I am looking for reducing mechanical hum of a big toroidal transformer (2000VA).
A DC-filter according
DC-Blocker - Scintilla-buizenversterkers
is already in use.
But in those cases where the mains voltage rises above 233-235VAC, suddenly annoying humming occurs again.
Using of a serial resistor is the wrong solution, but a choke with just the number of turns over which 5-10VAC drop (while at the same time the RDC value of the coil is so small that it can be neglected in order to the dynamic behavior of the associated power amp) should actually be a good approach.
Where I can order such inductor parts in a suited VA value above 2KVA ?
P.S.: An isolating transformator from 240VAC to 220-230VAC is the very best solution but too expensive due the necessary high VA-value.
A DC-filter according
DC-Blocker - Scintilla-buizenversterkers
is already in use.
But in those cases where the mains voltage rises above 233-235VAC, suddenly annoying humming occurs again.
Using of a serial resistor is the wrong solution, but a choke with just the number of turns over which 5-10VAC drop (while at the same time the RDC value of the coil is so small that it can be neglected in order to the dynamic behavior of the associated power amp) should actually be a good approach.
Where I can order such inductor parts in a suited VA value above 2KVA ?
P.S.: An isolating transformator from 240VAC to 220-230VAC is the very best solution but too expensive due the necessary high VA-value.
Last edited:
See -
Bucking Xfmrs
Section 3 - Bucking Transformer.
However, the mystery is why a slight supply voltage increase should cause humming.
Perhaps the surface it is mounted to is amplifying the hum; mechanical isolation may prove a more satisfying solution.
Bucking Xfmrs
Section 3 - Bucking Transformer.
However, the mystery is why a slight supply voltage increase should cause humming.
Perhaps the surface it is mounted to is amplifying the hum; mechanical isolation may prove a more satisfying solution.
If the core is running very close to saturation and you have the magnetising current spiking at the end of the mains sine wave that can cause it .
Yes reducing the input mains voltage will cure it ---in THIS case.
Yes reducing the input mains voltage will cure it ---in THIS case.
yes, check out therefore the images in post #39 under
Variations of DC Main Filter against buzzing Toroid Transformers - what is the right?
Variations of DC Main Filter against buzzing Toroid Transformers - what is the right?
Thank you for this advice.
Last edited:
In your case, the buzzing is probably caused by saturation-induced magnetostriction, or electrodynamic forces on untightened wires, also resulting from current peaks arising from saturation.
In both cases, the buzz and its harmonics are going to be even multiples of the mains frequency (unlike DC bias, which causes odd-order components).
Reducing the primary voltage will solve both, but using a series impedance to that effect has serious drawbacks: it will need to be substantial to reduce the voltage under no-load condition and this will cause a severe drop under full load.
A bucking transformer, or some additional primary turns are far more preferable
In both cases, the buzz and its harmonics are going to be even multiples of the mains frequency (unlike DC bias, which causes odd-order components).
Reducing the primary voltage will solve both, but using a series impedance to that effect has serious drawbacks: it will need to be substantial to reduce the voltage under no-load condition and this will cause a severe drop under full load.
A bucking transformer, or some additional primary turns are far more preferable
I guess that adding an external autoformer ist the most practicable solution.
I've modified a wall wart containing a 230/12 Vac 12 VA transformer by connecting both windings in series with correct phasing. The new 242 Vac primary connects to the 230 Vac mains, giving a voltage of 230²/242 = 219 Vac at the 230 V tap. This allows me to feed some older 220 Vac gear up to a power consumption of 242 VA from that device. Same may apply to the OP's task, whereas a more suitable tranny with a lower voltage secondary (5 Vac perhaps) may be needed.
Best regards!
I've modified a wall wart containing a 230/12 Vac 12 VA transformer by connecting both windings in series with correct phasing. The new 242 Vac primary connects to the 230 Vac mains, giving a voltage of 230²/242 = 219 Vac at the 230 V tap. This allows me to feed some older 220 Vac gear up to a power consumption of 242 VA from that device. Same may apply to the OP's task, whereas a more suitable tranny with a lower voltage secondary (5 Vac perhaps) may be needed.
Best regards!