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1.0 External details
This is a view of the external controls on the
Circle5A.
1.1 Master Volume Control
The
function
of
the
Master
Volume
control is really that of a sensitivity control - to scale
down excessive input signals. In a set-up where the
signal level is scaled so that set to maximum (fully
clockwise) an input of 0.775VdBV, on the loudest
peaks, will fully drive the power amplifiers. Since
many sources give a signal under normal pro-
gramme that is significantly greater than 0.775V, it is
expected that in most situations the Circle 5A's vol-
ume control wil be set to about half way i.e. 12
o'clock. This would apply in many studio's where the
'+4' signal reference is the maximum. Note: as you
will observe from the circuit diagram, the volume
control follows the input buffer stage, and the input
amplifier will overload and distort if the input signal is
excessive whatever the volume control is set to.
1.2 Input sockets and selector switch
There are two input connectors: a master input, an
isolated XLR following thenormal European wiring
convention:
Pin 1 = shield (ground*)
Pin 2 = Live, hot, + signal
Pin 3 = Cold, -, return signal
* Pin 1 is connected to the ground of the C5A's
electronics. There is no connection from the audio
ground to the mains (safety) ground. The metal
panel is the only part of the C5A's electronics that is
connected to the mains ground.
Also provided is a secondary input: a Phono (Cinch,
RCA) connector for unbalanced systems. The centre
pin is signal +, and the connector case is the ground.
The phono plug's case is connected to the C5a's sig-
nal ground, not the mains (safety) ground. Neither
input is transformer isolated, and therefore care
must be taken to eliminate hum loops.
The selector switch selects which of th two inputs is
fed to the input buffer IC.
Connect to EITHER the XLR or the phono, not both.
Only use the mains cable supplied. Replace the
mains fuse with the correct type. The Circle5A must
External view of C5A's version 3 panel
be earthed at all times, and is not suitable for use
outdoors.
Version 5.6
07.04.02
Page 3
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