|27th October 2003, 05:00 PM||#11|
Join Date: Jun 2003
Location: Maine USA
> since the negative terminal of U1A is a virtual ground
No it is not. Review your op-amp chapter. Virtual ground is the "-in" input on an inverter with grounded "+in" pin. In a follower, the "-in" pin is "virtual input" (it follows the "+in" pin). On an ideal amp, a cap from "-in" to "+in" does nothing at all. On a real amp, all that "virtual" stuff becomes untrue at 1MHz to 10MHz, where the amp's gain falls to nothing. So the effect of a cap here is not simple.
> should i be safe and move it to a real ground point?
Since Rod published it, I would use it as-is. With Rod's 100pFd cap across the pins. While you will get dozens of opinions "do this, it's better!", remember that Rod thought about the plan and built it. Surely most of those changes crossed his mind. Some of them are a matter of opinion. But the plan does not suck at all. And Rod and others have built it and seen it work. If you start tossing on every good idea you hear, it is easy to get to a place where it does not work.
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