Re: The other considerations
How would extending the shield too far hurt things?
I don't understand two things:
a) How grounding the shield will help. It's a magnetic field that we're trying to shield, not electric.
b) Why insulate the thing at all. Presumably it's mounted directly to the chassis, which is grounded. If not, why not? Where would the electric potential come from if not grounded?
-- Dave
How would extending the shield too far hurt things?
I don't understand two things:
a) How grounding the shield will help. It's a magnetic field that we're trying to shield, not electric.
b) Why insulate the thing at all. Presumably it's mounted directly to the chassis, which is grounded. If not, why not? Where would the electric potential come from if not grounded?
-- Dave
BudP, when you talk about attaching the shield metal directly to the core emitter is that shield metal the aluminium sheets that I was talking about also what is the core emitter? I'm still new to all this stuff and I don't understand a lot of the terms you mention like magnetostriction?
Also in your latest post you seem to suggest that my power supply may be causing this 'power growl'? It seems the problem is not in the power supply per se, but in the quality of the transformer. As I have mentioned before, the metal shielding does make the humm noticably faint as I have to put my ear to the driver to hear it. I may just decide to live with this or buy a new transformer at some point.
I'll put on my EL34 SET schematic in a bit....
Also in your latest post you seem to suggest that my power supply may be causing this 'power growl'? It seems the problem is not in the power supply per se, but in the quality of the transformer. As I have mentioned before, the metal shielding does make the humm noticably faint as I have to put my ear to the driver to hear it. I may just decide to live with this or buy a new transformer at some point.
I'll put on my EL34 SET schematic in a bit....
Many subjects at once
Dave,
When shielding free air flux lines, some consideration needs to be paid to their ballistic nature. They have a field gradient with a specific boundary nature, meaning that a specific gradient force level will describe a parabola across any given stack of narrow emitters. This parabola closely resembles the trajectory of a shell shot into the air and falling to earth, a given distance away.
When you interrupt this field gradient with a shield material that is more permeable than air, the force gradient truncates, spreads across the shield and re-emits into the air and reestablishes the original parabola, as near to the original shape as possible. When you have a shield that is only slightly wider than the emitter surface and of fairly low permeability this reestablished field will have a field gradient hole at the center of the far side of the shield because some of the field gradient remains trapped behind the shield. When you extend the size beyond this empiricly derived "optimum" the field strength applied to the shield itself begins to ovewhelm that materials permiability and the gradient force slides right around the shield and reconstructs the desired parabola, using the sheild as it's emitter surface. The hole diasappears and you once again have emitted field strength, strong enough to effect an induced magnetic and electrical signal in the reciever object.
Obviously you can do many things to alter this balance to your benefit. Higher permeability shield material, squared off U shaped shield construction. multiple shields etc. The least invasive shield will be the one that just provides the field gradient hole, of the size you need.
For audio signal transformers manipulating these stray field events also manipulates the phase coherency of the field gradient contained within the core window, where the antenna events that couple flux from winding to winding are supported, by a field gradient condensed to approximately 1/1000th of its unrestrained field dispersal area. Why these two events are in any way closely related goes beyond my knowledge and considering that the field gradient of both the unrestrained and window constrained "stray field" event are less than 1/100th of the actual field strength in the core, it makes even less sense.
However, when you get into the high level of resolution we are playing with in modern audio, these seeming minuscule events do loom fairly large. Not within the power transformers, but within the signal transformers, where minute discontinuities within the core window can have powerful effects upon phase and frequency response, especially above the frequencies where the core has any part to play in actual power transform i.e. above 600 hz for 26 M19, 1 khz for 29 M6, 3.5 khz for 48% nickel, 8 khz for 80% nickel and 15 khz for amorphous core material.
As for insulating the shield from the core itself, it is more effective to have a controlled gap between the core lamination plate edges and the shield, if you are trying to steer the field away from a specific spot with a low permeability material. It is beneficial to have no effective gap if you are attempting to absorb that field gradient with a high permeability material. Electrical dielectric shielding is not at issue here, but, you do not want to disrupt the oxide and varnish layer from core pieces at opposite sides of the core sheave stack with a magnetically permiable material, as you can short out the core and cause all sorts of surprising and damaging events to take place. Hence I am cautioning everyone to use some sort of insulator when playing around with shielding the magnetic material's fields.
audio_moksha
The shield metal I am referring to is the iron sheet you sandwiched between the aluminum sheets, unless I misunderstood your posting. The aluminum is essentially invisible to the core emitted field gradient.
The core emitter is just referring to the lamination plates, or sheaves used to construct the core "stack" of stamped E and I shapes that are laminated in an alternating directional pattern, in a typical power transformer stack. These E I laminations are all in the same direction in a SE output transformer, power and audio choke stack, where the E and I shaped stacks are often separated by an enforced "gap" of non ferrous material, like cardboard.
There are many different types of magnetic core shapes and many different grades of magnetic materials, but the predominant power transformer, at least in commercial applications, is constructed of E and I laminations. and they look exactly like E's and I's too.
Do not feel ignorant about transformer terminology and technology. It is a very obscure subject with very little common information available. This is why I joined this forum, not to confuse you and belittle you with my "superior knowledge." Please, ask all questions that come to mind, the only "stupid " questions are the unasked ones and that only because you might harm yourself or others by not asking.
Be certain that I do not have all of the answers, but, I might know where to find them.
Bud
Dave,
When shielding free air flux lines, some consideration needs to be paid to their ballistic nature. They have a field gradient with a specific boundary nature, meaning that a specific gradient force level will describe a parabola across any given stack of narrow emitters. This parabola closely resembles the trajectory of a shell shot into the air and falling to earth, a given distance away.
When you interrupt this field gradient with a shield material that is more permeable than air, the force gradient truncates, spreads across the shield and re-emits into the air and reestablishes the original parabola, as near to the original shape as possible. When you have a shield that is only slightly wider than the emitter surface and of fairly low permeability this reestablished field will have a field gradient hole at the center of the far side of the shield because some of the field gradient remains trapped behind the shield. When you extend the size beyond this empiricly derived "optimum" the field strength applied to the shield itself begins to ovewhelm that materials permiability and the gradient force slides right around the shield and reconstructs the desired parabola, using the sheild as it's emitter surface. The hole diasappears and you once again have emitted field strength, strong enough to effect an induced magnetic and electrical signal in the reciever object.
Obviously you can do many things to alter this balance to your benefit. Higher permeability shield material, squared off U shaped shield construction. multiple shields etc. The least invasive shield will be the one that just provides the field gradient hole, of the size you need.
For audio signal transformers manipulating these stray field events also manipulates the phase coherency of the field gradient contained within the core window, where the antenna events that couple flux from winding to winding are supported, by a field gradient condensed to approximately 1/1000th of its unrestrained field dispersal area. Why these two events are in any way closely related goes beyond my knowledge and considering that the field gradient of both the unrestrained and window constrained "stray field" event are less than 1/100th of the actual field strength in the core, it makes even less sense.
However, when you get into the high level of resolution we are playing with in modern audio, these seeming minuscule events do loom fairly large. Not within the power transformers, but within the signal transformers, where minute discontinuities within the core window can have powerful effects upon phase and frequency response, especially above the frequencies where the core has any part to play in actual power transform i.e. above 600 hz for 26 M19, 1 khz for 29 M6, 3.5 khz for 48% nickel, 8 khz for 80% nickel and 15 khz for amorphous core material.
As for insulating the shield from the core itself, it is more effective to have a controlled gap between the core lamination plate edges and the shield, if you are trying to steer the field away from a specific spot with a low permeability material. It is beneficial to have no effective gap if you are attempting to absorb that field gradient with a high permeability material. Electrical dielectric shielding is not at issue here, but, you do not want to disrupt the oxide and varnish layer from core pieces at opposite sides of the core sheave stack with a magnetically permiable material, as you can short out the core and cause all sorts of surprising and damaging events to take place. Hence I am cautioning everyone to use some sort of insulator when playing around with shielding the magnetic material's fields.
audio_moksha
The shield metal I am referring to is the iron sheet you sandwiched between the aluminum sheets, unless I misunderstood your posting. The aluminum is essentially invisible to the core emitted field gradient.
The core emitter is just referring to the lamination plates, or sheaves used to construct the core "stack" of stamped E and I shapes that are laminated in an alternating directional pattern, in a typical power transformer stack. These E I laminations are all in the same direction in a SE output transformer, power and audio choke stack, where the E and I shaped stacks are often separated by an enforced "gap" of non ferrous material, like cardboard.
There are many different types of magnetic core shapes and many different grades of magnetic materials, but the predominant power transformer, at least in commercial applications, is constructed of E and I laminations. and they look exactly like E's and I's too.
Do not feel ignorant about transformer terminology and technology. It is a very obscure subject with very little common information available. This is why I joined this forum, not to confuse you and belittle you with my "superior knowledge." Please, ask all questions that come to mind, the only "stupid " questions are the unasked ones and that only because you might harm yourself or others by not asking.
Be certain that I do not have all of the answers, but, I might know where to find them.
Bud
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