Is that indeed what diodes do? Eat voltage, make it disappear? I'm realising I've seen something like this phenomenon in 'diode clamps'.
Mmm, "eat current" more likely. The voltage drop is low, so the diode causes the component in series with it to "eat the voltage". Whether it likes to or not. If that series component is a power supply's own internal resistance, the voltage might indeed be eaten by that resistance... but the current won't be very friendly. And maybe the diode will eat itself after a few milliseconds!
A series diode could be said to "eat the voltage", because it has a high voltage drop when in reverse bias.
To Hero999, re your remarks about the consequence of putting an emitter follower after the pot: in some versions of my circuit (as I say, I've been playing around), I put my input signal through a source-follower JFET, then a resistor, then a big cap, before it reaches the voltage divider. I suppose it might depend on the values (JFET is 2N5458, source resistor is 22k, output resistor is 10k, DC-blocking capacitor is 10µF), but would I be right in thinking this is a different scenario, and I don't run the same risks?
He was referring to this:
Where the buffer is something like an ideal voltage source (i.e., a low output resistance, and capable of sourcing way more current than the base should ever see).
An emitter follower is not a perfect buffer, but it's very close: about hFE times worse than the base should want to see.
If you add a series resistor between buffer and base, you're back to the safe, current limited condition. (You also have a higher impedance, which means you can supply actual signals to it, say by coupling in with a DC blocking capacitor.)
Again, I should emphasise that the point here is not to make the transistor operate stably with predictable gain: it's just to see what's going on. If there's a wider agenda, I'm looking into the phenomenon of extreme clipping, as a way of producing pulse waves. At this point what I want to know is, am I going to blow anything up?
Extreme clipping as applied to what sort of input? If you start with sine waves, you can very easily apply enough gain and clamping to render a square wave, which might be considered "pulse waves". The common-emitter stage is generally less helpful for that goal, because the base draws current, which leads to clipping, yes, but also a shift in the DC offset of the stage (you will see a different voltage across the DC blocking capacitor depending on whether the source is 1mV, 1V or 10V).
A good solution is to drive the emitter voltage, not with GND, but with another transistor, so that the B-E diodes worth together without upsetting your signal -- this is called a differential amplifier, for its useful properties.
Diff amp stages can be cascaded to realize very high gain in the linear range, meaning it very quickly transitions from +saturation to -saturation, such as over a single mV at the input. These are called comparators.
Tim