> Dieter,
>
> that would be interesting as it would save me daisy chaining mixers and
> loosing an i/p
>
> david
>
> David Salter
> Senior Consultant
> PSG

David,

the mod is simple:

For the old version of A-138a/b remove the dual opamp IC1 (TL062) of one of
the two modules and connect pin #2 of IC1 (i.e. the inverting input pin of
the first opamp) of both modules. The module with the missing IC1 has no
longer a output signal available. If you want to have a output of this
module connect pin #7 of IC1 (i.e. output of the second opamp) of both
modules. Now you have two outputs with adjustable levels available.

For the new version of A-138a/b its similar but here a quad opamp (TL064) is
used. Remove the quad opamp IC1 (TL064) of one of the two modules and
connect pin #9 of IC1 (i.e. the inverting input pin of the first opamp) of
both modules. The module with the missing IC1 has no longer a output signal
available. If you want to have a output connect the output sockets of both
modules. In this case the output of the second module cannot be adjusted
(different circuit compared to the old version). But you may connect the pin
header JP2 of the first module to the output of the second module. Then you
have the inverted output available.

For the polarizing mixer A-138c remove IC3 (TL062) of one of the two modules
and connect pin #6 of IC3 (i.e. the inverting input pin of the mixing opamp)
of both modules. The module with the missing IC3 has no longer a output
signal available. If you want to have a output of this module connect pin #1
of IC3 (i.e. output of the final opamp) of both modules. In this case the
level is the same for both outputs. The master control of the second module
has no function.

We already discussed a simple "mixing expander" module that could be used to
add 5 more inputs to A-138a/b. It will be about 20-30% cheaper than an
A-138a/b as no integrated circuits and no power supply are necessary for
such a simple module (only a front panel with five sockets, five
potentiometers+knobs and five resistors). How about a poll

Good luck,
Dieter Doepfer