Replacement and Adaptation of the JBL ES250P Subwoofer Amplifier Module with Full Protection Integration and Thermal Improvements

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Hello. This is my first post here and I hope you like it. After taking my JBL ES250P subwoofer (12", 250W, 4 Ohm) to two authorized JBL technical support centers, it was found that the amplification board was defective and could not be repaired or spare parts were available. So I decided to try to recover this excellent subwoofer myself and it worked very well. I will share here what was done.

🎯 Objective​

To replace the faulty amplifier board of the JBL ES250P subwoofer with a new board based on the IRS2092S, ensuring the retention of all original protection features and optimizing thermal dissipation for safe operation within the subwoofer's sealed enclosure, without forced ventilation.

🧱 Original Configuration​

• The JBL ES250P comprises three main boards:
  1. Preamplifier, Filters and Limiter Board: Handles signal input, control, and crossover functions.
  2. Power Supply and Protection Board : Manages rectification and filtering with capacitors.
  3. Amplifier Board (see below): The original board was damaged beyond repair and unavailable for replacement.

🔁 Amplifier Board Replacement​

• Chosen Replacement: Chinese L30D Module (There are already some discussion forums about this amplifier here at diyAudio)
  • Based on the IRS2092S Class D amplifier IC.
  • Hybrid architecture combining elements from Infineon's designs:
    • IRAUDAMP7S: Manages input and control (pins 1–6 of IRS2092S) and +15V Vcc power supply (pin 12 of IRS2092S).
    • IRAUDAMP9: Handles output stage with totem-pole BJT + IRFB4227 MOSFETs (pins 7–11, 13-16 of IRS2092S).
      

🔥 Initial Thermal Challenges Identified in L30D board​

1. Vcc Power Supply (+15V)​

• Originally implemented using (see IRAUDAMP7S):
  • R114 (1 kΩ / 5 W)
  • Z102 15 V Zener Diode
  • Q105 TIP31 configured as an emitter follower
• Resulted in excessive power dissipation (~3.6 W) in R114, leading to significant heating.
  
  

2. Capacitors CP5 (bypass filter for Vcc supply) and CP6 (bootstrap)​

• Electrolytic capacitors rated at 47 µF / 63 V (as per the Chinese PCB version).
• Experienced considerable heating due to high-frequency ripple and 400 kHz switching cycles.

✅ Implemented Modifications for Thermal Optimization​

🔋 Vcc Power Supply Replacement​

• Removed the original TIP31 + Zener + R114 configuration.
• Introduced a XL7015 DC-DC Buck Converter Module:
  • Input: −75 V
  • Output: −60 V (=15 V relative to −75 V)
  • Provides ample current to power the IRS2092S and totem-pole stages with minimal heat generation.

🔧 Capacitor Upgrades for CP5 and CP6​

• CP5:
  • Replaced with a 10 µF / 25 V Tantalum Capacitor.
  • Added a 1 µF / 50 V Ceramic Capacitor in parallel.
• CP6:
  • Replaced with a 22 µF / 25 V Tantalum Capacitor.

✅ Outcome: Eliminated noticeable heating in these components.

🧠 Integration with JBL's Original Protection System​

🔐 Retained Active Protections:​

• Temperature Monitoring: Sensor relocated to the new L30D module's heatsink.
• DC Output Detection: Continuously monitored through original circuitry.
• Output Short-Circuit Protection: Ensured through original circuitry.
• Idle Timeout: Activates protection after 10 minutes of inactivity through original circuitry.
  
  

🛑 IRS2092S Shutdown Implementation (Extern SD):​

• The original JBL protection circuit outputs +15 V upon fault detection.
• This signal directly controls a transistor (2N5551) circuit that pulls the SD (Shutdown) pin of the IRS2092S to -5V, effectively disabling the output amplifier during fault conditions.

🔴 Protection Indicator LED:​

• A red LED was integrated into the protection circuit in case of SD (external or internal), using a BC557 transistor.
• Provides a clear visual indication when the system enters protection mode.

💡 Physical and Thermal Customizations​

• LED Placement:
  • Utilized two existing mounting holes from the original JBL amplifier PCB:
    • Installed the L30D's original green LED (indicating active PWM) in one hole.
    • Installed the new red protection LED in the other hole.

• Mounting the L30D Module:
  • Drilled two new holes in the JBL's metal backplate to secure the L30D module.
  • Mounted the module via its heatsink, utilizing two pre-existing holes in the heatsink.
  • Applied thermal paste between the L30D heatsink and the JBL metal plate to enhance heat dissipation.

✅ Final Outcome​

• Successfully restored the JBL ES250P subwoofer to full functionality.
• The L30D amplifier module operates now with enhanced thermal management and integrated protection features.
• Achieves optimized power consumption, cool component operation, and reliable performance.
• Retains original subwoofer behaviors: automatic shutdown, output relay control, and comprehensive fault protection.

This comprehensive guide aims to assist others facing similar challenges with the JBL ES250P subwoofer, offering a detailed roadmap for effective amplifier module replacement and system integration.