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Post by theadmans on Nov 10, 2009 16:36:23 GMT
I have recently bought a year old Little Dot III on Ebay.
I am getting what sounds like Transformer Hum on switch on. The hum is NOT through the headphones just in the room. I get the noise even if nothing is connected to the Little Dot. It is annoying whilst I am warming up the Little Dot and I can hear it between tracks whilst listening.
I have tried tightening the screws on the Transformer Case but this has not helped. Any other tips?
Is it possible that my mains is supplying too much voltage and causing the hum? The LD amp is expecting 220V but maybe getting 240V or more? I have no equipment to measure my mains voltage but just wondered if this was possible.
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Post by PinkFloyd on Nov 10, 2009 22:09:35 GMT
I have recently bought a year old Little Dot III on Ebay. I am getting what sounds like Transformer Hum on switch on. The hum is NOT through the headphones just in the room. I get the noise even if nothing is connected to the Little Dot. It is annoying whilst I am warming up the Little Dot and I can hear it between tracks whilst listening. I have tried tightening the screws on the Transformer Case but this has not helped. Any other tips? Is it possible that my mains is supplying too much voltage and causing the hum? The LD amp is expecting 220V but maybe getting 240V or more? I have no equipment to measure my mains voltage but just wondered if this was possible. The Chinese have a bad habit of supplying 220V transformers for the 230 / 240V market and, generally, this causes the transformer to get "hot"...... I have a lot of experience of humming transformers and, if it's an e-type transformer the laminations may need varnishing (a good quality Dulux spray varnish will do).... can you get access to the transformer / can you take a pic? If it's clamp mounted you will have to remove the clamp..... usually they are "punched" into the laminate and can be removed by prising apart with a screwdriver. Once you have got the clamp out of the way it's a simple matter of spraying varnish all over the laminates... you'll see it ingressing into the sections..... leave this to dry for a couple of days or put the transformer in the oven at about 120F for 2 hours. There are no quick fixes.... if it's mechanical hum then varnish is your friend. Me personally? I would send the bloody thing back and demand a replacement that doesn't hum.
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Post by theadmans on Nov 11, 2009 9:34:18 GMT
Mike - I have emailed you a photo of the transformer.
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Post by PinkFloyd on Nov 11, 2009 21:35:45 GMT
Mike - I have emailed you a photo of the transformer. Hi Adam, That's a toroidal, I wouldn't varnish it ;D I note it's a 110 + 110V transformer... they REALLY should be supplying a 115 + 115V for the UK market..... Have you tried tightening the nut on the toriod itself?
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Post by theadmans on Nov 11, 2009 21:58:38 GMT
- yes I had a go at tightening the Transformer down but it still hums. Any other ideas - is it likely that getting too much voltage from the UK mains would cause the hum. Are there step down devices that I could employ to help with this?
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Deleted
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Post by Deleted on Nov 11, 2009 22:21:41 GMT
Is the cover over the transformer steel, or aluminium ?
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Post by PinkFloyd on Nov 11, 2009 22:41:13 GMT
Is the cover over the transformer steel, or aluminium ? Hard to tell from the photo as the cover is painted black.... my guess would be steel though
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Post by PinkFloyd on Nov 11, 2009 22:44:01 GMT
I've uploaded it to my photo storage space..... here it is:
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Post by PinkFloyd on Nov 11, 2009 22:47:06 GMT
I still reckon @ 110 + 110V (220V) it's not at all suitable for UK mains voltage and, whether it hums or not, should not be in there!..... I've seen my supply clock in at 260V some days.... a 220V transformer is not recommended for UK voltage.
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Post by theadmans on Nov 12, 2009 8:50:00 GMT
I still reckon @ 110 + 110V (220V) it's not at all suitable for UK mains voltage and, whether it hums or not, should not be in there!..... I've seen my supply clock in at 260V some days.... a 220V transformer is not recommended for UK voltage. ...following this logic is there an external step down transformer that can be used to drop the voltage to 220V. I know you can get US/UK converters which switch between 110V and 220V - but is there something that can give me 220V from UK mains? ...by the way the plate I think is steel. I had thought about buying some dynamat and lining the inside of the transformer case. Alternatively I could stuff the transformer case with bubble wrap - or would this be dangerous?
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Post by Deleted on Nov 12, 2009 8:56:20 GMT
theadmans Is the hum still in evidence with this cover removed ? If it isn't, then make sure that the transformer is mounted absolutely dead centre in the enclosure. i.e. equidistant from all sides. You can slacken the mounting bolt slightly to accomplish this. Do NOT use bubblewrap internally. SandyK
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Post by theadmans on Nov 12, 2009 11:28:38 GMT
theadmans Is the hum still in evidence with this cover removed ? If it isn't, then make sure that the transformer is mounted absolutely dead centre in the enclosure. i.e. equidistant from all sides. You can slacken the mounting bolt slightly to accomplish this. Do NOT use bubblewrap internally. SandyK ..very interesting Sandy ! 1) If I remove the black transformer cover - there is a very slight audible buzz from the transformer. 2) If I put the cover back and don't screw it down there is a VERY noticeable hum. 3) If I then screw the cover back on the hum reduces but is still worse than with the cover off. Incidentally I have an older Little Dot amp (different model) which has a non toroidal 110v + 110v transformer and that doesn't hum at all. I wonder if the answer is to line the cover with dynamat. The cheapskate in was hoping I could get away with bubblewrap but I guess that is not a good idea.
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Post by theadmans on Nov 12, 2009 11:38:16 GMT
Further to my last post:-
If I tighten the screws on the transformer case to a normal degree the hum is worse than if I leave the screws loose!
I have lined the inside of the Transformer case (where it mounts onto the amp chassis with insulating tape) - hum seems better now.
Thanks for your help guys !
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