Just checked the "Audio Grade" ones I ordered and they have a epoxi center negating the need for metal sheets holding them down so you may very well be onto something with this, thanks.
There seems to be a pattern to the humming, I have galvanically insulated the metal holding down the trafo which helped (thx Jean-Paul).
Cold starting the amp it is now mostly quiet, I can still hear humming with my ears 10cm above each trafo which is a bit more than my other amps but not really a problem.
However, after a few hours with the amp running and trafo/casing getting to around 40C it starts to humm.
I checked the power draw and it's exactly the same as when cold so something must be going on with the temp and materials in toroid trafo?
Cold starting the amp it is now mostly quiet, I can still hear humming with my ears 10cm above each trafo which is a bit more than my other amps but not really a problem.
However, after a few hours with the amp running and trafo/casing getting to around 40C it starts to humm.
I checked the power draw and it's exactly the same as when cold so something must be going on with the temp and materials in toroid trafo?
Reporting back on this as promised and to help others deciding on what trafo to get.
I just switched the trafos to mid range audio versions ie not screened/covered by a metal box and they are in fact completely quiet as advertised/promised.
The audio grade ones were not more expensive either so all in all its a simple choice for anyone considering what trafo to get.
I just switched the trafos to mid range audio versions ie not screened/covered by a metal box and they are in fact completely quiet as advertised/promised.
The audio grade ones were not more expensive either so all in all its a simple choice for anyone considering what trafo to get.
Most commercial toroidal transformers are run at or near the maximum flux density
for the core material for cost reasons. They can easily saturate if the ac voltage is a little high
which will cause hum. Audio grade toroids are wound on a larger core ie a 500VA core for a 300VA
rated transformer. This is not the same as just using a larger transformer. You could ask your supplier if this is what they do.
for the core material for cost reasons. They can easily saturate if the ac voltage is a little high
which will cause hum. Audio grade toroids are wound on a larger core ie a 500VA core for a 300VA
rated transformer. This is not the same as just using a larger transformer. You could ask your supplier if this is what they do.
If that is true then these are not of good quality and probably low budget/Far East brands. I use Polytronic, Sedlbauer, Noratel in 230V versions and these are quiet except when the mains voltage is polluted but DC blockers are a must with toroids anyway.
It can still be that the parts of the OP have transport damage and that there is a crack in the core (there is only one way to find out) and maybe the shorted winding caused effects as well. We also don't know that when they were mounted wrong there was too much force applied as it is simple the wrong method to mount them like that. I use medical transformers and very small toroids in the 7 to 50VA class of the same brand and I don't hear these at all. So it might just be that this pair is behaving like this, maybe because of a user error. I would ask the manufacturer first (as it is a quality brand) if they are familiar with this and maybe they send a new pair. I recently had a tool breaking and a simple email and sending the tool resulted in a examination why it broke and this brand sent me a new tool.
To recommend audio toroids, well if it floats your boat... It is a better advice to switch to Rcore transformers if you ask me. Saves a DC blocker too.
It can still be that the parts of the OP have transport damage and that there is a crack in the core (there is only one way to find out) and maybe the shorted winding caused effects as well. We also don't know that when they were mounted wrong there was too much force applied as it is simple the wrong method to mount them like that. I use medical transformers and very small toroids in the 7 to 50VA class of the same brand and I don't hear these at all. So it might just be that this pair is behaving like this, maybe because of a user error. I would ask the manufacturer first (as it is a quality brand) if they are familiar with this and maybe they send a new pair. I recently had a tool breaking and a simple email and sending the tool resulted in a examination why it broke and this brand sent me a new tool.
To recommend audio toroids, well if it floats your boat... It is a better advice to switch to Rcore transformers if you ask me. Saves a DC blocker too.
Last edited:
I've been considering these Triad split bobbin transformers for preamp projects.
PC Mount Split Pack™ Class 2/3 Power Transformers On Triad Magnetics
How would these compare to the toroids being discussed?
PC Mount Split Pack™ Class 2/3 Power Transformers On Triad Magnetics
How would these compare to the toroids being discussed?
Despite Triad being a good brand for a preamp there is a better choice unless you mount these split bobbin types far away at a distance from the sensitive electronics and use a shield between these and the electronics.
Well I would repeat myself but for sensitive electronics Rcore transformers are the way to go (more than in a power amp). I have seen fellow DIYers that used these less than 10 mm from DAC circuits and although it is still wiser to mount them further away these devices had no hum issue.
Well I would repeat myself but for sensitive electronics Rcore transformers are the way to go (more than in a power amp). I have seen fellow DIYers that used these less than 10 mm from DAC circuits and although it is still wiser to mount them further away these devices had no hum issue.
Last edited:
again... which is? If not Triad, what?
I've assumed that best practice is to put the PSU in a separate box at a distance so... that's what I'm doing in any event.
I've assumed that best practice is to put the PSU in a separate box at a distance so... that's what I'm doing in any event.
If that is what you will be doing and the box is metal then the main issue will be the filtering properties of the transformer in which case toroids are the worst again and the split bobbin type (preferably with a screen) can be the right one. Rcore types being overkill. When power consumption is very low you could use slow curing epoxy and mold the transformers and then they will be as silent as can be.
With Rcore types I wouldn't bother using a separate casing and make it a one box affair with best user friendliness and least clutter. Personally I build like a madman (quantity and quality) and don't use separate boxes except when the devices use adapters anyway in which case I replace these with own designs. So any remark is in my experience of building devices.
With Rcore types I wouldn't bother using a separate casing and make it a one box affair with best user friendliness and least clutter. Personally I build like a madman (quantity and quality) and don't use separate boxes except when the devices use adapters anyway in which case I replace these with own designs. So any remark is in my experience of building devices.
Last edited:
Thanks for shining a light on this matter.
How do O-core transformers fit into this spectrum?
O core transformer_James transformer-custom toroidal transformer|R core transformer|O core transformer|C core transformer|EI transformer
How do O-core transformers fit into this spectrum?
O core transformer_James transformer-custom toroidal transformer|R core transformer|O core transformer|C core transformer|EI transformer
Seem them and only now realise I took them for toroids. I think Sony uses/used these in amplifiers. Wouldn’t know how these compare to other types as I use the same preferred type and toroids when it needs to be cheaper.
Not sure what's going on with you, do you work for Noratel etc? My findings are 100% true and the comparable trafos were 2 new 230v Noratels with a "passed" sticker well packed for transport and without any visible damage.
Please stop trying to confuse this issue, there are plenty of info on the interweb and others in this thread on how the core gets saturated and what can be done to minimize this which is what audio grade trafos is about. Even your DC filter does the same thing.
The audio grade ones I got was not more expensive either and they are dead quite without a DC blocker so all in all a much better choice and happy to share my findings with other DIY on here.
Good for you if you can make the Noratels work but if that takes a DC blocker it's really not that great...
You approach is not technical/analytical. You have 2 toroids of brand X that were both mounted wrong and had a shorted winding. It can be that just your pair is behaving like that and any 2 new ones of the exact same type may not exhibit the issue... So it would be OK to exclude transport damage, user error, batch error in production as possible causes.
No visible damage is clear as a cracked core can only be seen when dismantling the transformer. I would follow the advice by asking the brand if they can help out as their product should not operate like that. If they are a quality brand they will ask you to ship the transformers and they will test what is wrong. They will likely measure and dismantle it and report back. This is the only way in industrial stuff to know where and what went wrong. As they are located in Norway shipping won't cost an arm and a leg either. If they ship 2 new ones with a report what was wrong with the old ones you can draw a conclusion yourself. If your intention is to advise DIYers not to use toroids of brand X based on your experiences of just 2 of the same type then it is illogical not to mention the type number nor pictures. Suppose All the toroids to be perfect and only your pair to malfunction 🙂 it would then be logical to have these tested why they malfunction. It is most illogical to advise people to use audio toroids based on experience with just 1 pair of type Y by brand X.
If audio would need toroids for audio this would indicate industrial stuff to be less good which is simply not true. Your issue is 2 pieces A branded toroids humming heavily but a user error was done to both so it would be interesting to know what the brand thinks of this issue.
It may not be clear to you but any toroid can hum from DC on mains voltage. It comes with the type.
No visible damage is clear as a cracked core can only be seen when dismantling the transformer. I would follow the advice by asking the brand if they can help out as their product should not operate like that. If they are a quality brand they will ask you to ship the transformers and they will test what is wrong. They will likely measure and dismantle it and report back. This is the only way in industrial stuff to know where and what went wrong. As they are located in Norway shipping won't cost an arm and a leg either. If they ship 2 new ones with a report what was wrong with the old ones you can draw a conclusion yourself. If your intention is to advise DIYers not to use toroids of brand X based on your experiences of just 2 of the same type then it is illogical not to mention the type number nor pictures. Suppose All the toroids to be perfect and only your pair to malfunction 🙂 it would then be logical to have these tested why they malfunction. It is most illogical to advise people to use audio toroids based on experience with just 1 pair of type Y by brand X.
If audio would need toroids for audio this would indicate industrial stuff to be less good which is simply not true. Your issue is 2 pieces A branded toroids humming heavily but a user error was done to both so it would be interesting to know what the brand thinks of this issue.
It may not be clear to you but any toroid can hum from DC on mains voltage. It comes with the type.
Last edited: