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Humming 3802 ....

Discussion in 'AV Receivers & Amplifiers' started by dave48, Apr 20, 2002.

  1. dave48

    dave48
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    Finally got my Denon 3802.

    Got it configured so that I feed the front pre-outs to my Primare A30.1 amp. The centre and 2 surround speakers are connected directly to the Denon.

    When I put it in any mode which uses the centre + rears (e.g. DPLII or 5.1) I get a load of humming out of the centre + surrounds. It doesn't make any difference to the amount of humming whether the volume is on max or 1 level above mute. The fronts don't hum.

    It's the same even if I turn everything else off apart from the receiver.

    I can't see any obvious crossing of wires that will cause this and I moved the centre away from the tele in case this was the problem - but doesn't make any difference.

    Any ideas? Am I doing something stupid?

    Thanks,

    Dave48
     
  2. Colger

    Colger
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    Dave
    Sounds to me as tho you have an earth loop. If you disconnect the pre-out to the Primare does the hum disappear. If is does then its an earth loop.

    From experience in the past there should only be one earth to the mains via the Amplifier, all other components should be earthed via the audio connections.

    Hope this can be of help
     
  3. dave48

    dave48
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    Gerry

    Thanks for your answer - I think you've diagnosed my problem perfectly. If I disconnect the cinch cable between the front Pre-outs of the Denon and the Primare then the humming goes away completely. As soon as I reconnect even one of the two cinch leads then the humming is back - even if the Primare is switched off. If I disconnect the Primare from the mains, then the humming goes away again.

    However I'm still not sure how to implement your recommended solution.

    I've tried connecting both amps to separate electric circuits within the house (i.e. to independent links within the fusebox) - doesn't help.

    As far as I can see, only the Primare is actually earthed - this has a high-quality mains lead including an Earth. The Denon comes with a crappo mains lead that does not have an Earth connection.

    Any ideas how I can sort this out? It's a bit of a disaster if I can't get the front pre-outs to work through the Primare.

    Dave48
     
  4. dave48

    dave48
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    After searching through the archive on this website, I tried the suggestion of removing the earth lead on the primare A30.1 amp [I wired a special lead for this].

    This has removed the humming problem completely - however I am nervous to put it mildly using this amp without an earth connection, since I don't want to blow myself or the rest of my kit up.

    Is it:

    (a) safe to run in this configuration? [Nothing earthed to mains]

    (b) is there a better alternative solution? Is this all down to an incompatibility between the way the Denon 3802 earths things (star earth?) and the Primare

    (c) there is a "Ground" connection on the back of the primare - to quote the manual: "A ground terminal is provided below the input sockets to allow you to provide a direct ground connection for sources in order to remove hum loops." Any ideas what I should plug into this and if it would make the blindest bit difference to the humming problem?

    Thanks for any help on this.

    Dave48
     
  5. John Dawson

    John Dawson
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    Dave48

    I don't normally get involved in this sort of discussion but I too am uncomfortable about removing the grounding from your amplifier without a bit more investigation.

    It takes two grounded components to make an earth loop (by definition!) so something else in your system must also be grounded. Do you for example have a cable box? These are often grounded at the cable inlet and you need a ground cheater (as I think they are called in the USA) at the cable inlet to fix this.

    In any case you need to find the second grounded component first.

    HTH.

    John Dawson (Arcam)
     
  6. dave48

    dave48
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    John,

    thanks for getting involved - even though I haven't bought any of your firm's kit yet! [Please note that I very nearly did - it was just the lack of availability over here in Germany - and being a long long way from the nearest dealer - that stopped me].

    I think I have now found the cause of the problem - the second ground was via the FM radio antenna, which I had overlooked when I had removed all the other connections earlier in my problem hunting. I'm living in a flat with cable radio, so I presume this also acts as a true Earth, as compared to a normal FM antenna.

    Now that I have disconnected the antenna, the humming has gone completely. Strange - this was never a problem when I used my old tuner connected to the same amp (an old Yamaha tuner that I was quite glad to see the back of).

    Is there any solution to connecting the radio antenna without causing this problem again? Sorry to keep asking questions on a sunny Sunday afternoon .... Using a normal FM antenna here is not a particularly practical solution - and I am already paying for the cable connection (no choice - have to pay for it whether I like it or not). I'm not sure what the "ground cheater" you refer to actualy is.

    Thanks again for the help - I'm much happier about the electrical safety of my current solution ....

    Dave48
     
  7. Colger

    Colger
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    Dave
    Pleased you have finally resolved your problem and glad I was able to help initially. Incidentally, I thought that the 3802 was earthed as I understood amplifiers normally are.
    You have now prompted me to check on my earthing!!!!!
    Incidentally, I am unable to help with regard to your fm aerial as I am not familiar with cable at all.
     
  8. John Dawson

    John Dawson
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    Hi Dave48 - glad you found the problem and I am gratified I guessed more or less correctly :)

    You need either an RF isolating transformer (the cable company may be able to help you as this kind of thing is a common problem) or the DIY way is to break open the feed to your Denon's tuner input close to the Denon's input socket and wire in 2 x 1 nF ceramic capacitors in series with the core and screen of the co-axial cable. You obviously need to be competent with a soldring iron and would need to keep the wire lengths very small to avoid undue losses but I would expect the cable signal strength to be plenty so this would work well. One or the other of these is what makes up the "ground cheater" referred to earlier. Of course if in doubt you must seek professional advice closer to home but, whatever you do, don't break the grounding of your amplifier as that is safety critical....

    HTH. If in need of Arcam in Germany BTW, look at www.bridgeaudio.de

    Sincerely,

    John Dawson
     
  9. dave48

    dave48
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    John + Colger - many thanks for your help, I was getting a bit desperate yesterday about this ....

    John's DIY solution sounds a bit scary to me - I don't think I trust my soldering skills enough to do this. Last time I soldered anything like that it was on my BBC micro when I added the optional A to D port. Somehow it never worked in quite the same way again ....

    I will have a go at contacting the cable company to see if they know of a solution - but unfortunately the cable company is the German equivalent of BT (i.e. ex-State monoplist), so I am already a bit concerned about the level of useful help I will get from them ....

    Any more info on this would be gratefully appreciated, particularly if someone has had a very similar problem and managed to sort it out!

    Thanks again,

    Dave48
     
  10. dave48

    dave48
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    I think I've found the device I need - in German it is called a "Mantelstromfilter"*. Apparently an earth loop is called a "Brummschleife". One learns something new every day.

    Since these only cost about 5 Euros, I'll buy one and try that - sounds safer than getting my soldering iron out ....

    This seems to be a very common problem over here - once I worked out what word to search for on the Internet, I found dozens of pages explaining what the problem was and how to solve it.

    I now have my fully-earthed power cable back in - and after what I have read on the Internet this evening, anyone who has solved this problem by removing the earth from their amp should have a serious think about whether this solution is worth the risk! It seems there is generally always a safer solution out there!

    Dave48

    * this is almost a literal translation of John's "RF isolating transformer", so is preumably the same thing (the German web-sites also talk about using the 2 capacitors).
     
  11. Plump

    Plump
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    hi dave
    i do not know how much you want to inwest, but check aerial cable with "mantelstromfilter" from hms (german company so you shoul get it cheaper there).
    it might be pretty expensive but it is very decent product (more than that - great aerial cable) and you might never ever need another aerial connection in the future, even if you go one step further with your hifi.
    cheers
     
  12. dave48

    dave48
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    That's interesting - I didn't realise HMS did that. I already have an HMS power adaptor and HMS speaker cables for my front speakers. I am not convinced they are cheaper over here in the Fatherland - they were ******* expensive.

    Any internet references or similar where I can find these?

    Dave48
     
  13. Plump

    Plump
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    Hello,
    they sure are cheaper in GErmany, believe me. But they are definitely too expensive too.
    They do not have any internet presence apart from one site where they say it is coming soon etc, but it is there since ever.
    RF cable is new thing, you should best contact them directly to learn more about it.
    If you tell me where in GErmany you are I might help with dealers, since I travel very often there.
    Cheers
    Plump
     
  14. dave48

    dave48
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    I just got them to send me their broshures etc. - but the price for their antenna cable with filter is mad - 420 Euros for 1.0m - yes that is about £270!!

    As much as this is probably the best solution, I cannot see how spending that much on a bit of cable is going to make that much difference - particularly since the rest of the connection back to the cable company is probably cheap junk.

    I'll just have to go and buy a cheaper solution and see if that works satisfactorily.

    Dave48
     
  15. Plump

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    Well, that's really sort of nonsense,
    must be something hit Mr. Hans M. Strassner into his head while he was making prices.

    Nevermind, your other solution will surely also help.

    Lots of fun without hum!

    Cheers
     
  16. dave48

    dave48
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    I bought some of his loudspeaker cables which I am really pleased with - although also not exactly cheap.

    But £200+ for a radio antenna cable - sounds bonkers to me.

    Dave48
     

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