Hi Richard

> Is it possible to couple together two Doepfer A138 mixers to give me
> eight inputs
> Anyone know if this is possible

another suggestion (as potential alternative to Dieters instruction):

I have the output potentiometer always set fully clockwise. In other
words: I do not really need it.

So why not
- replace the poti electrically by fixed resistors
- mount a socket to the hole where the poti was mounted
- connect this socket with a fixed resistor pot and resistor
to the central mixing point of the mixer.

I do not know the real potentiometer and resistor values at the moment,
but try these.

Oldinputs O--+
P 100k
50k P<-----rrrrr---+
P |
| |
Gnd |
|
|
Oldinputs O--+ |
P 100k |
50k P<-----rrrrr---+
P |
| |
Gnd |
|
|
Oldinputs O--+ |
P 100k |
50k P<-----rrrrr---+-----To summing amps
P |
| |
Gnd |
|
|
Oldinputs O--+ |
P 100k |
50k P<-----rrrrr---+
P |
| |
Gnd | existing mixer
............................|........................
100k | new input
New Input O--+------rrrrr---+
|
r
r 47k
r
|
r
r 3k3
r
|
Gnd


So you would get a fifth input with fixed amplification, which can be
used as for stacking mixers.

Florian