4th order delay as an alternative to equal-staged phasers!

[Boofhead]

Does anyone else notice the similarity of the feedback networks to a bridged-T filter network?

That's actually where those circuits come from - it's all thought about on a topological level.  A good deal of filters are derived from:  Ladder Networks, Bridge-T's or Twin-T's, or manipulations of them.   If you apply an R <-> C swap you get double the number of circuits (that's called a Dual ckt).

If you look at the Sallen-Key Lowpass filter it's actually a ladder network with the ground and input terminal juggled about and then stuck in a feedback network.  The key to seeing  the underlying network is note that grounds and inputs can be interchanged - the reason is this doesn't affect the poles of the network (it does affect the zero's).  The common Delyannis-Friend single opamp band-pass circuit is actually a bridge-T circuit in a feedback loop.  The inverting low-pass on the other hand (like the one in the Boss BF-2 Flanger) is based on a bridge-T except the "normally grounded" capacitor is "loaded" by a parallel resistor - I call this structure an "internally loaded bridge T".  There's whole unified theories of the universe on this stuff in IEEE journals - spanning about 30 years.   There's even unified theories about the sensitivity to components.  Some years back I spent about two months deriving and analysing filter circuits at topological level like this - most of the circuits I came up with were already in the literature.

[puretube]

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[StephenGiles]

Boofhead said:

For the unwary: some high order circuits, like the one shown, can be very noisy (even though they use less opamps). Look at the output stage. It has a gain of 8 or so. Roughly speaking that means the noise of the three opamps is multiplied by about 8 from the start. The noise of the first order circuits isn't too bad.

So, may I be permitted to observe, are most fuzz boxes!!!!!!!!!!!!!
Stephen

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[StephenGiles]

Round one Ton.......typical wife eh!!!! Both our birthdays and wedding anniversary fall within 4 days in August - so 3 separate celibrations...
Stephen. Re the Eventide, I'm still having problems with grey background on digital pics of circuits, which I largely get rid of with Paint Shop Pro, but it's a pain. I am taking professional advice here.
Stephen

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[Mark Hammer]

When I turned 50 a couple years ago, I posted my thoughts and remarked that when you're young, you can't see how beautiful older women are.  You only get hot for the young ones of certain dimensions and appearance.  As you get older, the young ones still look pretty, but you begin to notice how beautiful the ones your own age are too, and some of the ones older than yourself (I had the good fortune to see author Anais Nin when she was in her 70's, and came to give a talk.  Talk about a dollface!!).  Any world and life that gets more full of beautiful women with each passing day can't be that bad, eh? :wink:  

[puretube]

I remember that post...

[lovekraft0]

Mark, I definitely have to concur with you - little girls will always be pretty, but it takes experience to appreciate the things that make a grown woman beautiful!
Puretube, you're a lucky man - she's a doll! Many happy returns!

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[StephenGiles]

Ton - Christ, you're up early again, I only get up at that time to catch a plane! Did they manage to squash that march by neo nazis yesterday?
Stephen

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