42004-431B
Pub. 42004-431B
GAI-TRONICS® CORPORATION
A HUBBELL COMPANY
370-301 Dual Channel
600-Ohm to 33-Ohm Converter
Confidentiality Notice
This manual is provided solely as an operational, installation, and maintenance guide and contains sensitive
business and technical information that is confidential and proprietary to GAI-Tronics. GAI-Tronics
retains all intellectual property and other rights in or to the information contained herein, and such
information may only be used in connection with the operation of your GAI-Tronics product or system.
This manual may not be disclosed in any form, in whole or in part, directly or indirectly, to any third party.
General Information
The Model 370-301 Dual Channel 600-Ohm to 33-Ohm Converter
allows GAI-Tronics’ Page/Party® systems to interface with standard
600-ohm networks for one- or two-way communication between
dissimilar transmission mediums.
The 370-301 includes two hybrid interfaces in each channel to isolate
the audio so that the received audio in one direction does not affect the
transmit audio in the other direction.
The 370-301 includes a VOX (voice activated switch) on each of the
outputs. The VOX samples the audio out to the line. In the presence
of audio, a relay is activated for receive amplifier activation.
Features

Two independent conversion circuits, one for party lines and one
for page lines

Individual gain and sidetone adjustment for each audio path

VOX detection on 33-ohm and 600-ohm interface for activating a
receiving amplifier

AC or dc power operation

33-ohm termination internal to unit
Figure 1. Outline of 370-301
GAI-Tronics Corporation 400 E. Wyomissing Ave. Mohnton, PA 19540 USA
610-777-1374  800-492-1212  Fax: 610-796-5954
VISIT WWW .GAI-TRONICS.COM FOR PRODUCT LITERATURE AND MANUALS
370-301 Dual Channel 600 to 30-Ohm Converter
Pub. 42004-431B
Page 2 of 9
Installation
Important Safety Instructions
1. Read, follow, and retain instructions – All safety and operating instructions should be read and
followed before operating the unit. Retain instructions for future reference.
2. Heed warnings – Adhere to all warnings of the unit and in the operating instructions.
3. Attachments - Attachments not recommended by the product manufacturer should not be used, as
they may cause hazards.
4. Servicing – Do not attempt to service this unit by yourself. Opening or removing covers may expose
you to dangerous voltage or other hazards. Refer all servicing to qualified service personnel.
5. This permanently connected apparatus must have a UL Listed 15-amp circuit breaker incorporated in
the electrical installation of the building.
USA and Canada Consult the National Electrical Code (NFPA 70), Canadian Standards Association
(CSA 22.1), and local codes for specific requirements regarding your installation. Class 2 circuit wiring
must be performed in accordance with NEC 725.55.
WARNING
In 24 V dc systems: Under NO condition should this equipment be operated
from a battery charger without the batteries connected.
In 24 V dc systems, most chargers have an unloaded output of 35 to 45 volts that can quickly damage the
equipment designed for nominal 24 volts. The maximum battery voltage should never exceed the
maximum specified input voltage.
Mounting the Enclosure
NOTE: The enclosure is intended for indoor use only.
Mount the enclosure using the four 0.312-inch (8 mm) diameter holes located on the mounting flanges
with ¼-inch (M6) hardware. The 370-301 is not supplied with conduit or cable openings.
Remove the front panel and drill or punch entry openings in the rear section of the enclosure
Refer to Figure 2 for the suggested locations. There must be a minimum of ½ inch (13 mm) of material
between entry holes. The station is suitable for top or bottom entry per Figure 2. However, GAI-Tronics
recommends bottom entry only wherever possible.
The standard orientation shown in Figure 2 locates the power supply housing in the upper left corner.
The orientation of the enclosure can be rotated 180º to allow clear access to the top.
The 69856-xxx PCBA can then be rotated for correct orientation.
For specific details including mounting hole dimensions, refer to Figure 2. When mounting the enclosure,
use caution to avoid damaging the internal components.
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370-301 Dual Channel 600 to 30-Ohm Converter
Figure 2. Mounting Details and Wire Entry Locations
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370-301 Dual Channel 600 to 30-Ohm Converter
Field Wiring
Refer to Figure 3, 69856-001 PCBA, for reference to connection locations.
Figure 3. 69856-001 PCBA
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Pub. 42004-431B
Page 5 of 9
370-301 Dual Channel 600 to 30-Ohm Converter
Power
The 370-301 Converter can be powered from a universal ac power source or 12 to 24-volt dc source.
NOTE
Do not use an ac or dc power source at the same time.
When using a universal ac power source, TB1 is used for field wiring and P1 or P2 are used to connect to
the ac to dc power supply in the unit. Attach #6 spade lugs to the wires before attachment to the terminal
blocks for the most secure connection. TB2 is not used in this configuration.
Table 1. Universal AC Power Connections – TB1
Pin Number
Pin Name
1
Input Line
2
Input Neutral
3
Earth
When using a dc power source, TB2 is used for the field wiring. Attach #6 spade lugs to the wires before
attachment to the terminal blocks for the most secure connection. TB1, P1 and P2 are not in this
configuration.
Table 2. 12–24 Volt DC Connections – TB2
Pin Number
Pin Name
1
12–24 V dc +
2
12–24 V dc -
3
Earth
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370-301 Dual Channel 600 to 30-Ohm Converter
Pub. 42004-431B
Page 6 of 9
Audio and Control Signals
The 370-301 allows access to the audio line inputs and output along with relay contacts for the VOX
detection.
Table 3. 600-Ohm Connections Channel 1, P4
Pin
Number
Pin Name
Function
1
NC 600-ohm active
Normally closed connection of 600-ohm output VOX detection.
2
COM 600-ohm active
Common connection of 600-ohm output VOX detection.
3
NO 600-ohm active
Normally open connection of 600-ohm output VOX detection.
4
GND
Ground reference for field wiring.
5
L1 600-ohm audio
Bi-directional audio for 600-ohm interface
6
L2 600-ohm audio
Bi-directional audio for 600-ohm interface
Table 4. 33-Ohm Connections Channel 1, P6
Pin
Number
Pin Name
Function
1
NC 33-ohm active
Normally closed connection of 33-ohm output VOX detection.
2
COM 33-ohm active
Common connection of 33-ohm output VOX detection.
3
NO 33-ohm active
Normally open connection of 33-ohm output VOX detection.
4
GND
Ground reference for field wiring.
5
L1 33-ohm audio
Bi-directional audio for 33-ohm interface
6
L2 33-ohm audio
Bi-directional audio for 33-ohm interface
INTELLECTU
Table 5. 600-Ohm Connections Channel 2, P10
Pin
Number
Pin Name
Function
1
NC 600-ohm active
Normally closed connection of 600-ohm output VOX detection.
2
COM 600-ohm active
Common connection of 600-ohm output VOX detection.
3
NO 600-ohm active
Normally open connection of 600-ohm output VOX detection.
4
GND
Ground reference for field wiring.
5
L1 600-ohm audio
Bi-directional audio for 600-ohm interface
6
L2 600-ohm audio
Bi-directional audio for 600-ohm interface
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370-301 Dual Channel 600 to 30-Ohm Converter
Pub. 42004-431B
Page 7 of 9
Table 6. 33-Ohm Connections Channel 2, P12
Pin
Number
Pin Name
Function
1
NC 33-ohm active
Normally closed connection of 33-ohm output VOX detection.
2
COM 33-ohm active
Common connection of 33-ohm output VOX detection.
3
NO 33-ohm active
Normally open connection of 33-ohm output VOX detection.
4
GND
Ground reference for field wiring.
5
L1 33-ohm audio
Bi-directional audio for 33-ohm interface
6
L2 33-ohm audio
Bi-directional audio for 33-ohm interface
Settings and Adjustments
Opening the Station
Remove the four screws from the front panel and place the front panel to the side.
Jumper Settings
Channel 1: 33-Ohm Activation P3 - Install the jumper in the ACT (default) position to enable the 33ohm audio output. Install the jumper in the NON position to disable the 33-ohm audio output.
Channel 1: 33-Ohm Termination P8 - The Page/Party® line can be terminated to 33 ohms as required
by the Page/Party® system. Install the jumper in the TERM position to terminate the line. Install the
jumper in the NON (default) position to leave the line unterminated. For the unterminated position, a
line balance assembly is needed in the system.
Channel 1: 600-Ohm Activation P7 - Install the jumper in the ACT (default) position to enable the
600-ohm audio output. Install the jumper in the NON position to disable the 600-ohm audio output.
Channel 2: 33-Ohm Activation P9 - Install the jumper in the ACT (default) position to enable the
33-ohm audio output. Install the jumper in the NON position to disable the 33-ohm audio output.
Channel 2: 33-Ohm Termination P14 - The Page/Party® line can be terminated to 33 ohms as required
by the Page/Party® system. Install the jumper in the TERM position to terminate the line. Install the
jumper in the NON (default) position to leave the line unterminated. For the unterminated position, a
line balance assembly is needed in the system.
Channel 2: 600-Ohm Activation P13 - Install the jumper in the ACT (default) position to enable the
600-ohm audio output. Install the jumper in the NON position to disable the 600-ohm audio output.
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370-301 Dual Channel 600 to 30-Ohm Converter
Pub. 42004-431B
Page 8 of 9
Level Adjustments
Channel 1 33-Ohm Volume Level - The 33-ohm volume level potentiometer, R11, adjusts the signal
level out to the 33-ohm line.
Channel 1 33-Ohm Balance - The 33-ohm balance potentiometer, R46, adjusts the sidetone present on
the 33-ohm side of the interface.
Channel 1 600-Ohm Volume Level - The 600-ohm volume level potentiometer, R37, adjusts the signal
level out to the 600-ohm line.
Channel 1 600-Ohm Balance - The 600-ohm balance potentiometer, R34, adjusts the sidetone present
on the 600-ohm side of the interface.
Channel 2 33-Ohm Volume Level - The 33-ohm volume level potentiometer, R57, adjusts the signal
level out to the 33-ohm line.
Channel 2 33-Ohm Balance - The 33-ohm balance potentiometer, R79, adjusts the sidetone present on
the 33-ohm side of the interface. It adjusts the amount of audio that is transmitted to the 33-ohm line
from being heard on the 600-ohm line.
Channel 2 600-Ohm Volume Level - The 600-ohm volume level potentiometer, R81, adjusts the signal
level out to the 600-ohm line.
Channel 2 600-Ohm Balance - The 600-ohm balance potentiometer, R74, adjusts the sidetone present
on the 600-ohm side of the interface.
Bi-directional Alignment
The unit is factory aligned for ideal conditions, such as the 33-ohm line terminated at the unit. For areas
where this is not the case, adjustments may be required to improve audio and sidetone levels.
For sidetone adjustments, the unit should be aligned as two one-way systems and then connected as the
two-way system. The following is the procedure to align the sidetone in each direction.
1. Remove the jumper P7 for Channel 1 or P13 for Channel 2 to deactivate the 600-ohm output. This
will set up the unit for a 33-ohm output only.
2. Apply a signal to the 600-ohm input and adjust the 33-ohm volume level potentiometer, R11 for
Channel 1 or R57 for Channel 2, for the desired output level on the 33-ohm side.
3. Monitor the signal level at pin 1 of P7 for Channel 1 or P13 for Channel 2. In the unit it is located at
the top of the header. This is the sidetone signal level. Adjust the 33-ohm balance potentiometer,
R46 for Channel 1 or R79 for Channel 2 for minimal signal level at pin 1.
4. Install the jumper P7 for Channel 1 or P13 for Channel 2 to activate the 600-ohm output and fine
tune the 33-ohm volume level potentiometer, R11 for Channel 1 or R57 for Channel 2, for desired
output level side.
5. Remove the jumper P3 for Channel 1 or P9 for Channel 2 to deactivate the 600-ohm output. This
will set up the unit for a 33-ohm output only.
6. Apply a signal to the 33-ohm input and adjust the 600-ohm volume level potentiometer, R37 for
Channel 1 or R81 for Channel 2, for the desired output level on the 33-ohm side.
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370-301 Dual Channel 600 to 30-Ohm Converter
Pub. 42004-431B
Page 9 of 9
7. Monitor the signal level at pin 1 of the header for the 33-ohm activation. In the unit it is located at
the top of the header. This is the sidetone signal level. Adjust the 600-ohm balance potentiometer
for minimal signal level at pin 1.
8. Install the jumper P3 for Channel 1 or P9 for Channel 2 to activate the 33-ohm output and fine tune
the 600-ohm volume level potentiometer, R37 for Channel 1 or R81 for Channel 2, for desired output
level side.
Attaching the Front Panel
After all adjustments have been completed, place the front cover on the rear enclosure, being careful not
to pinch any cables. Secure the front cover using the four screws and washers provided. Torque the
screws to 10–12 in-lbs (1.13–1.36 n-m).
Specifications
AC/DC Input
AC Power Supply
Input voltage ...................................................................................... 120/230 V ac (nominal), 50/60 Hz
Power factor @ nominal 120 V ac .................................................................................................... 0.98
Current draw @ nominal 120 V ac ............................................................................................. 100 mA
DC Power Supply
Input voltage .......................................................................................................................... 12–24 V dc
Current draw @ nominal 12 V dc ............................................................................................... 175 mA
Current draw @ nominal 24 V dc ............................................................................................... 130 mA
33-Ohm Audio Output
Output with 1 Vrms at 600-ohm input ................................................................... 1.5 Vrms, factory aligned
2.3 Vrms maximum
Distortion .............................................................................................................................. <1.5% @ 1 kHz
Sidetone ...................................................................................................................... -30 dB factory aligned
VOX threshold ........................................................................................................................... >150 mVrms
VOX activation time ............................................................................................................ <50 milliseconds
VOX holdtime............................................................................................................................... >4 seconds
600-Ohm Audio Output
Output with 1.5 Vrms at 33-ohm input .................................................................. 1.0 Vrms, factory aligned
1.3 Vrms maximum
Distortion .............................................................................................................................. <1.0% @ 1 kHz
Sidetone ...................................................................................................................... -30 dB factory aligned
VOX threshold ........................................................................................................................... >200 mVrms
VOX activation time ............................................................................................................ <50 milliseconds
VOX holdtime............................................................................................................................ >3.5 seconds
Relay Outputs
Maximum load ........................................................................................................................ 2 A @ 30 V dc
Dimensions ..................................................... 14.50 H  8.31 5.26 D inches (368.3  211.1  133.6 mm)
Shipping weight ................................................................................................................. 10.5 lbs. (4.76 kg)
Net weight ............................................................................................................................ 9.5 lbs. (4.31 kg)
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Warranty
Equipment.
GAI-Tronics warrants for a period of one (1) year from the date of shipment, that any
GAI-Tronics equipment supplied hereunder shall be free of defects in material and workmanship, shall
comply with the then-current product specifications and product literature, and if applicable, shall be fit
for the purpose specified in the agreed-upon quotation or proposal document. If (a) Seller’s goods prove
to be defective in workmanship and/or material under normal and proper usage, or unfit for the purpose
specified and agreed upon, and (b) Buyer’s claim is made within the warranty period set forth above,
Buyer may return such goods to GAI-Tronics’ nearest depot repair facility, freight prepaid, at which time
they will be repaired or replaced, at Seller’s option, without charge to Buyer. Repair or replacement shall
be Buyer’s sole and exclusive remedy. The warranty period on any repaired or replacement equipment
shall be the greater of the ninety (90) day repair warranty or one (1) year from the date the original
equipment was shipped. In no event shall GAI-Tronics warranty obligations with respect to equipment
exceed 100% of the total cost of the equipment supplied hereunder. Buyer may also be entitled to the
manufacturer’s warranty on any third-party goods supplied by GAI-Tronics hereunder. The applicability
of any such third-party warranty will be determined by GAI-Tronics.
Services.
Any services GAI-Tronics provides hereunder, whether directly or through subcontractors,
shall be performed in accordance with the standard of care with which such services are normally
provided in the industry. If the services fail to meet the applicable industry standard, GAI-Tronics will
re-perform such services at no cost to buyer to correct said deficiency to Company's satisfaction provided
any and all issues are identified prior to the demobilization of the Contractor’s personnel from the work
site. Re-performance of services shall be Buyer’s sole and exclusive remedy, and in no event shall GAITronics warranty obligations with respect to services exceed 100% of the total cost of the services
provided hereunder.
Warranty Periods.
Every claim by Buyer alleging a defect in the goods and/or services provided
hereunder shall be deemed waived unless such claim is made in writing within the applicable warranty
periods as set forth above. Provided, however, that if the defect complained of is latent and not
discoverable within the above warranty periods, every claim arising on account of such latent defect shall
be deemed waived unless it is made in writing within a reasonable time after such latent defect is or
should have been discovered by Buyer.
Limitations / Exclusions.
The warranties herein shall not apply to, and GAI-Tronics shall not be
responsible for, any damage to the goods or failure of the services supplied hereunder, to the extent
caused by Buyer’s neglect, failure to follow operational and maintenance procedures provided with the
equipment, or the use of technicians not specifically authorized by GAI-Tronics to maintain or service the
equipment. THE WARRANTIES AND REMEDIES CONTAINED HEREIN ARE IN LIEU OF AND
EXCLUDE ALL OTHER WARRANTIES AND REMEDIES, WHETHER EXPRESS OR IMPLIED BY
OPERATION OF LAW OR OTHERWISE, INCLUDING ANY WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Return Policy
If the equipment requires service, contact your Regional Service Center for a return authorization number
(RA#). Equipment should be shipped prepaid to GAI-Tronics with a return authorization number and a
purchase order number. If the equipment is under warranty, repairs or a replacement will be made in
accordance with the warranty policy set forth above. Please include a written explanation of all defects to
assist our technicians in their troubleshooting efforts.
Call 800-492-1212 (inside the USA) or 610-777-1374 (outside the USA) for help identifying the
Regional Service Center closest to you.
(Rev. 10/06)
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