Shielding, you can use metal foil (copper foil) wrapped around the line, both ends of the gap (both ends can not short circuit!), Copper and local connection, or with enameled wire plus a layer, one end of the idle, one end Connect with local. Shielding layer increases, to take up the transformer core window capacity, therefore, the thickness of copper foil or enameled wire diameter, try to use the minimum thickness or minimum diameter; shielding layer increases, but also makes the transformer winding process cumbersome, because the shielding Layer itself must also be with the primary, secondary between the higher dielectric strength, otherwise the hidden danger is very serious!

The usual method of audio toroidal transformer winding is done after the primary winding is completed, and then the secondary groups are wound.

Because recently wanted to build a small amp with a pre-level and a small audio toroidal transformer. Primary 220V, design conservative power of 20 watts; secondary high voltage 115V / 40mA, a group; filament 3.15V-0-3.15V / 1A, the first inter-stage shielding. EI66 iron core, an area of ​​2.2 * 2.8 square centimeters.

Preliminary calculation results: primary 0.22 line 1650 turns; secondary high voltage 0.15 line 863 turns; filament 0.73 line 51 turns; shield layer 0.15 line. With the window to accommodate the calculation, not only to accommodate the next, but also slightly surplus. According to the existing materials: primary 0.23 line, high voltage 0.15 line, filament wire 0.8, and then the window to accommodate the calculation, halo! Can not accommodate it! If you do not change the line, the only way is to remove the shield (including the use of insulation paper), winding system is completed, by hand shaping, or is expected to succeed.

Is the toroidal transformers for audio shield kept? Or quit? Re-weigh the principle and function of the shield: shield is also equivalent to a bypass capacitor, the main role is to the primary side of the common mode interference signal through the shield to return to the earth. Imagine: Transformer filament winding is not also one end of the ground? If I put the filament winding as a shield, between the primary and high pressure groups, not two things? Decided to try first!

So, around the primary, and do the insulation, the filament switch to 0.8 line, double and around 25.5 turns. With the usual winding order. The usual order is: primary - shield - high pressure - (other windings) filament. The order of this example is: primary - filament - high pressure (or other windings).

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