Quick Tour Video:

Circuit Diagram:

This circuit is suitable for low power amps ( up to 40v +v). Tweak the value of R4 for a LED current around 20mA.

For higher power amps use the circuit at the bottom of page.

Circuit for higher power amps ( v+ above 40v ):

Tweak the value of R4 for a LED current around 20mA.

Video: