1. Introduction
This document provides essential instructions for the assembly and operation of the Jolooyo LJM MX50 SE Dual Channel Audio Power Amplifier Board DIY Kit. This kit is designed for enthusiasts who wish to build a high-fidelity stereo amplifier with excellent control and resolving power. Please read this manual thoroughly before beginning assembly.
2. Product Overview
The MX50 SE amplifier board is a refined version of the classic MX50 design, offering improved performance with lower distortion, enhanced control, and superior resolving power. It features a single differential input, a single-ended voltage amplification stage, and a three-level inverted Darlington output stage.
Key Features:
- Low distortion for clear audio reproduction.
- Excellent control and resolving power.
- Utilizes imported KTB817 and KTD1047 original output transistors.
- High-quality components including ST, EVOX CBB capacitors, KEMET, TDK monolithic capacitors, and Japan original imported electrolytic capacitors.
- All resistors are genuine original copper foot metal film resistors.
Figure 2.1: Overview of the LJM MX50 SE DIY Amplifier Kit components, including two PCB boards, heatsinks, and various electronic components such as resistors, capacitors, and transistors.
3. Specifications
| Parameter | Value |
|---|---|
| Supported DC Voltage | ±15V to ±45V |
| AC Rectifying Voltage | Dual 12V to Dual 32V |
| Output Power (RMS) | 100W into 8 Ohms (±42V supply) |
| PCB Area | 76mm x 73mm (V7 MX50SE) |
| Voltage Gain (GAIN) | 34 times |
| Input Sensitivity | 1.2V for 100W RMS into 8 Ohms |
| Signal-to-Noise Ratio (SNR) | > 98dB |
| Total Harmonic Distortion (THD) | < 0.009% at 1K Hz, 10W output |
| Output Stage Quiescent Current (per channel) | Approximately 30mA |
Figure 3.1: Dimensions of the LJM MX50 SE PCB, showing a length of 75mm and a width of 63mm.
4. Assembly Instructions
This product is provided as a DIY kit and requires soldering for assembly. Component values are marked directly on the Printed Circuit Board (PCB) to guide the installation process. While a detailed printed schematic is not included with the physical kit, a visual representation is provided in this manual for reference (Figure 4.1).
Required Tools (Not Included):
- Soldering iron and solder
- Desoldering wick or pump
- Multimeter for testing
- Small hand tools (pliers, wire cutters)
- Safety glasses
Assembly Steps:
- Component Identification: Carefully identify all components provided in the kit. Refer to the markings on the PCB for component placement and values.
- Populating the PCB: Begin by soldering smaller components (resistors, small capacitors, diodes) first, then proceed to larger components (electrolytic capacitors, transistors, connectors). Ensure correct polarity for diodes and electrolytic capacitors.
- Transistor Installation: The power output transistors (KTB817, KTD1047) must be installed onto a suitable heatsink. Ensure proper thermal contact using thermal paste if necessary. The heatsinks provided in the kit are specifically for these components. This version does not require a 'fly line' for installation.
- Wiring: Connect the power supply, audio input, and speaker output according to standard amplifier wiring practices. Ensure correct voltage polarity for the DC power supply.
- Initial Inspection: After soldering, visually inspect all solder joints for bridges, cold joints, or misplaced components.
- No Adjustment Required: This version of the MX50 SE amplifier board does not require any post-assembly adjustments. The quiescent current for each output tube is approximately 30mA, set by the circuit design.
Figure 4.1: Simplified schematic diagram of the LJM MX50 SE amplifier circuit, illustrating component connections and signal paths.
5. Operation
Once assembled and connected to a suitable power supply, audio source, and speakers, the amplifier board is ready for operation.
- Power Connection: Connect the dual DC power supply (±15V to ±45V) to the designated power input terminals on the PCB. Ensure correct polarity.
- Audio Input: Connect your audio source (e.g., preamplifier, DAC) to the audio input terminals.
- Speaker Output: Connect your passive speakers (8 Ohm recommended) to the speaker output terminals. Ensure correct positive and negative connections.
- Power On: Apply power to the amplifier. It is recommended to start with the audio source volume at its lowest setting.
- Volume Adjustment: Gradually increase the volume from your audio source to the desired listening level.
Important: Always ensure proper ventilation for the heatsinks during operation to prevent overheating.
6. Maintenance
The LJM MX50 SE amplifier board is designed for reliable operation with minimal maintenance. However, periodic checks can help ensure its longevity.
- Dust Removal: Periodically clean any dust accumulation on the PCB and heatsinks using a soft brush or compressed air. Dust can impede heat dissipation.
- Connection Checks: Ensure all power, input, and output connections remain secure. Loose connections can lead to intermittent sound or damage.
- Visual Inspection: Occasionally inspect the board for any signs of component stress, discoloration, or bulging capacitors.
Always disconnect power before performing any maintenance or inspection.
7. Troubleshooting
If you encounter issues with your assembled amplifier board, consider the following troubleshooting steps:
- No Sound:
- Verify power supply connections and voltage.
- Check audio input source and connections.
- Ensure speaker connections are correct and secure.
- Inspect for cold solder joints or component misplacement on the PCB.
- Distorted Sound:
- Check input signal level; ensure it's not overdriving the amplifier.
- Verify power supply stability.
- Inspect for faulty components or incorrect component values.
- Overheating:
- Ensure heatsinks are properly attached to the power transistors.
- Verify adequate ventilation around the amplifier.
- Check for short circuits on the output or incorrect speaker impedance.
For complex issues, it is recommended to consult with experienced electronics hobbyists or professionals.
8. Warranty and Support
As this is a DIY kit, the warranty typically covers the individual components at the time of purchase. Due to the nature of user assembly, a full product warranty after assembly may not be applicable. For support regarding component defects upon receipt, please contact your retailer.
For technical inquiries or assistance with assembly, it is recommended to refer to online communities and forums dedicated to audio amplifier DIY projects, as specific manufacturer support for DIY kits can be limited.
