Started by Joe, August 20, 2006, 10:24:07 PM

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Circuit seems to work pretty well in place of a diodes-to-ground clipper:

Have Fun!


I like the fact that the symmetry of the clipping can be adjusted. This way I will finally know, if I prefer symmetrical to assymmetrical. :) Thanks!


quite intersting indeed.
I've gathered so many bits and pieces of circuits from all over the net, maybe it's time to stick some of them together and
see just what happens huh?  :-\

Marcos - Munky

Very cool!!! Need to give a try in a few circuits.


  Interesting fragment Joe !!
  I don't recall having seen this before.
  how does it work..soft clipping..I understand.
  It looks like the diodes are biased between the rails, interesting and a curiosity for me...
  When adjusting the R Values, is balancing the values on either side, [toward supply +/- from the signal path] needed to maintain bias?
  I'm used to looking at diodes from SP to ground or in an OA FB loop, It looks as though threshold is met 'from the other side' ie..they're biased near center between +/- [near opamp input/output idle bias], and using that as a reference point from which threshold is 'measured from' [instead of from ground or V+].
  I'm not sure I understand, but I'm sure I don't understand how this induces softer clipping than a SP To Gnd. type configuration...
  Very interesing and curious to me indeed. 
Convention creates following, following creates convention.


Once again, you the man.   :icon_cool:
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Peter Snowberg

I've used that exact circuit on the breadboard after finding it in a 1970s circuit for a CB radio speech processor.  :icon_biggrin: It was labeled AGC on the schematic IIRC.

Here's a version by Masaru Kuboda that I saved a few years ago (2002?) which keeps the diodes closer to ground, but runs the same amount of DC through them.

I'm really surprised it hasn't found its way into more fuzz effects, but it surprises me even more that I hadn't seen the single ended version of this circuit anywhere until the Vulcan. :icon_cool:

Pete, re-read all the vulcan stuff, but picture it being symmetrical. ;)
Eschew paradigm obfuscation


Something similar looking or same circuit topology in National Semiconductor Audio Handbook "cookbook circuit" simple and cheap tremolo circuit (DC control as mentioned before)... I must see if I can find the circuit


Joe, thanks for interesting circuit (as many times before) and sorry for hijacking this thread.

I took messy photos from old book which shows crude and simple tremolo. Circuit looks familiar but resistor values are *very* different, so I think Joe has done some optimising for good distortion sound and his circuit might work slightly different wise...


I'm going to hijack this thread even further and ask if someone could elucidate how this diode arrangement could be used in lieu of an LDR. That scanned document says that it would have a high THD, but that shouldn't be a problem for an LFO modulating some parameter of an effect right? I'm mainly thinking of modulating the delay time in a Rebote...

-- T. G. --
"A man works hard all week to keep his pants off all weekend." - Captain Eugene Harold "Armor Abs" Krabs


Well, I'll set it back on course.  How about driving this with 2 Vulcan stages?   :icon_cool:
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And I thought it was new...  :icon_mrgreen:

Interestingly, the diodes may be flipped around, with 2 top resistors and 1 bottom resistor in the center. Seems to work similarly. This would couple better to a transistor, and according to Spice the waveform looks a little smoother this way.

Edit: nevermind that last point, sounded raspy in real life.


Fired it up last night with a Dist+250YJM distortion and it sounded pretty smooth, even though the op amp was probably contributing a lot of clipping.  I used 1M resistors cause that is all I could find 3 of.  Seems to have low clipping threshold, as Joe said, (around 2 GE diodes worth) but that works fine into a SS amp.  Still plenty of level left.  I've been using Mosfet clippers so I have gotten used to that smooth distortion sound.  Now a dual op amp combo of the 2 methods.

I tried GE's, but don't think I ever got the polarity on both right.

Another cool deal.   :icon_cool:
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Last night I tried varying the bottom resistor values for asymmetry.  I added resistance to the 1M I was using and anything over 47K got louder and gatey and didn't seem to work (unless you like that kind of thing).  So 10K to 22K (in addition to the 1M) seemed to work out well, giving it a little fatter/thicker tone (I need to try a 50K trim pot there).   :icon_cool:
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For you guys looking for something different for your Dist+, DOD250, Boss DS-1, Rat, etc.  This is a nice sounding alternative.   :icon_cool:
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