The Line Magnetic LM-845 Premium is an integrated vacuum tube amplifier designed for high-fidelity audio reproduction. It operates in Class A, utilizing a Single Ended 845 output stage, delivering 2x30W of power. The amplifier's design emphasizes meticulous component selection and hand-made construction with point-to-point wiring to ensure optimal sound quality.
Function Description
The LM-845 Premium serves as both an integrated amplifier and a power amplifier, selectable via a dedicated switch on the front panel. It features a three-stage signal amplification process, employing 12AX7, 310A, and 300B input tubes, with 845 tubes handling the power amplification.
For connectivity, the amplifier offers five pairs of RCA line inputs, one balanced input, and a dedicated Pre-In input, allowing connection to various audio sources. Speaker terminals are provided for 4, 8, and 16-ohm speakers, ensuring compatibility with a wide range of loudspeakers.
A key feature is the integrated bias adjustment system, which allows users to monitor and adjust the bias current for the 845 and 300B tubes. This is facilitated by two bias meters on the front panel, each monitoring a pair of tubes (V1/V3 and V2/V4). A selector switch allows the user to choose which pair of tubes to monitor. The meters also function as power level meters when switched to "Meter" mode, indicating output power when music is playing.
The amplifier includes a "Hum Balancer" for fine-tuning hum levels in the V1-V4 tubes, contributing to a cleaner audio signal. A Negative Feedback (N.F.B) control allows adjustment between "Min" and "Max" feedback settings, offering sonic customization.
For user convenience, the LM-845 Premium incorporates a soft start and time-delay circuit (approximately 30 seconds) to protect the tubes and internal components during power-up. An IR remote sensor allows for remote control operation, including volume adjustment and muting. The front panel also features a power indicator that blinks during the warm-up delay and remains orange during normal operation.
Usage Features
Initial Setup:
Before operation, it is crucial to remove all protective foam pieces used for shipping. Ensure the local voltage matches the 230VAC ±5% (50Hz) requirement indicated on the rear panel to prevent damage. All connections, including speaker cables, source cables, and the power cord, should be made before turning on the amplifier.
Connecting Speakers:
Speakers are connected to the clearly marked RIGHT and LEFT output terminals. Users must ensure correct polarity (+ to + and - to -) and select the appropriate impedance terminals (4, 8, or 16 ohms) that match their speakers. It is critical never to operate the amplifier without connected loudspeakers, as this can harm the product. Dedicated speaker wires with a cross-section of 1.5 mm² or more are recommended, especially for cable lengths exceeding 3 meters.
Connecting Audio Sources:
Audio sources are connected using RCA (Cinch) stereo audio cables to the designated LINE 1, LINE 2, LINE 3, or BALANCE inputs. The "Pre-In" input allows the LM-845 Premium to function as a power amplifier, bypassing its pre-amplification stage.
Turning On:
- Set the volume knob to minimum (fully to the left).
- Switch the amplifier ON using the power switch.
- The front panel LED will light up orange and blink for approximately 30 seconds during the warm-up delay.
- Once the LED stabilizes, the amplifier is ready for use.
- Select the desired audio source using the "Selector" button.
- Adjust the volume knob to the preferred listening level.
Bias Adjustment:
Bias adjustment is not necessary for the first use. However, for optimal performance and tube longevity, it can be performed periodically.
- Turn on the amplifier and allow it to warm up for about ten minutes.
- Select the tube pair to adjust (V1/V2 or V3/V4) using the "Bias Current" selector.
- Using a small screwdriver, carefully adjust the "Bias Adj." screws for the selected tubes.
- Monitor the corresponding bias meter on the front panel, ensuring the needle is within the ia=70mA area.
- Ensure that the bias levels for V1 and V2 are the same, and similarly for V3 and V4.
Warning: Tubes become very hot during operation; exercise caution to avoid burns during adjustment.
Remote Control:
The LM-02 remote control provides basic functions: volume up/down and mute. Batteries (two 1.5V AAA) are installed by removing the back cover, inserting them with correct polarity, and re-securing the cover.
Maintenance Features
Cleaning:
The amplifier should be cleaned with a soft, dry cloth. If using a chemically treated cloth, refer to its safety precautions. For deeper cleaning, a soft cloth with a neutral detergent can be used, followed by wiping with a dry cloth. Always unplug the unit before cleaning and ensure it has cooled down.
Tube Replacement:
The LM-845 Premium uses specific tube types: 845, 300B, 310A, and 12AX7. The manual provides a list of common replacement tubes for each type, including alternatives like 12AX7EH, ECC83, E83CC, 5751 for 12AX7; Soviet Union/om12C, WE 310A for 310A; 300A, 4300B for 300B; and 845 A/B/C for 845. The guarantee of the product is linked to the exclusive use of tubes supplied by the official distributor and in accordance with assembly technical specifications.
General Observations and Safety:
- It is normal for the power transformer to become hot during extended operation.
- Unplug the product during lightning storms or prolonged periods of non-use.
- Never disconnect speaker cables while the unit is ON to prevent damage.
- To protect the tubes, allow at least two minutes before re-switching on the amplifier after turning it off.
- The manufacturer is not responsible for problems or damages caused by non-original replacement parts.
- Specifications may change without notice as products are upgraded.
- The amplifier should be placed on a stable, level surface, at least 15 cm away from surrounding walls, and in a well-ventilated area to prevent overheating.
- Avoid placing the unit near heat sources, direct sunlight, or sources of vibration, dust, cold, or moisture.
- Do not place objects filled with liquids on or around the unit.
- Do not attempt to service the product yourself; opening the cover may expose you to dangerous voltages. Contact a qualified service technician for repairs.
- Only use spare parts and accessories recommended by Line Magnetic.
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