© 2003 Wohler Technologies Inc. ALL rights reserved
20
AMP2A-4S
and
AMP2A-10S
User Manual P/N
821554
Rev-
B
Section 3: Technical Information
Input Select Analog Switch PCB (919013) Description
Input selection from multiple sources is accomplished via a ten channel analog switch circuit. Connection to each source is
facilitated by installing a three position plug-in "Phoenix" style connector on the end of the source cable. The Phoenix connector has
screw clamps for the ground and a balanced pair. The signal is coupled to the circuit through a capacitor and a 47.5K ohm resistor on
each line in.
Selection of an input is made by pulling the control pins high on a 4053 analog switch. Inputs to the 4053 are normally connected to
a neutral buss (circuit bias supply) until a switch pair is selected at which time the inputs are switched to the signal busses. The 4053
has three SPDT switches, so two ICs are required for every three input pairs. There are two signal summing busses for the balanced
line. The signals are summed into inverting amplifiers and then summed into a differential amplifier, which then drives the audio
monitor in which the board is installed. Balanced outputs are available from the inverting amps for audio routing purposes.
In monaural board versions, two balanced pairs of signal summing busses are joined into one balanced summing pair by solder
bridging pads, and two opamps with their associated components are left off the board. In stereo versions, all opamps are installed
along with enough 4053 switches to accommodate the desired number of inputs. The inputs can be independently selected in the case
of mono sources or simultaneous pairs for stereo sources can be selected by installing jumpers at H3 (channel select pins).
Selection from ten stereo sources is accomplished by stacking two ISS boards and jumpering their select lines together. One board
can select from up to ten mono or five stereo inputs. Channel selection is normally done with a rotary switch mounted on the from
panel of units with the ISS option installed. This switch can be remoted as an option.
Unusual input select configurations (L only, R only, phase invert, etc.), or simultaneous multiple input select, are available as
additional options.
Trouble-Shooting Tips
Since a single-sided 24V supply is used, all opamps are “biased” with a 1/2 supply reference. The CMOS devices are powered from
a separate zener-regulated 15V source on each analog switch board. The analog switch elements are in series with an opamp summing
junction, so they can handle very high input signal levels without any "breakthrough" effect. When not selected, each 4053 input is
shunted to AC ground for improved off isolation. The inverting input of any opamp is sensitive to any stray capacitance to circuit
common. Though the summing amp design includes stabilizing elements, care should taken to avoid capacitive loading of the
summing busses. They are jumpered between switchboards in some configurations. There is an "enable" bus connected to pin 6 of
each 4053. It is available on H3 and H4, pin 12 (for bank switching or other special functions).
If it becomes necessary to disassemble a stacked audio switchboard assembly, insure that the upper board is positioned directly over
the lower one when reassembling. Should it inadvertently be displaced toward either the front or rear, the power connections may
become shorted.
Input:
Impedance:
Maximum Input Level:
Crosstalk:
Distortion:
Response:
Output Gain:
Maximum Output:
Power:
Ten balanced
90K
Ω
+24 dBv
-65 dB
<0.05%
+/- 0.5 dB, 20 Hz - 20 kHz
0 dB balanced, -10 dB unbalanced
+24 dBv
Less than 30 mA with a 24 volt supply
919013 PCB Specifications
