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Appendix D – Audio Interfacing
Page 63
Appendix D: Audio Interfacing
All analogue audio inputs and outputs are electronically balanced. The screen pins are all directly connected to
the chassis at the point of entry to comply with AES/EBU grounding and EMC recommendations.
Balanced Circuits
It is strongly recommended that balanced connections are used wherever possible using high quality screened
c
able. The following diagram shows the recommended connection with both screens connected to the chassis:
On some older items of equipment the screen connection may still be referenced to the circuit 0V rather than the
chassis. In these cases it may be advantageous to disconnect the screen at this connection. Note however that this
practice will degrade the EMC performance.
Connecting to Unbalanced Equipment
Connecting to unbalanced equipment can be much more problematic. It is much more likely that earth and
induced RF currents will become referenced to the audio 0V which will give rise to audible hum and buzz.
The recommendation for connection of balanced to unbalanced equipment is to isolate unbalanced connections
by using a balancing transformer.
chassis
chassis
chassis
0V
chassis
0V
Balanced – Balanced
both screens connected to chassis
(recommended)
Balanced – Balanced
one screen connected to chassis
Balanced – Unbalanced
one screen connected to chassis
(recommended)