he said 1.5A
that's where I took it from.
This allows about 220W at maximum operating power into the mains transformer.
However the situation is much worse than this.
We all know that the current flow into a mains transformer feeding a capacitor input filter is not a sinewave. It is peaks of current that flow for ~10% duty cycle.
The peak current of those charging pulses must be less than 1.5A and this will probably limit the operating power of that typical example I showed to <<100W.
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Akis
Please bear in mind that if your transformer is from Farnell then it is highly likely that the transformer originated from China and is constructed from reclaimed or second hand core steel. The problem with toroids is that you cannot see the core and therefore a lot of cost cutting takes place in this area. I have seen some examples of cores in these products and they are just short of disgraceful!! They are made basically out of short strips of material welded together to produce one long strip that is wound up into a core.
The stuff coming out of China, due to the insistence of companies like Farnell of forever forcing market prices down, are probably OK for lighting or control use but are of little use to high quality audio supplies. It is just a fact of life these days!
Cheers
Ray
Please bear in mind that if your transformer is from Farnell then it is highly likely that the transformer originated from China and is constructed from reclaimed or second hand core steel. The problem with toroids is that you cannot see the core and therefore a lot of cost cutting takes place in this area. I have seen some examples of cores in these products and they are just short of disgraceful!! They are made basically out of short strips of material welded together to produce one long strip that is wound up into a core.
The stuff coming out of China, due to the insistence of companies like Farnell of forever forcing market prices down, are probably OK for lighting or control use but are of little use to high quality audio supplies. It is just a fact of life these days!
Cheers
Ray
Transformer came from RS Components, I unearthed the receipts. Unfortunately a few days past the warranty expiry.
However Farnell tech support said a quiet buzz is quite normal as long as it does not get hot (past 70C).
Why is the ferrite core so hard to make as you describe (welding strips together etc)? Steel is cheap and if you have a factory making these things it would be even cheaper still. I can buy a whole steel radiator for 20-50 pounds as an end consumer. The toroidal core is just a lump of iron, I cannot believe Farnell and RS are making any less than 300% profit on these items. Perhaps I am wrong and the toroidal core is encrusted with diamonds
However Farnell tech support said a quiet buzz is quite normal as long as it does not get hot (past 70C).
Why is the ferrite core so hard to make as you describe (welding strips together etc)? Steel is cheap and if you have a factory making these things it would be even cheaper still. I can buy a whole steel radiator for 20-50 pounds as an end consumer. The toroidal core is just a lump of iron, I cannot believe Farnell and RS are making any less than 300% profit on these items. Perhaps I am wrong and the toroidal core is encrusted with diamonds
Hi Akis
The core is not made out of ferrite material, it is made (or should be made!) from grain oriented silicon steel (basically an iron with 3% or so silicon and other odds and sods added) and this material is not as cheap as ordinary iron or steel. This material needs to have an insulating oxide coating on both sides for use with AC magnetisation before being wound into a core, and annealed after being formed into a core to restore the materials rolled magnetic properties. If it were solid, your transformer core would be cherry red in no time at all due to eddy current heating!!
The core should be made of a continuous strip of this material, wound up like a clock spring to form the core. I am not sure about RS components transformers as these I believe are made in India, but the Chinese are selling an awful lot of toroidal cores into the worlds transformer market. I am not saying all Chinese cores are rubbish, but a very high proportion of what I have seen leave a lot to be desired.
The components sold by RS/Farnell are very much general purpose components and therefore acoustic noise could be an issue in audio. However there is no reason why a well designed and manufactured toroidal component should hum under normal conditions of use and should always be quieter than it's equivalent EI laminated transformer
Cheers
Ray
The core is not made out of ferrite material, it is made (or should be made!) from grain oriented silicon steel (basically an iron with 3% or so silicon and other odds and sods added) and this material is not as cheap as ordinary iron or steel. This material needs to have an insulating oxide coating on both sides for use with AC magnetisation before being wound into a core, and annealed after being formed into a core to restore the materials rolled magnetic properties. If it were solid, your transformer core would be cherry red in no time at all due to eddy current heating!!
The core should be made of a continuous strip of this material, wound up like a clock spring to form the core. I am not sure about RS components transformers as these I believe are made in India, but the Chinese are selling an awful lot of toroidal cores into the worlds transformer market. I am not saying all Chinese cores are rubbish, but a very high proportion of what I have seen leave a lot to be desired.
The components sold by RS/Farnell are very much general purpose components and therefore acoustic noise could be an issue in audio. However there is no reason why a well designed and manufactured toroidal component should hum under normal conditions of use and should always be quieter than it's equivalent EI laminated transformer
Cheers
Ray
Simular problem - revive old thread
Hi. -I have a pair of LM3875 kits that have been running well for several months.
My transformers (Avel Lindberg 330VA 25v + 25v) have been making noise. This noise does not audible through the speakers. I can actually feel the transformers vibrating when they make noise. A few months ago, it happened once in the evening, and I turned it off and went to bed. In the morning I was going to check into the problem, but there was no noise... in the morning the problem was gone.
This problem happened a couple times over a couple of months, and then began to happen more often. The transformers would always make their noise at night, regardless if the amps had been running all day, or had been off all day and then turned on at night. I thought that maybe the Electric Company here was giving me "cheaper" electricity at night maybe?? -However now the problem happens during daytime hours too.
My suspicion was that I had a loose winding, or somehow something had come de-laminated, and so overtime this loose winding that was vibrating began to get looser and looser and the problem happening more often. Would this be covered by Warranty from Avel Lindberg?
Just a moment ago (and it's night time now) I disconnected the power cord, and plugged it into my test cord, which has a light bulb in-series on the live mains. -When I turned the amp on, the light flashed and immediately went dark. Power is on, light bulb is not illuminated and THERE IS NO NOISE coming from the transformer anymore.
What does this mean? The light bulb couldn’t possibly be blocking DC current could it?
Is there a way that I can measure the AC Mains to see if there is DC there before I go to the trouble of building a DC Blocker or Filter? I'm unsure if the meter I have is up to the job of measuring the mains. I think it can handle up to 10A/250V but in that mode I think it will only tell me that I have 125volts of AC power.
Would you try to return the transformers under warranty, or build a DC Blocker? Is there a way to test for DC on the mains without building a filter?
Thanks in advance for any guidance or suggestions you can offer.
Hi. -I have a pair of LM3875 kits that have been running well for several months.
My transformers (Avel Lindberg 330VA 25v + 25v) have been making noise. This noise does not audible through the speakers. I can actually feel the transformers vibrating when they make noise. A few months ago, it happened once in the evening, and I turned it off and went to bed. In the morning I was going to check into the problem, but there was no noise... in the morning the problem was gone.
This problem happened a couple times over a couple of months, and then began to happen more often. The transformers would always make their noise at night, regardless if the amps had been running all day, or had been off all day and then turned on at night. I thought that maybe the Electric Company here was giving me "cheaper" electricity at night maybe?? -However now the problem happens during daytime hours too.
My suspicion was that I had a loose winding, or somehow something had come de-laminated, and so overtime this loose winding that was vibrating began to get looser and looser and the problem happening more often. Would this be covered by Warranty from Avel Lindberg?
Just a moment ago (and it's night time now) I disconnected the power cord, and plugged it into my test cord, which has a light bulb in-series on the live mains. -When I turned the amp on, the light flashed and immediately went dark. Power is on, light bulb is not illuminated and THERE IS NO NOISE coming from the transformer anymore.
What does this mean? The light bulb couldn’t possibly be blocking DC current could it?
Is there a way that I can measure the AC Mains to see if there is DC there before I go to the trouble of building a DC Blocker or Filter? I'm unsure if the meter I have is up to the job of measuring the mains. I think it can handle up to 10A/250V but in that mode I think it will only tell me that I have 125volts of AC power.
Would you try to return the transformers under warranty, or build a DC Blocker? Is there a way to test for DC on the mains without building a filter?
Thanks in advance for any guidance or suggestions you can offer.
I don't have a definite answer to your problem. Are the transformer mounts secure? Have you checked the AC mains voltage during these different times? The voltage may be peaking at night, or certain times during the day. One thing I'm sure of is that you do not have DC coming in on your AC mains.
edit: BTW, your meter will read the AC mains. Select AC voltage mode, set to the 200V range, keep your fingers well behind the finger guards on the probes, and stick them right into the wall socket. You may have to angle the probe tips a bit to get good contact for a stable reading. Nothing to it; just proceed with care.
edit: BTW, your meter will read the AC mains. Select AC voltage mode, set to the 200V range, keep your fingers well behind the finger guards on the probes, and stick them right into the wall socket. You may have to angle the probe tips a bit to get good contact for a stable reading. Nothing to it; just proceed with care.
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Thanks sofaspud. That's a good idea. I'll measure the mains at various times of day and see if I notice any variance.
As far as how they are mounted, not pretty (old pic attached)… I never did get them off of the test rig, and into a proper chassis. After the first time I heard them make noise, I worried that I may have over tightened them. Since then they have been finger tight, rather than wrench tight. I have the big foam washers on top and bottom. Should I tighten them up more,… or am I right that they don’t need to be too tight?
Another interesting detail is that they both do it at the same time. Unless I plug one of them into the light tester, as I just learned a little while ago. Maybe I should build another light tester.... this just doesn't seem like "the right way" to fix the problem though.
Any other thoughts anyone?
As far as how they are mounted, not pretty (old pic attached)… I never did get them off of the test rig, and into a proper chassis. After the first time I heard them make noise, I worried that I may have over tightened them. Since then they have been finger tight, rather than wrench tight. I have the big foam washers on top and bottom. Should I tighten them up more,… or am I right that they don’t need to be too tight?
Another interesting detail is that they both do it at the same time. Unless I plug one of them into the light tester, as I just learned a little while ago. Maybe I should build another light tester.... this just doesn't seem like "the right way" to fix the problem though.
Any other thoughts anyone?
Attachments
With my toroidal, the buzzing would go away as the current increased. Can you put a dummy load of some kind and try to pull power out of the transformer and see if that stops the noise.
Thanks Akis,
I don't have any spare parts on hand right now. I assume that a dummy load would be to put a resistor accross the secondaries.
If that's right, what value resistor would I get if I go to town?
Additional thought: Did you find a way to solve your problem Akis? I just re-read the post, and I see that you were just past the expiration date of warranty. Like yours, mine don't get hot either. With the volume up, and back at the listening position, I don't think I notice it.... except that psycho-accoustics makes me wonder if the problem with the trafo is somehow affecting the quality of the sound that the amp can make. I just rechecked the output of the rectifier board, it's normal V+ & V- feeding the amp.
I don't have any spare parts on hand right now. I assume that a dummy load would be to put a resistor accross the secondaries.
If that's right, what value resistor would I get if I go to town?
Additional thought: Did you find a way to solve your problem Akis? I just re-read the post, and I see that you were just past the expiration date of warranty. Like yours, mine don't get hot either. With the volume up, and back at the listening position, I don't think I notice it.... except that psycho-accoustics makes me wonder if the problem with the trafo is somehow affecting the quality of the sound that the amp can make. I just rechecked the output of the rectifier board, it's normal V+ & V- feeding the amp.
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the bulb tester is intended as a protection device and when used in a "working" amplifier will have effects that can interfere with good performance.
The filament resistance when in line will have an effect on the total current passing through the primary of your toroid.
Now to a bit of guessing:
If the hum is due to excessive primary current (flux too high for the core type) then adding the bulb may just reduce it enough to make the hum inaudible.
If that last guess is correct then your transformer is not rated for the voltage you have at home. How do you prove that?
I would test the transformer, but I have some resources at hand and I know my range of mains voltage.
You are on a loser. You have few resources and you don't know your range of mains voltage.
The filament resistance when in line will have an effect on the total current passing through the primary of your toroid.
Now to a bit of guessing:
If the hum is due to excessive primary current (flux too high for the core type) then adding the bulb may just reduce it enough to make the hum inaudible.
If that last guess is correct then your transformer is not rated for the voltage you have at home. How do you prove that?
I would test the transformer, but I have some resources at hand and I know my range of mains voltage.
You are on a loser. You have few resources and you don't know your range of mains voltage.
Mine is making a mechanical buzz, but it's been in operation for years and the buzz is only there when there is no load. Of course the transformer has been in an enclosure for the past few years so I have no idea if it still buzzes.
I'd say you 'd need a 12W-25W resistor across the secondaries, at about 25-50R, but these are not cheap. In my case , I remember, the buzzing stops immediately with load, so it is not needed to stress-test the dummy load either, you can simply use a 1W or 5W resistor and as long as it's a small amount of time it should be OK. As a simple guide, with 25V secondaries, a 25R resistor would draw 1A of RMS current.
If you have a scope you can use it to check the secondaries of the transformer, that will also show you the shape of the mains but without needing to connect the probes to the mains. I'd connect a 3K resistor across each secondary before attaching the probes just to draw some current. Make sure you do not measure two secondaries at the same time with the scope because the earth lead might short things out.
Not a concern.
The scope is "earthed". The probe of the scope is also "earthed".
The secondaries of the transformer are isolated.
You can connect the probe and it's "earthed" clip to any of the isolated leads.
It's the isolation that allows this.
It's when you start connecting some of the PSU back into the PE ("earth") that you lose the isolation. THEN you must be careful where the "earthed" clip of the scope is connected to.
AndrewT THANKYOU.
Your guesses make perfect sense to me.
Here's what I know. At the moment it is daylight. The transformers are not buzzing, and I have measured the mains voltage at 120.5 Volts.
I will measure again at a later time in the day. I suspect that at night, when less of my neighbors are using electricity it will go up to 125V -Does that sound logical? I will report back after I measure the mains voltage when the trafo's are buzzing.
I have the primaries connected in parallel.
So if it turns out that the AC Voltage goes even higher at night, and this is what causes the buzzing because the transformers are supposed to get 115v -then what would be a solution? Is there something simple I can put in front of the transformer that will bring the AC Voltage down to 115?
Another idea I have is that if this problem isn't too big of a deal (i.e. not dangerous, and not affecting performance of amp) than maybe I need to simply build a proper chassis that would hopefully dampen the sound of the occasional vibration so as I wouldn't notice it.
Thanks again for your help!.
That's what I thought.
The lightbulb offers 45 ohms of resistance. It is not connected right now though.
Your guesses make perfect sense to me.
Here's what I know. At the moment it is daylight. The transformers are not buzzing, and I have measured the mains voltage at 120.5 Volts.
I will measure again at a later time in the day. I suspect that at night, when less of my neighbors are using electricity it will go up to 125V -Does that sound logical? I will report back after I measure the mains voltage when the trafo's are buzzing.
I’m not sure how to test it. The sticker on the Avel Toroidal says 330VA 50/60Hz then in the schematic on the picture where it lists the 8 wires and their colors of primaries and secondaries, on the primary side of that diagram between the two pairs it says 2x 115v
I have the primaries connected in parallel.
Thank goodness I have your help J
I will try to learn my range of mains voltage, by checking at various times.
So if it turns out that the AC Voltage goes even higher at night, and this is what causes the buzzing because the transformers are supposed to get 115v -then what would be a solution? Is there something simple I can put in front of the transformer that will bring the AC Voltage down to 115?
Another idea I have is that if this problem isn't too big of a deal (i.e. not dangerous, and not affecting performance of amp) than maybe I need to simply build a proper chassis that would hopefully dampen the sound of the occasional vibration so as I wouldn't notice it.
Thanks again for your help!.
Utility is using voltage regulators on the line, most likely. If voltage gets just a little high, say 124V, when load drops at night, the response will be to make a tap change and lower voltage, hence why it probably dropped to 118.
To improve your situation, if the load on the transformer is really constant, you could cheat and install a resistor in series with the primary. But the best way to drop voltage would be to install a small bucking transformer. There are a few threads around that describe how to do this. My suggestion would be to use a split bobbin and connect the secondary into the neutral end of the line voltage.
To improve your situation, if the load on the transformer is really constant, you could cheat and install a resistor in series with the primary. But the best way to drop voltage would be to install a small bucking transformer. There are a few threads around that describe how to do this. My suggestion would be to use a split bobbin and connect the secondary into the neutral end of the line voltage.
Now that we are getting noise vs supply voltage data, it seems to be not so clear whether it is saturation due to over voltage of the supply, or saturation due to DC component in the supply.
We need more data.
The two solutions are quite different. For the time being ignore the ideas in any posts.
We need more data.
The two solutions are quite different. For the time being ignore the ideas in any posts.
I appreciate everyone's efforts. Last night during buzzing time, I found that the mains voltage (after dropping to 118v) had returned to 120.5, which produced no buzz during the day time.
I presume that Art M's suggestion would lead me to find possible 'noise' in the mains current, and also to verify if I am getting 60Hz?? However I don't believe that I have the means to safely reduce the power to a level that I could feed it into my sound card.
Interestingly enough, to my untrained ear, when it happens it sounds a little slower than 60Hz. I have a little app on my phone that will generate tones, and a 60Hz square wave is a little bit higher pitched than the sound that my transformers make when they buzz at night time hours. Maybe the AC Mains drops to 50-55Hz at night?
My theory is that the end of the winding has come delaminated a little bit, and that this is a manufacturer error. Really I need to get the whole thing off of the silly piece of wood and into a proper chassis. I’ll call Avel’s phone number about the warranty while I’m in that process. Wouldn’t it be nice if I could just exchange them? They didn’t buzz at night when they were new 6 months ago.
Thanks again for the help!!
Sincerely,
Alex QS
I presume that Art M's suggestion would lead me to find possible 'noise' in the mains current, and also to verify if I am getting 60Hz?? However I don't believe that I have the means to safely reduce the power to a level that I could feed it into my sound card.
Interestingly enough, to my untrained ear, when it happens it sounds a little slower than 60Hz. I have a little app on my phone that will generate tones, and a 60Hz square wave is a little bit higher pitched than the sound that my transformers make when they buzz at night time hours. Maybe the AC Mains drops to 50-55Hz at night?
My theory is that the end of the winding has come delaminated a little bit, and that this is a manufacturer error. Really I need to get the whole thing off of the silly piece of wood and into a proper chassis. I’ll call Avel’s phone number about the warranty while I’m in that process. Wouldn’t it be nice if I could just exchange them? They didn’t buzz at night when they were new 6 months ago.
Thanks again for the help!!
Sincerely,
Alex QS
I am beginning to think that DC on the mains has become the intermittent problem.
This too leads to core saturation and the symptom is hum.
Try assembling a DC blocker. (very different from the filter cap on an amplifier)
But DO REMEMBER, the DC blocker is in the primary feed and is at MAINS VOLTAGE !!!!
This too leads to core saturation and the symptom is hum.
Try assembling a DC blocker. (very different from the filter cap on an amplifier)
But DO REMEMBER, the DC blocker is in the primary feed and is at MAINS VOLTAGE !!!!
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