Connections, Input connections, Balanced inputs – Lab.gruppen fP 3400 User Manual

Page 14: Unbalanced inputs, T= `lkkb`qflkp, Tkn= fåéìí=езеейенбзел

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The XLR input connectors are electronically balanced, and wired according to the IEC 268 (pin 2 =
“hot”), and wired in the following way:

PIN 1

GROUND/SHIELD

PIN 2

HOT (+)

PIN 3

COLD (-)

Figure 4: XLR input connector

Figure 5: XLR balanced


Within the Neutrik® Combojack there is a ¼”(6.3mm) phone jack wired in parallel with the XLR.

TIP HOT
RING COLD
SLEEVE GROUND/SHIELD


Figure 6: ¼” TRS plug

The input impedance is high enough (20 kohms balanced) to
allow ”daisy-chaining”, or multiple parallel input
connections. The headroom of the input circuits is also great
enough to accept the maximum output level from virtually
any low-level signal source. Balanced signals are less
sensitive to AC hum and radio interference. The source
impedance should be less than 1 kohms to avoid high
frequency loss in long cables.

To daisy-chain amplifiers, use the XLR-male connector provided on each channel, labeled “Link”. They
are connected in parallel with the Neutrik® Combojack on each input.

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To connect an unbalanced input source, connect pins 1 and 3 in the cable’s XLR plug (ring and sleeve in a
TRS plug). If you leave a pin disconnected, you will lose 6dB.
A better method for using unbalanced sources is shown in figure 8. This is similar to the connection for
balanced lines, but pin 3 is connected to the shield at the source end of the cable. The hum and noise
rejection for the cable is equivalent to that of a balanced line. To minimize hum in the audio signal, use
balanced inputs whenever possible.

Figure 7: Unbalanced line connection





Figure 8: Balanced line with unbalanced equipment

For 2-channel (stereo) operation, use both channels A and B. For tandem stereo or bridged mono
operation, use only one of the inputs. See “Operation Modes” (page

7

) for more details.

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