Good day everyone. I am working on a small power amp using assembled power amp modules rated at 100 watts per channel, The chassis that I am using is compact and I want to know how close can I mount the toroid to the modules without any problems arising. Do I need to box it in with metal just to safe.. As well, the transformer did not come with a mounting kit so I will need to fabricate my own.. Any ideas on the best and inexpensive way to mount this unit. I got the enclosure on EBay but it arrived bent so I have asked for a refund or replacement.. The power supply board will use 4 10,000 MFD caps and an 8 amp bridge for power and should power the unit well. The transformer is rated at 400 VA which should be enough.. Any thoughts on any/all of the info is appreciated. Thanks again Wayne
Hi,
Central bolt and steel and rubber washers. If you have
the measuring equipment (or ears) there is apparently
some mileage in trying various orientations of the
transformer to minimise induced hum. Why a toroid
should do this is beyond me and basic theory, but
D.Self says its worth doing in a power amplifier.
Its better to buy canned toroids than boxing them in,
though most power amplifiers seem to not need either.
rgds, sreten.
Central bolt and steel and rubber washers. If you have
the measuring equipment (or ears) there is apparently
some mileage in trying various orientations of the
transformer to minimise induced hum. Why a toroid
should do this is beyond me and basic theory, but
D.Self says its worth doing in a power amplifier.
Its better to buy canned toroids than boxing them in,
though most power amplifiers seem to not need either.
rgds, sreten.
Put the caps and the bridge near the transformer so the wires can be short. Twist the wires to minimise magnetic induction into the audio circuit.
Toroid transformers do have lower radiated field as most other types, but this property depends on the tight coupling between primary and secondary windings and the symmetrical placement around the core.
Usually at the point where the wires enter the transformer the external field components are higher, so it is best to orientate that point away from the audio circuitry.
If you have an oscilloscope at hand you could use the probe (connect the gnd clip to the probe tip) as sniffer to locate the regions with higher external field.
Usually at the point where the wires enter the transformer the external field components are higher, so it is best to orientate that point away from the audio circuitry.
If you have an oscilloscope at hand you could use the probe (connect the gnd clip to the probe tip) as sniffer to locate the regions with higher external field.
Additional remarks:
If the height of the enclosure is not a limiting factor it is worth to try an orientation where the transformer is sort of standing up in diameter direction, not laying flat.
Don´t forget the tips from the other posters; distance works, twisting the wires and careful location of caps and bridge rectifiers helps to get the radiating loops small, but will not help wrt to radiated field of the transformer.
Shielding of magnetic field requires material with higher permeability. Best (and most expensive) is something like mu-metal and that need attention during assembly, because it tends to loose its property during mechanical forming/drilling, which means it needs sometimes additional annealing to bring it back after processing.
Quite effective for shielding purposes is the material that is used to form the core. (Transformer manufacturers use this to provide magnetic shielding and wrap some layers of this material around the transformer before winding up the last outer foil)
Normal steel does not do much, but that depends on thickness....
If the height of the enclosure is not a limiting factor it is worth to try an orientation where the transformer is sort of standing up in diameter direction, not laying flat.
Don´t forget the tips from the other posters; distance works, twisting the wires and careful location of caps and bridge rectifiers helps to get the radiating loops small, but will not help wrt to radiated field of the transformer.
Shielding of magnetic field requires material with higher permeability. Best (and most expensive) is something like mu-metal and that need attention during assembly, because it tends to loose its property during mechanical forming/drilling, which means it needs sometimes additional annealing to bring it back after processing.
Quite effective for shielding purposes is the material that is used to form the core. (Transformer manufacturers use this to provide magnetic shielding and wrap some layers of this material around the transformer before winding up the last outer foil)
Normal steel does not do much, but that depends on thickness....
Mu-metal normally saturates at too low a flux to be useful for power transformer screening. If necessary, you put mu-metal around the sensitive circuits (or audio input transformers) where the magnetic field is much weaker. Mu-metal around the power transformer will make little difference.
The real solution is distance. A belly band may sometimes help too. Trying to use ferromagnetic material (such as steel) is as likely to make things worse as improve them - it doesn't work in the way that conductors can be used for screening electric fields.
The real solution is distance. A belly band may sometimes help too. Trying to use ferromagnetic material (such as steel) is as likely to make things worse as improve them - it doesn't work in the way that conductors can be used for screening electric fields.
Initially i feared the same, but some measurements and calculation around toroidal transformers said the opposite. And having first hand experience with toroidal transformers encapsulated in mumetal enclosures (ranging from around 25 VA to nearly 700 VA) in production quantities i have to say that it works as intended, but it is quite expensive (encapsulation might cost the same as the transformer inside).
Nevertheless, your are right (as already stated earlier) wrt distance, but if there are constraints you have to try something else.
Belly bands (as said earlier) made from the same ferromagnetic material that was used to form the core works to some degree.
Wrt ferromagnetic material, it helps to remember that screening relies on closed pathways around the source (i.e. transformer in this case) closed (or nearly closed); that´s the reason why the belly band works.
Encapsulation works best for that reason if totally closed; important point to remember is to avoid in those cases a screw from top to bottom as that would provide a nearly short turn on the transformer.
Nevertheless, your are right (as already stated earlier) wrt distance, but if there are constraints you have to try something else.
Belly bands (as said earlier) made from the same ferromagnetic material that was used to form the core works to some degree.
Wrt ferromagnetic material, it helps to remember that screening relies on closed pathways around the source (i.e. transformer in this case) closed (or nearly closed); that´s the reason why the belly band works.
Encapsulation works best for that reason if totally closed; important point to remember is to avoid in those cases a screw from top to bottom as that would provide a nearly short turn on the transformer.
By 'belly band' I meant a closed loop of copper (or other good conductor) to act as a shorted turn outside the transformer, not a ferromagnetic material. However, having thought about it, it may be that a belly band does not work so well for a toroid as there is not one orientation for the windings so nothing for the belly band to align to.
A ferromagnetic enclosure around the transformer will work. I take your point about mu-metal; your experience seems to be different from what others have reported.
A ferromagnetic enclosure around the transformer will work. I take your point about mu-metal; your experience seems to be different from what others have reported.
Having made hundreds of large mosfet power amps in the late 70's using toroids the method we used has been well proven by time. We used a 3mm horseshoe steel bracket mounted on the front panel of our 3U rack cases that were made 6mm thick aluminium plate. The U shaped bracket spring loads the trafo which we isolated from it internally using large rubber pancake washers thus forming a soft bed for the windings. We plugged up the center hole with bog and through bolted it snugly in place using plastic insulating washers to avoid the proverbial shorted turn. Now 40 years later with many of these big 2000 wrms mosfet amps still in regular use I can state honestly I have never seen a failure due to our mounting method.
I have never seen a toroid mounted like that. Your description sounds like it could be very effective at reducing the emi field sent out from the toroid, especially if due to unequal winding gaps there are peaks where the escaping field is above average.
Was the back panel to which the steel band was bolted also made of steel?
JE.Sugden use a short length of thick walled steel? pipe as a separate belly band around the toroid in some of their amplifiers.
Was the back panel to which the steel band was bolted also made of steel?
JE.Sugden use a short length of thick walled steel? pipe as a separate belly band around the toroid in some of their amplifiers.
And here... I read /understood that the worst field effects (when there are any 🙂 of a torroid.
Are thru the centre axis, as in where the bolt usually goes.
So .. don't point the axis/bolt at anything important or sensitive 😉
As far as shielding... even inexpensive Antek torroids feature a V effective shield band mitt drain / ground wire.
No profit in looking for problems... where few actually exist.
Are thru the centre axis, as in where the bolt usually goes.
So .. don't point the axis/bolt at anything important or sensitive 😉
As far as shielding... even inexpensive Antek torroids feature a V effective shield band mitt drain / ground wire.
No profit in looking for problems... where few actually exist.
yes, and the reason toroids are used in place of EI's is the low stray flux of toroids....
humming is caused by other reasons...people who actually build things will know...
humming is caused by other reasons...people who actually build things will know...
A shield with a wire connected is more likely to be an interwinding electrostatic shield.
The guass band wrapped around the outside has no wire connection. It is completely insulated.
One of the main reasons we used toroids in all our power amps was in fact the very low EMF they emit. The mounting bolt was never an issue in rack mounting situations. Securing them hard up against the front panel reduced the twisting forces really well and the cast aluminium heatsinks running down each side meant maximum chassis rigidity. No SMPSU's in those days.
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