Favorite New Clippers

[Nick C.]

I've been experimenting a lot with different diode clippers in a feedback loop ala TS etc.
Back to back LEDs with a 100k "softining" resistor gives a really nice dynamic effect that can run on the edge of breakup well. I originally thought that that much resistance would be too much. The 100k dosen't work as well with lower clipping knees. Can anyone explain the process that is taking place?

Nick

[WGTP]

It would appear that the clipping threshold is being significantly raised by the 100k resistor.  Do the LED's light up?  Maybe the op amp is distorting instead of the LED's.  Not sure.

Here are some more to try that may be of interest to you or others. 

http://www.aronnelson.com/gallery/main.php/v/WGTP/Diagram.GIF.html?g2_imageViewsIndex=1

[John Lyons]

100k ?! that's pretty high...It might be just the opamp clipping as stated.
Try removing the LEDs and 100k altogether and see if it's the same.

[Nick C.]

I ran an LtSpice model and it shows soft clipping at about 2v, about what you expect from an LED but rounded peaks. Also the waveforms are asymetrical even with identical LEDs. Also ran it though a PC ocilliscope and looks like soft clipping. I'm no expert at Spice or the scope.

Is the opamp clipping? I was thinking about that too, I have a dpdt center off for diode switching with the center being no diodes (BTW, makes a nice booster). In the center position I can raise the gain only 1/2 as much before clipping and it's much harsher. Also the volume out with no clippers is louder so I figure the LEDs must be doing some clipping.

In my tests on the board I never noticed any LEDs lighting up. I'll check it in the dark.

With the resistor the current would be lower so I wonder how that effects clipping?

[Nick C.]

Did some tests over the weekend. Set up on the breadboard basically a first opamp of a tube screamer with choices of clippers with a 100k pot in series. Feed a sinewave into it from Visual Analyzer and watched the waveform. The gain set to max 500k.

The results were when the resistance was turned up from 0ohms to 100k the wave output linerally increased. The wave just looked stretched. It didn't matter if the clippers were 2 or 4 si diodes, LEDs, or JFETs. During the test I open circuited and shorted the clippers just to make sure I was not looking at the 100k resistor parallel to the pot or opamp clipping. BTW opamp clipping in this setup, with the clippers pulled, was a higher output, but still has rounded peaks.

Having fun, Nick