Electronic – Grounding in space

To what do I connect the grounding-setup, as a whole? (The mat, or the wrist-strap, or whatever.) I've been told everything from a water-pipe (would have to run a wire to the ceiling, there's nothing down low in the room), to the center-screw of a wall-outlet (really!?) … and, practically-speaking, how do you suggest I do so? Wrap a bare/stripped copper wire around the screw, or around the pipe? Or what?

You want everything Earthed. The center screw of a wall outlet is probably easiest. Make sure you verify that your work area's electrical installation is up to code, and there isn't a ground neutral reversal, for example. Your mat and wrist strap will probably have spade lugs for making the connection.

I know I should be working on an ESD-disappating mat, with an ESD-disappating wrist-strap on at all times. To what do I connect these? Do I connect them together, i.e. to a common point, as well? (From my still-fledging understanding, there should be a single shared ground amongst all points in the circuit, which I suppose includes your body if you touch a conductive part of the board, so …)

Connect them both together, back at Earth.

Is the “ground”, as discussed in terms of dissipating triboelectric potential / electrostatic charge, the same as the “ground” in circuits I'm working on? i.e. should I be connecting “ground” in any circuit, with a wire, to the same grounding-system we're discussing here? Or is that a separate ground? I've also got a bench power-supply with a ‘ground’ banana-socket, which I'm sure will be used for circuits, so I suppose … if the answer here is yes, I should wire that to this common-ground as well?

This is a topic for a separate question all together. Ground has come to be a generic term for circuit common, or zero Volt reference. You may, or may not, be able to make Earth your circuit common, depending on your circuit in question. If your bench power supply is galvanically isolated, it's typically ok to make that connection. More often than not that is through the ground clip on an oscilloscope. For ESD purposes, you don't connect to your circuit. You need to be careful about this, and research it further.

The bench multimeter I've acquired has a grounding screw on the back, next to the three-prong power-plug. Should that grounding-screw also be wired to the common-ground discussed here, i.e. the same as my wrist-strap? (Also, why the hell is there two grounds on that, then; one as a screw, and one as the third prong in the power-cable?)

You can, but for your purposes, it probably won't help much. The safety ground for the chassis is part of the three prong cable. That lug is intended to be connected to a low impedance instrumentation ground. Such a ground will be at approximately the same potential as earth and likely on its own ground rod, but won't won't have all the noise of the building's main electrical safety ground. The safety and instrumentation grounds must be tied together at some point, by code. That is typically as close to the ground rods as possible.

(1) Does 'input 2' correspond to the +12V wire and 'input 1' to the -12V wire?

NO. This is connected to the power supply connector. (Pin 1 is the positive, pin 2 the ground or 0V). The INPUT connector is where the audio signal goes (2) is the live and (1) is the ground.

(2) When I see the symbol 'ground' on the schematic does that mean that I need to connect those to the -12V line? I have no 0 volt line in the circuit so what is the ground line?

All voltages are relative to each other. If you only have TWO wires from the AC/DC converter then the most positive is taken as the positive and the other one is the OV or ground. A simple check with a voltmeter will determine which is which.

(3) Why are C3, C5 non-polarized capacitors and why are the other ones polarized? The current flows from negative to positive. Does that mean that the polarized capacitors need to be placed with their positive legs pointing to the left?

C3 and C5 are small value capacitors (0.1uF). These can be easily made as physically small, non-electrolytic types. They have the advantage of being able to decouple (short out) the higher frequencies. The larger values (uFs) are made as electrolytics as these can be made with high values in small physical packages. They are generally much poorer at handling the high frequencies. By combining an electrolytic with a non-electrolytic capacitor in parallel (eg C3, C6) you get a much better response over a wider range of frequencies. In this case they are used for 'smoothing' the supply voltage, preventing hum and hiss. The positive plate of an electrolytic is shown as an open rectangle but left and right (or up, down) have no meaning in terms of connection as this will be determined by board layout. Conventionally current is taken to flow positive to negative.