Transformer Hum (again)

Loki, it's not quite like that.

The problem is magnetostriction caused by an asymmetry in the mains waveform.  This means that the magnetism induced by one phase of the mains isn't precisely balanced by the other phase - this results in a residual static magnetic field in the transformer core.  As a result of this static magnetic field, the magnetic field in the core hits the magnetic saturation level on each mains cycle.  This is the cause of the hum.

The output windings of a balanced isolation transformer re-balance the +ve and -ve phases around zero, so preventing the static magnetic field building up in the core of the equipment transformer.

Huge posted:

Loki, it's not quite like that.

The problem is magnetostriction caused by an asymmetry in the mains waveform.  This means that the magnetism induced by one phase of the mains isn't precisely balanced by the other phase - this results in a residual static magnetic field in the transformer core.  As a result of this static magnetic field, the magnetic field in the core hits the magnetic saturation level on each mains cycle.  This is the cause of the hum.

The output windings of a balanced isolation transformer re-balance the +ve and -ve phases around zero, so preventing the static magnetic field building up in the core of the equipment transformer.

Thank Odin that Asgaard has not these issues. But in truth, how is one to re-create mains waveform symmetry?

Piscovery posted:

I have a Isotek Synchro to my Nap250.2. No humming sound now. I do not think that the synchro change the sound from the 250.2 except eliminate humming sound.

Interesting device, I might have to try one of these out! 

Loki posted:

Thank Odin that Asgaard has not these issues. But in truth, how is one to re-create mains waveform symmetry?

I'm sure that Heimdallr wouldn't ever allow such contamination from Miðgarðr to enter Ásgarðr.

However should you need to assist us mere mortals, you need something that will pass AC but not transmit anything of an unvarying nature; this way the waveform is re-balanced about the average point.  This prevents the magnetic offset in the transformer core.

Isolation transformers and capacitors will both do the job (but you need very different circuit configurations to make them work).

Let us hope that we can keep Jörmungandr at bay.

So in effect are we trying to filter out DC?

Hmm, sort of.  You can interpret it as a DC component superimposed on a distorted AC waveform.

The reality is that one cycle of the mains is larger than the other (i.e. +ve cycles are larger than -ve or vice versa).

Thank you for your ever lucid explanations Sir Huge. Perhaps we could employ Brísingamen as a filter?

Got Hi-Fi? posted:

Interesting device, I might have to try one of these out! 

Go careful, try before buy.    It will filter AC waveform distortion  (DC offset),  but if your transformer is 'naturally' noisy, it will do nothing.   If the hum/noise changes during the day/evening its probably DC & it probably will help/fix that,  but if the hum is constant in tone & volume,  you might have a naturally noisy transformer & better to try before buy. 

Loki posted:

Thank you for your ever lucid explanations Sir Huge. Perhaps we could employ Brísingamen as a filter?

In that case, you'd better be quick before Heimdallr comes after you.

P.S.  The seal disguise isn't going to work.

Damn and blast you have the foresight of Heimdallr but mortal you cannot yet foretell what shall become of his Gjallarhorn or, indeed, Gulltoppr.

Mike-B posted:

Got Hi-Fi? posted:

Interesting device, I might have to try one of these out! 

Go careful, try before buy.    It will filter AC waveform distortion  (DC offset),  but if your transformer is 'naturally' noisy, it will do nothing.   If the hum/noise changes during the day/evening its probably DC & it probably will help/fix that,  but if the hum is constant in tone & volume,  you might have a naturally noisy transformer & better to try before buy. 

Thanks for the info Mike. Most of the time I cannot even hear it, it is very quiet. Then all of the sudden it will start buzzing like crazy, loud enough to wake me up, then it will stop again in 5 - 10 mins. Some days I can hear a low level buzz coming out of it as well, and other days nothing. I do know we have dirty power here, lots of surges and brown outs too. Ideally, I would like to find a good all around protection/filtering device that wont affect sound to much. 

I am using a syncro with great results to remove DC-led buzz. As you can see in my profile, this plugs into a good passive powerbar, which I can recommend.

what I dont understand is that you write that syncro into 250.2 has no results. Do you mean that it does not stop the buzz/humm, or that the amp does not get enough power?

i will myself try to take the syncro out to see if that opens up in case its the second one you mean

lars

Got Hi-Fi? posted:

Mike-B posted:

Got Hi-Fi? posted:

Interesting device, I might have to try one of these out! 

Go careful, try before buy.    It will filter AC waveform distortion  (DC offset),  but if your transformer is 'naturally' noisy, it will do nothing.   If the hum/noise changes during the day/evening its probably DC & it probably will help/fix that,  but if the hum is constant in tone & volume,  you might have a naturally noisy transformer & better to try before buy. 

Thanks for the info Mike. Most of the time I cannot even hear it, it is very quiet. Then all of the sudden it will start buzzing like crazy, loud enough to wake me up, then it will stop again in 5 - 10 mins. Some days I can hear a low level buzz coming out of it as well, and other days nothing. I do know we have dirty power here, lots of surges and brown outs too. Ideally, I would like to find a good all around protection/filtering device that wont affect sound to much. 

Sounds like you could have a dodgy appliance somewhere, maybe a fridge or heating system cutting in. Can you turn off non-HiFi circuits or individual items and see if that improves things? 

Got Hi-Fi? posted:

Thanks for the info Mike. Most of the time I cannot even hear it, it is very quiet. Then all of the sudden it will start buzzing like crazy, loud enough to wake me up, then it will stop again in 5 - 10 mins. Some days I can hear a low level buzz coming out of it as well, and other days nothing. I do know we have dirty power here, lots of surges and brown outs too. Ideally, I would like to find a good all around protection/filtering device that wont affect sound to much. 

OK,  thats a good clue,  most likely a device using half wave rectification to reduce power or speed. Its rare these days to use this type of control with the exception of hand held hairdryers,  modern fixed devices like fridges & heating/cooling systems have moved on,  but you might have an old or maybe defective item.  You need to try to find if its something in your property that is switching on & off at the same time & the rest is up to you.   If its not in your property then its a neighbour on the same phase & there's not much you can do about that - except try & maybe buy a DC blocker .    

Although many devices have moved on from basic SCRs and the like, switch mode powersupplies can still cause DC offsets, as they draw current for only part of the duty cycle.. such as washing machines, variable speed vacuum cleaners, tumble dryers, microwaves ... you name it may all cause varying degrees of DC offset  in the mains in various modes of operation.. and this can be acculumaltive on your mains distribution phase between your house and your substation/distribution transformer.. Short of using a DC blocker I am not sure there is any other reliable solution if you are plagued by this... and it's highly efficient large toroidal transformers as used in hifi  power amps and large power supplies that are most sensitive to it. I guess as long as the transformer under no load does not get unusually warm no harm should ensue

All true,   but this is not low level DC mush that Got Hi-Fi? is reporting  - " it will start buzzing like crazy, loud enough to wake me up, then it will stop again in 5 - 10 mins." - this is indicative of half wave rectification & involving quite high current draw to cause such offset.    Whatever,  if he can find the cause it will make the DC block filter purchase path a little clearer.    

ChrisSU posted:

Got Hi-Fi? posted:

Mike-B posted:

Got Hi-Fi? posted:

Interesting device, I might have to try one of these out! 

Go careful, try before buy.    It will filter AC waveform distortion  (DC offset),  but if your transformer is 'naturally' noisy, it will do nothing.   If the hum/noise changes during the day/evening its probably DC & it probably will help/fix that,  but if the hum is constant in tone & volume,  you might have a naturally noisy transformer & better to try before buy. 

Thanks for the info Mike. Most of the time I cannot even hear it, it is very quiet. Then all of the sudden it will start buzzing like crazy, loud enough to wake me up, then it will stop again in 5 - 10 mins. Some days I can hear a low level buzz coming out of it as well, and other days nothing. I do know we have dirty power here, lots of surges and brown outs too. Ideally, I would like to find a good all around protection/filtering device that wont affect sound to much. 

Sounds like you could have a dodgy appliance somewhere, maybe a fridge or heating system cutting in. Can you turn off non-HiFi circuits or individual items and see if that improves things? 

The only thing I have found so far is an electric Kettle. For some reason it drives my HiCap bonkers. 

Aside from the Kettle, which I did catch, I have a feeling it may be the neighbours as everyone in the house was asleep every other time it happened. Emotiva has a DC blocker for $150 cdn. I guess I could always try that before spending more on something better. 

Mike-B posted:

All true,   but this is not low level DC mush that Got Hi-Fi? is reporting  - " it will start buzzing like crazy, loud enough to wake me up, then it will stop again in 5 - 10 mins." - this is indicative of half wave rectification & involving quite high current draw to cause such offset.    Whatever,  if he can find the cause it will make the DC block filter purchase path a little clearer.    

There is a slim chance that it could be the furnace fan when it first comes on as well, I say slim only because I think i would have heard it do this more if it was that. Still a possibility and one I couldn't really do anything about other than a blocker. 

If it was the furnace fan then maybe a replacement fan motor would be worth trying? Or try running it from a hired mains generator instead of thermal mains. But I don't really know the furnace technology well enough to know whether that is a realistic thing to try.

best

David

If it can be pinned down to the furnace fan,  & if the fan has full & half speed (only) operation,  its very possibly that.  Also irrespective of any fan speed control its might be its start or run capacitor gone belly up.

It is a brand new furnace, and runs very well so i doubt any of its parts are defective. I will have to try and be around the system when it kicks in during the day sometime so I can know for sure. If it is caused by this, the cap only buzzes for a few mins then quiets down, so it would have to be on furnace start up only. 

HansW posted:

I think you should replace the Isotek Sirius power board with a non-filtered, non-switched power distribution block.  The Sirius is probably holding back the whole system. Try a standard cheap one to start, plug it inte the Syncro, and your whole system will probably benefit. 

 

Best regards

Hans

Or it will not, but a test is a good idea.

Claus   

Got myself a AH! DC Offset Killer. No hum/buzz since. I'm sure other offset killers will do the trick too, it's not an overly complicated design. 

I have a custom build Airlink balancing transformer that has eliminated the hum. I had 2 problems - a relatively high incoming mains voltage that was typically 246v, coupled with some DC offset. I initially tried a standard BPS150230, but under low loads the impact of transformer regulation pushed the outputs to around 254v, which is outside of spec. Airlink proposed a custom wound 10kVA with primary taps at 230, 240, and 250v with a balanced output of 230v. I use the 250v primary to effectively step down my input voltage to a tad under 230v and eliminate the DC offset through the grounded centre tap on the secondary.