Lowell MA30 User manual

Optional Accessories (sold separately):
Lowell Manufacturing offers the optional 30WK wall kit (used to wall mount the MA30 Mixer/Amplifier), the 30RK
rack kit (used to mount the MA30 Mixer/Amplifier in a 19" rack), the 30HRK half-rack kit (used to mount the MA30
Mixer/Amplifier in a half rack), along with a full line of 19" equipment cabinets, half-rack cabinets, wall mount
shelves, rack mount AC power panels, AC power strips, and cooling fans that can be used to install the Lowell
Amplifier products. See www.lowellmfg.com for product details.
Getting Started:
Please study carefully the “IMPORTANT SAFETY INSTRUCTIONS” that are given on page 2 before applying power
to your MA30 mixer/amplifier. Those experienced with the use of a mixer/amplifier will find that the input jacks,
output jacks, and controls follow industry standard conventions and will be very intuitive. Standard 4W, 8W, 25V,
and 70V speaker outputs are provided. Those that are not familiar with the speaker wiring required for these
industry standard outputs will find a very helpful section covering this topic on pages 6, 7, and 8 of this “Installation
Sheet and Owner’s Manual”.
1
REMOVABLE
PHOENIX
CONNECTOR
Instruction Sheet
IS-MA30
Issued: 2-8-19
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: [phone] Click: www.lowellmfg.com
MA30
INSTALLATION SHEET
AND OPERATORS MANUAL
1
MA30 General Description:
The MA30 is equipped with a 30 watt power amplifier with 4W, 8W, 25V, and 70V speaker outputs available at screw
terminals. The unit is powered by 120VAC 60Hz. The main AC input is protected by a circuit breaker on the rear
panel. An unswitched convenience AC outlet is provided on the rear panel that is protected by a separate circuit
breaker. The mixer/amplifier includes 3 input channels. The first channel (marked MIC/TEL on the front panel) is
switchable for microphone or telephone inputs and also includes a switch to select the AUX 2 dual combining RCA-
phono connectors. This channel also includes a TEL/MIC switch. In the TEL (telephone) position, this switch pads
the input to allow the channel to be fed by a 600Wbalanced line level telephone page port output signal. The first
channel includes a MUTE ON/OFF switch. When the mute switch is turned ON, a dynamic microphone or
telephone input will mute the AUX 1, Aux 3, or Program inputs. The second channel (marked PROGRAM on the
front panel) is switchable for program input screw terminals or AUX 3 dual combining RCA-phono connectors. The
third channel (marked AUX 1 on the front panel) is for the AUX 1 dual combining RCA-phono connectors. The front
panel also includes BASS and TREBLE controls, a power-on LED, and an output level LED indicator.
30RK 30HRK
30WK

2
REMOVABLE
PHOENI X
CONNECTOR
Instruction Sheet
IS-MA30
Issued: 2-18-19
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: [phone] Click: www.lowellmfg.com
Read these instructions. Keep these instructions. Heed all warnings.
Follow all instructions. Do not use this apparatus near water.
Clean only with a dry cloth.
Do not block any ventilation openings. Install in accordance with manufacturer’s instructions.
Do not install near any heat sources such as radiators, registers, stoves, or other apparatus (including amplifiers)
that produce heat.
Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two blades with
one wider than the other. A grounding-type plug has two blades and a third grounding prong. The wide blade or
third prong is provided for your safety. If the provided plug does not fit into your outlet, consult an electrician for
replacement of the obsolete outlet.
Protect the power cord and plug from being walked on or pinched particularly at plugs , convenience receptacles,
and the point where it exits from the apparatus.
Only use attachments and accessories specified by the manufacturer.
Use only with the cart, stand, tripod, bracket, or table specified by the manufacturer, or sold with the apparatus.
When a cart is used, use caution when moving the cart/apparatus combination to avoid injury from tip-over.
Unplug this apparatus during lightning storms or when unused for long periods of time .
Refer all servicing to qualified service personnel. Servicing is required when the apparatus has been damaged in
any way, such as power supply cord or plug is damaged, liquid has been spilled or objects have fallen into the
apparatus, the apparatus has been exposed to rain or moisture, does not operate normally, or has been dropped.
The plug on the power cord is the AC mains disconnect device and must remain readily operable . To completely
disconnect this apparatus from the AC mains, disconnect the power supply cord plug from the AC receptacle.
This apparatus shall be connected to a mains socket outlet with a protective earthing connection.
When permanently connected, an all-pole mains switch with a contact separation of at least 3 mm in each pole
shall be incorporated in the electrical installation of the building.
If rack mounting, provide adequate ventilation. Equipment may be located above or below this apparatus, but
some equipment (like large power amplifiers) may cause an unacceptable amount of hum or may generate too
much heat and degrade the performance of this apparatus.
This apparatus may be installed in an industry standard equipment rack . Use screws through all mounting holes
to provide the best support.
WARNING: To reduce the risk of fire or electric shock, do not expose this apparatus to rain or moisture. Apparatus
shall not be exposed to dripping or splashing and no objects filled with liquids, such as vases, shall be placed on the
apparatus. This product may contain chemicals known to the State of California to cause cancer, or birth defects or
other reproductive harm.
NOTE: This equipment may generate, uses, and can radiate radio frequency energy and, if not installed and used in accordance
with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference
will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which
can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more
of the following measures: Reorient or relocate the receiving antenna.
Increase the separation between the equipment and receiver.
Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
Consult the dealer or an experienced radio/TV technician for help.
CAUTION: Changes or modifications not expressly approved by Lowell Manufacturing will void the manufacturers warranty .
IMPORTANT SAFETY INSTRUCTIONS

Instruction Sheet
IS-MA30
Issued: 2-18-19
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: [phone] Click: www.lowellmfg.com
3
Amplifier Block Diagram
Technical Specifications
Dimensions: 8.35" wide x 3.46" high x 10.83"deep (212mm wide x 88mm high x 275mm deep)
Frequency Response: 50Hz-20KHz + 3dB (Test signal inserted at aux input)
AC Supply Voltage: 120VAC 60Hz + 10%. External circuit breaker: 1.5A
Switch Defeatable Circuit Mutes AUX1, AUX3, and PROGRAM Inputs
Mixing
And
Control
Section
Power Consumption: 90W@Rated Power. Internal fuses: 2) 5X20mm 3A
Shipping Weight: MA30: 10.0LBS. (4.54KGS)
Color: Black
Speaker Level Outputs: Screw terminal strips,
Main Output: 4W, 8W, 25V, 70V, 30W RMS
Music-On-Hold: (MOH), 1W @ 8W
Convenience AC Outlet: 500W maximum unswitched outlet. External circuit breaker: 4A (convenience outlet only)
Mic Input: Screw terminals, 1mV @ 600Wbalanced (Phantom power is not available.)
Aux Inputs 1-3: Dual parallel unbalanced RCA-phono jacks, Stereo converted to mono, 150mV @ 10kW
Total Harmonic Distortion: Less than 1% at 1kHz at rated power.
Signal to Noise Ratio: 80dB (Test signal inserted at Aux input)
Tone Controls: Bass + 10dB @ 100Hz, Treble +10dB @ 10kHz,
Weight: MA30: 8.82LBS. (4KGS)
Bass and
Treble
Controls
Power
Amplifier
30W RMS
AUX 1
Input
AUX 1
Volume
Control
PROGRAM
Volume
Control
G COM HOT
PROGRAM
Input
AUX 3
Input
MIC /TEL
Volume
Control
G COM HOT
MIC / TEL
Input
AUX 2
Input
G
COM
8W
8W
70V
25V
COM
4W
SPEAK ER
LEVEL
OUTPUTS
MUSIC-ON-HOLD
(MOH)
OUTPUT
MOH
Level
Control
Telephone Input: Screw terminals (switchable, same terminals as mic input)
100mV @ 10kWbalanced
Program Input: Screw terminals 100mV @ 10kWbalanced
Accessories: 30WK (wall mounting kit), 30RK (rack kit), and 30HRK (half-rack kit) are sold separately.
Note: The MOH output is only
fed by the AUX 1, AUX 2, and
AUX 3 input signals. The MIC/
TEL and PROGRAM inputs are
NOT fed to the MO H output. No
front panel controls aff ect the
MOH output.
Amplifier Muting-Priority Scheme
The amplifier includes unique voice-activated (VOX) ducking/muting circuitry. The mute circuit is only active when
the “MUTE” switch on the rear panel has been turned “ON”. When a page is made into the microphone or
telephone input (Channel MIC/TEL), the PROGRAM, Aux 1, and Aux 3 music inputs will duck in volume (not be
completely muted). If the incoming page is strong enough in level, the music volume will be completely muted.
When the page has been completed, the volume of the music will return to its normal level. Note that AUX 2 is not
involved in the muting circuit, because when the Mic/TelAux 2 switch is in the Aux 2 position, the Aux 2 input is
active but the MIC/TEL input is defeated so muting by the MIC/TEL input is not an issue.

4
REMOVABLE
PHOENI X
CONNECTOR
Instruction Sheet
IS-MA30
Issued: 2-18-19
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: [phone] Click: www.lowellmfg.com
MA30 Front Panel MA30 Rear Panel
9101
112131415
1617 181920 22 23 24 25
Amplifier Installation and Connection
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 indications 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 materials, in order to process the claim.
INSPECTION
Before installing the amplifier, continue the inspection by running a quick performance check. Connect an 8Wtest
speaker to the 8Wdirect output terminals and a tuner, tape deck, or CD player to one of the aux inputs and set the
controls for operation. CAUTION: TO PROTECT THE SPEAKER FROM DAMAGE, DO NOT TURN THE UNIT ON
UNTIL ALL CONNECTIONS HAVE BEEN MADE. IN ADDITION, MAKE SURE THE UNIT IS GROUNDED
BEFORE TESTING. In this way you can check the basic operation of the amplifier before actually installing the unit
and making all of the final terminations required for the permanent installation. If shipping damage has resulted in
the amplifier being inoperable out of the box, call Lowell Customer Service to arrange for a replacement.
INITIAL PERFORMANCE CHECK
GENERAL WIRING AND INSTALLATION GUIDELINES
DO NOT run microphone cables near AC power wires, data cables, telephone cables, or speaker wiring to avoid
picking up extraneous signals in the sound system.
DO NOT run speaker output cables near data cables, telephone cables, or other low voltage wiring that could pick
up the signal from the higher level speaker cables.
DO NOT run high impedance unbalanced wiring more than 20' to avoid picking up noise and affecting the frequency
response of the sound system.
DO use shielded cable for all microphone and line level cables (except the balanced 600 ohm input line from a
telephone system may be twisted pair cable).
DO make sure that all speakers are wired in phase with each other .
DO make sure there are no short circuits on the loudspeaker lines before connecting them to the amplifier output .
Music-On-Hold (MOH) Output (Screw Term)
18
Music-On-Hold (MOH) Level Control
19
Mute Switch (Switch “ON”, MIC/TEL Input
Mutes AUX 1, AUX 3 & PROGRAM Inputs)
20
Program or Aux 3 Selector Switch
21
Aux 3 Input (RCA Jacks)
22
Aux 2 Input (RCA Jacks)
23
MIC/TEL Input Pad Switch
25
MIC/TEL or Aux 2 Selector Switch
24
Speaker Output (Screw Terminals)
12
Program Input (Screw Terminals)
13
MIC/TEL Input (Screw Terminals)
14
AC Line Cord
9
Circuit Breaker for Amplifier
10
Earth Ground Connection Screw
1
1
Aux 1 Input (RCA Jacks)
15
Convenience AC Outlet
16
Circuit Breaker/Convenience Outlet
17
1MIC/TEL Volume Control
2PROGRAM Volume Control
3AUX 1 Volume Control
6Power Switch
Power Indicator LED
7
Output Level Indicator LED
8
4Bass Control
5Treble Control
21
123 4
7 8
56

Instruction Sheet
IS-MA30
Issued: 2-18-19
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: [phone] Click: www.lowellmfg.com
5
POWER WIRING
The MA30 includes a power cord with a standard 15A 120VAC 3-prong grounded plug. A push-to-reset circuit
breaker for the amplifier is provided on the rear panel. An unswitched 500W maximum convenience outlet with a
separate circuit breaker is also provided on the rear panel. Warning: THIS UNIT MUST BE EARTH GROUNDED.
PASSIVE CONVECTION COOLING AND VENTILATION
This unit is cooled via passive convection and therefore designed for continuous operation . Excessive heat due to
poor ventilation can shorten the lifespan of electronic equipment and could void the manufacturer’s warranty. Do
not block the amplifier’s vent slots located on the top and bottom of the chassis.
LINE LEVEL “AUX” INPUT CONNECTIONS
The amplifier includes high-impedance unbalanced auxiliary inputs which may be used for connecting signal
sources such as an AMFM tuner, CD player, or cassette deck. A push switch is provided on the MIC/TEL channel
that selects either the MIC/TEL screw terminal input or the Aux 2 input. A push switch is provided on the
PROGRAM channel that selects either the PROGRAM screw terminal input or the Aux 3 input. Two (2) RCA-phono
connectors are provided for each aux input so stereo input cables can be connected . The stereo input signal is
converted internally to a mono signal. Mono inputs need only use one or the other of the RCA-phono connectors.
MIC LEVEL INPUT CONNECTIONS
The amplifier includes a low-impedance balanced microphone input at the MIC/TEL channel with the TEL/MIC
switch in the MIC position. Phantom power is NOT available. If Phantom power is required for your application, you
may use an outboard phantom power supply (sold by others), or consider an upgrade to the Lowell MA60 Mixer/
Amplifier which does have phantom power available on the microphone channel inputs .
MOUNTING THE AMPLIFIER
This MA30 may be placed on a wooden or metal wall-mount shelf. Do not remove the plastic feet from the bottom
of the amplifier chassis. When the amplifier is placed on a countertop or is shelf-mounted, the plastic feet maintain
the proper spacing under the amplifier for passive convection cooling. Do not place anything on top of the amplifier
where the vents on the top of the chassis would be blocked . If the amplifier will be rack mounted, we recommend
that you provide a minimum of 1.75” of open space above and below the unit to assure proper ventilation. Provide
ventilation fans in the equipment cabinet if that is required to maintain an amplifier operating temperature of no
higher than 92oF. To mount the amplifier in a Lowell equipment cabinet, use standard 10-32 Phillips-head machine
screws (like the Lowell model RS or RSP rack screws) with integral plastic washers to protect the finish of the front
panel of the amplifier. Lowell rack brackets 30RK (rack mounting kit) and 30HRK (half-rack mounting kit) for the
amplifier are sold separately. The 30WK (wall mounting kit) for the amplifier is also sold separately. The wall
mounting kit brackets may be used to mount the amplifier to a telephone wiring board or a any flat wall surface .
MUSIC-ON-HOLD (MOH) OUTPUT
The music-on hold output (MOH) is an 8 ohm speaker level output that may be used to feed external devices
including the music-on-hold input of a telephone system. It is important to understand the signals that will be
present at the MOH output. The microphone, telephone, and program inputs are never present at the MOH output.
The AUX 1, AUX 2, and AUX 3 inputs are the only signals that are fed to the MOH output. The front panel controls
(including the treble and bass controls) have no effect on the MOH output. The aux inputs are routed to the MOH
output directly. The only control that affects the MOH output is the MOH level control on the rear panel of the
chasis.
TELEPHONE INPUT CHANNEL
The amplifier includes a telephone input at the MIC/TEL channel with the TEL/MIC switch in the TEL position. This
input accepts a low impedance balanced 600Wline level input that would typically be available as a page port output
from a telephone system. TELEPHONE CHANNEL INPUT WIRING
GND COM HOT
MIC/TEL INPUT
(Set switch on TEL)
From the
Telephone
System
Page-Port
Output
600WTwisted-Pair Wiring
Shielded wiring from the telephone system is typically not required, but if
shielded wiring is used, drain the shield at the telephone input and butt
the shield (no connection) at the telephone system page port output.
BUTT SHIELD
(No connection) DRAIN
SHIELD

Instruction Sheet
IS-MA30
Issued: 2-18-19
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: [phone] Click: www.lowellmfg.com
6
Result:
One speaker
receives the
total amplifier power.
AMPLIFIER
OUTPUT
8W
4W
70V
25V
COM
One 8WSpeaker
SP EAKER
+
_
8WResult:
Each speaker
receives ½ of the
total amplifier power.
Two 8WSpeakers
wired in Parallel
AMPLIFIER
OUTPUT
8W
4W
70V
25V
COM
SP EAKER
+
_
8W
SP EAKER
+
_
8W
AMPLIFIER
OUTPUT
8W
4W
70V
25V
COM
Result: Each speaker
receives ¼ of the
total amplifier power.
Four 8WSpeakers
wired in Series/Parallel
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
AMPLIFIER
OUTPUT
8W
4W
70V
25V
COM
Result: Total amplifier power is reduced due to
impedance mismatch. Each speaker receives
1/3 of the reduced total amplifier power.
Three 8WSpeakers wired in Series
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
Speaker System Connections
The amplifier includes a speaker output screw terminal
strip. Connect the speaker line common to “COM” and
the hot side to the 70V, 25V, 8W, or 4Wterminals.
70V
25V
8W4W
COM
Never connect an 8Wor 4Wspeaker system (that has no 70V or 25V matching transformers) to the 70V or 25V outputs.
8 Ohm Series/Parallel Speaker System Wiring
Lowell amplifiers include 8Wand 4Woutputs that can drive basic 8Wspeakers without the use of any line matching
transformers. The impedance of the speaker load must always be equal to or greater than the impedance of the
amplifier output. For example, it is safe for the amplifier if the 8Woutput is used to drive an 8Wload or a 16Wload,
and it is safe for the 4Woutput to drive a 4Wload or a 6Wload, but it is not safe for the 8Woutput to drive a 6Wload
and it is not safe for the 4Woutput to drive a 2Wload. Overloading the amplifier output can cause distortion and can
damage the amplifier and void the manufacturer’s warranty. It is also important to pay attention to the power rating
of the speakers used. If an 8Wspeaker is fed from the 8Woutput of an amplifier and the amplifier is turned all the
way up, the speaker will receive the maximum power output of the amplifier. A speaker must be chosen with
sufficient power handling capacity for the amplifier used. For example, if an 8Wspeaker can handle 150 watts and
it will be fed from the 8Woutput of the amplifier, an amplifier with a power output of 150 watts or less should be
chosen so that if the amplifier is turned all the way up, the speaker will be able to handle the amplifier’s full power
output. All of the Series/Parallel configurations shown below will result in load impedances that will be safe for the
amplifier when connected as shown. Depending on the size of the amplifier used, verify that the maximum amplifier
power when divided between the speakers, will not exceed the power rating of the speaker chosen.
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
SP EAKER
+
_
8W
AMPLIFIER
OUTPUT
8W
4W
70V
25V
COM
Result:
Each speaker
receives 1/8of the
total amplifier power.
Eight 8WSpeakers
wired in
Series/Parallel

Instruction Sheet
IS-MA30
Issued: 2-18-19
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: [phone] Click: www.lowellmfg.com
7
5W
2W
1W
.5W
.25W
COM
5W
2W
1W
.5W
.25W
COM
5W
2W
1W
.5W
.25W
COM
AMPLIFIER
70V
COM
To More
Speakers
70 volt and 25 volt “Constant Voltage Distribution Systems” have been a source of confusion for people for a long
time. Our Series/Parallel speaker wiring discussion on page 6, illustrates why industry engineers developed the
“Constant Voltage” concept. Series/Parallel configurations are manageable for small localized systems using up to
8 speakers and when no expansion is anticipated. Even with only 8 speakers, wiring a Series/Parallel configuration
can be confusing. Nobody would ever want to attempt Series/Parallel wiring for 8000 speakers spread over an
entire office complex. The 70V and 25V speaker systems (and the 100V system which is used in Europe) rely on
inexpensive line matching transformers to simplify the “impedance matching” and “amplifier loading” issues. The
line matching transformers allow all of the speakers in a 70V or 25V speaker system to be wired in parallel
regardless if there are 8 speakers or 8000 speakers in the system, as long as the total of all transformer taps
used does not exceed the power rating of the amplifier. Parallel connections make field wiring easy and it
makes it possible to add speakers anywhere along the speaker string without any concern about Series/Parallel
load impedance. The term “Constant Voltage” can be misleading. “Constant Voltage” means whether you have a
10W 70V amplifier, 100W 70V amplifier, or a 1000W 70V amplifier, the output will be at 70.7V when the amplifier is
turned all the way up. When a 70V amplifier is turned down, it will be running at less that 70V. The key thing to
remember is that the transformer power tap values are calculated for when the amplifier is running at a full 70V. A
70V speaker transformer tapped at 5 watts, will only draw a full 5 watts, when the amplifier is at it’s full 70V output.
70V / 25V Speaker System Wiring
Individual Speaker Transformer Tap Settings:
A 70V or 25V speaker that is chosen by the system designer, has a matching transformer
with a maximum power rating . For example, the Lowell R1810-72 (shown to the right) has
a Lowell TLM-572 5-watt 70V/25V dual voltage transformer. That means that this speaker
can be used on both 70V systems and 25V systems. The 8Wsecondary of the
transformer is connected directly to the 8Winput terminals on the 810 speaker. The
primary has transformer taps for either 70V or 25V at 0.25W, 0.5W, 1W, 2W, and 5W.
When a designer is mapping out the coverage of these ceiling speakers, he/she will
determined how many speakers are required and in what locations, and what power tap
will be used for the speakers to be loud enough for this application. Let’s say for example
that the designer has determined that 100 speakers will be required tapped at 1W each at
70 volts. That means that our total speaker load is 100 watts. The speakers will be wired
in the field in parallel as shown below making sure the connections are made with the
proper polarity to keep all of the speakers operating in phase with each other.
Lowell R1810-72
A 70V or 25V speaker system is easy to design and easy to wire in the field because all speakers can be wired in
parallel. The higher transmission voltages used greatly reduce the power lost in the speaker lines so smaller less
expensive speaker wiring can be used. The volume of a single speaker on the line can be adjusted louder or softer
by adjusting the power tap used on that speaker’s matching transformer. That adjustment does not affect the
volume of the other speakers in the system. The volume adjustment of a single speaker on the line or the volume
adjustment of groups of speakers in a zone can be made accessible to the user by way of inexpensive wall-mount
autoformer-based volume controls. The settings on wall-mount volume controls can be easily bypassed during
pages or during emergency announcements. (See Lowell “priority attenuator” volume controls that include a “-PA”
in the model number). It is easy to add speakers to the system in the future without having to change any of the
existing wiring. If adding additional speakers in the future will require a more powerful amplifier at the head -end, an
amplifier with a higher output power capability can replace the existing unit without changing any of the existing
speaker wiring or any of the existing speaker transformer tap settings. For example: A Lowell MA60 could be
replaced with a Lowell MA125 so that more speakers could be added to the system, with no other changes required
to the existing speaker wiring or transformer taps.
70V / 25V Constant Voltage Speaker System Advantages:
SP EAKER
+
-
8W
SP EAKER
+
-
8W
SP EAKER
+
-
8W

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Instruction Sheet
IS-MA30
Issued: 2-18-19
Lowell Manufacturing Company 100 Integram Drive Pacific, Missouri 63069 U.S.A.
Call: 800-325-9660 Fax: [phone] Click: www.lowellmfg.com
8
Cable distance should be kept as short as possible to minimize power loss . The chart below can be used as a
general guide showing various wire sizes and the maximum distance related to cable loading that speakers can be
placed from the unit for an approximate 0.5dB loss (-12.5% power).
Wiring Size and Length:
70V and 25V Amplifier Load Calculations and Amplifier Selection:
In fact, it is good design practice to limit the speaker load to 85% of the amplifiers power rating. That designed-in
headroom allows for future expansion (adding a few speakers) and also the reduced load will increase the lifetime of
the amplifier by allowing it to run cooler. Continuing with the example from page 7, the designer knows that the
expected speaker load is 100 watts. What would be an appropriately sized amplifier for that system? If the
designer considers a 125W amplifier, 125 X .85 = 106.25 watts. It would be good design practice to limit the
speaker load to no more than 106.25 watts, so since the speaker load in the example is 100W, the 125W watt
amplifier would be a good choice. Sometimes the amplifier has already been purchased and the number of
speakers required is known, but the question becomes what transformer tap setting to use. Desired speaker SPL
calculations to determine the speaker transformer tap required are beyond the scope of this paper , but there are
some practical considerations when choosing the power tap. If a 125 watt amplifier has already been purchased,
using the 85% loading rule of thumb, 125W X .85 = 106.25 watts. It would be good design practice to limit the
speaker load to no more than 106.25W. Since we know from our example that 100 speakers would be required, it is
obvious that tapping the speakers at 1W is the best choice.
Some system designers feel it is best to tap the speaker transformers as high as possible. Consider an example
where a sound system that has a 125W 70V amplifier, only has 10 speakers. If the transformers are tapped at
0.25W each, the total speaker load will be 0.25W X 10 speakers = 2.5W. If the amplifier is turned all the way up so
its output is 70 volts, those speakers will still only draw a maximum of 0.25W each and it would not be possible to
get the speakers any louder. That would result in tons of headroom but you wouldn’t have much volume out of the
speakers. Some designers would suggest that the speakers in this example should be tapped at 5W each so the
speaker load would be 5W X 10 speakers = 50W. Again, plenty of headroom for the amplifier but more than 12dB
more sound pressure level out of the speakers. Other designers would prefer that the speakers be tapped at 1W
each (if they are sure that the 1W tap would provide sufficient SPL) because the 1W tap provides 2 higher powered
taps that are available if this particular speaker needs to be louder, and 2 lower-powered taps if this speaker is too
loud. The designer needs to determine the appropriate tap setting after considering the requirements of the system
design. The question might be asked, what happens when the designer has a 125 watt amplifier, and needs 25
speakers tapped at 5 watts each? That results in a speaker load of 125 watts with no headroom. Sometimes a
designer is confident that adding speakers in the future will not be necessary, and competitive pressure in a bid
situation will not make it possible to use a larger amplifier to provide the desired headroom. Although headroom is
always desirable, be assured that the Lowell amplifiers will survive and operate safely when fully loaded.
Never use a speaker load (the sum of all speaker transformer taps) that exceeds the amplifier power rating.
Overloading the amplifier can cause distortion and could damage the amplifier and void the warranty.
WIRE LENGTHS IN FEETWIRE LENGTHS IN FEET