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700:7R Buzzing

Discussion in 'TAG McLaren Audio Owners' Forum' started by Mike-D, Jun 15, 2005.

  1. Mike-D

    Mike-D
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    Do all 700:7Rs suffer from intermitent buzzing?

    Ever since I aquired my 700 back in March it has suffered from an intermittant buzzing, not on the output but from the unit itself. I would have asked this question earlier but I was hoping that a pattern would emerge. It hasn't and it does seem pretty random.

    There are two levels of noise. The most frequent is loud enough to hear from my listening position but only during the 'quiet bits'. This never happens immediately on waking up the amp but often when it has been on for a few minutes. The noise will eventually disappear sometimes after just a few minutes but sometimes longer. It cuts in and out rather than fades. A straightforward 'warning up' issue you might think but sometimes it will cut in again after hours of use. I am fairly sure that the volume and the number of channels in use makes little difference. It is mounted in a rack with ventilaton all round.

    Less frequently it moves up a gear and a more violent buzz happens. This you can hear at normal listening levels. It normally lasts for just a few minutes. The first time it happened I was sure that the unit was about to go bang.

    For a long while I thought that the unit would either fail or the issue might go away when it was run in. It now seems clear that it is probably not going to do either.

    Its something I can just about live with, but I would like to know if this is normal. I'm guessing it is something to do with the mysterious Cascode Compensation. If anyone can explain in laymans terms exactly what this does I would be very interested.

    No problems with the output at all. It sounds great.
     
  2. Steve.EX

    Steve.EX
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    I have no idea if this is related but about 5 years ago i suffered a similar situation, occasionally a mild buzz and very occasionally a real growl from a Rotel power-amp. It drove me to distraction simply because i knew it was there. Oddly another power sat directly atop would also be affected. My initial response was too monitor both the voltage and frequency of my mains supply for anything odd. I was not optomistic as at that time i was using plenty of power-amps and subs and the condition was not universal to all. I of course verified that the mains tranformers (to which the noise was clearly emanating from) were mechanically secure. After many hours researching and speaking to people as to why a toroidal will do this. One explanation given to me by a well informed aircraft systems engineer seemed well founded to me. It is apparently related to structural inconsistancies within the winding layers.
     
  3. liam_b

    liam_b
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    The normal answer given for the type of transformer noise is that is caused by 'poor mains quality' or DC offset on the mains.

    If you can easily take the 700:7r somewhere else and plug in to check for noise that could rule in/out those possibilities.

    The term 'cascode compensation' relates to the way the input of the VAS stage of the amplifier is referenced to ground via the cascode buffer transistor in the input section rather than the (hot) input of the input section, this has nothing to do with the transformer noise.
     
  4. GrahamMG

    GrahamMG
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    If the transformer buzz is audiable at normal listening distance over the music then the offending transformer needs to be changed as that is well beyond what i'd consider normal transformer noise, I assume it is under warenty so pick up the phone and get it sorted.... Its all down to production tolerances whenthe Toriodal is made, some are quieter than others but I'd suggest that if you hear it above the music then that is simply not good enough and well beyond manufacturers tolerances. See if you can isolate it to one or two channels to coinfirm this, if ALL the channels emit the same racket then either your very unlucky to get all the duff transformers in one box or your mains is seriously wonky....
    For info I've not heard a silent 100x5R as far as I am concerned they all have mechanical hum but they can't be heard from more than a couple of feet away in a quiet room and never whilst music is being played....
     
  5. WillyP

    WillyP
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    Back to IAG I would say and get it fixed. Free of charge of course.

    Before I bought my TAGMcLaren I have tried three Harman Signature and two Citation power amplifiers. They all had problems with noise and buzz, especially the Citation power amplifiers. Poor quality control in my opinion, but the Citations were directly imported from the US so I always have thought that it also had something to different power in the US.

    After all these adventures the misses was completely disgusted (did I tell you already that I have tried four Signature and Citation processors?) and she cried that she didn't care what the price would be but that I should buy some gear that would function right.

    That was the time that I bought a complete TAGMcLaren set, but I won't repeat here what she whispered when my DVD32R stopped working.
     
  6. johnson

    johnson
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    Hi,
    If you get it back from IAG (with a new transformer) and the noise is still there it could well be DC offset as already stated by Liam.
    This is not uncommon apparently.
    PSaudio manufacture a device that removes DC offset.You may want to check their web-site
    Regards
     
  7. GrahamMG

    GrahamMG
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    The DC offset must be pretty big to be audiable over normal music levels......
     
  8. Stevesky

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    The hum comes from the windings in the transformer vibrating as they're not as tightly bonded as they should be. The most likely cause that makes the transformer intermitently hum is DC offset on the mains (it requires very little). Often this can be produced by fridges, light dimmers, hair dryers etc. that are on the same mains ring as they load one 1/2 cycle of the mains more than the other.

    A few solutions:
    1. Get the transformer changed... holiday to IAG central I'm afraid.

    2. Get a dedicated spur for your hifi.

    3. If you're a bit handy with electronics the problem can be fixed with 2 diodes (add more diodes to block more DC) and a capacitor... as we're dealing with mains I would not recommend this route. There used to be a product called the Hum Buster made by PS Audio (http://www.psaudio.com) that worked on this principle.

    4. Plug it into a different socket from elsewhere in the house!

    Good luck!
     
  9. GrahamMG

    GrahamMG
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    "very little" , what to hear transformer hum over normal music playing levels? That is pretty loud.......and just has to be into replacement toriod territory surely?
     
  10. Omardris

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    Hi,

    i have much problems with DC offset of the mains. The Revel B15 subwoofer is very sensitive and growls like a lion.
    Than i take the DC-Filter "GF1" from tk-audio (www.tk-audio.de) and the lion is quiet now.
    The principle was explained by Stevesky above.
    Mister Killermann (tk-audio) is very nice and one can test the filter before the purchase.

    Regards

    PF

    PS: Mister Killerman told me, that you can use the GF1 for 110 Volts too !!
     
  11. Mike-D

    Mike-D
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    So its definitely not a common fault then. I will try different sockets and see if this has any effect.
     
  12. GrahamMG

    GrahamMG
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    Not as loud as you seem to be describing, the forum would be full of it if it were common...... I suppose for paranioa's sake you might turn off everything else in the house and see if it makes any difference, just remember to turn the fridge freezer back on! Wandering round to a local mate and try it there would be an alternative.....
     
  13. Mike-D

    Mike-D
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    Well guys I followed all your advice but could not isolate a source, until now!

    The buzzing problem had reoccured from time to time but seemed to be less frequent and not last for so long. However since the weekend the low level buzz has been permanant. The trigger turns out to be a new air pump fitted to my garden pond at the same time.

    Obviously as the pump is new, previous buzzing must have been triggered by something else but this does seem to confirm that the problem is related to the mains supply.

    I would appreciate any advice on how to address the problem I'm not sure if I should be concentrating on the supply to the amp itself or somehow isolating the offending pump. The pump is on a completely separate circuit the feeds the garden. Does this still sound like a DC ofsett issue or a more straightforward form of interference?

    Perhaps this is not really a TAG issue any more but I'm sure you will point me in the right direction.

    Thanks in advance.
     

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