BL20 - "Baby" Leach Power Amp Design


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BL20 is the "Baby" Leach amp. Where most similar designs are aimed at 100W+, BL20 is targeted for <100W per channel. In these days of multi-channel surround systems and bi-amping, few people actually need so much power per channel.

  • fully symmetrical circuitry
  • 14 transistors
  • Locanthi-T triple-EF output
  • flexible compensation options
  • board size: 3.2x3.5" 81x89mm

BL20 uses modern high-beta beta-sustaining output and driver devices to produce up to 100W, but is optimally designed for powers up to 60W. As its name suggests, BL20 can be used for 20W with +/-24V supplies. The original Marshall Leach "Low-TIM" design from 1976 is the basis for the BL20. We have added optional forms of compensation that the builder can experiment with.

There is no protection circuitry on-board.

The free version of this info package, BL20 FREE (392 KB) includes enough info for the home hobbyist to make his or her own printed circuit boards, and includes the following PDFs:

  • schematic
  • parts overlay
  • top foil
  • bottom foil
  • bill of materials

Click HERE to download BL20 FREE.

BL20 COMPLETE (2,056 KB) includes all of the above info, plus comprehensive notes detailing how the circuit works, how to substitute components, how to use the flexible compensation options, proper wiring, building a power supply, Gerber and Excellon files for professionally manufactured PCBs, and saftey notes. BL20 COMPLETE includes:

  • schematic
  • parts overlay
  • top foil
  • bottom foil
  • comprehensive notes - 16 pages
  • Gerber and Excellon files
  • power supply design
  • safety notes

Click "Add to Cart" above to order BL20 COMPLETE.

About London Power

London Power was founded in 1990 by Kevin O'Connor, after two decades of research into innovative audio amplification techniques. Kevin is an audio designer, author and speaker, known for his proprietary methodology called Power Scaling, and for his eleven books on audio subjects. Whether you seek amps, kits or information, you'll find useful answers here on not just the "how" but the "why" of audio amplifier design. Please enjoy the information on this site, and don't hesitate to contact us with questions.

Contact Us

(807) 473-0952
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PO Box 10012, Thunder Bay, ON P7B 6T6 CANADA