I have an audio signal that's amplified by an op-amp. The output impedance of the op amp is around 100 ohm (is that right?) My speaker is 8ohms. How can I match this better?
I have an audio signal that's amplified by an op-amp. The output impedance of the op amp is around 100 ohm (is that right?) My speaker is 8ohms. How can I match this better?
The impedance doesn't need to be matched. The amplifier needs to have a much lower output impedance than 8R which is why an op-amp isn't suitable for driving a speaker, as Nigel said.
A puny half-Watt in an 8 ohm speaker is a peak current of 250mA.
But the max output current from an opamp is only 30mA. The output power at clipping into an 8 ohm speaker is only 0.004W.
The max output current from a little LM386 power amp IC is about 375mA. Then the output power in an 8 ohm speaker at clipping is 0.5W.
The op amp only has a low closed loop impedance until it's maximum current output limit is reached (generally a few 10's of milliamps) above which the closed loop feedback loses control and the output impedance becomes very high.