often a dominant CMV component

    However, the Achilles’ heel of the CMV transformer is the fact that the decibels of cancellation fall off at the low-frequency end of the noise spectrum.

    In Figure 3, the power amplifier comprising the LT1797 high-frequency op amp and MOSFET forces the driven core to precisely cancel CMV as sensed in the ground-reference connection. The result is such a large multiplication of the apparent winding inductance that you can reduce the “windings” to a simple single pass-through of the toroid core. In other words, you need to thread a multiconductor-signal cable only once through the “hole in the doughnut” to achieve CMV of 40-dB or more cancellation, extending from tens to millions of hertz.

    http://m.eet.com/media/1134309/14350-figure_3.pdf

    Reply
  14. Melodee says:

    Definitely believe that which you stated. Your favorite justification appeared to
    be on the internet the simplest thing to be aware of. I say to you,
    I definitely get annoyed while people consider worries that they just
    do not know about. You managed to hit the nail upon the top and also defined out the whole
    thing without having side-effects , people can take a signal.
    Will probably be back to get more. Thanks

    Reply
  15. Jani says:

    According to an analysis launched by a coalition of California tribes, a legal and licensed intrastate
    online poker market might generate $845 million for state government and greater
    than 2,600 new jobs inside five years.

    Reply
  16. tomi says:

    Thank you for your feedback.

    Reply

Leave a Comment

Your email address will not be published. Required fields are marked *

*

*