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Operating Manual - VCM-88, VCM-88E, RD-8, RW-8 Level Controllers
8
7. Audio Connections and Cables
7.1 Balanced and Unbalanced Signals
Balanced signal connections are preferred in pro
audio applications because of their improved immunity to
induced hum and noise. A properly shielded and wired
balanced input stage on any product will by design reject
most unwanted noise picked up by the cable as well as mini-
mize ground loop problems. Therefore it is always advan-
tageous to use balanced connections when running signal
more than ten or fifteen feet, although particularly noisy
environments (high RFI, EMI, etc.) may require that even
short cabling be balanced. Ashly TRS (tip-ring-sleeve) bal-
anced connections use the tip as (+) and the ring as (-) sig-
nal, with sleeve used for ground. Ashly XLR connectors
use pin 2 (+) and pin 3 (-) with pin 1 ground.
Unbalanced connections are used mostly for short
distance, high level signals (0dBu nom). Most external EMI
noise pick-up will be masked under the noise floor of the
signal, assuming there is little or no gain following the un-
balanced signal. If a gain stage does follow a signal, or if
externally sourced noise persists, use balanced connectors.
The VCM-88 and the VCM-88E are factory con-
figured for separate input and output connectors. Used this
way, inputs and outputs can be wired balanced or unbal-
anced. An internally selected single connector insert is also
available (see section 8.1).
7.2 Input Connections
The VCM-88 uses balanced 1/4" input jacks (see
fig. 7.1), while the VCM-88E uses Euroblock connectors
(see fig. 7.2). Both unit's inputs are 20K ohm active bal-
anced and 10K ohm unbalanced. If the VCM-88E uses un-
balanced inputs, connect the input signal to (+) and con-
nect the (-) pin to ground. Note: If the single connector
insert mode is selected (see section 8.1), the In jack serves
as the TRS insert on the VCM-88 and the (+) and (-)
euroblock connections serve as the input and output respec-
tively on the VCM-88E.
7.3 Output Connections
The VCM-88(E) audio outputs are 200 ohm
pseudo-balanced (balanced impedance but signal drive on
tip or (+) only). For unbalanced euroblock outputs on the
VCM-88E, connect the signal wire to (+) and the shield to
ground (see fig. 7.3).
Note: If the single connector insert mode is selected
(see section 8.1), the output signal is taken from the ring or
(-) of the Input jack, while the Output jack is not used.
Tip (+)
Ring (-)
Sleeve (Gnd)
Stereo Phone Plug
used for balanced
Tip (+)
Sleeve (Gnd)
Mono Phone Plug
used for unbalanced
Fig 7.1
Fig 7.2
Fig 7.3
+
-
G
+
-
G
+
-
G
+
G
Unbalanced
Output
Balanced
Output
Euroblock
Output
Connections
Euroblock
Input
Connections
+
-
G
+
-
G
+
-
G
+
-
G
Unbalanced
Input
Balanced
Input