Archive of the former Yahoo!Groups mailing list: MOTM

Hi all,

My reasons for doing a balanced output signal is nothing really to do
with hum reduction through common mode rejection, but more to do with
the removal of a need for a connected common earth between systems. By
sharing the earth/ground connection between mixer and modular you are
likely to get ground loops. In other words allowing more than one route
between the two units for the ground signals to travel. Now, in an ideal
world this shouldn't matter, but because of resistance/impedance in the
audio cables and mains supplies, you will get difference of earth
potentials in each piece of equipment. Only small, but enough to cause
some signals to become superimposed on your audio path. Now, the classic
way is to remove one of the earths, either by clever design or by
removing the earth pin of your main plug (ouch). You can isolate your
system ground from earth, but this is hard when every jack socket that
is connected to ground is also connected to the metal panel. The metal
panel is also required to be connected to earth in most systems.
Although in a complete Oakley Modular this is not neccessary.

Using an elecronically balanced system, so long as the earth potentials
are not out by a huge amount, we can safely send the audio signal
without need for a <signal> ground joined at both ends. In a CV/gate
system this can be doubly useful since many commercial midi-CV
convertors actually earth the CV ground lines, my Kenton Pro-2 included.

In a well designed studio, this need not be a problem since the desk has
floating balanced inputs. And you have more control of your earths. But
I have found that pseudo balanced inputs, using a TRS jack as a non
balanced input, using the T and R and ignoring the S tends to have a
detrimental effect on hum.

So in summary, although not absolutely neccessary, its rather handy. Its
very useful with effects boxes too.

Er... I think that right, its been a long day, and I had to look after
the kids all day. ;-)

Regards,

Tony Allgood Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan