Garmin GMA 340 AUDIO PANEL INSTALLATION MANUAL
Brand: Garmin, Pages: 43
Page 6 from 43
Page ivGMA 340 Installation Manual
GMA 340 HARDWARE MOD LEVEL HISTORY
The following table identifies hardware modification (Mod) Levels for the GMA 340 audio panel. Mod
Levels are listed with the associated service bulletin number, service bulletin date, and the purpose of the
modification. The table is current at the time of publication of this manual (see date on front cover) and is subject
to change without notice. Authorized Garmin Sales and Service Centers are encouraged to access the most up-to-
date bulletin and advisory information on the Garmin Dealer Resource web site at www.garmin.com using their
Garmin-provided user name and password.
DATEPURPOSE OF MODIFICATION
1 0103 2-2-01Configurable option to mute other com audios when
2 0113 6-13-01Provides times ten gain (20 dB) for entertainment music
3 0208B 5-17-02Provides correct marker beacon output loading for interface
with a Sandel SN3308 EHSI.
4 0209 5-2-02Provides failsafe operation when monophonic headsets are
used in a stereo installation.
5 0210 5-2-02Provides switchable On/OFF times ten gain (20 dB) for
entertainment music system.
6 0212 7-16-02Filter capacitors added to prevent power supply noise from
interfering with a GDL 49.
702138-26-02Prevents current limiting resistors from becoming shorted to
80221*Adds a failsafe warning audio to the GMA 340.
* Not released at time of publication.
Page 7 from 43
GMA 340 Installation ManualPage 1-1
This manual provides the installation and operating instructions for the Garmin GMA 340, GMA 340H and
GMA 340 Dual ADF Audio Panel. Reference to GMA 340 throughout this manual refers to all versions of the
unit. Information pertaining to the maintenance of the unit can be found in the GMA 340 Maintenance Manual,
P/N 190-00149-02. After installation of the GMA 340, FAA Form 337 must be completed by an appropriately
certificated agency to return the aircraft to service.
1.2 GENERAL DESCRIPTION
The Garmin GMA 340 Audio Panel meets the needs of aircraft owners and operators who require reliability and
versatility in the essential audio switching function. LED-illuminated push-button simplicity and intuitive panel
layout allow audio selection of both NAV and COM audio. Large, single-button activation of the COM
microphone and audio for up to three COM transceivers simplifies cockpit workload. Photocell dimming
circuitry automatically adjusts the brightness of the LEDs to a level appropriate for ambient cockpit light. A fail-
safe circuit connects the pilot’s headset and microphone directly to COM1 in the event that power is interrupted
or the unit is turned off. In the event of power loss a fail-safe warning audio will be heard.
Additionally, the GMA 340 includes a six-position intercom (ICS) with electronic cabin noise de-emphasis, two
stereo music inputs, and independent pilot, copilot, and passenger volume controls. To further simplify the
cockpit workload, the intercom provides three selectable modes of isolation. One hundred percent solid state
circuitry and extensive use of surface mount technology are employed. A pilot-selectable cabin speaker output
can be used to listen to the selected aircraft radios or to broadcast PA announcements. The PA function is pilot
The GMA 340 is FAA TSO approved to C50c and C35d and JTSO approved to C50c and 2C35d. Also standard
is the marker beacon receiver with dual sensitivity and audio muting with automatic re-arming. 14V or 28V
operation, including the full rated range of headphone and speaker output power, is available without the
requirement for external voltage converters or dropping resistors. The GMA 340 is the standard version audio
panel as pictured on the cover of this manual. The GMA 340H is the helicopter version in which the pilot and co-
pilot control knobs on the front panel are reversed. The GMA 340 Dual ADF version, also pictured on the cover,
accepts two ADF audio inputs.
•User-friendly, intuitive front panel layout
•LEDs indicate selected function
•Six position intercom: pilot, copilot, four passengers
•Three stereo headset amplifiers: one for pilot, one for copilot, and one for the passengers
•Two stereo music source inputs (one in Dual ADF version)
•Three selectable intercom operational modes
•Selectable aural pushbutton annunciation (beep) for the crew.
Page 8 from 43
Page 1-2GMA 340 Installation Manual
•Independent pilot, copilot, and passenger volume controls
•Individual VOX circuits for each of six (6) mic inputs
•Automatic selection of radio audio source when corresponding mic is selected
•Split COM transceiver function. Copilot may transmit and receive on COM2 while pilot
transmits and receives on COM1
•COM swap function
TMmarker audio muting
•Speaker output for radios or PA function
•Power-off fail-safe to connect Pilot PTT, mic, and Headset to COM 1 if unit is turned off
•Power loss fail-safe warning audio
TSO Compliance TSO-C50c, C35d, JTSO-C50c, and JTSO-2C35d using DO-160C,
DO-170, and DO-143
-20°C to +55°C
Weight (Unit Only) 1.2 lbs. (0.6 kg)
(Installed with rack and connectors) 1.7 lbs. (0.8 kg)
Physical Dimensions: Bezel Height: 1.30 inches (33 mm)
Bezel Width: 6.29 inches (160 mm)
Rack Height (Dimple to Dimple): 1.33 inches (34 mm)
Rack Width: 6.30 inches (160 mm)
Depth Behind Panel with
Connectors (measured from
face of aircraft panel to rear
of connector backshells)7.12 inches (181 mm)
Power Requirements Supply Voltage: 11.0 to 33.0 VDC; Operating Current: 2.2 A (normal
operation, 13.8 V, speaker on)
Altitude 50,000 Feet
Audio Panel Transceiver inputs: 3
Receiver inputs: 5 (6 in Dual ADF version)
Unswitched inputs: 2
Input impedance: 500
DME input in Dual ADF)
Input isolation: 60 dB minimum
Special functions: Fail-safe operation
Page 9 from 43
GMA 340 Installation ManualPage 1-3
Intercom Positions: 6 (pilot, copilot, 4 passengers)
Volume controls: 3 (pilot, copilot, passengers)
VOX level controls: 2 (pilot, copilot/passengers)
VOX circuits: 6 (one per mic input)
Music inputs (stereo): 2 (1 in Dual ADF version) (one input mutable)
Music input impedance: 460 ohms minimum
Music input level: Less than 500 mVac RMS for full output (typical).
1 Vac RMS MAX (3 Vac p-p)
Microphone signal processing: 9 pole characteristic and special cabin
noise band de-emphasis
Intercom isolation modes: 3
Special functions: Configurable aural push-button annunciation for
Headphone Outputs Output amplifiers: 3, stereo (pilot, copilot, passengers)
Fidelity: Power into 150
50 mW <0.5%
100 mW <5%
Frequency response: music; 100 Hz to 15 kHz nominal
Aircraft radio: 100 Hz to 6 kHz nominal
ICS mic: (Special cabin noise band de-emphasis)
Speaker Outputs Outputs selectable: 1, pilot selectable
Output power: 10 Watts into 4 or 8
, @ any normal supply voltage.
Frequency response: 350 Hz to 6 kHz nominal
Special functions: PA Mode, pilot selectable, including split operation
Marker Beacon Receiver Frequency: Crystal controlled at 75 MHz
Sensitivity: LO 1000 µV hard; HI 200 µV hard
Selectivity: 6 dB @ ±10 kHz min, 40 dB @ ±200 kHz max.
Input impedance: 50
External lamp drive: 125 mA max each output
Other outputs: Middle MKR sense
TMmarker audio muting
GMA 340 Audio Panel, Ship Level Assembly, P/N 010-00152-( ) includes the following, depending on part
•011-00401-( )GMA 340 Unit Assembly (011-00401-10 replaces 011-00401-00)
•011-00652-00Connector Kit, GMA 340
•011-00678-00Rack Backplate, GMA 340
•115-00262-00SMP, Install Rack, GMA 340
(The installation kit is the same for the GMA 340, GMA 340H and GMA 340 Dual ADF)
1.5 INSTALLATION ACCESSORIES
•Marker beacon antenna kit (P/N 010-10175-00). [Note: A marker beacon antenna approved to
TSO C35( ) that has been installed to meet the requirements of this manual may be approved for
use with the GMA 340].
Page 10 from 43
Page 1-4GMA 340 Installation Manual
1.6 ADDITIONAL EQUIPMENT REQUIRED
•Antenna sealant (use manufacturer’s instructions, install according to FAA AC 43.13-2A).
•Cables: The installer will fabricate and supply all system cables. Interconnect wiring diagrams
are detailed in Appendix B.
•Hardware: #6-32 100
° flat head screw (6 ea.) and #6-32 self-locking nut (6 ea.). Hardware
required to mount the installation rack is not provided.
•Stereo headphone jacks (up to 6), microphone jacks (up to 6), 3.5mm stereo jacks (up to 2), and
insulating washers for all.