BFX - Best All-Tube Effects Loop Kit


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BFX can be incorporated into any tube amp, providing a tube solution to active effects loop requirements.

  • tube-buffered input and 'send'
  • tube mixing stage using virtual-earth mixer
  • 'send' and 'return' level controls
  • 'send' and 'return' jacks
  • 'series/parallel' switch
  • local decoupling included
  • operates from 160-450Vdc 2mA
  • heaters can be run at 6V 300mA or 12V 150mA
  • PCB included

This is a kit form of the "Best All-Tube Effects Loop" from our book TUT - The Ultimate Tone. It offers series or parallel operation, 'send' and 'return' level controls and jacks, and transparent mixing. The 'send' is buffered, eliminating problems with long cables to your effects. The return input has enough gain to support pedals used in the loop even if the loop is inserted in a high-level signal point in your system. Everything is quiet enough that the loop can be used at the front end of your guitar rig, too. Any 12A_7 can be used. PCB construction makes assembly quick. The entire board and tube (tube not included) can be enclosed in the chassis.

The BFX can be used with the QRK-MNR FX Loop Controller to be a switchable loop, or as a switched-gain boost, following the guidelines in our book TUT5 - The Ultimate Tone Vol. 5. The BFX + ERK - Electronic Relay Kit can be used as a stand-alone effects controller powered from a PSU-PRE - Power Supply for Preamp supply.

Typical system location for the BFX effects loop would be between the preamp and the power amplifier. If reverb is incorporated, then the BFX should precede the reverb. When retrofitted into an existing amp, wire the heater connection for 6V. When used with London Power's Preamp Kits and the PSU-PRE power supply, wire the BFX heaters for 12V.

Would you like to receive your BFX pre-assembled? Just add BFX-BLT to your order and add a note in the 'comments' section which tube orientation you require: Internal Tube, with all the parts and tube socket on the same side as the board, or External Tube with the tube and components on oppositie sides of the board.

PCB size: 3.9 x 1.5" (99 x 38mm)

The BFX comes with helpful installation notes including layout and schematic diagrams of the kit.


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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.

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