Methods and Measures to Reduce the Interference of Transformer to Amplifier(Part 2)

3. When the primary impedance of the transformer is equal to the parallel value of the source resistance and the reflection resistance of the load, a low-frequency cut-off will appear, increasing the noise from the transformer, so the power transformer must also have sufficient inductance. But this cannot be a reason to blindly increase the output power of the transformer. Because the primary inductance of the transformer changes with the magnetic flux density of the iron core, when the secondary load power is small, the magnetic flux density of the iron core will also decrease, causing the inductance to drop. Generally, the power of the power transformer can be selected between 1.4-2 times of the secondary power supply, which is more appropriate.

4. The iron core of a high-quality transformer has high magnetic permeability and a high magnetostrictive effect. It is sensitive to the influence of the external magnetic field, pressure, and vibration, and can generate additional voltage and cause interference. For this reason, when assembling or installing the transformer.

Take the following measures:

—The core or shield must be demagnetized before assembly.

—Avoid short circuit of the iron core, generating eddy current, reducing magnetic flux, and reducing inductance.

—The transformer should be vacuum impregnated so that the laminations cannot move to each other.

—The transformer should be installed on the shock-absorbing base, and any magnetic field source should also be shock-absorbing.

—If the installation space permits, the transformer should be acoustically isolated.

5. The form of the transformer is also very important to reduce interference. Generally, toroidal or O-type transformers have high efficiency and low magnetic leakage, but the magnetic flux is easily saturated, which is not conducive to resisting the interference of the power grid. The EI type is the opposite, and because there is a certain air gap, the magnetic permeability of the iron core can be stabilized. The R type is somewhere in between. Due to the serious pollution of our country's power grid, many "enthusiasts" choose EI transformers as audio power sources.

The information is provided by the power transformers supplier.