The 1N4148 has leakage x1000 the input of TLC BiFet so the drive to the OA input is very well defined and is a convenient way of implementing a peak h old without using an extremely large valued resistor. Also, anyone can see the LEDs are intended to avalanche. The OP didn't think a 12V supply was im portant, so it caught up with him. The circuit is very clever and works wel l for audio frequencies.
9 years ago