[sdiy] coupler module

[Czech Martin]

Every synth needs a coupling module to the tape machine or mixing desk.

I plan to build some soon, containing:

-4 balanced inputs, 2 balanced outputs (trafo or electronic)
-2 or 4 (several) unbalanced inputs (for other synths)
-input or output scaling circuits (the analog synth can have +-13V or +-100mV
 as extremes), the usual levels are -10dBu = 0.245 V RMS ~ 0.35V peak
                                 or   6dBu = 1.55  V RMS ~ 2.2 V peak 

 assuming that 0 dBu = 0.775V RMS and sine wave form.
 So gains of 37,    0.29,  5.9 , 0.045
          or 0.027, 3.4,   0.17, 22    (reciprocal)
 can be needed, so a range of 37 to 0.027 seems to appear.
 This is no problem since resistor networks can be changed
 if necessary. Plug in connections of resistors on the PCB
 seems to be a good idea.

-A good question is if any EQ is needed. Shelving bass and treble
 and perhaps some mid bell shaped EQ.

 I'm not sure if this needed. It could save a mixing desk.

-Another question is if any external effects send/return is needed
-Certainly a level meter plus overload indicator with hold/reset
 is needed for the line out.

If all features are build, I end up with a little mixing desk.
That is certainly too much. 

So what is your practical experience?
What is needed?

Martin Czech