I have a write-up on this issue and a short YouTube video showing how transformer 'growl' (as opposed to rattling from a loose core or electrically induced hum from EM radiation) can be reduced by a simple mains DC blocker. You almost never get 'growl' from a small transformer because the winding impedance + primary resistance is high. On a big toroid (1.2 kVA) I measured the primary DC resistance at 1.4 Ohms. It doesn't take much DC offset on the mains to get quite large unsymmetrical currents to flow in a low primary resistance like this and that shifts the BH curve which in severe cases can result in saturation and a popped mains fuse. I use very high quality mains transformers that have the core inside a plastic over-mold actually filled with resin so there is zero mechanical noise. The final transformer is cloth wound and double vacuum impregnated. But, this solves mechanical noise but not transformer growl with bad mains supply - you really have to employ a DC blocker if you want to get rid of that problem.
(I am a bit surprised at the Prima Luna solution - it will not block mains DC with those low value caps).
https://hifisonix.com/soft-start-dc-blocker-for-mains/
(I am a bit surprised at the Prima Luna solution - it will not block mains DC with those low value caps).
https://hifisonix.com/soft-start-dc-blocker-for-mains/
Last edited:
Plug a hair dryer into a mains socket and switch it to half power. You will get DC on the mains.
You will not see the issue with low VA transformers and it’s much reduced in EI core types. It’s s specific issue with high VA toroids. Watch the video posted in #62 to see this issue in practice.
You will not see the issue with low VA transformers and it’s much reduced in EI core types. It’s s specific issue with high VA toroids. Watch the video posted in #62 to see this issue in practice.
the solution then is obvious, do not use hairdryers, microwave ovens, washing machines, induction cookers when listening to your audio gears....the best imho is to identify the source and do something about it, such as unplugging them when not in use...
my best solution is to use a 240:240 isolation traffo for another layer of protection...
my best solution is to use a 240:240 isolation traffo for another layer of protection...
Attachments
You can do that, but often you don't have control over that - for example if you live in an apartment or demi-detached house.
This is just one of the things you have to accept with big toroids - you get very low radiated fields, very compact transformers compared to EI but they are prone to growling because of the BH curve shift unless you take special measures.
This is just one of the things you have to accept with big toroids - you get very low radiated fields, very compact transformers compared to EI but they are prone to growling because of the BH curve shift unless you take special measures.