Q-SR – Single Relay Controller Interface for Q-System

CAD $14.00


Q-SR, the “relay controller” member of London Power’s Q-system of switching kits, allows up to four voice control lines to interface with a a group of relays switched in tandem. Q-SR is equivalent to one-quarter of the Q-RLY quad relay controller.

  • controls one relay group
  • function LED driver
  • requires 12Vdc
  • accommodates DIP switches for easy programming (order Q-DIP)


Most guitar amp switching functions only need one or two things in the actual audio path switched. The amp might have three or more voices overall and benefit from the direct-random-access selection that Q-LATCH provides, but may not need internal selection of as many things as there are voices. In such cases, using one or two Q-SRs plus Q-LDV to drive the voice LEDs will save space and money compared to installing the Q-RLY that controls four relay groups and drives the voice LEDs.

Use RLY or similar mechanical relays located with the audio circuitry. More than one RLY can be switched simultaneously by Q-SR. Each RLY requires 12V at 12mA, where Q-SR requires about 10mA only if it drives a LED – otherwise, it requires no current for the driver itself.

An onboard LED driver allows an indication of the status of the function being switched. The stock LED is 3mm round, green and standard brightness.

The relay controller can respond to up to four voice lines, determined by soldering in jumpers where the DIP switches would be. For easier programming, add Q-DIP to allow changes any time without soldering.


Kit requires assembly.

PCB size: 1.35″ x 1.1″ (35 x 28mm)

See also Q-DIP – 4-way DIP switch

For more information:
– see our page, About Our Switching Kits
– download our informative PDF: London Power Switching Kits Selection & Application (135 kB, 22 pages)