"Funky MF (Multimode Filter)" - LM13700 Multimode Envelope Filter

[fuzzo]

Yeah, you can use other stuff to modulate the filter then. Don.t forget a resistor between your modulator and pins 1/16.

this is the only change we have to do to put another enveloppe controller ?

I bump this old thread 'cause I'm thinking about building that kind of filter but I'd like to put a enveloppe detector with an Up/down switch (I think using the one in the old yellow boss (don't remember the name))

I've a question to people who built that circuit , Does the resonance control bring a volume boost ? (this is for an old box I drilled years ago and never found a circuit to put in (tired of fuzz/Od/boost) so I'm limited on knob holes)

[Stabby]

I would love to build this filter too, but for keys instead of guitar. What should be changed to optimize this filter for line level?

I would like to work with a pedal as well, so could I just leave out the entire opamp section? (except the LM13700 of course)

[frequencycentral]

I've used mine with my Rhodes (I know you're a Rhodes player) going directly in, the Rhodes is after all closer to guitar levels than keyboard levels. Now, Rhodes >> overdrive >> Funky MF is somethin' else ;¬) Just be warned, many have had issues with this circuit. I should probably revisit it and breadboard it again......maybe build another.

[Stabby]

Hey, you remember me!

I don't have a Rhodes myself. I wanted to build a pedal for my cousin who has one. I play on a Yamaha Motif myself though which is line level.

Here's a schematic of the Korg MS20 filter (which uses the LM13700) for line level:

http://www.synthforum.nl/forums/showthread.php?t=138512

There are some demos as well in the link. It's proven to work for everyone. It's just LP and HP though. Any idea what to change to make it a bandpass filter?

[frequencycentral]

Yeah, Rhodes players are rare around these parts!

How you go from lowpass to bandpass to highpass is all a matter of phase cancellation. Some multimode filters do it by where they put the input (ie Synthacon) others do it by where they take the output from (ie Oberheim SEM).

I'd certainly think the Escobedo LPF could be modified easily to do bandpass. Take a look at it's two seperate feedback loops - pin 4 > pin 8, pin 13 > pin 9, I'd hazard a guess that if you just had a single loop, pin 4 > pin 9 you could take a bandpass tap from pin 8.

BTW, the Funky MF filter does work well, the filter part anyway, any build issues seem to lie with the envelope section and the use of LM324. Like I said, the design is due an overhaul, I'm haunted by this thread - it reappears every so often I think to myself there's gotta be a redesign soon.

[frequencycentral]

I'd certainly think the Escobedo LPF could be modified easily to do bandpass. Take a look at it's two seperate feedback loops - pin 4 > pin 8, pin 13 > pin 9, I'd hazard a guess that if you just had a single loop, pin 4 > pin 9 you could take a bandpass tap from pin 8.

In fact, looking at the state variable filter on the LM13700 data sheet, disconnect the 220k resistor from pin 13 (on the Escobedo lowpass) and connect it to pin 4 instead. Pin 8 will then give you a bandpass output.

[Pakaloabob]

...Like I said, the design is due an overhaul, I'm haunted by this thread - it reappears every so often I think to myself there's gotta be a redesign soon.

Ha Ha! I have been watching this thread for quite a while, waiting for the project to move forward.  I haven't attempted it even on the breadboard yet because you yourself (Rick) said it was a "problematic circuit." That scared me 
And this post:

Anything new with version 2? Should I wait for it or build V1?

Wait.............................

Really got me intrigued...

[The_Armadillo]

Does anybody have a perf layout for this? I'm not really into etching, and I've never gotten a good result out of it.

[Caramthros]

Is there a working PCB that I could buy or has someone designed a stripboard layout that I could use.

Found this today and want to make an envelope filter for my bass but on the cheap. This seems suited for my price range

[Masuto]

Layout! Layout! Layout! Layout! Layout!

[Ben N]

Sentence, sentence, sentence!

[Joe Viau]

Has anyone built this?

[sshrugg]

Is there a way this pedal could be controlled with an expression pedal like a conventional wah?  I happen to have an enclosure from a broken pedal that includes expression...

I've always wanted to build this.

[StephenGiles]

Is there a working PCB that I could buy or has someone designed a stripboard layout that I could use.

Found this today and want to make an envelope filter for my bass but on the cheap. This seems suited for my price range

I have never needed a layout for any of my stripboard builds - you just practice!!

[sshrugg]

Sorry to pester, but...bump?

Is there a way this pedal could be controlled with an expression pedal like a conventional wah?  I happen to have an enclosure from a broken pedal that includes expression...

I've always wanted to build this.

[Mark Hammer]

Back from the dead.
This gives you an idea of just how many populated boards I have lying around that still need to be debugged and wired up.

The circuit works fine for me...sometimes...and soimetimes not.  It behaves very well and sounds terrific if I play a bunch of notes and don't give it a chance to come to rest.  But if I do, the thing produces a jarring thwap at the start of the next notes I play.  It ceases to be a filter that stands up, sits down, and stands up again.  Rather, it behaves like a guy sleeping under a pile of beer cans who suddenly jumps up.  The artifact is not dependent on Range or Resonance settings, but entirely on how long it has been since the last note plucked.

I can hear a bit of it in the ticks at the start of some notes in the soundclip Rick provides very early on in this thread, except its worse in my case.  For a moment I thought it may simply be a bad electro providing an unstable Vref, but I replaced it and that made no difference.

I'm stymied.

[avandelay]

I built this filter last night on breadboard and it works great.  I am building a groovebox with current controller oscillator and the filter sounds amazing.  I dont really know how the envelope section works, technically speaking, but I am hoping to be able to trigger the envelope with a clock signal.  Anyone have any ideas about that?  I don't have any gate control, so I have many tied notes which of course do not trigger the envelope.  Of course I can mute a step and the following note will trigger the envelope.  I could introduce some very cool rhythmic variation if I could use a clock signal.  Any help would be much appreciated!

[Mark Hammer]

I agree.  It sounds very good...when it sounds good.  If you listen to Rick's soundclip - http://www.aronnelson.com/DIYFiles/up/Funky_MF_Bass.mp3 - around the 10-second mark you'll here this godawful click/pop at the start of each note.  I wish I knew how to prevent it on my build, because it spoils an otherwise excellent filter.

[avandelay]

Mark, are you using the filter for guitar?  I am using it with a synth, and I can replicate the annoying pop within certain parameters which probably line up pretty well with the range and style of a guitar player.  I agree it is pretty bad in those spots.  Seems to have to do with the overlap of the attack and release...

[frequencycentral]

In hindsight, I think it may be down to the envelope sweeping the filter too widely, perhaps it needs limiting. I've built the filter part as a +/-12v module with no issues. Th  problem must be the envelope.

If I recall the envelope was a rail to rail LM324, the LM13700 certainly can't handle rail to rail signals. Perhaps swapping the LM324 for a TL084 would be a good place to start? I'll have to dig out that old pedal sometime and give it a whirl.