> hi,
>
> putting together my shopping list mail to doepfer (better than
> xmas), and i'm undecided how many a138e's i need/want/can afford.
>
> a138 as crossfader: in the central position, are both signals at
> full volume the description only states equal volume.

The full volume appears only at the CW/CCW positions. With the switch in the
left position about 50% of each signal appears at the output in the center
position of the knob.

> if sub unit 4 is used as a sum for the first three, what does the pot do

The sum of the outputs 1...3 is added to the input (socket A) of unit 4. The
idea is to use unit 4 as a summing amplifier for the outputs of the units
1...3 (i.e. to save an external mixer).

Best wishes
Dieter Doepfer