Interconnection-5
Floating, Pseudo, and Quasi-Balancing
During inspection, you may run across a ¼" output called
floating unbalanced, 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 bal-
anced or unbalanced input, depending if a TS or TRS stan-
dard 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 bal-
anced connections.
• Use special cable assemblies when unbalanced lines can-
not 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 bal-
anced 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 intercon-
nect can be achieved, nor is there a definite scheme that will
assure noise-free operation in all configurations.
References
1. Neil A. Muncy, “Noise Susceptibility in Analog and Digi-
tal Signal Processing Systems,” presented at the 97th AES
Convention of Audio Engineering Society in San Fran-
cisco, CA, Nov. 1994.
2.
Grounding, Shielding, and Interconnections in Analog
& Digital Signal Processing Systems: Understanding the
Basics
; Workshops designed and presented by Neil Muncy
and Cal Perkins, at the 97th AES Convention of Audio
Engineering Society in San Francisco, CA, Nov. 1994.
3. The entire June 1995 AES Journal, Vol. 43, No. 6, available
$6 members, $11 nonmembers from the Audio Engineer-
ing Society, 60 E. 42nd St., New York, NY, 10165-2520.
4. Phillip Giddings,
Audio System Design and Installation
(SAMS, Indiana, 1990).
5. Ralph Morrison,
Noise and Other Interfering Signals
(Wi-
ley, New York, 1992).
6. Henry W. Ott,
Noise Reduction Techniques in Electronic
Systems
, 2nd Edition (Wiley, New York, 1988).
7. Cal Perkins, “Measurement Techniques for Debugging
Electronic Systems and Their Instrumentation,”
The Pro-
ceedings of the 11th International AES Conference: Audio
Test & Measurement,
Portland, OR, May 1992, pp. 82-92
(Audio Engineering Society, New York, 1992).
8. Macatee,
RaneNote
: “Grounding and Shielding Audio
Devices,” Rane Corporation, 1994.
9. Philip Giddings, “Grounding and Shielding for Sound and
Video,”
S&VC
, Sept. 20th, 1995.
10. AES48-2005:
AES standard on interconnections —
Grounding and EMC practices — Shields of connectors
in audio equipment containing active circuitry
(Audio
Engineering Society, New York, 2005).
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