Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

Is there any particular reson you want to use discretes for the output stage ?
You'll increase complexity lots.


DC coupled with frequency response DC to 20KHz

Do you mean audio ?


Input signal level 1-2V
4 to 12 volts single supply

If it's a single supply you'll have to AC couple the signal ! Unless you want a
bridge tied load of course (more complicated).


Low power DIP op amp, suited to battery operation if required

Well, power dissipation is likely to be predominantly determined by any quiesent
current in the output stage (to avoid cross-over distortion) actually.


Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

Other specs are non-critical.

Are any of these, such as the wide supply range, inherently
contradictory to a predominantly fixed value circuit?

Any help would be very much appreciated.

The simplest best bet might be to look at some car audio amplifier chips.

Graham