The nice thing about op-amps in DIP-8 packages, is that most of them use the same pinout, so it’s very easy to swap them out and test different brands and types. The TLV2472 only supports up to 6V as power supply, most of the other ones go much higher – usually above 30V, i.e. ±15V.
Here’s the list of op-amp chips I tried (yeah, got quite a bunch of them in my lab, for various reasons):
All of them had similar behavior, i.e. clipping at both limits of the voltage range, except for the LT1413:
Still nowhere near a sine wave, BTW. But what’s more interesting, is the the voltage swing of this signal was just 4.5 Vpp, while the op-amp was being driven from a ±15V power supply in this particular case. So for some reason, it was “oscillating” at 1.25 KHz (about 8x higher than the other mode).
I have no idea what was going on. When trying to reproduce this a second time, I couldn’t get this behavior back. I suspect a loose connection, or perhaps some odd interaction due to the breadboard.
I’m not really interested in tracking down this issue, since it looks like this quadrature oscillator circuit is not suitable for a Component Tester – not without some sort of amplitude regulation anyway.
So there you have it – analog circuits also need to be debugged, as you can see!
Update – this issue has now been resolved, see the comments on yesterday’s weblog post.