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Bought a poweramp off the forums...and have some problems :(

Discussion in 'AV Pre-Amp/Processors & Power Amps' started by Smurfin, Feb 12, 2005.

  1. Smurfin

    Smurfin
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    hi all

    Wonder if anyone can give me some advice please? A few weeks ago I bought a Rotel 985 mkI 5 channel, THX power amp from the classifieds. Unfortunately I needed longer interconnects than those that came with it, so it wasn't until 2 weeks after I'd received the amp that I got to try it out properly.

    I've bought some good quality Belden interconnects, and have hooked them up from the poweramp to the pre-outs on my Pioneer AX5i. The problem I have is a low level - but distinctly audible - buzz/humming sound. The noise is constant unless the AX5i is switched off, in which case the humming changes slightly, but is still there. Only when the poweramp itself is switched off does the humming completely stop (as you would expect). The buzzing is also audible in EVERY channel.

    The possible causes could be:

    * The AX5i is the problem, and is introducing noise into the chain.
    * The interconnects are the problem
    * The poweramp is the problem
    * It's a simple mains issue

    I don't believe it's the AX5i as previously I had active monitors hooked up to it via the pre-outs, and there was no hum/buzzing at all, regardless of what power sockets in the room were used.

    I don't believe it's the interconnects as this morning I've tried a couple of others and the hum has not changed or disappeared:(

    The most obvious answer is a mains issue, but then I've previously had 5 powerful active monitors in my room and there's not been ANY issues with hum (but I don't know if this means that other kit should be fine also).

    Which leads me to believe that the problem lies within the power amp. But what exactly could the problem be? Is there a way round it? Has anyone come across this before?

    Advice would be appreciated, because as of this morning I've removed the poweramp from my system....I really can't cope with that buzz :( :mad:

    I would add that the guy who sold me the poweramp has been helpful so far, and this post isn't intended to get a refund of the money I paid. I just want the poweramp to work :suicide:

    Cheers
    Matt
     
  2. Parmenion

    Parmenion
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    Try plugging the poweramp into the same socket as the Pioneer.

    regards

    Parmenion
     
  3. Smurfin

    Smurfin
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    Maybe I'm being stupid, but what exactly do you mean?
     
  4. Parmenion

    Parmenion
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    If you have twin sockets on the wall, make sure that the Pioneer is plugged into, say, the left one and the Rotel is plugged into the right one.

    regards

    Parmenion
     
  5. Mark Grant

    Mark Grant
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    Hello Matt,

    Do you have anything connected to the AV amp that is connected to a satellite dish or TV aerial ?

    I would unplug the interconnects from power amp, power the rotel up and see if it still buzzes with no inputs, just speakers connected.

    If that cures it, unplug everything from the AX5i, just leaving the interconnects to power amp and power of course.

    Add cables one at a time until you find what causes the buzz, which I guess is a ground loop/problem.

    A process of elimination.

    Good luck !

    Mark.
     
  6. Parmenion

    Parmenion
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    I agree, sounds like a ground loop problem to me too.

    Don't forget my suggestion for a 'quick fix'.

    regards

    Parmenion
     
  7. Smurfin

    Smurfin
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    Thanks Mark. I've disconnected the interconnects from the power amp, switched it on...and the buzz has gone. As soon as I plug in the interconnects, the buzz returns, and this is regardless of whichever interconnect I use (tried 2 different brands).

    So where do I go from here? :confused: Could it be the pre-outs from my AX5i (despite not having a problem previously with actives connected via the pre-outs), or is it the poweramp :confused: I've completely removed the poweramp from the system now as the buzz is just too annoying. I don't notice if I'm playing movies loud (although even at -5 to -10db, in very quiet scenes I can hear it), but it becomes more pronounced late in the evening as the general noise floor of the environment lowers and especially as I don't play movies quite as loud:mad:

    Matt
     
  8. eviljohn2

    eviljohn2
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    Seems odd. Do you know if it has a UK (50Hz) power supply or a US (60Hz) power supply?

    If you're running a US power supply at the UK mains frequency it could well induce a hum like this.
     
  9. Smurfin

    Smurfin
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    It's a UK one.
     
  10. eviljohn2

    eviljohn2
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    Right. It could be an earth loop between the 2 units. Get some loose wire and attach it to the power amps chassis (with it all plugged and humming), case screws are good for binding these down. Now try touching the other end of the wire to your other pieces of equipment, if that cures it then attach the flying lead to the chassis of that piece of equipment.

    If that doesn't work, it might be worth looking at how the appliances are earthed. You may not have had a problem with your Blue Sky's as they probably weren't actually earthed to the mains so "shared" whatever potential your Pio used as earth. :)
     
  11. Smurfin

    Smurfin
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    Cheers, will try that:)

    Hmm I didn't understand that part :D :blush:
     
  12. Mark Grant

    Mark Grant
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    Hello Matt,

    I would disconnect all inputs to the pioneer AX5i, just connecting the preouts to the power amp. all other sockets not connected to anything.

    If no buzzing with this, add inputs one at a time to the AX5i and see what causes it.

    Often caused by a cable from a sky box or freeview box, as these are usually not earthed devices, but the dish or aerial can have a little bit of earth reading on the cable, as is fixed to the chimney or gable end of the house etc.


    Mark.
     
  13. eviljohn2

    eviljohn2
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    Not to worry, suffice to say that not everything you plug into the wall actually uses an electrical earth. Older or powerful equipment usually does (like your power amps) whilst smaller bits (like your speakers) usually don't. If the flying lead technique works then you needn't worry!

    Good luck with it otherwise Matt. :thumbsup:
     
  14. avanzato

    avanzato
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    Do the interconnects go anywhere near a power cable or power supply?
    My experience has been that with earth loops I got 'hum' and with power cable interferance I got 'buzz'.
     
  15. GaryG

    GaryG
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    If it's a ground loop problem, use the power amp as the main 'earth' and disconnect the earth lead in the mains plug on the equipment you connect to the the power amp leaving the interconnects to provide the earth via the power amp.
     
  16. Smurfin

    Smurfin
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    Thanks guys, I'll try a couple of things tomorrow and let you know how I get on:)
     
  17. Hawklord

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    Hi,
    I have had a similar issue with other equipment in the past (my current components seem to be fine together:)) where an audible hum was present. I tried most of the things already suggested to no avail:( and as a last resort bought one of these:-

    http://www.beststuff.co.uk/xitel_ground_loop_isolator.htm

    It worked for me and cleared the hum up altogether with no degridation (sp?) to the signal. It's fairly expensive but sturdily built and of better quality than others I have seen (which were cheaper), but, worth it imo to get rid of you irritating hum. There's even a useful diagram explaining what causes the effect at the bottom of the page in the link above;). Worth a try as a last resort.

    hope you get it sorted :smashin:
     
  18. General Skanky

    General Skanky
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    I used to get a loud but intermittent buzzing through my active speakers, regardless of how it was all connected.

    I did all sorts of trial and error things to cure it.

    In the end, I discovered it was the TV causing a buzz to come through, but only when it was on, and even when not connected to anything!

    So we now have a plasma.

    No idea if it helps, but just shows that it really could beanything.
     
  19. John

    John
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    What an excellent excuse for an upgrade :D :smashin:

    JS
     
  20. Smurfin

    Smurfin
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    Yeah I thought that, except I already have a plasma;)
     
  21. Smurfin

    Smurfin
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    Finally got round to plugging the power amp back in and playing around with things, and I've discovered that my plasma is the component that's causing the problem:(

    The plasma is plugged into the same extension block as both the power amp and the Ax5i, and if the plasma isn't plugged in, there's no issue at all...only when the plasma is plugged in do I get problems.

    Anyone got any solutions to rectify this?
     
  22. eviljohn2

    eviljohn2
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  23. Smurfin

    Smurfin
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    Yeah tried that....didn't work. How dodgy would it be removing the earth from the plasma?
     
  24. eviljohn2

    eviljohn2
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    That was going to be my next suggestion. It shouldn't be a problem, you need to check by the plasma's power receptacle that the supply is of a closed design. This is indicated by 2 concentric squares (one inside the other). Much of your other equipment will have this arrangement so you can have a look on them to see what to look for if you need to.

    If the double box logo is on your plasma then you can remove the earth with no trouble at all. If it isn't then you mustn't remove the earth and will have to think about a different solution. :)
     
  25. Steve.EX

    Steve.EX
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    It is unlikely that an earth conductor will be connected in any supplied cable on a product that is class 2 or double insulated.
    A coupling of the plasma chassis to your amp's chassis will no doubt eliminate the buzz, i would not personally recommend the removal of an earth conductor from an amplifier if it requires one, this can be potentially dangerous.
    If memory serves correctly the mk1 was indeed an earthed product, subsequent series (certainly the mk2 etc) were class 2.

    Regards

    Steven
     
  26. lardy

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    thread hi-jack alert....:eek: :eek:
    I have a similar problem with a new power amp (a Musical Fidelity X-A50 monobloc to be used with receiver). I get a really loud hum caused by any one of the following being energised: DVD player (pioneer double insulated), TV (tosh) and freeview box (netgem) all problematic in standby too...... tried moving the power amp, using the same socket outlet, different socket outlets, a Belkin powerstrip with smoothing/protection and moving the relevant signal cables away/disconnecting them. The hum is still there - surely all my video components can't be at fault??
    help..........:lease:
    LL
     
  27. GreenEagle

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  28. lardy

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    thanks, greeneagle, just got me dad (TV, radio, hifi engineer as was) round and we checked the amp without any input - still got the hum - he suspects a problem with RF being picked up from the TV's frame signal generator (whatever that means....), short of moving the amps away and shielding not sure what to do - live with it I suppose - or try blocking the aerial signal path to earth - but we did remove the aerial at source and no difference.....
    Ian
     
  29. Thunder

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    Had this problem with both a Rotel 991THX and a Parasound HCA2205. Both were double insulated designs, so removal of the earth connection in the plug solved the problem:smashin:
     
  30. GreenEagle

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    Hi lardy,

    Please give the RFI filter a go, am sure it will get rid of this problem because I went through everything you mentioned until, I found this and it worked a treat.

    If you are near the Windsor area, I can lend you mine to try out.
     

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