18
Floating, Pseudo, and Quasi-Balancing
During inspection, you may run across a ¼" output called floating unbal-
anced, sometimes also called psuedo-balanced or quasi-balanced. In this
configuration, the sleeve of the output stage is not connected inside the unit
and the ring is connected (usually through a small resistor) to the audio signal
ground. This allows the tip and ring to “appear” as an equal impedance, not-
quite balanced output stage, even though the output circuitry is unbalanced.
Floating unbalanced often works to drive either a balanced or unbalanced
input, depending if a TS or TRS standard cable is plugged into it. When it
hums, a special cable is required. See drawings #11 and #12, and do not make
the cross-coupled modification of tying the ring and sleeve together.
Winning the Wiring Wars
• Use balanced connections whenever possible, with the shield bonded to the
metal chassis at both ends.
• Transformer isolate all unbalanced connections from balanced connec-
tions.
• Use special cable assemblies when unbalanced lines cannot be transformer
isolated.
• Any unbalanced cable must be kept under 10 feet
(3 m) in length. Lengths longer than this will amplify all the nasty side
effects of unbalanced circuitry's ground loops.
Summary
If you are unable to do things correctly (i.e. use fully balanced wiring with
shields tied to the
chassis
at both ends, or transformer isolate all unbalanced
signals from balanced signals) then there is no guarantee that a hum-free
interconnect can be achieved, nor is there a definite scheme that will assure
noise-free operation in all configurations.
