Aphex 228 - Manual (Page 15)

Aphex Systems Ltd. Model 228 Page 14
228
instruction Manual
Page 15 Aphex Systems Ltd. Model 228
228
8-channel audio interface
Sometimes it just comes down to brute force grounding. That means providing such heavy, low resistance,
ground current paths that little current is left to flow through your audio grounds. You can try adding heavy
gauge, for example 12 gauge, copper wire from chassis to chassis. You will need to locate a metal screw that
solidly binds to the metal chassis of the gear. You may even need to drill a hole through the chassis and install
a screw yourself. Equipment in rack shelves can have their chassis grounded to the metal rack frame by a
heavy wire and the frame itself can act as a brute force ground. You just have to try everything you can think
of. Usually a combination of all these methods will be needed to completely clean up a badly humming audio
system.
Balance Out the Audio
Remember, balanced lines are inherently hum free. If you can balance out your unbalanced equipment, you will
be able to stop the hum.
Pseudo Balancing
You will find in Table 2 an interconnecting method called Pseudo Balanced. This works when connecting an
unbalanced output to a balanced input. This breaks up the ground loop by requiring the shield to be grounded
only at one end. For best results always ground the shield only at the receiving end.
Level Interface Units
Aphex manufactures the Model 124 Level Interface box which is designed to electronically convert two unbal-
anced inputs and outputs two balanced inputs and outputs, and at the same time translate the -10dBV IHF
unbalanced levels to the pro +4dBu balanced levels. This cost effectively gives your non-professional unbal-
anced equipment a fully professional I/O equal to the world’s best pro audio gear. Seriously consider putting
one of these on each unbalanced piece of gear you use.
Avoid Transformers
The use of balancing transformers is an option, but you will invariably lose audio quality due to transformer
limitations. Try everything else first.
Appendix C: Wiring Techniques
A true balanced line should be used wherever your equipment allows. Use “twisted pair” shielded cable. For
unbalanced wiring you should use high grade, low capacitance shielded wire for best results. If you have
an unbalanced output but have a balanced input, the “pseudo-balanced” configuration may help deal with
ground loop hum. This method and others are illustrated in Table 2.
CONNECTOR WIRING STANDARDS
The 3 pin XLR, 1/4” (63.5 mm) TS mono phone and the 1/4” (63.5 mm) TRS stereo phone are the most com-
monly used line level connectors in pro audio. Less common is the use of the “RCA” phono jack, which is
essentially a consumer type connector. The XLR and the TRS are three conductor and are used for balanced
connections. The TS and the RCA are two conductor and are used for unbalanced connections.
In addition to the three main contacts on an XLR there is also a grounding lug contact. This lug is connected
to the connector’s case (shell). In all Aphex products audio ground and chassis ground are one and the same.
Aphex products that use XLR connectors tie Pin I to the XLR case automatically.
Therefore it is not necessary to
use the XLR case-ground lug. This also makes possible the use of XLR ground drop adapters (see Note 3).
TABLE 1: The following wiring convention is now standardized in 17 countries including the USA. Please note
Appendices