Opamp or Power Amp?

[audioguru]

Hi Guys,
In another post we have discussed why this part of a project doesn't work at all, or produces severe distortion and noise.

This audio amplifier's input is near line level, and its output load is an earphone, 8 ohms or more, from a cell phone, home stereo or Walkman.

Why doesn't this 741 amplifier circuit work?
1) The 741's inputs are connected to its negative supply voltage, so they won't work properly:

Common Mode Voltage Limits
One of the practical op-amp limitations is that the inputs must stay within a certain voltage range (usually significanly less than the supply voltages) for proper operation. Op-amps are subject to drastic gain changes and bizarre behavior if these ranges are exceeded. For a 741 operating on +/-15 volts, the common mode input swing should be within +/-12 volts. Some other amps are designed to allow common mode voltages down to the negative supply voltage.

Maybe this 741 amplifier will work better if its negative supply pin 4 is connected to -9V, instead of to ground, then the grounded inputs will properly be within the common mode voltage limits.

2) No negative feedback. The 741 has a typical voltage gain of 200,000. Without an input signal, it will amplify its up to 6mV of input offset voltage so that its output will be resting near a supply voltage, instead of its output being biased near half-supply voltage. Therefore when an input signal is applied, its output will half-wave rectify it, causing severe distortion.
The high gain will also amplify the high internal noise level of the 741, so that its output will be full of noise.
3) 8 ohm load? That is like a dead short to a 741 that is spec'd for a minimum of a 2K load. A 741 is guaranteed to supply only 10mA of output current. Therefore its peak power to an 8 ohm earphone is only 800 microwatts, which is an extremely low sound level.

The faulty circuit that makes me sick to look at it is here:

[audioguru]

Hi again Guys,
Perhaps the author of this audio amplifier meant to use an LM386 1/2W power amplifier IC instead of a 741 opamp, but forgot and called the LM386 a 741 by mistake. Then later realized that the pin numbers were wrong for a 741 and changed them.
The LM386 has advantages in this circuit:
1) It has built-in biasing and PNP input transistors that work fine when connected to its negative supply voltage (usually ground).
2) It has built-in negative feedback for a voltage gain of 20.
3) It is designed to have a load of 8 ohms or more.
4) It needs a zobel network (3.9 ohms in series with 0.1uF) across its output which the author has already provided.

The schematic is very similar to the faulty one that has a 741 opamp. The LM386 circuit is here: