David Looser wrote:
Is there something I'm missing here ? Is it
possible
to connect two virtual grounds together at a star point ?

No it's not. Why on earth were you trying to do that?


What I meant was two or more...even worse.

The reason is that I need multiple inputs *and* outputs from that star
point. It seems that either:

a) I can have any (reasonable) number of inputs connected to a single
virtual ground summer as the output device. A standard mixer. In other words
a star point with multiple inputs and one output.

OR

b) I can have a single input device with any (reasonable) number of outputs
using op-amps configured as high input impedance buffers. A star point with
one input and multiple outputs.

Both a) and b) work fine seperately. Is there any way to combine both ? I'm
beginning to think not...


The beauty of the virtual ground mixer is that it is insensitive to
changes in the number of inputs (what you are calling "fan-in"). If
you are getting level changes as you vary the number of inputs you
are doing something wrong somewhere.


Sorry, I'm probably not explaining myself very well. With a single virtual
ground mixer it behaves as it should. I'm getting into difficulties when I
try to combine a) and b) above to get several outputs from the same star
point.


What sort of op-amp are you
using?, and what value are the input and feedback resistors?


TL074 with Rf equal to Rin on each input. I used 10K resistors.