Hi ! i have found this very interesting video on Yotube
my thoughts immediately went to the toroidal power transformers and the iron screws used to secure them to the chassis
Question
has anyone ever tried to secure the toroidals without using metal accessories? using nylon cable ties for example?
I've seen that there are rather thick silicone rubber mats that resist heat and should also absorb vibrations
these could be placed under the toroid
then two diametrically opposed holes and two cable ties at 180 degrees from each other and voilà
is it a load of crap? I've never seen anyone do it to be honest
my thoughts immediately went to the toroidal power transformers and the iron screws used to secure them to the chassis
Question
has anyone ever tried to secure the toroidals without using metal accessories? using nylon cable ties for example?
I've seen that there are rather thick silicone rubber mats that resist heat and should also absorb vibrations
these could be placed under the toroid
then two diametrically opposed holes and two cable ties at 180 degrees from each other and voilà
is it a load of crap? I've never seen anyone do it to be honest
Stick out your right hand, and give a "thumb up". If your thumb is a wire with current flowing towards the tip, your fingers curling around it would represent the magnetic field lines that would form around it.
The video was of an air-core crossover inductor, and they were introducing a ferrous wire directly into the magnetic field at the center axis of the coil. For this doughnut shaped coil of wires all passing current in the same direction, the magnetic field has a toroidal shape, all of it passing through and concentrated most at the center hole of the coil and wrapping all around the outside circumference, using only air to conduct the magnetic field. (This is like the far right side of the picture below.) Air has a high magnetic reluctance, or resistance, if you will, so sticking a wire directly into this magnetic field and giving the field a super easy pathway to flow through like a ferrous wire right in the center concentration will maximize interaction with the coil. This has a behavior more like the center part of the image below- some flux travels in the wire, some in the air.
It's a shame they did not indicate setup conditions and show a scope plot- sounds like it was introducing a harmonic into the fundamental. I am assuming that it was changing the value of the inductor, therefore changing the cutoff frequency, or perhaps the loosely held wire was able to vibrate and introduce a frequency not in the original content? Iron cores are used inside some crossover inductors, but they are part of the designed inductance, and rigidly fixed within the coil so they cannot vibrate and add content. Either way, this is why zip ties and glue are used to avoid either problem in air core inductors.
For the toroidal power transformer, the permeable toroid doughnut core is at the center of the windings which are wrapped around it, so unlike the air core inductor virtually all of the magnetic flux is contained within the closed circuit of the toroid core. (like the far left side of the picture below.) Unlike the wire inserted into the air core inductor, which places a disturbance within the path of the magnetic flux, a bolt passing through the center of the toroidal power transformer is not within the flow of the magnetic flux. As far as the flux is concerned, the bolt is not "inside" the transformer, so the flux won't even see the bolt.
The video was of an air-core crossover inductor, and they were introducing a ferrous wire directly into the magnetic field at the center axis of the coil. For this doughnut shaped coil of wires all passing current in the same direction, the magnetic field has a toroidal shape, all of it passing through and concentrated most at the center hole of the coil and wrapping all around the outside circumference, using only air to conduct the magnetic field. (This is like the far right side of the picture below.) Air has a high magnetic reluctance, or resistance, if you will, so sticking a wire directly into this magnetic field and giving the field a super easy pathway to flow through like a ferrous wire right in the center concentration will maximize interaction with the coil. This has a behavior more like the center part of the image below- some flux travels in the wire, some in the air.
It's a shame they did not indicate setup conditions and show a scope plot- sounds like it was introducing a harmonic into the fundamental. I am assuming that it was changing the value of the inductor, therefore changing the cutoff frequency, or perhaps the loosely held wire was able to vibrate and introduce a frequency not in the original content? Iron cores are used inside some crossover inductors, but they are part of the designed inductance, and rigidly fixed within the coil so they cannot vibrate and add content. Either way, this is why zip ties and glue are used to avoid either problem in air core inductors.
For the toroidal power transformer, the permeable toroid doughnut core is at the center of the windings which are wrapped around it, so unlike the air core inductor virtually all of the magnetic flux is contained within the closed circuit of the toroid core. (like the far left side of the picture below.) Unlike the wire inserted into the air core inductor, which places a disturbance within the path of the magnetic flux, a bolt passing through the center of the toroidal power transformer is not within the flow of the magnetic flux. As far as the flux is concerned, the bolt is not "inside" the transformer, so the flux won't even see the bolt.
Good morning and thank you very much for the very kind and precious explanation
I always have the bad ignorant habit of trivializing problems
First I am only interested in the case of the power transformer mounted inside a metal chassis
In my primitive mind the transformer is a generator of mechanical vibrations and magnetic fields that can find a means of propagation in the metal case
Actually i have at hand a little amp NVA ap10 where the bottom rear and top panel are in aluminum, the side panels in wood and the front panel in plastic
I remember the DNM preamp and amps with a transparent plastic case I wonder what was the reason for this choice
Do I understand better now that in the case of a toroidal transformer the dispersed magnetic field will be negligible? Good !
Anyway I think I will try a thick silicone rubber mat under the toroidal mains transformer and fix it to the case with nylon ties For what it costs
At most there will be no difference
i would like to try the silicone mat also under the circuit board Better to place the board on it and use nylon screws to the chassis
Metal for chassis is really needed because it works as heatsink for the output transistors (British way They save everywhere they can Love this attitude)
In the case of a class A amplifier since the absorbed current is constant you could even physically extract the transformer from the case
Both the vibrations and the magnetic fields could be captured by the circuits and cables that run inside the devices
I will try as soon as I can find the space to work The lack of space is putting me to the test
Thanks again and have a good day
gino
I always have the bad ignorant habit of trivializing problems
First I am only interested in the case of the power transformer mounted inside a metal chassis
In my primitive mind the transformer is a generator of mechanical vibrations and magnetic fields that can find a means of propagation in the metal case
Actually i have at hand a little amp NVA ap10 where the bottom rear and top panel are in aluminum, the side panels in wood and the front panel in plastic
I remember the DNM preamp and amps with a transparent plastic case I wonder what was the reason for this choice
Do I understand better now that in the case of a toroidal transformer the dispersed magnetic field will be negligible? Good !
Anyway I think I will try a thick silicone rubber mat under the toroidal mains transformer and fix it to the case with nylon ties For what it costs
At most there will be no difference
i would like to try the silicone mat also under the circuit board Better to place the board on it and use nylon screws to the chassis
Metal for chassis is really needed because it works as heatsink for the output transistors (British way They save everywhere they can Love this attitude)
In the case of a class A amplifier since the absorbed current is constant you could even physically extract the transformer from the case
Both the vibrations and the magnetic fields could be captured by the circuits and cables that run inside the devices
I will try as soon as I can find the space to work The lack of space is putting me to the test
Thanks again and have a good day
gino
Sorbothane is good under power transformers where they contact the chassis. Also need to have something between the top and washer also.
Hi thank you very much for the kind advice Mine is one of those cases in which the bottom side of the chassis is used as heatsink and so gets hot
silicon pads are very good and durable
https://novozestllc.com/index.php/p...dining-table-blacktrivet-mat-x-4coasters-x-2/
silicon pads are very good and durable
https://novozestllc.com/index.php/p...dining-table-blacktrivet-mat-x-4coasters-x-2/
I removed the bolts too, they transmit vibration directly to the chassis/electronics. Is that wrong of me?
Hi interesting An idea to check for microphonicity (i dont know the right word) could be to hit various spots on the pcb with a little plastic hammer and listen through the speakers
But if with inputs shorted there is no noise from the speakers there is nothing to worry about That is the decisive test
No noise no problems
But if with inputs shorted there is no noise from the speakers there is nothing to worry about That is the decisive test
No noise no problems
A ferrous wire placed inside an air core toroid will indeed generate harmonics. The eddies in the metal dissipate some energy at twice the excitation frequency.
If the air core is placed flat against aluminum or copper sheet, the inductance will drop, this due to exclusion of the field lines by the eddies generated in the metal. Losses will again be at twice the excitation frequency.
A conductive path around a toroidal transformer through the center will create a shored secondary turn. It can be held into a chassis with a metal bolt and a metal plate on the top without fear of creating a shorted turn. There will be some parasitic flux outside the windings of course, but not much.
John
If the air core is placed flat against aluminum or copper sheet, the inductance will drop, this due to exclusion of the field lines by the eddies generated in the metal. Losses will again be at twice the excitation frequency.
A conductive path around a toroidal transformer through the center will create a shored secondary turn. It can be held into a chassis with a metal bolt and a metal plate on the top without fear of creating a shorted turn. There will be some parasitic flux outside the windings of course, but not much.
John
Hi ! thank you for the very helpful advice Then why use a ferrous bolt ? no alternative ?
thanks a lot If i understand well the only real issue with a toroid transformer could be vibrations transmitted to the chassis ?
those can be dealt with very easy An high density foam could absorb them quite nicely
If the chassis gets hot i could always use one of those silicone mats for oven between the chassis and the high density foam (i.e. even a piece of carpet could work fine)
I will do for sure Thanks a lot again
Here's a lot of good info on toroids. Don't use anything else than the supplied rubber gaskets.
Foam or carpet might be fire accelerators in worst case scenarios. The gaskets are all you need.
https://www.hilltech.com/products/power_components/toroidal-transformers.html
Foam or carpet might be fire accelerators in worst case scenarios. The gaskets are all you need.
https://www.hilltech.com/products/power_components/toroidal-transformers.html
A conductive bolt, aluminum, stainless, or copper, will have eddy currents created within. That will be double frequency losses as well.
Magnetostriction is a double frequency effect. As is conductor vibration within a transformer.
John
Magnetostriction is a double frequency effect. As is conductor vibration within a transformer.
John
hi thank you very much for this precious advice
what about this material ?
https://www.amazon.com/Silicone-Flexible-Vibration-Anti-Slip-Protection/dp/B09T6D94TD
Hi thanks a lot again do you mean some kind of rubber ? i place a unit with rubber feet above an amp using the chassis as heatsink
The rubber feet got stick for the heat Since then i have decided to use only heat resistant silicone rubber mats Like those used in the kitchen
Some of these products can be placed even in ovens for food baking
Hi ! this is why i would use plastic strappings They are very common for xover coils But they should be heat resistent and robust enough also for power supply toroids