RE: Experimenting with Op Amps: Open-Loop DC Gain (Again!)

jc2048 — Sat, 02 Apr 2022 22:08:24 GMT

I've found a 741 (a recent one, not one that's 40 years old), so I thought I'd have a go at measuring it.

Like the OP27, the gain moves with temperature whilst it is heating up. Again, like the OP27, the gain started high
and declined. This isn't very scientific, but the gains I measured from start were 77,596 (97.8dB), 74,257 (97.4dB),
and 73,736 (97dB). That's with an interval of several minutes between each reading. As you can see, the gain value
isn't all that spectacular for an op amp. It's higher than the datasheet minimum (only 50k), but less than the typical
figure, so I haven't got a particularly good specimen here.

The respective offset values were 961uV, 957uV, and 955uV (close to the typical value of 1mV). The offset didn't
change as much as I thought it might, but it does move as the device self-heats.

The main thing to take away from this is that, although op amps are wonderful with lots of feedback wrapped around
them, standalone as dc amplifiers they're much less good.

RE: Experimenting with Op Amps: Open-Loop DC Gain (Again!)

DAB — Tue, 29 Mar 2022 19:30:43 GMT

Very interesting experiment.