Specifications

NOTE: To prevent high-frequency oscillation, do not wire a
channel's Gate Out terminal to its own Mute In terminal until
the Mute to Inhibit change has been made.
Preventing Room Noise Modulation
This connection keeps at least one microphone on to
eliminate varying background noise or "pumping" [see Figure
151. The channel to which the transistor collector is con-
nected will be turned on whenever all other microphones are
gated off [see AMS Theory section].
GATE OUT
LOGlC GROUND
MUTE
IN
OVERRIDE IN
ROOM NOISE MODULATION PREVENTION
FIGURE
15
Microphone Lock-On
The circuit described in the preceding paragraph can be
expanded using diode isolation to perform a new function.
Even with the advantages offered by the AMS, there may be
installations where it is desirable that the last microphone
gated on should remain on until another microphone turns
on. For instance, the sound reinforcement requirements of a
church may dictate that an altar microphone remain on as
the minister moves outside the acceptance angle. Normally
the AMS would not remain gated on after the initial hold time
elapsed if the minister continued to speak outside the accep-
tance angle.
With the circuit shown in Figure 16, the last microphone
to gate on remains on indefinitely. When a new microphone
gates on, it will release the lock-on for the previous
microphone, and the new microphone will lock on. The result
is the ultimate in automatic mixing: each logic-wired
microphone is capable of remaining on until no longer need-
ed. Note that if two or more AMS microphones are
simultaneously gated on, normal AMS action will take place.
Since at least one microphone is always on, this circuit also
prevents room noise modulation. Bath the Mute In and
Override In remain usable for additional functions.
For each microphone to be given lock-on capability, the cir-
cuit uses a
2N2222 general-purpose amplifier NPN tran-
sistor [Motorola], a
I-megohm, %-watt resistor, and a
number of 1
N4148 diodes [GE] equal to the total number of
AMS channels involved. For instance, if the installation has
five AMS channels to be wired, a circuit containing one tran-
sistor, one resistor, and five diodes must be constructed for
each channel [a total of five transistors, five resistors, and
25 diodes]. The circuit in Figure 16 shows only one lock-on
circuit; similar circuits must be constructed for all
lockan
channels.
GATE OUT
LOGlC GROUND
MUTE IN
OVERRIDE IN
MICROPHONE LOCK-ON
[ONE CHANNEL SHOWN]
FIGURE
16
Diode Isolation of Logic Controls
Two or more control functions using the same logic ter-
minals can be isolated with diodes. Here a channel can be
muted by an overall group mute switch, or by its own cough
button [see Figure 1
71.
GATE OUT
LOGlC GROUND
MUTE IN
OVERRIDE IN
D= IN4148
OR EQUIVALENT
GROUP
f
MUTE
COUGH BUTTONS
DIODE ISOLATION OF LOGIC CONTROLS
FIGURE
'I7
External Logic Devices
The AMS logic levels are directly compatible with TTL and
5-volt CMOS logic families. The following example [Figure
181 uses logic gates to perform the same function as the
diode isolation of logic controls. Suggested
TL, LSTTL, or
CMOS NAND gates in Figure 1 8 are
I/2-7420,74LS20 and
74C20. Suggested AND gates are 7408, 74LS08 and
74C08. In the example, the output of the Channel-On in-
dicator goes to logic High if any channel gates on. [For infor-
mation on logic gate use, see the
TTL Cookbook and
CMOS Cookbook, both by D. Lancaster, Howard Sams
Publishing Co.]
c3
+3
-
--
GATE OUT
NAND GATE
0
MUTE IN
0 0
EXTERNAL LOGIC DEVICES
FIGURE
18