[Solderless breadboards] encourage 'fiddle until
it seems to work'
designing,
That's not what I'm talking about. [...]
My apologies.
Actually, I didn;'t think you would do something like
that...
I have done it, actually, though I think without the "no real
understanding of why" part. For example, I once built a phase-shift
oscillator out of three RC phase-shift stages and an op-amp. But I
wanted something as close as feasible to a sine wave. So I put a
variable resistor in the op-amp fedback, to control the gain. Then I
fiddled with that. Crank the gain up and I got a severely clipped
waveform; crank it down and it wouldn't oscillate (neither of which was
surprising in the least). I fiddled with it until I found a setting
that made the amplitude just barely grow, growing until it just barely
clipped, at which point it stabilized. (It grew fairly slowly; it took
multiple seconds to reach the point of clipping and stabilizing.)
Finding the exact resistor value theoretically would have required
knowing precise values for the components in the R-C network, the other
resistor in the op-amp feedback, loading from parasitic capacitance
(actually, the frequency - something in the audio range, I think - was
low enough that one might have been ignorable), etc.
I considered trying to build some kind of AGC for it, but never
actually got the round tuits for that.
It fits the "fiddle until it seems to work" words you used, but I don't
think it's the kind of design-without-understanding you appear to have
meant to be (correctly, IMO) castigating.
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