Amplifying bass frequencies

[awesomelumens]

I am sure the LM1875 will sound fine, but I don not like bridge amplifiers as they introduce more distortion and can get into a tangle with some music and difficult-to-drive speakers. There are much better integrated amplifiers.

To get the best from an amplifier you need direct coupling, which means plus and minus supply lines, and good components: metal film resistors and polypropylene capacitors or good quality aluminum electrolytic capacitors for the high values.

spec

I added filter capacitor of 470uf in it too. But it is sending bur bur (4 in a second) in the 4" speaker. Help plz. Previously I had only worked with printed boards only.

 

[audioguru]

I think your power supply filter capacitor is too small and/or the power supply voltage has series resistance causing its voltage to jump down when loaded then go back up when unloaded. Since the amplifier is non-inverting then the power supply fluctuations causes positive feedback and oscillation. Try increasing the value of the 10uF capacitor to 22μF or 33μF that is filtering the bias voltage.
Maybe the 19V is also powering the input signal source? Try disconnecting the input signal from the amplifier and report back if the bur bur sounds stop.

You said your power supply voltage is 19V. Then the LM1875 output power is only 3.5W when it begins clipping.

 

[awesomelumens]

I think your power supply filter capacitor is too small and/or the power supply voltage has series resistance causing its voltage to jump down when loaded then go back up when unloaded. Since the amplifier is non-inverting then the power supply fluctuations causes positive feedback and oscillation. Try increasing the value of the 10uF capacitor to 22μF or 33μF that is filtering the bias voltage.
Maybe the 19V is also powering the input signal source? Try disconnecting the input signal from the amplifier and report back if the bur bur sounds stop.

You said your power supply voltage is 19V. Then the LM1875 output power is only 3.5W when it begins clipping.

I am going to add 4700uF on supply. There is a 6A protection diode I added for reverse pol protection. I think 18.3V is not good for this. My experience for power leds is also not good. As 6A6 got damn hot with 2amp continuous. So I will remove it. The other 10uf is fine or should I change it also.. no input. It was idling and bur bur. Heatsink was very hot after 2 mins.

 

[audioguru]

The idle current of an LM1875 at your 19V supply is a maximum of 70mA. Then it heats with a max of 19V x 70mA= 1.71W and will be very hot without a heatsink. The datasheet tells you all about it.
Maybe the bur bur output was it overheating and shutting down then cooling and working again before heating and shutting down again, over and over.