Something Rich And Strange

[Joe Kramer]

O.K. now I hear what yer saying about phase shift.
man, that filter is phat! I was hanging out as her band was practicing, the whole shed was vibrating, I mean you could hear the rustling of the tin roof!
I'm gonna try yer suggestions of the buffer and the lower F.B. resisters. not sure about clipping diodes, got another problem, a wierd fuzzed out "ghost note" mixed in the background, not relly noticable with a full band, but it's there!
Any Ideas?
-matthias

Hey Matthias!

To get the max effect from that psuedo phase sound, your settings should be: high and low bands all the way up, mid band all the way down, and no resonance at all--that makes the notch as deep as possible.  As you add resonance, the notch gets filled in, so to speak.  Make sure you've got the option for zero resonance and you're cool!

Ghost notes, hmm.  This could be unintentional feedback within the circuit due to the way it's wired or laid-out.  Make sure you don't have inputs and outputs crossing over each other or too close together.  If you're running louder signals (like a full band), you may need to put some big electrolytics (100uF) near the chip power supply pins for extra juice on transients.   Maybe even up the power supply to 15 or 18 volts.  That would be one downside of doing a single-supply version of that circuit--less headroom.  Hope maybe this helps.

I still have to do some more experimenting with how to use clipping diodes in that situation.  I know that some synth filters use this technique, but it's a matter of finding where you want the clipping threshold, otherwise you'll just have out-and-out fuzz all the time.  You could always try a pair of 1N914s in series with a trimpot in the feedback loop of the first op amp.  Adjust the pot so that the diodes kick-in only when the feedback threatens to smoke your tweeters.   That might work. . . .

Joe