Knowledgebase Contact Us
How Can We Help?
< Knowledgebase

Use with Tacho Feedback Board

The circuit of the standard tacho-generator feedback board is described on the site and a drawing with other information is available. Mechanically, this board is designed to plug into the NCC and Pro series controllers.

Electrically the tacho board is simply an absolute value amplifier (precision rectifier) and an error amp, so that it can (in theory) be used with any controller. This page describes its use with the 4QD series controllers.

Because of the lack of mechanical compatibility, the installation is not suitable for the electronic novice and these notes are provided without any guarantees as to fitness, suitability etc. In particular, there is no easy place to mount the tacho board inside the controller, so this will require some ingenuity. Electrically however there is no problem.


Four wires are needed between tacho amp board and 4QD top board.

  • Earth. Pin 9 to top board 6 way connector pin F.
  • Positive: from pin 4 (or 2) to pin B.
  • Input.
  • Output.

These are shown in the diagram below, which is an issue 12 board. Earlier boards did not have the required break point. See 4QQ series Modification history.

Power supply

The tacho board draws very little more current than that required by the LM324, so can be powered from the 4QD’s internal 12v supply.

Earth. It is important that the earth be taken to the 4QD top board and not to any power earth such as battery negative. Suitable points are the 6 pin connector, or any point on the earth track (which is peripheral to the entire board).

Positive. Can be taken from pin 2 of the connector: this comes via a diode from the internal 12v supply.

The drawing below shows other possible earth and +12v connection points.

Input and Output

Since issue 12, the 4QD series top board have had a break point fitted. This must be scratched through and a 2 way pin strip (or other connector) can be fitted so the tacho board can be disconnected easily.

The drawing identifies the scratch through (red line) and the four connection points, including suitable alternative 12v and 0v feeds.



The 4QD series include armature voltage feedback as standard. This stabilises the controller’s gain against supply voltage fluctuations and means that the tacho feedback can be closer tuned to optimum performance.