[sdiy] Continuously variable waveshaping (was Behringer Neutron)

[David G Dixon]

My wavefolder (as found in the Intellijel uFold) uses TL072, and doesn't
generate "high-frequency hash".  Also, I've achieved what looks a lot like a
resonant filter output with a sawtooth wave, without a filter.  Given the
way that this folder works (with diode "turnaround" circuits) I'm not sure
that slew rate is a significant factor.  The opamp outputs in the folder
chain are confined to relatively small voltages -- the first one to about 3V
or less, and the subsequent ones much less.  Other folders may have
significantly different modes of operation where slew rate is important, but
not the ones based on diode turnarounds.

> It's probably best *because* it's slowest. There are plenty 
> of examples in the stompbox world where people prefer the 
> rubbish old slow op-amps over more modern "hi fi" options 
> because the limited slew rate reduces the "edginess" of the 
> high frequencies. Effectively, you're adding a bit of roll-off.
> 
> For a wave folder, that might be true too - you want the wave 
> folded, but lots of sharp spikes is just making high 
> frequency hash, as you say. A little bit of rounding of some 
> of those points might reduce the hash and still leave the 
> interesting harmonic evolution in place.
> 
> Tom