Clipping diode frequency control?

[mills]

So, I had an OD250 based overdrive on my breadbord recently, with the goal of optimizing it for bass...  I found some great mods and suggestions from Mark Hammer in older threads to control the opamp frequency response, and tweaked them a bit to taste.  Definately more lows coming through.

Then, I had what I thought was a clever idea... and here's where my question is.  I thought that rather than cutting the highs after clipping, with a cap parallell to the diodes, what would happen if I had it in series with them.  What I thought should happen is  that the lows pass the lowpass filter, and the highs pass if they are under the 0.7V cutoff of the diode and above the corner frequency of the capacitor.

Is that close to right, or does the cap even change things?  After some more pondering (I'm still really trying to wrap my head around the absolute basics) I think that reality has to be more complicated, because of the progressive rolloff of the highs... so would the first few Hz above the lowpass cutoff be unclipped as the rolloff hasn't crossed the 0.7V threshold, and as more highs are directed to ground, this is limited to a 0.7V drop and just squares off the peaks of the highs that much? (and probably a harder squaring at higher frequencies?)... I guess I can make it almost make sense if the highs are clipped by 0.7V, or limited to 0.7V, and I'm not really sure which, if either, is accurate...

So, can anyone comment if I'm way off base and set me straight?  When I tried it out, it sounded like there was a bit more in the upper end than with a simple cap to ground, but that could've been a placebo since that's what I wanted to hear... Is this a redculous train of thought, and would I be better off with more carefully selected lowpass values, or a second order filter at a higher corner frequency?  (...from here on its even more speculative rambling than before, so if you read this far, thanks a bunch.  If you keep going, thanks again!)

Not long after trying this, I realized why the idea seemed so familiar and probably wasn't as clever as I'd thought...  I think that the cap before the diodes in a big muff do the same thing, but with feedback instead of to ground.  I don't think I've ever seen this mentioned in modding a muff for bass, but if I'm right, making the feedback cap smaller means the clipping is applied more to the high end and more lows and low mids are unaffected? 

I think I've got to try this with a muff, and maybe a cleaner, higher headroom opamp clipper setup...  it seems to me that if this works, it might be a simpler way to help with low end loss than a blend (which I'm not a huge fan of). And, I think that if this is  right, it lends itself to some interesting variations on the AMZ style "warp" controls... 
Between this, and rat style gain shape controls I think that it should be possible to minimize low end loss, stop flab from clipping the lows, and not need to deal with the extra hassle of a blend.  I've come to the conclusion that controlling low end at certain points in a design is essential to getting the overdrive or distortion sound you want, but I need to find a way to get them back into my final signal... and also to not just have "bass overdrive" mean the highs are rolled off until you just have a muffled, flabby blur of lows.

[Gus]

take a look at this.
http://www.aronnelson.com/gallery/main.php/v/gus/plus.GIF.html?g2_imageViewsIndex=1

[mills]

Hey Gus,  I actually can't see the picture.  I just get what looks like a ripped photo logo...

[Derringer]

the picture is there

it's just really big

try copying it and resizing it in MS paint or any other image manipulating program

[mills]

the picture is there

it's just really big

try copying it and resizing it in MS paint or any other image manipulating program

Thanks... I can't believe I didn't notice that.   

So, now I'm not sure exactly what's going on there.  That looks like a pre-gain highpass filter, but I'm not totally sure why  we've involved the 1/2V connection.  I'm a little weak on what altering that value does, and why specific values get chosen in opamp circuits, but I'm not entirely sure where to look to learn... any keywords to search, or places I might start reading to try to understand?  I've started looking at op amp biasing, but I'm not quite sure thats the right place to be looking as that seems to be talking about setting the 1/2 supply value, and not the resistor that joins 1/2V to the input.

Sorry for the basic questions... like I said, I'm pretty new to all this and have some huge holes in what I understand.

Thanks though, I appreciate the direction and something new to learn about.

[Gus]

The "new" thing is the tunable high pass before the distortion stage to remove just the right amount of bass.

[mills]

So, that provides an alternative to something like an input cap selector or blend... just changing the resistor rather than the cap in the highpass.  What throws me off, is why the 1/2 supply voltage connection?  Does that change the filter response, or opamp function?

[Gus]

The fixed resistor and pot wired as a variable resistor acts as the R part of the High Pass RC and provides a path to the opamp to bias it at 1/2 the supply voltage.

  You did ask the right questions.

[Caferacernoc]

Back to your original question. Yes a cap in series with diodes to ground will limit the bass clipping.