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

[frequencycentral]

Some good ideas there for bass mods. However - I'm not planning to mod this for bass myself, I only play bass for recording demos, and usually keep it clean aside from a little compression. So if anyone wants to take the bass mod ideas and run with them - be my guest! I would agree re highpass and bandpass being difficult to use with bass though - so maybe for bass this design isnt worth the extra effort - no point making a multimode filter and only ever using lowpass!

On another tack:

I mentioned in my first post about a few tiny tweaks I'm considering. Having lived with the unit for a while, I'm planning to make the 10K resistor between the Release control and ground a little bigger. This resistor sets the minimum release time. As I have it now with the 10K resistor it's too short - there is a weird low frequency hum when Attack and Release are both at minimum, so I'll try going up in small increments (22K, 47K, 68K, 100K) until its perfect. Not really a major fix, and in practice at the moment I'm just keeping the Release control a few degrees off minimum.

[Mark Hammer]

It bears noting that the original circuit from which the filter section was extracted was an electronic cymbal.  So clearly it was not conceived as something intended to handle low end.

[frequencycentral]

It bears noting that the original circuit from which the filter section was extracted was an electronic cymbal.  So clearly it was not conceived as something intended to handle low end.

That said, this filter sounds incredibly close to my Oberheim SEM filter (which is 3080 and multimode), my old EDP Wasp filter (again 3080 and multimode), so maybe bandpass and highpass are operating out of the frequency range of bass guitar. Put a low freq sawtooth through this filter and is sings! I think the main issue with this filter and bass guitar has to do with the setup of the envelope follower rather than the filter itself.

[Boogdish]

I put the filter section of this pedal into my slackfilter the other day and I really like it.  Much less of a headache to get it to work right.  Once I get it tweaked to near perfect I'll be posting some sound samples and vero layouts (unless the winter monster of laziness gets to me).

[Radamus]

It bears noting that the original circuit from which the filter section was extracted was an electronic cymbal.  So clearly it was not conceived as something intended to handle low end.

Which circuit is that? I thought this came from the FSH-1 a lot? Or did I read that somewhere else?

Anyway, I know the multimode part is not really for bass, but I wonder sometimes why. I guess it makes sense that the bass frequencies can't be heard as well, but maybe it also adds up to the steps between the modes being too drastic.

Maybe I ask for too much. Anyway, awesome project, and I'll keep checking back.

[Mark Hammer]

It bears noting that the original circuit from which the filter section was extracted was an electronic cymbal.  So clearly it was not conceived as something intended to handle low end.

Which circuit is that? I thought this came from the FSH-1 a lot? Or did I read that somewhere else?

Anyway, I know the multimode part is not really for bass, but I wonder sometimes why. I guess it makes sense that the bass frequencies can't be heard as well, but maybe it also adds up to the steps between the modes being too drastic.

Maybe I ask for too much. Anyway, awesome project, and I'll keep checking back.

The very first post in this thread has the link, which you may have simply misread as an underlined phrase; "in this circuit" links you to http://experimentalistsanonymous.com/diy/Schematics/Full%20Synths%20Drum%20Synths%20and%20Misc%20Synth/Synbal.pdf

Multimode/state-variable filters (which this is) are most definitely for bass.  That's one of the many reasons why the Mu-Tron remained so popular with bassists for so many years.  What is not recommended for bass are the bandpass and highpass settings on state-variable filters, since one loses so much of the "meat" of the bass tone.  That's why the Q-Tron has a "Mix" setting in addition to BP/LP/HP.  The Mix combines bandpass and clean signal so that you get the character of a bandpass without losing the oomph.

[Radamus]

That's why the Q-Tron has a "Mix" setting in addition to BP/LP/HP.  The Mix combines bandpass and clean signal so that you get the character of a bandpass without losing the oomph.

My meatball also has that. I might have to check it out that way. Would that provide the "resonance filter" sound? I've been trying to figure that out for a while, because I know they exist, but I have no idea what they are. My old digital multi-effects had one and I know the same sound come up a lot in Les Claypool's solo/non-primus stuff. I bought some crappy 9v adaptors, so I'll have to do some soldering before I can test again. The gauge is the smallest I've ever seen. There's like two strands in there.

Anyway, thanks for the clarification. I've been looking for something with a little more consistency in the filter section as the meatball has a tendency to do some banshee sounds with color turned up too high. The randomness can be cool, but I'd rather have the consistency. The LED-less designs are more consistent, I'm assuming, or am I totally wrong on that?

[Boogdish]

I recorded a sample of my build that used this filter. 

http://www.aronnelson.com/DIYFiles/up/philter_hartman_demo.mp3

Excuse the slop playing and the little bit of hiss my sound card added to it.  First few samples are the pedal by itself, last few are with a Slacktave, Nyquist Aliaser and modded big muff respectively.   Like I stated earlier, mine has an LFO and an adjustable frequency pot since it's based on the slackfilter.  With the frequencies really low, the bias on the LM13600 gets sort of starved and things start sounding mucho weird.

[Radamus]

I hope you guys don't mind this, but I'd like to ask a few questions about how this thing works. From what I can tell, like in the meatball, this has one section that uses an opamp to convert volume into voltage. Then that voltage is put into one part of the lm13700. There seems to be two filter stages, which, I think I read somewhere, increases the "talky" sound of the wah. Where does the parametric filter come from? I will admit I have no idea how the lm13700 works, so maybe there's something there that I'm missing. Any explanation would be awesome.  Thanks.

[Mark Hammer]

Read up on state-variable filters.  This is simply another form of one.

[frequencycentral]

I hope you guys don't mind this, but I'd like to ask a few questions about how this thing works. From what I can tell, like in the meatball, this has one section that uses an opamp to convert volume into voltage. Then that voltage is put into one part of the lm13700. There seems to be two filter stages, which, I think I read somewhere, increases the "talky" sound of the wah. Where does the parametric filter come from? I will admit I have no idea how the lm13700 works, so maybe there's something there that I'm missing. Any explanation would be awesome.  Thanks.

Worth reading: "The Technology of Auto-Wahs / Envelope-Controlled Filters" at http://www.geofex.com/

.....and http://en.wikipedia.org/wiki/Voltage-controlled_filter

[captntasty]

Is a layout for this in the works?

[frequencycentral]

Is a layout for this in the works?

I built the prototype on perf - so I've no plans to do a layout sorry. Why not try one yourself using 'DIY Layout Creator' software - and then post it here!

[captntasty]

I'll give a shot...
edit: which opamps are which?  would the 324 be all the sections on the top and left of the schem and the 62 be on the right?  If you can't tell, I'm pretty new to layouts - I've only done a few very simple circuits...

[captntasty]

Definitely beyond my ability - sorry....

[frequencycentral]

I'll give a shot...
edit: which opamps are which?  would the 324 be all the sections on the top and left of the schem and the 62 be on the right?  If you can't tell, I'm pretty new to layouts - I've only done a few very simple circuits...

It really doesnt matter which opamps are which. I just used the 324 and the 062 because thats what I had available. You could use any opamps really - 3 duals if you wanted. I'm particularly fond of the 324 as a quad because the pinout is so easy to remember.

There is a fair amount of off-board wiring in this build - more than double the average fuzz or distortion. I'm not trying to put you off, but being swamped by too much off-board could be very frustrating - and tough to debug. Good luck, and help is always available here should you choose to go ahead.

Rick

[frequencycentral]

Definitely beyond my ability - sorry....

[Boogdish]

Here, this isn't a full layout for the Funky MF, but this is the layout of the board of the filter seciton that I used for my build.  Ignore the unused rows.

[orangetones]

I thought I would take up the challenge of creating a layout for this effect.  Would someone kindly double check this?  I am not sure I am going to build it, but thought since people were asking for a layout that I would create one.

Here it is:
http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=38445

If there are any corrections or errors please let me know.

Cheers,

Steve

[Radamus]

I hope you guys don't mind this, but I'd like to ask a few questions about how this thing works. From what I can tell, like in the meatball, this has one section that uses an opamp to convert volume into voltage. Then that voltage is put into one part of the lm13700. There seems to be two filter stages, which, I think I read somewhere, increases the "talky" sound of the wah. Where does the parametric filter come from? I will admit I have no idea how the lm13700 works, so maybe there's something there that I'm missing. Any explanation would be awesome.  Thanks.

Worth reading: "The Technology of Auto-Wahs / Envelope-Controlled Filters" at http://www.geofex.com/

.....and http://en.wikipedia.org/wiki/Voltage-controlled_filter

I think I've read both of those, so let me be a little more specific. How does this filter work without using LEDs? The one in the GEOFEX article uses LEDs and the Meatball that I built uses LEDs. The FSH-1 and this project don't, and I've been curious about the difference. Also, is this one more controlled in sound? I know the meatball, with certain settings, can have some strange sounds. Then again, that probably depends on the detector, not the filter. Anyway, thanks again, and I'll take another look at those articles.