ERK - Electronic Relay Kit


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ERK Features:

  • A, B exclusive selection
  • ground-referenced jfet shunt switch elements
  • silent operation
  • use with push-on push-off remote switch (order FSW)
  • easy wiring for panel control (switch not included - order PSW)
  • can control panel LEDs (LEDs not included)
  • 6-poles included; infinitely expandable
  • use for channel muting or selection
  • use for gain selection via cathode-bypass caps
  • low current consumption of <2mA
  • operates from -12Vdc or high-voltage AC

ERK uses "shunt" switch elements for silent, reliable channel selection or gain stepping. Three transistors create and control two control lines that respond to a remote footswitch. Any required number of jfet switches can be connected to these lines. For example, using the ERK to select the channels of the LP-PRE Preamp Kit or the FPM Fender Preamp Mod requires one jfet on the control line to mute the 'Clean' channel, and two jfets on the second control line to mute the 'Lead' channel. Because jfet gates present practically zero loading to the control lines, there is no real limit to how many jfets you tie on.

ERK has a fourth BJT to control one or two LEDs, or a bicolour 3-lead LED, to indicate which channel is 'on'.  It is recommended that when LEDs are used, ERK be supported by a proper -12Vdc supply rather than the high-AC voltage.

There is also wiring accommodation for a front panel switch, which is over-ridden when a foot-switch cable is inserted into ERK's 1/4" jack. Use a latching switch such as PSW which is a high-quality C&K toggle, or similar as a push-button or rocker.

For most builders and hobbyists, the type of switches and LED colours on their front panel is an aesthetic issue, so we do not include them in this kit.


Photo above shows ERK with FSW.

Power is easily obtained from the raw bias supply or the plate winding in typical tube amps. London Power's Preamp Power Supply Kit (PSU-PRE) provides a polarity-programmable 12V heater winding to accommodate switching circuits. PCB construction makes ERK assembly and installation easy.

The ERK includes complete installation notes with helpful diagrams.

Includes PCB.
PCB size: 2.15 x 1.15" (55 x 29mm)


For more information, download our informative PDF: London Power ERK, RLY & QRK-series Switching Kits Selection & Application (2.2 MB, 22 pages).

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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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