the open-loop gain

The open-loop gain is the op-amp's raw, untamed amplifying power — the gain with no feedback wrapped around it, the chip working all alone. It is staggeringly large: a tiny voltage difference between the two inputs gets multiplied by a hundred thousand or more. Imagine a microphone so sensitive it deafens you at a whisper; that is an op-amp open-loop. Useful as raw material, useless as a finished amplifier.

Concretely, the open-loop gain Aol at DC is typically 100,000 to over 1,000,000, which is 100 to 120 dB. Multiply it out: a 1 mV difference between the inputs times a gain of 100,000 demands a 100 V output — far past the supply rails, so the output simply slams into a rail and clips. That is why a bare op-amp behaves as a comparator, not an amplifier. Crucially, the open-loop gain is not constant: it is huge only at DC and low frequencies, then rolls off at 20 dB per decade once past an internal corner often just a few Hz away.

Why this matters: the open-loop gain is the raw capital that negative feedback spends to buy precision, bandwidth, and low distortion. The honest truth is that this gain is wildly variable — it changes part-to-part, with temperature, with load, and with the output voltage. That unreliability is exactly WHY we never use the op-amp open-loop and instead trade most of this gain away through feedback for a modest gain we can trust.