Query, re: Boss DF-2 and/or CD4046

[Mark Hammer]

Brian Duguay sent me a question that has both piqued my interest, but also left me unable to provide a clear answer.  Perhaps some of you can help.  To do this, you will need to have a Super Feedbacker Distortion schem and possibly the 4046 datasheet.

The DF-2 provides a simulated "feedback" sound by locking onto the fundamental of the input note the user is holding and providing a same pitch and octave-up tone using a 4046 as simple pitch tracker/oscillator.  This "feedback" lasts as long as the pedal treadle is held down, and the user can actually play on top of it.  A single op-amp oscillator provides some modulation of pitch at a fixed modulation rate and a fixed modulation depth.  Of course, it is a mono device in feedback mode so while the distortion works "normally", don't expect a feedback tone related to what you're playing unless you are holding a *single* note when holding down the treadle.

So here is the deal.  Brian sent me a sample that sounds wonderful, but appears to be a product of an intermittent of some sort that he'd like to be able to replicate.  After listening, so would I.  The basis of the effect would seem to be VERY wide sweep oscillations in the modulation of the feedback tone generator.  In other words, instead of providing very subtle pitch modulation to create the sense of finger vibrato, it makes the pedal behave as if the user is going a little nutz with a wide range bidirectional whammy bar when you hold the treadle down.

Can anyone suggest what components in the basic DF-2 circuit might be responsible for such an outcome?  In other words, what would make a 4046's oscillator be frequency modulated more?

[J. Luja]

well if the lfo was going slower than normal, the lp filters on the way to the 4046 would have less of an impact and you could end up with fairly large sweeps, or if the supply voltage to the 4046 was smaller than normal, the range the lfo covers would appear to be increased. neither seems all that likely though. recreating it should be easy enough, just change the mix ratio of the two vco control signals, or change the size of the lfo output.