CDXL test … and a question for anyone building it -

I Love Music

New member
I put a red led in place of the vactrol to see how sensitive the input is on the CDXL circuit.

Well, the answer seems to be "zero" - no LED flashes at all. The LED dimmed with the "range" knob, but never flashed. I removed the 4.7 uF cap from the board, and measured - pin one of the tl072 is slammed to the positive rail at all times. Of course I switched tl072 chips, no difference.

Now ... the cool part .... I switched pins 2 and 3 of the tl072 , and bingo - pin 1 of TL072 follows the 4volt input from the op amp divider, and the LED sitting in the vactrol holes flashes as it should.

Can anyone verify that their CDXL board works without switching pins 2 and 3 of TL072 ?