J. W. Davis & Company D-250AL User manual

NEWTECHNOLOGY OLDRELIABILITY
J.W. Davis & Company •
3030 Canton Street • P.O. Box 710219 • Dallas, Texas 75371-0219
Sales 800-527-5705 • Fax [phone] • Corp 214-651-7341 • Fax [phone] • [email protected] • www.jwd.com
USER’S MANUAL
The Mark of the Professional...
090705123
Unpacking Procedures
The Back Panel
Specifications The Auto-Mute Circuit
TroubleshootingThe Front Panel
Maintenance
Installation Information
Speaker Installation
Using Horn Speakers
Product Overview
Product Description
Warranty & Service
Accessories
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D-250AL POWER AMPLIFIER

NEWTECHNOLOGY OLDRELIABILITY
J.W. Davis & Company •
3030 Canton Street • P.O. Box 710219 • Dallas, Texas 75371-0219
Sales 800-527-5705 • Fax [phone] • Corp 214-651-7341 • Fax [phone] • [email protected] • www.jwd.com
The Mark of the Professional...
The D-250AL is a 2-channel input high fidelity commercial mono audio amplifier that will deliver 250
watts of continuous RMS power into a direct coupled 8-ohm voice coil load or into a constant voltage
25V or 70.7V line. Only 2 racks in height, the D-250AL uses a toroidal power transformer to reduce
weight, height, and noise. The D-250AL, designed for commercial sound or “all-in-one” telephone
paging applications, offers a balanced 600-ohm/tel-page input that is capable of muting the two high
Impedance inputs that are strapped in parallel (thereby offering a convenient auxiliary input bridge to
additional amplifiers). The 600-ohm/tel-page level is controlled via an independent tamper-resistant
control.
-2-
CAUTION: In the event the transformer’s
thermal breaker does not reset, have the
trouble investigated by an authorized service
technician or return unit to the factory.
WARNING: TO REDUCE THE RISK OF FIRE
OR ELECTRIC SHOCK, DO NOT EXPOSE
THIS UNIT TO RAIN OR MOISTURE
CAUTION: These devices are not intended for use
in hazardous locations as defined by the National
Electrical Code (NEC) and by the National Fire
Protection Association (NFPA).
WARNINGS
Features
Rack mount standard 2 RU
•
WARNING: THIS AMPLIFIER MUST BE
GROUNDED. DO NOT REMOVE GROUND PIN
FROM AC PLUG OR USE A DEVICE TO CHANGE
FROM A 3-PIN AC PLUG.
Inputs
Distortion at Rated Output
Power Output
Audio Output
Frequency Response
Power Source
Hum/Noise
Dimensions
Auxiliary, 2 RCA Connectors in Parallel for Input and Bridging. High Impdeance
Unbalanced, 0.50V, 10k Ohm.
Telephone Page, Screw Terminal, 50mV, 600 Ohm Balanced, with VOX Mute.
Line Level, 600 Ohm Balanced Input, 0.50V
250 Watts RMS Rated at 8 Ohm Direct, 25V, and 70.7V
4-8 Ohm, 25V, or 70.7V
</= 0.3% THD
±1dB 20 to 20kHz (Direct Output); ±1dB 50Hz-15kHz on 25V, or 70.7V output
90dB Below Rated Output
120VAC 60Hz
3.5" (H) x 19" (W) x 12" (D)
SPECIFICATIONS
Weight
Finish
26 lbs.(11.8 kg)
Flat Black
•Fully isolated output transformer for 25 and
70.7 volt line operation
•Auxiliary RCA type inputs for receiving source
signal and bridging source signal out
•Independent input gain control for 600 ohm
telephone paging
•250 watts continuous RMS power
•8Ω, 25V or 70.7V outputs
•Automatic voice activated Hi-Z muting
Low-cut filter for horn protection
•
Convection cooled, reliable “no maintenance”
design
•
Multiple protections including relay, short
circuit and A/C circuit breaker
•
•UL Approved

NEWTECHNOLOGY OLDRELIABILITY
J.W. Davis & Company •
3030 Canton Street • P.O. Box 710219 • Dallas, Texas 75371-0219
Sales 800-527-5705 • Fax [phone] • Corp 214-651-7341 • Fax [phone] • [email protected] • www.jwd.com
The Mark of the Professional...
I. UNPACKING PROCEDURES
INSPECTION
This unit was carefully checked and packed before leaving the factory. However, each shipment should be
inspected by observing the shipping container and unit for indications of improper handling. If damage has
been found, an immediate claim should be made to the shipping company. Keep all cartons and packing
material for inspection. Do not call J. W. Davis & Company or return the shipment to J. W. Davis &
Company until the shipment has been examined by the shipping company. Failure to permit the shipping
company to examine the shipment at the arrival point may void subsequent settlement. If there is a problem after
the shipping company has made its inspection, then call Customer Service at J. W. Davis & Company for
assistance.
INITIAL PERFORMANCE CHECK
Complete the inspection with an initial performance check. Connect a test speaker to the 8-ohm direct output
terminals. Then, connect a tuner, tape deck, or CD player to the auxiliary input and set the controls for operation.
If the unit should be inoperable and no damage is noted, please contact J. W. Davis & Company’s Customer
Service Department for directions (800-527-5705).
III. INSTALLATION INFORMATION
RACK MOUNTING
For best results use a 10-32 class UNF-2B or 12-24 class UNC-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 to protect the
finish from unnecessary scratches. Nylon or plastic washers are recommended which will not only help protect
the finish but also aid in retaining the screws.
CONVECTION, FAN COOLING, AND VENTILATION
This unit is cooled via convection and therefore designed for continuous operation. Do not block the unit’s
heatsink fins or the vent holes located in the cover. If the unit will be rack mounted, a cooling fan must be used
that is capable of exhausting not less than 300CFM. The fan must be mounted to the inside top of the rack,
above the amplifier.
II. PRODUCT OVERVIEW
-3-
Outputs:
4-8 ohm/25V/70.7
Tel-Page
Microphone
Input
Patch Feature
For Additional Amplifier
Two Aux Inputs
Strapped
in Parallel
Music Input
Source
Inputs
Auto-Mute
Amplification:
250W
D-250AL POWER AMPLIFIER
CAUTION: TO PROTECT THE SPEAKER FROM DAMAGE, DO NOT TURN
THE UNIT ON UNTIL ALL CONNECTIONS HAVE BEEN MADE. IN ADDITION,
BE SURE THAT THE UNIT IS GROUNDED BEFORE TESTING.

NEWTECHNOLOGY OLDRELIABILITY
J.W. Davis & Company •
3030 Canton Street • P.O. Box 710219 • Dallas, Texas 75371-0219
Sales 800-527-5705 • Fax [phone] • Corp 214-651-7341 • Fax [phone] • [email protected] • www.jwd.com
The Mark of the Professional...
IV. THE FRONT PANEL
V. THE BACK PANEL
-4-
1. Volume Control: Adjusts the amplifier’s output level.
2. Circuit Breaker: If the amplifier is continuously over-
loaded, this AC line circuit breaker will trip. Another cause
for the circuit breaker to trip is that the internal temperature
surpasses the safe operating range. Pushing the plunger will
reset the breaker. However, it is important to first correct the
problem causing the overload or overheating. (Additional
protection is provided by fuses in the power supply.)
3 & 4. Power Switch and Indicator (ON - OFF): Controls
power to the unit. The green LED will light when power is
being received.
5. Peak Power Overload Indicator: LED will light/flash at
full power and on peaks. A steady bright glow could indicate
a shorted speaker line, too much load, or oscillation in the
system.
Relay. A relay has been added to the D-250AL circuitry to
prevent any DC from reaching the output. A slight delay of the
audio will be noticed when the unit is turned on as well as an
abrupt disconnect of the audio when the unit is turned off.
Overload protection.If a short circuit or overload occurs in
the amplifier, or if the speaker line is overloaded or shorted,
the AC line circuit breaker on the front panel will open.
Correct the problem, then push the button to reset. If the
circuit breaker will not reset, have the unit serviced by a
qualified technician.
1. AC Line Cord: Three conductor line cord for AC voltage.
2. AC Convenience Outlet: Grounded outlet to run
additional equipment (2 amp maximum).
3. Input Terminal Screw Strip: This strip is designed to accept
either a 600Ωbalanced input or a tel-page balanced input. These
inputs, differing only in sensitivity, are
designed for wide acceptance without the
need for any accessories.
Tel G600Ω
4. Gain Control for 600ΩΩ
ΩΩ
ΩTel-Page Input: This control adjusts
the level of the 600Ω tel-page input without affecting the level of
the high impedance input. It works in conjunction with the volume
control located on the front panel. Both controls effect the 600Ω
tel-page input, and will automatically mute the Hi-Z (music)
inputs. To defeat VOX mute, see Section VIII, page 6.
5. Input/Patch: Two high impedance inputs connected in
parallel for signal input and for strapping to a second ampli-
fier that will increase the wattage of the entire system.
6. Output Terminal Strip: 8 OHM - Bridged output for
an 8Ωdirect voice coil speaker. Do not ground either
terminal. 25V/70.7V - For constant voltage speaker lines
using speakers with line matching transformers. Connect
the speaker line to “common” and either 25V or 70.7V
output.
7. 25V/70.7V Line Output Switch: Dual purpose switch
connecting the output transformer in and out of circuit. It
also controls a low-cut filter designed to prevent low
frequency in and out of circuit. It is designed to prevent low
frequency overload of speaker line transformers and horn
type speakers. For either 25V or 70.7V operation, the
switch must be set to the LINE IN position.
12345

The Mark of the Professional...
The D-250AL is designed to be connected to 8-ohm speakers directly, or to variable impedance speakers that
match the amplifier’s line output voltage of 25V or 70.7V speaker lines.
VI. SPEAKER INSTALLATION
CONNECTING FOR DIRECT 8-OHM OPERATION
Connect 8-ohm speaker(s) to terminals 1 (-) and 2 (+). See page four. To maintain proper phasing, observe
correct polarity. NOTE: This is a bridged output. Do not ground either of these two terminals.
For 25V output, connect the load to terminals 3 (-) and 4 (+). For 70.7V output, connect the load to terminals 3 (-)
and 5 (+). See page four.
CONNECTING FOR 25V or 70.7V LINE OPERATION
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). To allow for future expansion and
distributed cable line loss, it is recommended the total system wattage should not exceed 80% of the amplifier’s
rated output. To determine the total system wattage, sum the wattage tap of all speaker(s)/horn(s) used.
USING THE PROPER WIRE SIZE AND LENGTH
70.7V SPEAKER LINE
(FOR 25V LINE DIVIDE ALL 70.7V LENGTHS BY 8)
NOMINAL POWER IN LOAD
LOW IMPEDANCE
SPEAKER LINE
AWG
SIZE
2-WIRE COPPER CABLE LENGTHS FOR SPEAKER LINES AT -0.5dB LOSS IN SPL (12.5% POWER LOSS IN WATTS)
VII. USING HORN SPEAKERS
THE LOW-CUT FILTER
The D-250AL is equipped with a low cut filter that is activated by the LINE OUTPUT switch. When the switch is in
the IN position the 25 and 70.7 volt ouputs will roll-off any frequencies below 120Hz. Low frequencies can damage
horn diaphrams, as well as compression drivers, if no filter is used. NOTE: Some installations may require
additional electronic equipment to protect a total horn, or compression driver type installation.
NOTE: When using the amp’s 25V or 70.7V line operation, the proper tap setting of the impedance matching
transformer determines the individual speaker’s power level. Using these transformers allows the speakers to be
placed at longer distances from the amplifier without significant power loss. The number of speakers for a line-
driven central amplifier system is limited to the power available from the amplifier. The sum of all connected
speakers’ power settings must not exceed 80% of the total power available from the amplifier.
NEWTECHNOLOGY OLDRELIABILITY
J.W. Davis & Company •
3030 Canton Street • P.O. Box 710219 • Dallas, Texas 75371-0219
Sales 800-527-5705 • Fax [phone] • Corp 214-651-7341 • Fax [phone] • [email protected] • www.jwd.com
-5-
4 OHMS 8 OHMS 16
120 240 480
75 150 300
50 95 190
30 60 120
20 40 75
15 25 50
10 15 30
7.5W 15W 30W
- - 5,000
- 6,200 3,100
7,600 3,800 1,900
4,800 2,400 1,200
1,500
1,920 960 480
1,200 600 300
60W 100W 125W
2,500 1,500 1,100
1,550 940 750
950 600 450
600 370 290
375 230 180
240 150 110
150 95 -
250W 400W 500W
550 365 275
375 230 185
225 140 110
145 90 -
90 - -
---
---
10
12
14
16
18
20
22
WIRE LENGTHS IN FEET
3,000 750

NEWTECHNOLOGY OLDRELIABILITY
J.W. Davis & Company •
3030 Canton Street • P.O. Box 710219 • Dallas, Texas 75371-0219
Sales 800-527-5705 • Fax [phone] • Corp 214-651-7341 • Fax [phone] • [email protected] • www.jwd.com
The Mark of the Professional...
VIII. THE AUTO-MUTE CIRCUIT
The JWD series of mixer amplifiers include a built-in automatic mute circuit. The MIC/tel-
page 600-ohm input channel can automatically mute the AUX channel. This unit is factory
installed to auto-mute; however, the mute is defeatable by moving the internal mute
jumper to its other position.
To defeat the auto-mute circuit follow these steps. 1) Unplug the A/C cord. 2) Remove
the hood and find the input board located on the back panel. 3) On the board locate the
header X2 (See the figure to the right). Change the shunt position from positions 1 and 2
to 2 and 3 and the auto-mute will be defeated.
DISABLING THE AUTO-MUTE CIRCUIT
If a the unit is overloaded or it overheats, the AC line circuit breaker on the front panel will open. Before
resetting the circuit, determine and correct the problem causing the overload of overheating (see
“Troubleshooting” on page 8 for a chart to help guide you in determining the cause of the problem). If after
exhausting the possibilities the circuit breaker will not reset, have the unit serviced by a qualified technician.
The D-250AL is built to last and therefore comes equipped with multiple built-in protections including relay, short
circuit and AC circuit breaker. If the unit is overloaded (e.g., too many speakers, shorted speaker line,
mismatched line impedance [e.g., 8-ohm speaker on 70.7V line]) or overheated (e.g., obstructed or poor
ventilation of the unit, mismatched line impedance) the unit will fail to provide output. Overloading and overheating
of the amp can lead to premature output failure.
RESETTING THE AC CIRCUIT BREAKER
REPLACING THE FUSES
Additional protection is provided by fuses in the power supply which protect the transformer. If an output is
shorted, the fuses will blow. Before replacing the fuses, determine and correct the problem causing the fuses to
blow (see “Part X. Troubleshooting” on page 8 for a chart to help guide you in determining the cause of the
problem). To safely replace the fuses: 1) Disconnect the AC power cord; 2) Remove the top cover screws and
cover; 3) Replace blown fuses with the same type and size; 4) Reinstall the top cover securely; 5) Reconnect
the AC power cord.
IX. MAINTENANCE
Connect shunt here to
disable the Auto-Mute
Connect shunt here to
enable the Auto-Mute
(Fa cto ry-Pres et)
The Auto-Mute Circuit
X. WARRANTY & TECHNICAL SUPPORT
For a period of five (5) years from the date of original purchase, J. W. Davis & Company warrants that it will
correct any defects in material or workmanship in the D-250ALwithout charge. However, this warranty does not
apply to equipment which in the opinion of J. W. Davis & Company has been subjected to abuse or accident,
improper installation or alteration in any way. If the D-250AL fails to operate during this period, return it prepaid to
J. W. Davis & Company Warranty Service with a letter explaining the problem and proof of purchase.
Should you require further technical support, please contact our Customer Service Department for assistance
through any of the channels shown below.
-6-
NOTE: If the unit is rack mounted, you must utilize a cooling fan that is capable
of exhausting not less than 300CFM.

SCHEMATIC FOR D-250AL AMPLIFIER
-7-

NEWTECHNOLOGY OLDRELIABILITY
J.W. Davis & Company •
3030 Canton Street • P.O. Box 710219 • Dallas, Texas 75371-0219
Sales 800-527-5705 • Fax [phone] • Corp 214-651-7341 • Fax [phone] • [email protected] • www.jwd.com
Power Indicator on
Front Panel Does
Not Glow:
Overload Indicator
on Front Panel
Glows Steadily:
No Audio
Output:
No Automatic
Muting of Input
Signal:
No AC power present
Unit’s AC circuit breaker is
tripped
• Verify the unit is receiving AC power.
• Verify the AC circuit breaker is not tripped. If so, depress the
plunger to reset.
• Verify the unit’s internal fuse(s) has not tripped. If it has,
replace the tripped fuse with the same type and value fuse.
Input or output impedance not
matched
Signal in level too high
•Check that the proper input/output line impedance matches
the selected input/output connections used.
• Lower the signal in level.
No input signal source
Incorrect input signal connection
Incorrect output connections
600-ohm/tel-page gain control on
back panel too low
• Verify that proper signal/level is being supplied.
•Verify that the signal input connection is correctly connected.
•Check that the ouput connection has been properly made.
• Check 600-ohm/tel-page gain control setting (recessed on
back).
Internal jumper setting
Insufficient 600-ohm/tel-page gain
• Check that the internal mute jumper is not disabled. (See
page 7.)
• Check 600-ohm/tel-page gain control setting (recessed on
back).
Low, High, or
Distorted Level:
Volume setting
Signal input level is too low
Signal input level is too high
Input or output impedance not
matched
• Check the corresponding gain control on the front panel or
the 600-ohm/tel-page control (recessed on the back).
• Check that adequate input signal level is strong enough.
•Reduce input signal accordingly.
• 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
SYMPTON POSSIBLE CAUSE POSSIBLE SOLUTIONS
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XI. TROUBLESHOOTING
• Verify the AC outlet has proper AC voltage available.
XII. OPTIONAL ACCESSORIES
Optional 600-ohm Isolation Transformer (IT-600)
Speaker Lightening Suppressor (SLS)
Tel-Page Line-lightning Suppressor (TLS)
Universal ADD-ON-AMP (AO-1A) used to match 4 or 8-ohm, 25V and 70V speaker line to MIC or
Auxiliary input of amplifier
Signal Matching Attenuator (AT-20A), Matches Signal from Tuner or Other high Z Device to Amplifier MIC Input
Signal Matching Attenuator (AT-20B), Matches Signal from Telephone Line or Other Low Z Device to Amplifier
MIC Input
•
•
•
•
•
•
-8-
• Check and correct system wiring.
Signal Matching Attenuator (AT-20C), Matches Signal from 70V Speaker Line Output to AUX Input of Second
Amplifier
•