PS Engineering
PMA8000BT Audio Selector Panel and Intercom System
Installation and Operator’s Manual
200-890-0702
Page 2-4
Rev. 1, Oct. 2010
2.4.5
Audio Panel interface
The PMA8000BT is designed to interface with standard aircraft avionics, and presents a 510
receiver
impedance. For best results, a twisted-shielded cable is recommended from the avionics audio source to
the audio panel, with the shield grounded at the audio panel end.
Some avionics do not provide a separate audio low, and may introduce additional electrical noise into the
system. For best results, connect the audio low from the audio panel to the radio ground, using one con-
ductor of the twisted-shielded cable.
2.4.5.1 Speaker Load
The PMA8000BT contains one speaker amplifier. Some units with internal speaker a mplifiers, such as
the King Radio KX170-series, require a resistive load to prevent damage if their speaker amplifier is not
used. Connect the speaker output from the unit to the COM 2 Speaker load input on the PMA8000BT (J1
27 WRT 28). The speaker load is 16
, 3W.
2.4.6
Transmit Interlock
Some communications transceivers use a transmit-interlock system. To fully utilize the Split Mode fea-
ture, this function must be disabled. Consult that manufacturer's installation ma nual.
2.4.7
Backlighting
The PMA8000BT has an automatic dimming of the pushbutton annunciation LEDs and marker lamps
controlled by a photocell. Control of the unit backlighting is through the aircraft avionics dimmer For 14
V aircraft, connect J2 Pins 6 and 7 to the aircraft dimmer bus, and pin 5 to ground. For 28-volt systems,
connect pin 7 to the aircraft dimmer, and pins 5 and 6 to ground.
If an external dimmer control is
not
used, a constant back light illumination can be established for nigh t-
time viewing. Pin 6 or 7 (depending on system voltage) must be tied to power (J2, pin 8 or 9) for the back
lighting system to work. The photocell mounted in the unit face will automatically adjust the inte nsity of
the push-button annunciator LEDs.
2.4.8
Unswitched inputs
J1, pins 31, 29 and J2 pin 15 are unswitched, unmuted (by transmitter keying), inputs # 1, 3 and 4, re-
spectively. These inputs are presented to the pilot and copilot regardless of the audio configuration, and
will always mute the entertainment inputs. These 510Ω inputs can be used for altimeter DH audio, GPS
waypoint audio, autopilot disconnect tones, or any other critical audio signal. Unswitched #1 is always
presented to the speaker, plus to the crew headphones, and is available to the pilot in fail -safe (off) mode.
Unswitched 3 and 4 inputs are always presented to the crew headphones and to the aircraft speaker.
Unswitched
Input
Hear in
Fail Safe
Hear in
Crew Headset
SPR button
Select
Gain
1
Yes
Yes
No
1:1(fixed)
2
No
Yes
Yes
1:1(fixed)
3
No
Yes
No
Adjustable
4
No
Yes
No
1:1(fixed)
5 (jack)
No
Yes
No
1:1(fixed)
Table 2-2 Unswitched input table
Unswitched #2, J1 pin 44 is unswitched is always connected to the Pilot’s headphone. However, this
unswitched audio is only presented to the aircraft speaker when the SPR push button has been selected.
This input would be suitable for air-to-ground (Flitefone) telephone ringer. This input is not related to the
cellular telephone interface.
The audio low for unswitched #4 (J2, pin 15) should be connected to a convenient audio low. However,
this should NOT be connected to Music Low.