Clipping indicator design ?

[mikebuzz]

Here is a design for a clip indicator for the SCA series pre's , If U see any problems or design errors please let me know ! .

I set the threshold for 90% of the supply Vcc , this may change to 95% depending on results ( change the 2k resistor to 1k !! )



LAter
Buzz

http://machineband.com/clipindicatorboard.JPG OK heres the image

[mikebuzz]

Ok so the J99 /N72 /A12 have different reference voltages for clipping so each circuit has to have a separate source to refer to based on the power supply's on the board , I have a new design that addresses this that I will post later

Later
Buzz

[tpryan]

That's a start. The output of the LM339 is an open collector, though, so you'll have to turn the LEDs around if you ever want to see them light up. The LM339 can only sink current, not source it.

You'll need to think about the reference levels a bit more. Because of the transformer outputs, the peak levels of the N72 and A12 can extend well above the positive rail. It's probably better to establish a local 5v supply for the comparators, and then scale the input voltages accordingly.

Also, as drawn the comparators only trip on positive going peaks. What about the negative peaks?

Peaks are very brief, frequently too brief to light the LEDs in any satisfying way. You may want to add a pulse stretching circuit to the output of the comparators to guarantee a minimum LED on time. Conveniently, you can use the LM339 to build a suitable "one shot" circuit as well.