Grommes~Precision Precision Electronics G228 User manual

Grommes~Precision
Precision Electronics
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic components for use in commercial, consumer, and industrial applications since 1946.
Grommes~Precision
847-678-5350 · 800-SINCE-46 · FAX [phone]
9101 King Ave. · Franklin Park, IL 60131 · USA
www.grommesprecision.com
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic equipment for use in commercial, consumer, and industrial applications since 1946.
Grommes~Precision
Grommes~Precision
847-599-1799 · 800-SINCE-46 · FAX [phone]
1331 Estes Ave. · Gurnee, IL 60031 · USA
www.grommesprecision.com
G228
INSTRUCTION MANUAL
Unpacking Procedures .... 2 Ou pu Connec ions .... 5
Ins alla ion Informa ion .... 2 The Au o-Mu e Circui .... 6
Descrip ion & Specifica ions .... 3 Opera ion Of Con rols .... 6
Produc Overview .... 4 Grounding .... 7
Inpu Connec ing .... 4 Troubleshoo ing .... 8

I. UNPACKING PROCEDURES
INSPECTION
This unit was carefully checked and packed before leaving the factory. However, it is always a good
idea to inspect the shipping container and unit for indication of improper handling. If the unit has
been damaged, make an immediate claim to the dealer or distributor from whom it was purchased. If
the unit was shipped to you, notify the transportation company without delay, saving all packing ma-
terials, in order to process the claim.
INITIAL PERFORMANCE CHECK
Continue the inspection by running a performance check. Connect the preamplifier output to an am-
plifier and speaker. Connect a microphone or test signal to the inputs. If the preamplifier fails to oper-
ate and no damage is visible, notify the factory. CA TION: TO PROTECT THE SPEAKER FROM
DAMAGE, DO NOT T RN THE NIT ON NTIL ALL CONNECTIONS HAVE BEEN MADE. IN AD-
DITION, MAKE S RE THE NIT IS GRO NDED BEFORE TESTING. If the unit should be inoper-
able and no damage is noted, please notify the factory at 1-847-599-1799 and ask for Technical
Support.
II. INSTALLATION INFORMATION
RACK MOUNTING
For best results use a 10-32 class NF-2B or 12-24 class NC-2B rack and 0.625 inch machine
screws (metric: M5X8-6H or M6X1-6H, 15.88mm). It is recommended that the drive of these screws
be phillips in order to protect the finish from unnecessary scratches. Also recommended are nylon or
plastic washers which will not only help protect the finish but also aid in retaining the screws.
TECHNICAL SUPPORT
A troubleshooting chart is located at the end of this manual for your convenience. If you are in need
of further assistance, you can reach our design engineers at 1-847-599-1799. Grommes~Precision
is based in Gurnee, Illinois and is on Central Standard Time. Our hours of operation are Monday -
Friday from 8:00am to 4:00pm. Troubleshooting information can also be found at our website www.
grommesprecision.com.
G228 INSTRUCTIONS
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Grommes~Precision
Precision Electronics
847-599-1799 · 800-SINCE-46 · FAX: [phone]
1331 Estes Ave · Gurnee, IL 60031 · USA
www grommesprecision com
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic equipment for use in commercial, consumer, and industrial applications since 1946.
Thank you for purchasing from Grommes~Precision!
Grommes~Precision and its commercial audio division, Precision Electronics, has been designing,
engineering, and manufacturing quality sound equipment in the United States since it started opera-
tion in March of 1946 Over a half century of quality, service, and flexibility as “Your Personal Manu-
facturer” have made us one of the last American audio manufacturers If you have any questions
with this or any one of our other fine products, give us a call When you talk with a member of the
Grommes~Precision team you’ll be speaking with someone who had a hand in concept, design, pro-
duction, or testing of this very product

III. DESCRIPTION & SPECIFICATIONS
Dis or ion @ RPO:
<0.05%
Mixing Channels:
7
Inpu s:
From 6 MIC & 1 A X to 7 A X.
Ou pu s:
600 ohm BALANCED / MIC LEVEL / LINE LEVEL
Frequency Response Direc
Line:
+/-0.5dB 20-20kHz
+/-1dB 20-20kHz
Microphone: Screw Terminals With Optional Isolation Transformer
SPECIFICATIONS
G228 INSTRUCTIONS
· Optional Input Isolation Transformer (T) for
MIC Inputs
· Tel-Page Line Lightning Suppressor (TLS)
· Rack Mountable with RP-1 A Kit · 600 ohm Line Lightning Suppressor (LLS)
ACCESSORIES
DESCRIPTION
The Grommes~Precision G228 is a solid-state commercial high fidelity mixing preamplifier using IC
circuitry. It has 6 Microphone / Auxiliary channels, plus another A X-only channel having two
selectable inputs. Also featured is a mute Precedence switch that enables the 1st channel to mute
all other channels, or channels, or channels 1-6 to mute the A X-only channel. A red “Peak” LED
indicates relative signal levels. Optional isolation transformers are available for the 6 Microphone
inputs. G228 height is only 1 R (1.75 inches).
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Grommes~Precision
Precision Electronics
847-599-1799 · 800-SINCE-46 · FAX: [phone]
1331 Estes Ave · Gurnee, IL 60031 · USA
www grommesprecision com
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic equipment for use in commercial, consumer, and industrial applications since 1946.

G228 INSTRUCTIONS
V. INPUT CONNECTIONS
INPUT CONNECTIONS
Microphone:
The G228 volume control should be fully OFF (fully counterclockwise) when making any connection
to a microphone input. Any low impedance 150 to 600 ohm microphones may be used: Connect the
microphone cable shield to the ground screw terminal. Connect the two “hot” wires to the - and +
microphone input terminals on the G228.
IV. PRODUCT OVERVIEW
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Grommes~Precision
Precision Electronics
847-599-1799 · 800-SINCE-46 · FAX: [phone]
1331 Estes Ave · Gurnee, IL 60031 · USA
www grommesprecision com
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic equipment for use in commercial, consumer, and industrial applications since 1946.
Auxiliary:
The Input Impedance of each Auxiliary input is 10K ohms. Connect a CD player, radio tuner, or tape
deck to any Auxiliary input using and audio patch cable having standard RCA type phono plug at
each end. The Auxiliary input of each channel is internally mixed with the MIC input. If you have both
a microphone and an auxiliary signal source connected simultaneously to a channel and you want to
hear only the microphone, the microphone , the volume control on the auxiliary signal source must
be turned down. If you want to hear only the auxiliary signal source, then the microphone’s on-off
switch (located on the microphone body) may need to be switched off.
MAIN
TAPE
MIX

VI. OUTPUT CONNECTIONS
G228 INSTRUCTIONS
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Grommes~Precision
Precision Electronics
847-599-1799 · 800-SINCE-46 · FAX: [phone]
1331 Estes Ave · Gurnee, IL 60031 · USA
www grommesprecision com
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic equipment for use in commercial, consumer, and industrial applications since 1946.
OUTPUT CONNECTIONS
600 Ohm Line:
This is a 600 ohm IC output balanced to ground. se this output for long distance line runs to a
power amplifier. Do not ground either side of this line, but connect the shield of this line to the
ground terminal on the G228 output terminal strip. For grounded unbalanced line, you have a choice
of using either one of the “hot output screw terminals and the ground terminal or you can use the
Main output jack.
Main:
This is an unbalanced-to-ground output. Its output impedance is about 300 ohms. Connect with an
audio cable having a standard RCA type phono plug . The other end of this cable will go to the high
impedance or unbalanced input of the power amplifier.
Microphone Level Ou pu :
This is a 150 to 600 ohm microphone level output, balanced to ground. This output is for connecting
to a microphone input of another system. Balanced shielded microphone cable must be used.
Connect the shield to the G228 ground screw. Connect the other end of the shield to the ground of
the other system. Connect the two “hot” wires to the “hot” microphone input of the other system (if
any XLR input, this will be pins 2 and 3; the shield goes to pin 1.)
OTHER CONNECTIONS
Tape Ou pu :
This output is unaffected by the G228 Master volume control. Connect this output with standard RCA
type audio patch cord to a high impedance input of your tape recorder.
Mix Bus:
This connection is for connecting to the mix bus of another preamplifier or amplifier in order to
expand your system. This connection should not be used for any other purpose. The G228, as well
as the rest of the system, should be turned OFF before connecting to, or disconnecting from, this
jack.

VII. THE AUTO-MUTE
G228 INSTRUCTIONS
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Grommes~Precision
Precision Electronics
847-599-1799 · 800-SINCE-46 · FAX: [phone]
1331 Estes Ave · Gurnee, IL 60031 · USA
www grommesprecision com
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic equipment for use in commercial, consumer, and industrial applications since 1946.
VIII. OPERATION OF CONTROLS
Two different ways to set the G228 individual channel level controls are as follows.
Note: Each step must be done in the order given:
Method 1:
A. Turn the G228 Master level control all the way down (fully counterclockwise).
B. For normal gain your power amplifier’s level control is set from about 70% to 100%.
C. Turn each G228 input level halfway up (12 o’clock).
D. Turn the G228 Master level control up to desired system loudness.
E. Re-adjust each input level on the G228 to desired loudness.
Method 2:
A. Turn your power amplifier’s level control all the way down (fully CCW).
B. Turn each channel level control on the G228 all the way down (fully CCW).
C. Turn the G228 Master level to 70% of its rotation (approximately 2 o’clock).
D. Turn the 1st channel level control up until the G228’s red LED flashes occasionally
(about once every 2 to 4 seconds). Make a note of this position, then turn it back down
(fully CCW).
E. Do step D for each channel, making a note of each control setting.
F. Now turn each level control to the setting you noted for each channel.
G. Turn your power amplifier’s level control up to desired system loudness.
MUTE PRECEDANCE SWITCH
In the P position this switch causes the 1st channel to mute all other channels. In the DOWN
position channels 1 through 6 will mute A X inputs 7A and 7B.
PEAK LEVEL LED
When this red LED flashes, it indicates that the G228 is at or very close to peak output level. The
more it flashes, the more likely it may be that the G228 is clipping. A steady glow may indicate that
signal levels are too high, or perhaps a ground connection somewhere in the system may have
come loose, or oscillation. The internal trimpot adjust the sensitivity of the Peak LED.
PEAK LEVEL LED
This switch helps reduce bass boominess when using wide response microphones. This switch
should also be engaged ( P position) whenever horn or rumpe speaker are connected to the
power amplifier.

G228 INSTRUCTIONS
7 of 8
Grommes~Precision
Precision Electronics
847-599-1799 · 800-SINCE-46 · FAX: [phone]
1331 Estes Ave · Gurnee, IL 60031 · USA
www grommesprecision com
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic equipment for use in commercial, consumer, and industrial applications since 1946.
IX. GROUNDING
The 3-wire AC power cord provides a ground to the AC power line conduit. If your AC outlet is wired
correctly, grounding if the G228 is accomplished merely by plugging into the outlet. Otherwise, to en-
sure a good ground it may sometimes be necessary to attach a ground wire to the ground terminal of
the G228 output strip and connect it to a cold water pipe (provided the entire pipe is metal and is well
grounded).

X. TROUBLESHOOTING
G228 INSTRUCTIONS
SYMPTOM POSSIBLE CAUSE POSSIBLE SOLUTION(S)
No Fron Panel
POWER ON In-
dica ion
• No AC power present. Verify the unit is receiving AC power.
Verify the AC outlet has proper AC voltage available.
No Audio
Ou pu :
• No input signal source. Verify that proper signal/level is being supplied.
• Incorrect input signal
connection
Verify that the signal input connection is correctly
connected.
• Incorrect output con-
nections
Check that the proper load is correctly connected to
the desired output terminals.
No Au oma ic
Mu ing of
Inpu Signal
• Mute Switch Rear
Panel
Check that the switch is in the correct position.
(See page 6).
• Insufficient MIC/600
ohm/Tel-Page gain
Check MIC/TEL gain control setting.
Check that MIC/TEL audio signal level is sufficient.
Low, High, or
Dis or ed Level:
• Volume setting Check the corresponding gain control on the front
panel.
• Signal level Check that adequate input signal level is strong
enough.
• Input or output imped-
ance not matched
Check that the proper input/output line impedance
matches the selected input/output connections used.
• Possible low resistance
or shorted wiring across
the audio in and/or
across the speaker out
Check/correct system wiring.
Grommes~Precision is an American manufacturer of original, custom, and private labeled audio/electronic equipment for use in commercial, consumer, and industrial applications since 1946.
Grommes~Precision
Grommes~Precision
847-599-1799 · 800-SINCE-46 · FAX [phone]
1331 Estes Ave. · Gurnee, IL 60031 · USA
www.grommesprecision.com
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SERVICING
If the unit requires service: 1) Obtain a Return Authorization (RA) Number at 847-599-1799; 2) In-
clude a detailed written explanation outlining the nature of the problem and your contact information;
and 3) Ship pre-paid to Grommes~Precision, 1331 Estes Ave., Gurnee, IL 60031, SA. If the unit is
under warranty, repairs or a replacement will be made in accordance with Grommes~
Precision’s warranty policy.