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New set up annoying buzz / hum I can't get to the bottom of....

Discussion in 'audio' started by Weeman1973, Mar 15, 2019.

  1. Weeman1973

    Weeman1973 pfm Member

    I've just set up a new system using pre-loved items mostly procured from this parish - WLM La Scala Speakers, Croft 5c Power & Gate Pre Amps.

    No matter what I do, I cannot stop background hum, or buzz through the speakers when there's no source playing which I can't help thinking isn't right?

    I've tried different cables (speaker, interconnect & power), different wall sockets & although I can find some improvements depending on combinations, the hum is still audible with no source (magnified when using the TT input).

    I thought it may have been the speakers as they are super efficient at 93db but it also happens when I've used the amps with my Naim Allae's (for sale actually....)

    Sometimes the speaker cones actually move in & out if I turn the volume about half way (with no source playing of course) which does worry me if I'm doing damage to them? The hum is still there even with the pre off & just the power is on feeding the speakers as well.

    I can live with it as obviously most times when the amp is on there is music playing but would prefer it not be there of course but I also worry if it is damaging the speakers at all?

    Any thoughts?
     
  2. early

    early pfm Member

    It might sound daft but is the amp grounded ? , I have had amps in the past that needed a separate ground .
     
  3. Weeman1973

    Weeman1973 pfm Member

    Can't see how or where I would do this?

    Thanks.
     
  4. early

    early pfm Member

    Does any of your kit have a signal ground connection ? , if so run a wire from this to the case of the humming amp .

    I have a similar problem with my Yamaha AS2100 , I have connected the signal ground connection to the earth pin on a standard three pin plug and plugged it onto a wall socket , my amp is now silent .
     
  5. Weeman1973

    Weeman1973 pfm Member

    My pre amp has a grounding connection where I connect my TT to.

    So if I were to run a cable from the grounding connection on the pre to the case of the power amp you think I might stop the hum (he says as he runs off to try it.....)
     
  6. early

    early pfm Member

    It won't hurt to try , just make sure it makes an electrical connection to the power amp case , ie no paint ect in the way . Screw heads are a good place for a temporary connection .
     
  7. Tony L

    Tony L Administrator

    Sounds like a typical earth loop. From a recording studio perspective, where such things are common, the usual approach is to ensure the mixer (the thing you touch all the time) is earthed, and then to lift the mains earth on any other component that causes buzz when plugged in. In a hi-fi context this usually translates to ensuring the preamp has a functional mains earth and then lifting the earth on any component either up or downstream that causes a buzz. You *need* a system earth somewhere.

    PS To do this with any real confidence (which you should) you really need a multimeter in order to ensure you maintain earth continuity with the components that you have lifted the earth on (i.e. via the signal returns). I’m always reluctant to suggest on an internet forum that anyone meddles with anything to do with electricity unless they understand what they are doing, but this is almost certainly the way to lose the buzz. Do some research on ‘earth loops’.
     
  8. Weeman1973

    Weeman1973 pfm Member

    Alas no joy I'm afraid - ran a length of speaker cable from the case of the Power amp (cleaned paint off so just bare metal) to the grounding connection of the Pre amp (where I ground my TT) but has zero effect - buzzing still present.
     
  9. Weeman1973

    Weeman1973 pfm Member

    Thanks Tony.

    I made a IEC cable with bits I got from MCRU & noticed the Belden cable has another strand of cable inside the jacket outside of the usual earth, live & neutral. I haven't used this & trimmed it off. If I did attach this to the earth of the plug & IEC socket, do you think this would be sufficient?
     
  10. simon g

    simon g Grumpy Old Man

    The 5c isn't really a Croft 5, in a sense. It dates from the time when the Distributor was calling the shots, more than Glenn, IIRC. I also seem to recall that this model did suffer on the quality front. If you haven't done so already, I'd have the amp checked out by someone who knows what they're doing. In the meantime, if you have any spare valves, then try swapping over. Even merley re-seating them may well help if you don't have spares.

    It is most likely an earth loop though. Is it more of a buzz or a hum? A buzz would lead me more to look at the amp, a hum then a lop of some kind.
     
  11. Weeman1973

    Weeman1973 pfm Member

    More of a hum - I have a video of it but not sure how I go about uploading to the forum?
     
  12. Tony L

    Tony L Administrator

    I assume you mean it is a screened cable? If so convention is that you connect that to earth at the mains plug end only, though unless you can make cables to a truly professional level using heat-shrink etc I’d not bother with it, just make absolutely sure it can not possibly short anything at all. Again I find this rather worrying to be honest as if you need to ask what it is you maybe shouldn’t be making mains leads from a safety perspective. Anyway, I doubt this is your issue. I suspect you just have a typical system earth-loop as I describe above. I’d do all the diagnostics using bog-standard factory-made IEC leads.

    PS I strongly advise buying a multimeter so you can check everything and be absolutely sure what is going on.
     
  13. Weeman1973

    Weeman1973 pfm Member

    I've managed to upload the video's of what I'm talking about on both my Naim Allae's & WML La Scala Speakers to YouTube. Links below:

    WML Speakers:


    Naim Speakers:


    Hopefully you can see what I mean about the cones moving?

    Thanks.
     
  14. JemHayward

    JemHayward pfm Member

    The cone movement issue is probably a separate thing to the hum. The cone movement is caused by a very low frequency or really variable DC being present on the output of the power amp. If it's doing this without the preamp connected, the issue is with the power amp. The fact it is volume dependent, suggests you may have an issue with the preamp.

    The first thing I would try is replacing all the valves with known working good ones, and if this fixes it, you can work out which valve is the problem by elimination. I suspect that if you solve the cone flap issue, then the hum may go away with it. They could be totally separate problems.
     
  15. Weeman1973

    Weeman1973 pfm Member

    After lots of fettling, I think I can narrow it down to the Power Amp...

    I set my Croft Integrated (active pre & power sections) to the speakers & powered up with nothing connected - very low hum but only if i put my ears very close to speakers - this hum doesn't go up & down with volume.

    Connected my X40 Streamer and powered up, all is good no extra hum there.

    I then connected a SS Power Amp (Cympol CPA3) to my speakers with no source connected to that - absolute silence. Same when I use my X40 as the pre so all is good there.

    I then connected the Gate Pre Amp to the Cymbol PA & used the X40 as a source then. With nothing playing there is silence except when I tun the volume on the Gate up & down - no hum but a sort of white noise sound but again very low. When playing a source this way there's no hum either.

    So I think it must be the PA - trouble is how do I solve it?
     
  16. Tony L

    Tony L Administrator

    I’d send it to Croft for a service. Hum can very often be a sign of aging capacitors on the way out, and if it is a fairly old hot running amp this may well be the case. I’d be inclined not to use it from this point as you don’t want to risk additional damage should something actually blow.
     
  17. Weeman1973

    Weeman1973 pfm Member

    Yep, I'll give Glenn a call & see what the deal is but as you say, probably for the best that I leave it out the system for now.
     
  18. awkwardbydesign

    awkwardbydesign Officially Awesome

  19. Weeman1973

    Weeman1973 pfm Member

    Thanks All for the comments - have just spent the best part of an hour trying all various combo's & have massively reduced the hum...

    I now have the power plugged into to a different mains socket to the rest of the kit. Also using some Van Damme studio interconnects with locking connectors & have tightened the input connections on the back of the power amp as noticed these were easily spun round by hand.

    There is no only a very slight hum when ear is next to the speakers which is usual with Valve amps when using a normal line, however when using the Phono (MM) input on the Gate pre amp, the hum gets louder as I increase volume (no source playing of course) & also noticed the speakers flapping again???

    Beyond bemused!!!
     
  20. Weeman1973

    Weeman1973 pfm Member

    Anybody know of any competent engineers in the Cambridgeshire (or Northamptonshire) area that could take a look at the Pre Amp as I think that could be the bigger culprit?
     

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