Design problem: Deliberate crossover distortion

Discussion in 'The Projects Forum' started by daviddeakin, May 30, 2010.

  1. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
    I am designing a guitar pedal to do pitch shifting, and I have most of it built and working reasonably well, but there one final point which could make it really great.

    The audio signal is used to trigger a comparator, but the problem I have is that low-level harmonics cause spurious triggering that spoil the rest of the circuit's operation.

    What I'd really like is a circuit that would totally ignore signals in the crossover region, in the range of about 4.45 to 4.55V, or perhaps a little narrower (the circuit operates from +9V, not bipolar). Hopefully this would cut out the annoying harmonics, at least 90% of the time.
    I have attached a picture to show what I mean better. I don't much care what happens in the x-over region; it could either switch directly between the two levels, or decay gradually as shown by the dots, whatever.

    Obviously a pair of anti-parallel diodes could normally do this job, but the signal levels are too small in this case (very limited headroom). I've also tried SIMing a complementary pair of transistors biased just below cutoff, but it just doesn't seem accurate enough.

    Any suggestions?
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    Window comparator to select only the voltage area in which you are interested in.

    During the high and low areas (4.45 and 4.55) you can route the signal to filter, cut-out or just about anything.
  3. daviddeakin

    Thread Starter Active Member

    Aug 6, 2009
    Now why didn't I think of that? :D