This is an easier build and is perfect for someone who wants the Klon tones without having to mess around buying charge pumps and curing squeals. This came from a thread on FSB where earthtonesaudio wrote the following:
But here's the thing. When the gain pot is at maximum, the only signal hitting U2A has already been clipped by the diodes, so a typical Ge diode will limit the signal going to U2A to under 1V p-p. For this signal U2A has a gain of about 8.3. Granted, this would clip a TL072 with a 9V single supply. BUT, if you used a rail-rail op-amp, then you'd get no clipping.
That would ensure no signal coming from the distortion stage could cause clipping in U2A, even if you used +9V and 0V as the rails.
From U2A the signal goes into the tone section, where the maximum treble boost gives a gain of about 8.2 to the highest frequencies. Again referring to the situation where the gain pot is at max, that means the signal coming from U2A into U2B is about 5V (.6V p-p signal times U2A's gain of 8.3), so U2B will try to make the highest frequencies into a 40V p-p signal. The power supply can't reproduce anything (even with a rail-rail op-amp) greater than 27V, so the op-amp clips.
Another useful scenario to analyze is when the gain is set to minimum. For high frequencies, the maximum gain from lug 1 of the lower half of the dual gang Gain pot to the output of U2B is 266. An average guitar signal (especially if boosted) can easily make a .1V p-p signal, which would cause op-amp U2B to clip if the gain was set to minimum, and the treble at maximum. Of course, before the signal gets to the that lug of the gain pot, it is attenuated by the input voltage divider as well as the network at the output of U1A.
Anyway, my point is that there is some op-amp clipping possible in the Klon at normal settings, even when using the charge pump. To me, the whole point of using a charge pump is to avoid op-amp clipping. But the Klon uses a charge pump and still clips the op-amps. So why not just ditch the charge pump and use op-amps that sound better when distorted (or will operate at their rails to minimize the amount of time they spend in clipping)?
For those people that would like to fit a Klon into a smaller package (though that is of course limited by the dual gang pot and other hardware), or those who just want to use fewer of the Earth's resources in their pedal building, I think it would be nice to have a Klon alternative which operates from a single supply, with no charge pump.
And mictester very kindly produced a schematic based on the discussion. Thankfully there's some very clever people on FSB to keep us busy!