importance of voltage Gain of an audio Op amp
Anyone who claims that only the open loop gain matters for distortion doesn't understand how distortion in circuits with feedback works.

Let's say that you have an opamp with a open-loop gain (so at DC and very low frequencies) of 1000.

You want to use it to make an amplifier which amplifies an input signal 10 times.

To do this you would be using the opamp in a feedback configuration, don't worry about how the schematic would look like, that's not relevant yet.



To get the closed loop gain of 10 you would need to make \$\beta = 1/10\$

That then results in a closed loop gain of \$A_{ol} \beta = 1000*1/10 = 100\$

This is also called the "excess loopgain" as it is gain that is "too much", you need only 10 gain and you "waste" 100. But that does not mean that this excess loopgain is useless! In fact it is what decreases distortions created inside the loop.

Suppose that the opamp is slightly non-linear and instead of outputting 100 mV (when the opamp has a Vin = 0.1 mV, like so 0.1 mV * 1000 = 100 mV) it outputs only 90 mV. Oh dear, that's a 10% error !!

Luckily that's where the excess loopgain comes in. Since the opamp is monitoring it's own (distorted) output voltage with the (non distorted) input signal it can "detect" it's own distortion! This mechanism then reduces the distortion by the excess loopgain factor so in our case by a factor 100. So 10% distortion becomes 0.1%, that's much better.

Now what would happen if the opamp didn't distort 10% but we'd use a better opamp which also has an \$A_{ol}\$ of 100 but distorts 10x less so only 1%. Then the total distortion at the output will be 1% / 100 = 0.01%

So in conclusion: it is not only the loopgain that matters but also how much distortion the opamp adds. So a 10 higher \$A_{ol}\$ is pointless if the opamp also has a 10x higher distortion!

Both excess loopgain and intrinsic linearity of the opamp matter.

Disclaimer: I am aware that above numbers aren't 100% accurate, as commented below the actual excess loopgain is really 99 instead of 100. I prefer to explain with rounded off numbers to show the principle, not the exact values.