Ground loop freesat

Discussion in 'Satellite TV, Sky TV & FreeSat' started by AlexSA, Dec 11, 2018.

  1. AlexSA

    AlexSA
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    Hi

    I have a ground loop issue.

    I'm plugged in like this

    Free sat communial coax (wall) -> Panasonic Plasma TV.
    Then audio from TV does to Arcam Alpha 2 amplifier via screened RCA leads.

    Note the freesat tuner is actually built into the TV.

    There is low hum in the Arcam speakers unless I disconnect the freesat cable at the wall or wherever.

    Any ideas on how to resolve this? I tried this isolator but retrospectively I don't think it works for satalite systems, it completely cut out all signal anyway:
    https://www.amazon.co.uk/dp/B07CNQSYJJ/ref=cm_sw_r_cp_apa_i_lg8dCb36VV6M2

    Many thanks!
     
  2. noiseboy72

    noiseboy72
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  3. AlexSA

    AlexSA
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    Thanks. I'll check that out!

    But is there any way of isolating the coax cable between the wall socket going to the dish and the TV itself? There is no product for this?

    Communial Sat point -> isolator -> TV.

    Thanks.
     
  4. noiseboy72

    noiseboy72
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    Not that I am aware of. The need to pass a voltage back to the LNB - plus the high frequencies involved make conventional isolating techniques quite tricky.
     
  5. pedro2000uk

    pedro2000uk
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    I'd definitely recommend putting a test meter between the Panasonic and satellite wall socket just to check 'what' voltage is causing the hum. I'm guessing the Panasonic has an earth? It could be the design of the Panasonic &/or the communal system or there's a fault and it's seeing it's earth bonding. If there's a fault you should track that down and get it fixed or if it's very old, think about replacing it.
     
  6. grahamlthompson

    grahamlthompson
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    The polarising voltage used to switch polarisation. itself should not be an issue as it's should be pure DC 12/18V. If not pure it suggests a power supply issue in the TV imposing a 50Hz ripple on the DC control signals (often down to blown capacitors used to smooth the DC output). a oscilloscope would be be needed to check this. . It would normally be relatively simple to remove the ac component except for the 1kHz tone required for band switching.

    Communal installs should have one grounding point for safety reasons (as a single dish can/will be connected to locations on a different mains supply phase to the locations. . All other kit connected externally will normally double insulated so there is no potential for a ground loop at all. The single earth connection will carry no current except in circumstances where a phase to earth fault in connected location occurs. Anyone with a modern split load consumer unit will remove this fault in milliseconds. Those with outdated fused based protection will take much longer.

    I would try a different sateliite receiver instead of the one in the TV (say a old Sky-HD box).

    Old Thomson Sky boxes are known for this problem, and create issues for anything else connected to the same lnb.
     
    Last edited: Dec 11, 2018
  7. AlexSA

    AlexSA
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    Hmm I've got loads of mains leads. Maybe I should try them to see if it makes a difference. I'm using ferrites everywhere.

    I'll have to borrow a sat receiver for testing that will take a month.

    When you say use a meter, you mean just a simple volt meter?

    Thx guys.
     
  8. grahamlthompson

    grahamlthompson
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    You will not see a 50Hz ripple on a simple voltmeter. You need a oscilloscope that shows the DC output on a CRT screen. In effect you zoom in to a point where you can actually see the 50Hz ripple.

    What is oscilloscope? - Definition from WhatIs.com

    You can buy a Sky-HD box for next to nothing.

    eg

    SKY HD BOX AMSTRAD DRX890 500gb Inc Remote And Power Cable | eBay

    SD generic FTA boxes for even less.

    Ferrite rings (effectively won't help), though they increase the impedance of an interconect to mains induced pick up they will block the 1Khz tone required to switch the the lnb/remote multiswitch between low band and high band working.

    Anything connected with a mains cable with only two connectors (live and neutral only) cannot be involved as there is no way to create a earth loop unless someone has circumvented the double insulation to create a second earth reference locally to the supply neutral connector. If you have added ground connections simply try removing them.
     
    Last edited: Dec 11, 2018
  9. noiseboy72

    noiseboy72
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    I would suggest the issue is that as you say, there is an earth point at the dish end and also at the TV. Small earth currents (Well below those that will trip an RCD) are circulating and these are getting into the audio ground due to lack of isolation between audio ground and mains earth in the TV. This is a known issue with HDMI connections between some TVs and AVRs, but also affects any type of connection with a common ground.

    I doubt very much that it's a power supply problem, as this would manifest itself in other ways.

    I don't agree with your comment that all the other equipment will be double insulated, as many TVs use a 3 pin connection, as do a lot of AVRs and it can therefore be assumed that they have a mains earth - usually connected to the audio ground, but possibly via a high impedance circuit to reduce hum and buzz. The chances are that the earth is used as a functional connector to dissipate EMI from the power supply.

    In a communal block with TN-C-S incoming supply connection, this would not cause any issues, as the earth and neutral are tied together up until the incomer into the building and will be held at a very similar potential throughout the building.
     
  10. AlexSA

    AlexSA
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    This will be slow progress so forgive me I'm just too busy to troubleshoot quickly.

    Thanks for tips.

    Quick question, if I take out the earth from the TV mains plug just to test (temporary, not permanent) that's very unlikely to cause a problem is it?
     
  11. noiseboy72

    noiseboy72
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    It is unlikely to cause a problem and might improve matters - or make things worse!!

    Even if it cures the fault, it's not really telling you very much, as you cannot isolate the mains earth very easily in any safe manner.
     
  12. grahamlthompson

    grahamlthompson
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    I have and have owned in the past a lot of AV kit, none of which has a earth connection or ever had a earth connection. Most new kit has an external or internal SMPS (The external ones output 12V DC) The first thing a SWMPS - Switch Mode Power Supply does is convert the ac input into smooth DC which feeds a inverter to turn it back into a higher frequency ac sinusoidal voltage. SWPS maintain a stable output voltage over a wide range of input voltages - typically 110V to 220 V AC.


    It's no good bonding the Earth and Neutral on entry to a building - what happens if you get a broken neutral within the buliding - answer is a PD of up to 415V between adjacent properties and loads of destroyed kit.

    The earth bonding at the dish is purely to the coax connection screens, there is no connection to the coax centre cores. It purely to prevent a transfer of dangerous voltages to a metal Belling Lee or F connector via the screens or F connector that someone can touch.

    https://cpc.farnell.com/labgear/psc...MIy_bB3Kaa3wIV2fhRCh28PAuAEAQYASABEgJf8PD_BwE



    Broken neutrals cost energy supply companies thousands of pounds in compensation on older not PME (Protective multiply earthed systems - Like light line 11KV systems) . I should mention I had over 40yrs experience in the Electricity Supply industry until I retired from National Grid back in 2000.


    Panasonic TX47 AS802B TV
    Two HDR-FOX-T2 Freeview Plus Pvrs
    One Humax FVP -5000T PVR (2TB Hard Drive)
    Yamaha CD Player
    LG Smart Blu-ray Player
    One Freesat+ Humax Foxsat-HDR
    One Humax Smart (G2) HDR-1000S Freesat pvr

    Yamaha RXA840 AV Receiver

    Active Subwoofer

    Past kit includes Humax 9200T, Topfield 5800, Humax Foxsat-HD box.

    I haven' t seen a TV with an earth in over 30 yrs, you have to go back to Valve designs with a all metal chassis.

    On a new TV there is nothing to earth.
    What make and model of TV do you have that has a 3 core cable on it ? Guessing it has to be a CRT TV. Modern TV's usually have a 2 pin figure of 8 input socket with no earth capability. Frankly I don't think your issue is a ground loop problem in the first place.
     
    Last edited: Dec 12, 2018
  13. davemurgatroyd2

    davemurgatroyd2
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    Try removing the earth screening connection to the RCA plugs at one end of the lead to the amplifier
     
  14. AlexSA

    AlexSA
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    I disconnect Freesat coax humming stops. My TV has Freesat and Freeview built in, both plugged in coax via a freeview and Freesat, except when testing (I've tried all lead combinations for testing).. It's a Panasonic Vierra plasma 5+ years old, model not in front of me right now. Pretty convonced it's a loop involving Freesat coax.
     
  15. TJT1

    TJT1
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    If one earth connection is the freesat coax, where is the other earth that is needed to constitute an earth loop? If there isn't one, there cannot be an earth loop.
    Or do as davemurgatroyd said and report back. Only one audio lead of the two connecting any two devices should be earthed at both ends to prevent earth hum loops. You can usually achieve this by pulling the connector half out so that only the centre 'prong' makes contact.
     
    Last edited: Dec 12, 2018
  16. grahamlthompson

    grahamlthompson
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    Which supports the dirty dc power option. If you disconnect the freesat cable the TV tuner cannot power the lnb. You have to have two to create a loop. At the dish a single earth bond connects the screens of the four cables presumably used to feed the system multiswitch.

    Check with a multimeter with one end connected to earth that there is infinite resistance to earth from the screen outer connections in of any rca inputs or outputs on any kit involved after turning each item off. proving the box is double insulated. Pull out the plug and check to the larger earth pin on the plug. If no continuity there is no possible earth loop.

    Because the screens are effectively floating at the remote ends the minute current generated by the tone switching tone through the core to screen capacitance will show a tiny voltage. using a sensitive solid state voltmeter because they have a very large input impedance. A mechanical meter like a AVO will collapse the voltage simply because of the current it draws. If you connect the live conductor at one one end of a length of mains twin cable to live and use a voltmeter to measure the voltage to neutral or earth you will get a ac voltage measurement. The longer the cable the the larger the reading. That's because there is capacitive coupling between the live and neutral conductors in the twin cable.
     
    Last edited: Dec 12, 2018
  17. noiseboy72

    noiseboy72
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    Sorry @grahamlthompson , I still disagree on a number of fundamentals here.

    I too come from an engineering background, having completed my degree in Electrical and Electronic Engineering in '92 and then worked on temporary event power ever since.

    I have managed, specified and installed literally millions of pounds worth of AV equipment over that time and have extensive experience getting rid of earth loops and hums on both video and audio circuits on consumer, prosumer, professional and broadcast equipment.

    The OP clearly stated that the problem only occurs when the coax is plugged in. Unless this is causing some sort of loading effect on the PSU, it is highly unlikely that it is DC ripple on a supply. Easy test of this is to test the system with the TV plugged in but switched off. If the hum is still there, it's got to be an earth loop, as there's no live electronics to produce the ripple. If not, further investigation would be required.

    The neutral will be bonded to earth on entry to the building in 90%+ of UK domestic installations. PME/TNCS uses PEN to the supply head - typically the fuse before the meter, where the household earth is derived. In a communal building, I would expect all the apartments to be on the same phase - or at least with a common neutral and earth and that the potential difference will be less than 10V between them under normal loading conditions.

    Lots of AV equipment is Class 1 with an earth connection. My 8 year old Panasonic VT series plasma has a 3 pin IEC on the back of it and a quick check with the multimeter proves that the AV sockets, HDMI, aerial points and case are all connected to it.

    Look at this picture of the inside of an Arcam Alpha 9. The earth to chassis can clearly be seen. There's also a high impedance connection from this point to the board's audio ground point.
    [​IMG]

    Earth loops are still extremely common and you are correct in that manufacturers are now using Class 2 products to try and remove this issue. You have been lucky in that none of your equipment has an earth, but in my system I have amplifiers, TVs and a bass processor all with earth connections and I am not alone. Much of this equipment uses the earth as a functional earth to reduce EMI from the switched mode power supply. This is the characteristic zinging buzz from laptops when plugged into earth amplifiers.

    There's a pint with your name on it if an audio isolation transformer on the input to the amplifier does not fix this!!
     
    Last edited: Dec 12, 2018
  18. noiseboy72

    noiseboy72
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    With un-balanced connections, you need a return path for the audio via the ground. If you can remove the plug such that the ground connection is broken and still hear the signal, there is another ground connection between the 2 pieces of equipment - probably via the mains earth.
     
  19. noiseboy72

    noiseboy72
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    Does the hum stay even if the TV is switched to standby, but plugged in to everything? This will tell you if it's likely to be a hum loop. If the hum goes, it might still be a loop, but the issue is within the TV and not between the TV and amplifier.
     
  20. TJT1

    TJT1
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    I agree, but if he has RCA plugs, there will be two of them, L and R. I only suggested removing the earth from one of them and the other provides the earth continuity required. But as you imply, if he removes the earth from both L&R, then your scenario of another earth somewhere holds good.
     
  21. davemurgatroyd2

    davemurgatroyd2
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    What else is connected to the amplifier? Any DAB or FM Tuners connected to the communal system?
     
  22. stevelup

    stevelup
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    That's just not true! Of the five TVs in this house, three are indeed two pin fig-8, but of the other two, one has an IEC C6 ('Mickey Mouse') and the other an IEC C14. On both units there's continuity between the ground pin of the power inlet and the shield of a HDMI socket - just tested.

    None of these displays are more than 5 years old.

    I run an audio-visual install company and I can tell you now that earth loops are literally a day-to-day problem that we have to deal with, and the OP's problem is a perfect example of one. They are particularly a problem in communal systems. We've started using Fibre LNBs instead now on most new installs - they have solved a multitude of issues, but £££...
     
    Last edited: Dec 13, 2018
  23. stevelup

    stevelup
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    OP, I just realised, you're connecting to the amplifier with analogue audio connections. You can put an isolator here (between the TV and the amp).

    You can get a cheap one for a fiver (they're sold as a car audio accessory mainly) - not audiophile kit but it will prove the point and if it solves it, we can explore better options.

    https://www.amazon.co.uk/dp/B000NVW...=9045597&hvtargid=pla-420088663336&th=1&psc=1

    Another solution could be to come out of the TV on an optical cable (if it has a port), and use a little DAC like this:-

    CYP AUD3-192
     
  24. Clem_Dye

    Clem_Dye
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    This audio hum loop thing sounds vaguely familiar. I used to live in a flat and had a/v kit connected through an Arcam amp. At the time I was only using Freeview, via an old Nokia box, but hum was present when using the amp with the Nokia box connected to it via RCA leads. I killed 95% of the issue by using a mains conditioner. I did wonder whether a piece of kit in another flat may have been the cause, but never did get to the bottom of the problem, even when replacing the kit. Ferrite chokes on all mains cables made a slight difference, but it was the mains conditioner which cleared things up to an acceptable level.

    Clem
     
  25. noiseboy72

    noiseboy72
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    I refer you to my first response to this LOL :) :)
     
  26. stevelup

    stevelup
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    Good grief. Completely missed that somehow...!
     
  27. pedro2000uk

    pedro2000uk
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    You can measure stray voltages with even a farely basic digital test meter although they dont give you all info & I do have Oscilloscopes they are useful to show the voltage if it is at 50Hz. Stray voltages on AV equipment in households today are very common where they are typucally extensively interconnected & especially where aerial distribution &/or multi output lnbs on satellire dishes are included.

    As most know on here I install loads of motorised satellite systems, it's the 22kHz diseqc signals to the motor that can serve as a unique but very useful indicator of stray high AV voltages on household AV setups because uniquely those signals can get affected by stray AC voltages even if they are of low power as they usually are. The motor also can act as an earth path. On almost every occasion this happens a fault can be measured as spurious AC usually on the common chassis ground but can be on the 'core' too.

    Often stray voltages faults are 1st highlighted by actually receiving a shock when disconnecting / connecting leads & definitely imo should not be solved by attempts to circumvent them but tracked down to their source.
    The most common devices to have such faults are old Sky boxes number 1#, old tvs, any older AV gear and some poorly designed / cheap PSUS.

    Find the fault and remove it or fix it properly, not just a couple of capacitors but replace whole aging PSUs and these sorts of faults happily track over any interonnecting cables.

    Only if it's say a genuine incompatibility issue or a build up of touch voltages & not a fault should a 'fix' be used imo, otherwise you can be masking a potentially serious fault that can cause damage to other newer equipment, or worse, a fire.

    I've seen too many of these, it's an issue that now needs addressing, the CAI did offer a bonding solution but I think a device similar to an RCD but designed for this lower power issue and I'm not 100% it should be called an earth loop issue, it's more likely stray voltages.
     
  28. pedro2000uk

    pedro2000uk
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    Other issues around this are SMPSUs producing high frequency energy /AC etc.. hey are amazing how they can be made so much cheaper, smaller & lighter than traditional linear psu' but the main problem with the way they work is the high frequency energy they produce as a byproduct. That when it becomes a problem can't be reliably measured with a basic test meter, doesn't always respect normal electrical separation as it can dance over normal circuitsl design and components, depending 'what' frequency it is and can act as a bridge for larger power.
     
  29. AlexSA

    AlexSA
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    Sorry it's been a long time since I replied. I am the OP of this issue. I decided to make a video please let me know what you think.
    Freesat mains loopback issue.


    BTW forgot to show you, but the issue does persist exactly the same way if I unplug the TV from the mains.
     
    Last edited: Dec 29, 2018
  30. noiseboy72

    noiseboy72
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    AlexSa, I think the phono isolator on just the TV input will cure this. You won't need to fit them anywhere else.

    Worth a punt for £6 or so.

    Please let me know how you get on.
     

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