I brought a cheep 2.1 subwoofer kit recently. Even though it works fine, I found continues hum comes from the subwoofer. This subwoofer kit was built with two KA2206B ICs . one IC is used as a mono amplifier for the Subwoofer (as it’s shown in the diagram) and the other one is used as a stereo amp for two Left-Right speakers. When I check the data sheet of the IC, I saw subwoofer circuit was built without including the capacitors I have marked in red circles in the picture….


Can you please tell me this can be the reason for the hum from the subwoofer ??

 

The two 470uF caps are for DC blocking, try putting them in the circuit and see if it cures it, possibly the humming is caused by the poor dc power supply ripple, try putting a 1000uF 25V capacitor, across the chip power supply pins.

 

And that is why they are cheap.

 

The two 470uF caps are for DC blocking, try putting them in the circuit and see if it cures it, possibly the humming is caused by the poor dc power supply ripple, try putting a 1000uF 25V capacitor, across the chip power supply pins.

Thanks for the idea,

about DC blocking Caps,... is it Ok to put these caps for subwoofer speaker ? does it reduce the bass sound of the subwoofer ? what about the 0.15Uf caps in the diagram ????

 

The datasheet has the dc blocking caps in, so try them, the 150nF caps will be for high frequency cut off.

 

You might try powering the circuit with a 12V car battery, to verify that the hum is from the power supply. If the hum is still present, it will tell you that the hum is from the input picking up power line hum. If the hum stops, you know that it was coming from the power supply.