VACUUM TUBE MONOBLOCK POWER AMPLIFIER
LM-503PA
Thanks for choosing our Line Magnetic LM-503PA Mono Block Tube Power Amplifier.
Please read this manual carefully before installation and operation.
In order to prevent damage during transportation, the amplifier and its tubes are packed with
protective foam, please remove these foam pieces before operating your amplifier to avoid any risks !
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Table of Contents
Table of Contents ------------------------------------------------------
Package Contents ------------------------------------------------------
Product Features -------------------------------------------------------
Specification ------------------------------------------------------------
Safety Precautions -----------------------------------------------------
Connection --------------------------------------------------------------
Functions Description ------------------------------------------------
Turning on --------------------------------------------------------------
Tube Replacement -----------------------------------------------------
Maintenance ------------------------------------------------------------
Warranty Statement ---------------------------------------------------
Troubleshooting -------------------------------------------------------
Suggestions:
The LM-503 PA integrated amplifier is designed and manufactured with our original parts for reaching
the best results. We are not responsible for problems and damages caused to the amplifier by non-original
replacement parts.
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Please check the cartonbox carefully for any damage before opening it.
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Package Contents
1. Line Magnetic LM-503PA 1
2. Main Fuses 2
3. Power cord 1
4. User’s Manual 1
5. Warranty Card 1
Note:All other parts except above are not included.
Recommendation:
Keep all packing materials for future use and please fill in the warranty card for registration of warranty.
Note:
Please make sure that your local voltage is the same as indicated on the rearpanel.
A too low or too high voltage can cause serious damage to your amplifier!
In case you find an improper voltage, please contact our company or your local dealer,
Product features
1. Hand-made construction with the finest point-to-point wiring.
2. LM-503PA uses specially designed high grade EI type of Class A output transformer with wide bandwidth.
3. Specially designed toroid transformer for power supply.
4. In the pre-stage we are using 310A tube developed by our company and in the driver stage it is 300B tube we
have used.
5. 845 tube has been used for Single ended Class A power amplification.
6. User bias control has been used for bias adjustment and meters are available for monitoring the value.
7. In the input stage it is selectable between Balance transformer input and RCA input.
8. Soft Start and time delay Circuit.
9. Big loop Negative Feedback and Small loop Negative Feedback are available in order to meet different listening
requirement.
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Specification
Safety precautions
1. Unplug the powercord if your are not going to use the amplifier for an extended periode of time.
2. The temperature of the amplifier will rise after a working for a long periode of time. Please keep the
amplifier at a well ventilated place and make sure the ventilation openings are not blocked !
3. Forbidden to operate the amplifier when there are no speakers connected !
4. Do not short-cicuit the output terminals !
5. Do not attempt to service the amplifier yourself. Opening the cover will expose you to lethal voltage
and / or other hazards.
6. We are not responsible for any problems caused by checking and opening the amplifier without per-
mission of our company. Please contact a qualified service technician.
7. Do not place any object filled with water around or on top of the amplifier
8. Clean only with a dry cloth.
9. Please move the amplifier carafully,do not drop it or subject it to strong shocks.
10. Unplug the powercord if you are not using the amplifier during a thunderstorm.
Carefully read and follow the Manual for installation:
1. Do not place the amplifier near heat sourches such as radiators and other produts that produce heat.
2. Please keep the amplifiers ventilation openings open to prevent overheating.
3. Do not expose this amplifier to rain or moisture.
4. The amplifier should be installed on a stable surface and make sure the feet are on the same level.
5. Keep the amplifier at a certain distance , so connections can be made easily.
6. Keep the amplifier at 15 cm from surrounding walls for adequate ventilation.
The lightning flash with arrowhead symbol, within an equilateral triangle, is intended to alert users
to the presence of uninsulated “dangerous voltage” within the product’s enclosure that may be of
sufficient magnitude a risk shock to persons.
The exclamation point within an equilateral triangle is intended to alert the user to the presence of
important operating and maintenance (servicing) instructions in the literature accompanying the
appliance.
RISK OF ELECTRONIC SHOCK
DO NOT OPEN
CAUTION
.To reduce the risk of electric shock, do not remove the cover.
.No user serviceable parts inside. Refer servicing to qualified service personnel.
.To reduce the risk of fire or electronic shock, do not expose the unit to rain or moisture.
Note: Input voltage level of the amplifier is 230VAC～±5% and please make sure that the supply
voltage is proper. Too low or too high voltage may cause problem or reduce its life.
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Suggestions:
Connection method of LM-503PA with other audio equipments, take pictures below for your reference:
Audio Connection
1. During installation please always refer to the other equipments operation manual.
2. Please do not insert the powercord into the mainsocket before all other equipment is well connected .
3. R refers to the left channel while L represents the left channel.
4. Please take care of the correct channel guidance because wrong connections may cause noise and
low grade operation.
5. Do not fasten signal cables together with powercables to avoid disturbance and noise.
Safety precautions
Connection
The front stage
Check the impedance of your speakers. Attach the positive (+) side of you speakercable to the 4, 8 or16 Ohm terminal
and the negative (-) side to the 0 Ohm terminal. If your speakers are 6 Ohm or otherplease experiment with the 4,8 or
16 Ohm terminal to get the best result from your speakers.
Please take care of the right channel connections , don't mix them up as this will cause noise and badstereo imaging.
How to connect the speaker cables:
1.Unscrew the terminal knobs,
2.Insert the speaker cables,
3.Screw the terminal knobs.
speaker terminal
U type terminal
Note: Connect the speaker cables with the amplifier after it is well connected with the speakers.
Please notice the right direction indication of the cable and do not mix up the positive and
the negative end.
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Speaker Connection
Connection
音箱
Bias Adjustment/Hum Adjustment:
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Note:
1. Be careful of the high temperature of the tubes during the adjustments.
2. Input-, Driver- and Power tubes must be matched for the best results.
Overview from the top
V1、845 Power Tube V2、 300B Driver Tube V3、310A Driver Tube V4 Power rectifier
V1 Screen flow adjustment method
Functions Description
Turn on the amplifer and wait for around ten minutes. Choose and turn the Bias Current selector to ON position.
Turn down V1 BIAS ADJ. to its MIN. position first and then adjust the bias current. Inspect the ampere meter on
the front panel and make sure the pointer is at the position showed as in the pictures below. If you have any questions
please contact with our company or local service agent.
Hum Adjustment V2
Hum Adjustment V1
Bias Adjustment V1
In order to make the machine work condition of the best, it is recommended to use about 150 hours, according to
the above method to test the working state of power tube.
Adjustment method: noise when the machine appear hum noise, adjust the V1, V2 potentiometer
noise, and listening to the corresponding channel speaker to minimize noise.
V1 Anode current meter
Note: Once the bias has been
set up turn Bias Current to ON
position you will read the bias
level of V1 tube. If turned to V1
the bias monitering will be turned off.
Note: please open the knob on the
lock before the adjustment
2010.10.12
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Functions Description
Front Panel:
Rear Panel:
Power Switch
Power Socket
Signal Input
Fuse
Speaker Output
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Precautions:
Connection of the power cord:Connect the speaker cables and signal cables first and then plug the power cord into
the power socket. Before turning on the amplifier please make sure all connections are right and power supply is stable.
Turning ON
Warning: Please make sure the your local voltage corresponds with the one of the amplifier.
We are not responsible for any damage caused by an insuitable voltage.
Note:
1. It is normal the powertransformers become hot after an extented periode of operation.
2. Please unplug the powercord , if you are not gone use the amplifier for an extended periode.
3. Please only connect the powercord to the mainsocket if all other equipment is well connected.
4. To prevent damage to the amplifier never cut off your speakercables while it is on.
5. For protecting the tubes,please wait 2 min before switching back"ON"in case it was switched off.
Connect to
AC 230V～50Hz
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Tube Basics Common Replacements
5U3C
310A
300B
2748、5931
WE310A、10ж12C
300B、300A、4300B
845 845A/B/C
Tube Replacement
Clean the amplifier with soft dry cloth and please do not use any chemicals for cleaning.
Maintenance
1. Limited Warranty: One-year limited warranty from the date of purchase except vacuum tubes which are warranted for six months.
2. Limited to original purchaser. This warranty is for the sole benefit of the original purchaser of the covered product, and may not
be transferred to a subsequent owner.
3. Conditions & Limitations. This warranty is subject to conditions and limitations, as follows. This warranty is void and
inapplicable if the product has not been used or handled other than in accordance with the instructions in the owner’s manual,
or if it has been misused, abused, damaged by accident or neglect, or in transport once in possession of purchaser, or the defect
is due to the product being repaired or tampered with by anyone other than Zhuhai Line Magnetic Audio Co., LTD or an
authorized Line Magnetic Audio Representative.
4. Remedy: If the product contains material, or manufacturing defects, it must be packed in original packaging and returned to
Zhuhai Line Magnetic Audio Co., LTD or an authorized Line Magnetic Audio Representative at his or her sole expense.
A returned product must be accompanied by a written description of the defect and the warranty card with an authorized dealer’s
stamp on which indicates the model and series number, the date of purchase, the name and address of the purchaser.
Zhuhai Line Magnetic Audio Co., LTD reserves the right to modify the design of the product and change the specifications
without notice or obligation to any person.
5. Miscellaneous. Any implied warranties relating to the above product shall be limited to duration of this warranty. This warranty
does not extend to any incidental or consequential costs or damages to purchaser. Our liability will be no more than the amount
you paid for the product that is the subject of a claim. This isthe maximum amount for which we are responsible. This warranty
gives you specific legal rights. You may also have other rights which vary from country to country, state to state
Warranty Statement
Terms & Conditions:
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Troubleshooting
Please follow the instructions in this manual to keep the amplifier working in a reliable and safe manner.
If problems arise or you think there is a problem , please first check the tips given below to checkfor the excact reason.
Sometimes problems could be caused by other related equipment , please check the connections . After doing so and
the problem still exists , please contact our factory or your local dealer.
Problem
Cause
Remedy
NO OUTPUT
Power LED is ON.
Power LED is OFF.
Power cord is not well-connected
Main fuse is out.
Troubles of inner parts
or components
Please check the power cable connection or
power outlet connection
Replace with the same type and value fuse
Please contact your local agents
or our factory
NO signal input
Volume is at ZERO
Turn up the Volume
Check the function of the sound source
Check the input connectors and/or
switch to the proper input
Stereo image
is not so good
Noise output
Sound Distortion High input signal level
Ground of input signal cable is
open or bad contact of the input
signal cable
Components or circuits are
in trouble
Signal input cables or speaker
cables are wrongly connected
Turn down the volume to suitable position
Replace the input signal cable with a
new one
Please contact with local dealer or
our factory
Reconnect it as suggested in the manual
Line Magnetic logo is registered trademark of Zhuhai Line Magnetic Audio Co., LTD.
Copyright of Zhuhai Line Magnetic Audio Co., LTD. All Rights Reserved.
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