CMOS Rail to Rail Op Amps

[gez]

Thanks for the report.  Probably a silly question, but looking at all those ?MOSFETS? in the lay outs, would those all be clipping at once when driven hard?  Like in a Rat or Dist+?  Like a multi-stage distortion???

As in any multi stage amp, when the output is clipping it's entirely possible that previous stages are also clipping.

[stm]

Well, took some time off from soldering and quickly breadboarded a circuit.

Set up the first stage of an ICL7621 for variable gain and the second stage as a non-inverting buffer.  Had the load set up to switch between either output.

1. No soft clipping (dives straight in) Edit: tested with a scope by the way.

2. There is asymmetry, but not how I imagined it would be.  The output ends up being half-wave rectified: positive output cycles only, so both Paul and HC were right about the p-channel being able to source more current.  Had I made the load lighter so that -ve cycles weren't loaded to the point that they were obliterated, I doubt clipping would have been soft, and even if it were the current sourcing/sinking mismatch would mean that +ve output cycles are always going to hard clip when reaching the +ve rail.

3.  Sounds bad.  There's a slight octave effect around the 12th fret, as you'd expect, other than that it sounds like a woolly Ge diode clipper...probably slightly softer than a normal opamp driven into clipping but that's about it.

Perhaps other chips might be more successful at doing this?  Nice idea, shame it didn't pan out.

About two weeks ago made a Distortion+ clone (based on the Liquid Drive), and tried the following opamps: TLC2262, TLC2272 (higher slew rate), JRC4558D (the one with the mojo), TL072 and LF353.  Differences were subtle but noticeable.  I couldn't tell for sure which one I liked best, except for the fact that the TLC2262 was slightly "softer" than the others. Nothing that would make a real difference if you are playing along with a full band, IMHO.  I finally set with the TLC2262, perhaps because of the slightly softness and the previous knowledge that it is used in NY Tech effects especially for this purpose.  At the time I did the experiments I didn't try to load the output as I suggested, cause that Idea came to my mind after reading this post. Now the D+ is gone since I'm using the protoboard for other things--the D+ sounded reasonably good, but not enough to make me box it.

[gez]

I think there's some mileage in your idea Sebastian, just not as a soft clipper/logic inverter sound alike.  As I mentioned, the sound was somewhat akin to a Ge diode clipper - not necessarily a bad thing, so I was being harsh when I said it sounded poor - with a definite octave effect heard around the 12th fret (which you'd expect from a half-wave rectifier).  I didn't have much time to mess with this circuit, but perhaps a subtle octave fuzz could be had from the basic idea?  Edit: A twin-T used as a tone stack does wonders for this type of distortion sound.  With a dual amp the second stage could be set as the filter but with low input impedance to do the loading.  AC coupled with a NP cap, it could sound good.