The most accurate way to do any measurement is with differential probes,
but
not everyone has them and they have limited dc offset capability
(although
you can externally cap couple to get rid of this limitation).
Ah, but I have a very good diff probe (well, as good as what's inside the glass): a CRT! ;-)
Very good "DC offset capability", and AC CMRR, though focus and astig change a bit in the process...
If you were referring to measurements like probing power supply points, that's something entirely different. Hmm......but nah, the CRT isn't sensitive enough to do that (10V/div). Hehe.
I know, I'll build another mostly-good deflection amp, this time JFET-buffering both inputs to the diff amp stage, and probe around with that!...
Hmm, come to think of it, a high bandwidth diff amp with wide CMRR (say,
30V) would be useful, and not too hard to build out of 2N3904's and whatnot. Hmm, keeping dissipation down while keeping speed up would be a problem.
Tim
-- Deep Fryer: A very philosophical monk. Website @
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