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How to exclude amplifier noise during tuning

Tuning process, often encounter different procedures for the noise problem, the circuit board has been fabricated, the following methods can cure or reduce noise.

First, the power amplifier board after the current hum

1, the speaker into the amplifier, turn on the power, move the power transformer position until the hum weakened, then the metal cover (which can be iron) and live fixed.

2, if the transformer leads to the secondary cable, it should be opened for braided stranded wire.

3, the output of the circuit board speaker output negative terminal welding, after the filter capacitor copper foil at a large area can be found at a lower noise point of welding.

4, increase or replace the filter capacitor. This method is rarely used, I have done a number of tests to prove that more than 25V, the power amplifier last stage current 2 ~ 7.5A power supply, filter 3 capacitance value of not less than 3300 F will not appear current hum.

5, change the installation position of the power amplifier board, the radiator transverse placed between the transformer and the circuit board, play a magnetic shielding effect, reducing the current hum.

6, appropriate changes in component pin height, especially the feedback resistance and coupling capacitance. The discrete components of the voltage amplification part should also be noted that the height of their pins from the circuit board 2 ~ 5.5mm better.

Second, the power amplifier level sound

1, take 1000pF porcelain dielectric capacitance, diode in the rectifier circuit and welding one. After the filter capacitor between the positive and negative power supply branch and the ground into each of 1 ~ 3 100F electrolytic capacitor and 0.1F MKT capacitor.

2, take the capacity of 220 ~ 1500pF between the film capacitor into the signal input and audition between the ground, use the smallest chime beats earbuds sound of a capacitor; and play a familiar music, with hearing requirements without affecting the high frequency Features prevail.

The above noise prevention method is performed by cutting off the front input. The same can be used for pre-amplification noise reduction.

Third, the amplifier's pre-hum

1, the DC power line "+" side disconnect, string into the 100 ~ 300mH inductance, non-welding.

2, with a plastic stick or bamboo chopsticks to clip the audio input to beats by dre the preamplifier board lead, look for a hum at the smallest fixed.

3, change the front and rear amplification board grounding point. If the two are connected Cheap Beats By Dr Dre by a shielded cable, the shielding mesh at one end of the shielded cable should be soldered to the input of the rear stage and the other end ungrounded. The front and audio input interface wiring is also true, only one end of the audio input beats by dre grounded. In this way, no ground loop will be formed and no annoying hum will be coupled.

Fourth, the power amplifier before sound

Mainly in the feedback tone circuit, especially scaffolding welding, high-frequency sound serious. The solution is to use a thin copper sheath to shield it, or change into passive attenuation type tone circuit, which can effectively reduce the squeal sound.

Several of the above noise reduction measures are limited to transistors, integrated circuit amplifier applications. Of course, the circuit board design is crucial, such as power, audio signal routing, analog and digital ground and so on.