QRK-SF - Single Jfet Controller Interface for Multi-Voice Control


In Stock
Product Code:


 QRK-SF allows multiple voice control inputs to interface with a set of jfet control lines, linked to series and shunt connected jfet audio switches. QRK-SF is the equivalent to one quarter of QRK-FET quad jfet controller.

  • controls shunt-connected n-jfets
  • controls series-connected n-jfets
  • function LED driver
  • requires only -12Vdc if shunt-only is used
  • requires +/-12V if series is used
  • requires <3mA if no LED is connected
  • requires <12mA if LED is used
  • accommodates easy programming DIP switche (order QRK-DIP)

Jfets can be used to switch signals up to a line level in amplitude, and can do so with very little power consumption compared to mechanical relays. Shunt-connected jfets can mute audio or enable cathode-bypass caps for gain boosts, requiring just -12Vdc to control them. Series-connected jfets can switch audio but require +/-12Vdc for proper control. QRK-SF provides proper interface with the jfet gates and the "voice" selection for the amp.

Shunt-wired jfet gates can tie directly to the control line. Series-connected jfet gates require diode isolation conveniently provided by QRK-JFT, which has a jfet and gate diode on a small PCB.

QRK-SF will produce symmetric control lines for shunt wired jfets while using just -12Vdc, by linking VP to V0.

With +/-12Vdc supplies, the series output can be used to control grounded-source n-channel power mosfets to switch high-power and/or high-voltage loads, such as cathode selection of power tubes, and Power Scale control selection.

QRK-SF is useful where the number of elements to be switched does not require the four-times capability of QRK-FET. QRK-SF is also useful when more than the capability of QRK-FET is needed but not that of two.

The status of the jfet output control lines are set so that if both types of audio mute are used within a circuit, the shunt element and series element will be in the correct state to allow signal through.

DIP switches provide easy programming of which voice control lines will interface with the jfet controller. Add QRK-DIP for this option. If this easy programming capability is not required, solder in wire jumpers where the  DIP switches would be.

QRK-SF comes with a standard-brightness 3mm round green LED. The onboard LED driver can drive any LED the builder wishes to use.

The PCB makes assembly fast and simple.

PCB size: 1.8" x 1.35" (48 x 35 mm)See also:

QRK-DIP - 4-way DIP switchets

Photos (2)

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
11 am - 6 pm, M-F
PO Box 10012, Thunder Bay, ON P7B 6T6 CANADA