Need to Built Amplifier, Need Help

[tsiros]

yeah ok fine whatever

why would a clipped signal, that has rms below the max sustained, damage a speaker?

[gmphadte]

A clipped signal is like a switched DC supply. Its rise/fall time may be slow.

Gajanan Phadte

[gohar]

I want to know that how a subwoofer is connected with a L+R channel??
i'm in the process of making LM3886 chip amps, one for Left, one for RIGHT and one more for subwoofer as suggested by "Mooly". My inputs are stereo cable from computer. Left amp connected to Left RCA, and RIGHT amp with right RCA but what about subwoofer amp?? As subwoofer plays both left and right low frequency signals, i am confused in how to OR where to connect subwoofer amp, i mean what is the input of subwoofer amplifier?? Left RCA? right RCA? or both Left and Right RCA??

[Mooly]

It's both

You can just combine them resistively at the subwoofer amp input. Try something like two 10k resistors one from the left and one from the right and take the subwoofer feed from the junction.

[gohar]

In this schematic,

if i changed Rf to 20k and R3 to 1k, what were the changes produced? As i can't able to find 22k for Rf so i decided to go with 20k for Rf. and what about the schematic? is it fully functional with original component values?
I am going to place 50k pot for Rin instead of 25k. what changes does it make?

[Mooly]

Rf and R3 work together to set the gain. The difference of 22K and 20K probably won't make any noticeable difference in practice. The actual gain is (RF + R3)/R3 Maybe drop R3 to 560 ohm if you use 20K for Rf.

The opamp will be classed as stable for "gains above xx" so make sure you don't decrease the gain to much if you alter these values.

Using a 50k pot is no problem. Thecircuit looks fully functional although I would have thought the pot wiper should be AC coupled both to minimise altering the DC offset as the pot is rotated and also to minimise noise as the pot is turned.

[gohar]

And if i eliminate the pot then?

[Mooly]

Originally Posted by gohar

And if i eliminate the pot then?

then you have no volume control

[gohar]

Input DC decoupling capacitor and RF attenuation is required for this? And if i change Ci to 150uF or 220 uF then?

[Mooly]

Originally Posted by gohar

Input DC decoupling capacitor and RF attenuation is required for this? And if i change Ci to 150uF or 220 uF then?

Ci works in combination with R3. Increasing Ci will extend the low frequency cut off point. If you go to big on these then you may suffer with switch on and off thumps (depending how well the LM3886 controls these).