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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Simple active filters?
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Silesius



Joined: Feb 12, 2010
Posts: 61
Location: Berlin

PostPosted: Wed Sep 15, 2010 7:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

Top Top: thanks a lot for the information. I've been trying your suggestions and I found that playing with the cap near the resonance pot (and with the one an the front of the filter) tune the filter and gives you more resonance. Now it's time to solder three or four with different values.

Also, I've been trying to make this one work (it sounds amazing!), but it has been difficult for me to follow the indications DGTom made.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

I've never studied electronics, and I'm beginning to understand an schematic, so I've tried this:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

ehemm... sorry for the watermark as well Rolling Eyes It's the first time I use an editor...

I know I'm missing a lot, but that's the best I can do for the moment. With this scheme, the filter filters in some way, but it's very far from being usable. I would be very happy if somebody (specially DGTom, of course Wink ) explains what is needed to work as it should; of course an schematic would be great. It would be very helpful for people like me, who only have skills to make simple filters. Thanks in advance!
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Psyingo



Joined: Jun 11, 2009
Posts: 247
Location: Canada

PostPosted: Wed Sep 15, 2010 7:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

i believe its r6 and r7 that are cutoff, not r5 and r6.
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Silesius



Joined: Feb 12, 2010
Posts: 61
Location: Berlin

PostPosted: Wed Sep 15, 2010 7:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Psyngo! I must try that. I didn't check the posts when I tried to breadboard the filter and I thought r5 and r6 were the ones.

But I thought I was missing more than that. Will it work just changing r5-r6 for r6-r7 (with a dual ganged 10k pot)? Just with that? It would be great!
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Top Top



Joined: Feb 02, 2010
Posts: 198
Location: California

PostPosted: Wed Sep 15, 2010 7:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Silesius wrote:
Thanks Psyngo! I must try that. I didn't check the posts when I tried to breadboard the filter and I thought r5 and r6 were the ones.

But I thought I was missing more than that. Will it work just changing r5-r6 for r6-r7 (with a dual ganged 10k pot)? Just with that? It would be great!


Looking it over, and from what I understood of the instructions, it looks correct to me (other than the alterations to the cuttoff pots).

I haven't tried it myself yet though, so that is just going from what I understood of the other posts. Its on my list of things to try.

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Silesius



Joined: Feb 12, 2010
Posts: 61
Location: Berlin

PostPosted: Wed Sep 15, 2010 8:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Top Top. I'm at work now, but I will try it when I arrive home, and post the results.
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DGTom



Joined: Dec 08, 2008
Posts: 210
Location: Adelaide
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PostPosted: Wed Sep 15, 2010 11:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry guys! Embarassed

Must have been looking at it cross-eyed. It is indeed R6 & R7 which you want as a dual gang, or rather in seris with a dual gang because having 0 Ohms there might not be all that great for the gates.

R4 & R5 are the main feedback resistors, I don't have an "R1" as such, I'm using 100K -> -| 220nF |- -> pin#1 of the 4069

@Silesius - if you use a pot as a variable resistor for R3 ( kind of the way you have drawn it, except you'd use the middle & one or other of the outer lugs of the pot) you will need to add a fixed resistor, so that feedback loop doesn't go all the way down to 0 Ohms.

The way I've done it is tap the BP output put that into one side of the pot, the other side goes to ground & the middle is connected to R3
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Silesius



Joined: Feb 12, 2010
Posts: 61
Location: Berlin

PostPosted: Fri Sep 17, 2010 12:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've been working a little on the filter, and this is what I've got so far:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

This works, and sounds quite well. But I wouldn't say it has high pass, band pass, and low pass. The three outputs sound different, but not exactly as it should. For me it's not a big problem, but it would be nice to have a proper response. I would say the three sound more or less lowpass.

I've noticed the input level determines the sound of the filter a lot (and the resonance). In fact, I'm not using the resonance pot in R3 anymore. I've placed a 10k pot at the input which behaves more or less like a resonance control.

The other thing I've discovered is the oscillation. With a 33k resistor in R3, the filter oscillates and it's perfectly controlled by the freq pot (with no input). So, if I'm not wrong, we have here a lunetta sine oscillator (I don't have an oscilloscope, but it should be a sine, right?). I use a switch to select between oscillator and filter (the filter works better without R3). 33k for R3 is ok for audio level.

What I want to do now is make an LFO, and have the possibility of choosing between filter, audio oscillator and LFO (I love sines for modulation Wink ). But I'm having problems with that. The smaller R3 is, slower is the oscillation. But this has a limit. I've used a 10k trimmer in R3 and the sound stops somewhere when you adjust it; you began to hear the pulses, but it's not slow enough to use it as LFO, and if you try to make the resistance smaller, the sound stops. I'm stuck here. Any ideas will be very appreciated.

The last thing will be make it voltage controlled. It would be great to have a vcf, vco, and vclfo in the same chip (and you still have half chip!). I'm not sure if I will use a double homemade vactrol (I don't know if two vactrols will work fine), or the Ray Wilson trick with a transistor. We'll see.
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Psyingo



Joined: Jun 11, 2009
Posts: 247
Location: Canada

PostPosted: Fri Sep 17, 2010 12:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Silesius wrote:


What I want to do now is make an LFO, and have the possibility of choosing between filter, audio oscillator and LFO (I love sines for modulation Wink ). But I'm having problems with that. The smaller R3 is, slower is the oscillation. But this has a limit. I've used a 10k trimmer in R3 and the sound stops somewhere when you adjust it; you began to hear the pulses, but it's not slow enough to use it as LFO, and if you try to make the resistance smaller, the sound stops. I'm stuck here. Any ideas will be very appreciated.

The last thing will be make it voltage controlled. It would be great to have a vcf, vco, and vclfo in the same chip (and you still have half chip!). I'm not sure if I will use a double homemade vactrol (I don't know if two vactrols will work fine), or the Ray Wilson trick with a transistor. We'll see.


if you want an lfo, you will probably have to use a rotary switch with two poles to switch out differnt caps in pairs. the lower the cap, the lower the frequency should be. this would also mean that with low frequency you could use it as a voltage controlled portamento as well.

i would personally suggest vactrols because i love the way they sound. they will certainly work.keep in mind they are rather slow. you can get faster commercial ones but those arent nearly as cheap or fun as building your own.
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DGTom



Joined: Dec 08, 2008
Posts: 210
Location: Adelaide
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PostPosted: Fri Sep 17, 2010 6:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

my crappy mac scope says it is a pretty nice sine, of course the waveshape changes quite alot over the freq. range, but hey - its CMOS & its "sineish" I'm quite happy with that as well, it sounds a damn sight more sine than heavily filtered squarewaves Very Happy

an input attenuator is a good idea as well, but, I really would use a pot for resonance, there are a number of interesting sounds to be had right at the edge of oscillation you will miss out on by having an on/off switch. For instance, you can "ring" the filter by feeding it a sharp transient - great for percussion sounds etc. Like the ones at the start of this;

http://dl.dropbox.com/u/252415/HVK_PLSR_EG_LPF_1.mp3

Again, I'd put something like 20K from (as you have it drawn) pin 1-1 of the pot to pin 3 of the 4069 & pin 2-1 to pin 5; this will also drop your freq range.

The other important thing is HF oscillation suppression. Put a very small 47-68pF ceramic, in parallel with R2. I found this helped alot with the frequency pot all the way up & I think 10K is too small a value for the main resistors, I found the overall sound much improved with larger resistors & smaller caps - especilly for use as an oscillator.

Attached is a quick snip of the 3 differant outputs on mine; lowpass, highpass & bandpass - in that order. Its not as clean / precise as a linear SVF but the 3 do sound as they should. Be carefull not to overdrive the input too much as that may effect the responses.

I'm using Silonex NSL-26 vactrols.


4069_SVF.mp3
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corex



Joined: Mar 02, 2010
Posts: 107
Location: Las Vegas

PostPosted: Sat Sep 18, 2010 11:43 am    Post subject: Reply with quote  Mark this post and the followings unread

I live in Saudi right now, and Ramadan has ended and the holiday following it, too, so this weekend (being Thursday & Friday), local electronics shops were open and back to regular hours. I picked up a few parts and I built the WSG filter and this three-inverter Havok filter of DGTom's. I also picked up a bunch of different CMOS chips I didn't have before.

Here's my new build (huge breadboard pic so I'll link it rather than embed)
http://phlake.org/lunetta/IMG_0036%20-%20breadboard%20-%2040106,%204093,%204070,%20filters.JPG

The idea here is that I run two 40106-based oscillators into a 4070 XOR. The XOR goes to a 4093 oscillator. Then I run that output to one filter or the other (suddenly I realized I haven't run them serially -- i should try that), then to a passive attenuator and then out.

Here's a sample:
http://phlake.org/lunetta/STE-097%20-%20WSG%20filter%20and%20havok.mp3

First is the raw signal, then the WSG filter at 00:07. I sweep the cutoff from high to low, then I turn the resonance up all the way and sweep the cutoff back up. It sounds interesting, but doesn't cut off the highs as much as it could. Also it sounds a bit high-passed.

At 00:56, I switch to the Havok filter. I built mine a little differently -- for one thing, I eliminated R3 completely (that feedback loop is actually disconnected. It can get good and squealie with it but I was trying to get a cleaner signal out) -- and I also only put a pot in for R7. I don't have any dual-gang pots handy, but that one seems to do something noticeable. All that I do in this part of the clip is sweep the cutoff with R7. Sound very resonant even with R3 effectively set to infinite resistance (edit: I just realized this is coming from R2). It's interesting and it sound like maybe it cuts steeper than the WSG filter (which I guess makes sense with three gates as opposed to the single op-amp).

Neither filter does a very good job at being transparent (by that I mean if you turn the cutoff up and resonance down, you would ideally get the original signal), but I guess that's easy to handle with modular routing. They both definitely sound like filters, and a bit different than each other so that's neat. Also with the resonance circuit, the Havok filter can sound even more squealie.

Also I made this longer without any filters... this is just the two 40106 oscs into the XOR and then to the 4093 osc. The XOR can make some interesting (and sometimes very harsh) timbres.
http://phlake.org/lunetta/STE-098%20-%2040106%20into%204070%20into%204093.mp3
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textual



Joined: Dec 05, 2009
Posts: 78
Location: New York City
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PostPosted: Wed Oct 13, 2010 11:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Psyingo wrote:
i posted these on the other lunetta forum, the sounds of logic; ill repost here as its relevant to the topic.
its probably the easiest multimode vcf's i have seen. it is called a sallenkey. i n the schematics i have used vactrols for the voltage control.

the first one is a sallenkey filter transcribed from this article: http://experimentalistsanonymous.com/diy/Schematics/Filters%20Wahs%20and%20VCFs/Sallen%20Key%202P%20Filters.pdf
the second is one with some modifcations, including an output stage with a gain control.


Original
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Modified
Posted Image, might have been reduced in size. Click Image to view fullscreen.[/url]


Hey Psyingo, is the cv input resistor 220K? or what?

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-minus-



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PostPosted: Wed Oct 13, 2010 10:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'd think that the 220 resistor was 220 Ohm....
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Rabiat



Joined: Jan 23, 2010
Posts: 7
Location: Sweden

PostPosted: Tue Oct 19, 2010 4:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

What would be the best way to wire up Silesius last design on a breadboard?

I'm sitting with a headache and a layout program and end up with
spiderwebs. I think i need to find a better primer about converting
schematics to circuits and how to simplify connections :/

edit:

Ok, went alot better the second try, does this look somewhat ok/functional? (using 2 Freqpots
instead of one double, also skipped the sine oscillator)
Posted Image, might have been reduced in size. Click Image to view fullscreen.

If so then i just need to rearrange it a bit more compact and go full throttle Smile
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Pehr



Joined: Aug 14, 2005
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PostPosted: Wed Oct 27, 2010 6:24 am    Post subject: Reply with quote  Mark this post and the followings unread

Here's a 5-9V discrete filter from the leploop-synthesizer:

Posted Image, might have been reduced in size. Click Image to view fullscreen.
http://4.bp.blogspot.com/_bJQpr-7ZtW0/SnFv4NQsrsI/AAAAAAAAACk/iFxrg3uLEHA/s1600-h/12db_l.e.p_filter.jpg
Posted Image, might have been reduced in size. Click Image to view fullscreen.

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rich decibels



Joined: Apr 01, 2010
Posts: 59
Location: Wellington, NZ
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PostPosted: Mon Nov 01, 2010 3:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

that 4069 filter has an excellent radness to easiness ratio! while I was tinkering with it I found some really cool sounds by touching various circuit points with my fingers. at different settings I got heart beats, clinking glass bottles, bouncing basketballs, motorboats... I wonder if anyone has suggestions for how to make these sorts of percussive noises a bit more reliably? is there a particularly good circuit to feed the 4069 with? or more broadly, do any of you have percussive circuits of any kind?
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-minus-



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PostPosted: Mon Nov 01, 2010 4:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

rich decibels wrote:
while I was tinkering with it I found some really cool sounds by touching various circuit points with my fingers. at different settings I got heart beats, clinking glass bottles, bouncing basketballs, motorboats... I wonder if anyone has suggestions for how to make these sorts of percussive noises a bit more reliably?



LSD 25? Laughing

Seriously though... I've been looking at these circuits quite a bit lately. I'm going to work my way through them on the breadboard. I'll post findings here soon....

Post some sounds! I wanna hear the heart boats, clinking basketballs, bouncing glass bottles, and motorbeats! Laughing
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PostPosted: Tue Nov 02, 2010 12:39 am    Post subject: Reply with quote  Mark this post and the followings unread

yeah... just tried this 4069 filter on breadboard and although I'm noticing three different sounds to the filtering, I'm certainly not getting those wild sounds DGTom has posted.

I need more time to play around with this. It must have something to do with the resistor values. Perhaps they need increasing? Part of the problem (aside from lack of sleep Laughing ) is deciphering the posts so far. I'm not sure what resistors are being referred to when R1 etc are changed from the original schematic scratch

Perhaps someone who has something working can post a confirmed schematic with correct resistor and cap values... until then, I might have to put this on the already crowded back burner! Laughing
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rich decibels



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PostPosted: Tue Nov 02, 2010 4:53 am    Post subject: Reply with quote  Mark this post and the followings unread

I have temporarily removed my PC from my workshop for the sake of productivity so no recordings at the moment sorry. recordings to come though.

I use 100kB pot for resonance, 8k2 resistors from the pot to pin 1 and pin 1 to pin 2, 47k from pin 1 to pin 6, 68n caps, and 10k log pot for the cutoff. I only bother with the LP output, HP seems kinda pointless with square waves.

next thing to try is to merge this filter with the sea moss tone sequencer concept (http://www.milkcrate.com.au/_other/sea-moss/#amp), with 8 dual pots making a sequenced filter. I hope that will result in percussive sounds at high speeds.
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PostPosted: Tue Nov 02, 2010 1:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info Mr Decibels! I'll have another go at this soon....

I have just breadboarded the top top filter from the previous page. This is the first one he posted. I have replaced the res pots with 1m resistors. Getting some OK results from this. It does seem however that all the action is at the full turn of the pot cycle... and some noticeable stuff at the zero end of the pot. Not a lot happens in between. Still, I'm beginning to understand filters a little more than I once did Laughing !

I'm just about to breadboard the MFOS WSG filter. The OLD version with the single pot. The one Uncle Krunkus turned into a stripboard 5 years ago! I guess I've been spoilt by that sound. I'm not one for subtlety! Rolling Eyes
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textual



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PostPosted: Tue Nov 09, 2010 7:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, so i breadboarded and finally built 4 of the sallen key 'original' recipe that Psyingo posted, using home made vactrols. Sounds pretty awesome when being CVd with a triangle LFO. Decent variance in the resonance sweep as well as variance in BP, LP, HP outs. I am just sending it standard 40106 oscillators with fine tuners as signal. I did have to up the cv input resistor to 510 ohms to fire the vactrols, 220 wasn't happening. I plan to make 4 more soon, but will likely test all the vactrols by hand since some of the LDRs i have may be a bit wonk. grab bag style..
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Monotremata



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PostPosted: Fri Nov 19, 2010 7:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Some questions on that same Sallen-Key vcf that Psyingo posted..

1. Whats powering the circuit? My plan is to throw it into a 1590 enclosure and run it off a 9v.. Will this work??

2. It doesnt appear to have a cutoff pot?? Im assuming the CV/vactrol section is controlling the cutoff? If I really have no need for the CV section anyways, would I just remove it, and connect those two LDR spots to a dual-ganged pot like shown in the 4069 based layouts also in the thread?

Ill have to order some TL082s before I can breadboard it and try it out but might have a TL072 or something laying around I can try it out this weekend with.. I can swap in a single op-amp if I drop the gain stage at the end right?
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textual



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PostPosted: Sat Nov 20, 2010 7:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Monotremata wrote:
Some questions on that same Sallen-Key vcf that Psyingo posted..

1. Whats powering the circuit? My plan is to throw it into a 1590 enclosure and run it off a 9v.. Will this work??


2. It doesnt appear to have a cutoff pot?? Im assuming the CV/vactrol section is controlling the cutoff? If I really have no need for the CV section anyways, would I just remove it, and connect those two LDR spots to a dual-ganged pot like shown in the 4069 based layouts also in the thread?


Ill have to order some TL082s before I can breadboard it and try it out but might have a TL072 or something laying around I can try it out this weekend with.. I can swap in a single op-amp if I drop the gain stage at the end right?


I am runnig mine of 9V, works fine.
The CV / vactrol is controlling cut off. I don't see why you can't connect it to dual gang pot and be fine.
I am also only using 1 stage of an op-amp. I built 4 of these (now Cool filters with 1 quad op-amp.

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Monotremata



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PostPosted: Sun Nov 21, 2010 5:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

That is awesome news to hear hehe..
One of my musical 'heroes' asked me if I could build him up a HP filter but Ive only ever really worked with stuff like fuzzs and distortions so this filter business is new to me (not to mention the schemes for most of this stuff is wired up to be used inside a modular)..

I may have to try a quad op-amp just to give him some extra options to play with now! Very Happy
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acidblue



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PostPosted: Fri Feb 04, 2011 9:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey silly question.
If I leave off the low pass filter on the Hill-Tree filter
do I still need a dual gang pot?

Seems to me I could just use a regular pot.
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rich decibels



Joined: Apr 01, 2010
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PostPosted: Fri Feb 04, 2011 11:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Instinct says you will. The two halves of the pot work together, they're not separated into high-pass and low-pass.

I think Smile
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