SUPER SIMPLE 12db RESONANT LOWPASS FILTER-with AUDIOSAMPLES!

[tokyomatik]

recently im abusing of this incredible filter designed by a friend of mine
is really interesting for his interaction between resonance and frequency
and the sound has his own character
can run on different voltages from 9v to 12v,
at 12v can really scream!!!
no cv controll but in combination with the sn voice module could fit without problems behind the same panel for example

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[tokyomatik]

here also the pcb layout
ready for press n peel

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[tokyomatik]

parts placement

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[kaputtpanzer]

Ahh yes, I saw this thing a few times here. Looks very simple and interesting. I am curious how it sounds. Can someone please post an audio sample? Thanx

[vladosh]

As this is so small parts count it'd be great to make 3 or 4 and wire them in parallel .. if i only knew how to change the range ,so one can act like bpf .. it's great for that purpose i think ,some samples would be great

[tokyomatik]

i also was thinking about some possible mods
but im a complete beginner, so i dont know if what im thinking could really work or not
for exmple trying to split the 100k stereo log pot of the frequency with 2 mono
maybe also different values..... ???
and another idea was to add some kind of slew with a vactrol somewhere in the path, like scott stites did with Ray Wilson's filter.....

somebody waana try??
in the while i'll make some samples
to give an idea of the character of this filter

[tokyomatik]

here some samples of a squarewave(sn voice) with different settings of resonance

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squarewave-filter seep-no r.mp3
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squarewave-filter seep-25% .mp3
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squarewave-filter seep-50% .mp3
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squarewave-filter seep-100%.mp3
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[Dego]

Easy to build. Might try it on veroboard. I have built my sn voice but never panelled it. Might be an easy addition to it.

[kaputtpanzer]

Thanks for the audiosamples! Sounds very interesting, I will breadboard it later.

[BloodMaster]

That sounds really good. Would be interested how it sounds with a more "musical phrase" and some cutoff and reso screwing.

[predok]

Dual 100K pot - is it a stereo pot? I've assembled this scheme, but it works a bit strange...

Thank you for the scheme, tokyomatik!

[tokyomatik]

yep 100k stereo logar. the resonance interacts a lot with frequency pot,if u like it dirty & screachy i hope u will enjoy this filter. peace

[predok]

Yes, it sounds very warm and good for a low bass sound. Filter cuts high frequencies too much but anyway I like it.

[gasboss775]

The first time I tried this circuit I tried to adapt it to work of +15 V supply, but it was very unstable. Today I built it as is and powered it from +9V and it worked well. There is a lot of variability in the output amplitude, particularly with high resonance, perhaps some sort of post filter soft clipping would be good.

I want to try making a VCF out of this by substituting the dual pot with a dual vactrol.

[gasboss775]

Provisionally I can say it works well with a dual vactrol ( VTL5C3/2) just using a 10K pot and a resistor in series with the vactrol led.

Also the filter definitely sounds better with a lower frequency signal, I was using a 98Hz squarewave.

It is a bit of a screecher particularly at high cut off and high resonance control settings. At lower cut off frequencies is quite fat and warm if the resonance control is kept down.

[gasboss775]

I've done a fresh schematic showing the vactrol and a simple driver for the vactrol LED. I also included a simple voltage regulator to keep the supply around 9 volts ( assuming a +15 volt input. If using a +12 V supply change the 3K6 resistor to 3K0.

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[gasboss775]

This makes a great little VCF when adapted with vactrols! Have made a few wee refinements to the schematic. Perhaps someone could design a PCB for the vactrol version as I'm not great at that type of thing, though might build it on stripboard, ATM it is on a breadboard.

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[L´Andratté]

Hi gasboss!
I don´t know if you´re interested in the sound of the whacky transistor configuration *which probably guarantees strange behaviour* or in the simplicity of it...? Because it would be easier with opamps, which I have built several times.

On both outer legs of your double ldr you could put a little series resistance like 2k or 3k3, because the resistance of a vtl5c3 can become very small and the transistor (or opamp) won´t be happy driving a capacitive load to ground (aka instability/squeeling). That´s for the first resistor and the second to keep the resistances of the RCsections equal in value.
With one or two transistors you can build excellent lin or log led drivers: look at Scott Stites Multiphase project! (or René Schmitz´ cmos vco)

[gasboss775]

[Yangushii]

[gasboss775]

[gasboss775]

Yangushii This is quite a quirky circuit and there could be other reasons that it won't work. At first I used bc549C transistors and it didn't work at they had too much current gain and the transistors were biased close to ground. In general biasing a transistor with one resistor as is the case with Q1 isn't a very reliable method of biasing as the operating point is very dependent on the gain ( hFE / Beta ) of the transistor which varies from device to device and with temperature.

I used a 9 volt regulator as I found the circuit too unstable when operated above 9 volts, some people might actually like that quirkiness so that's up to you.[/b]

[Yangushii]

Thanks Gasboss.
I used a 100k dual pot.

I did used bc547c but socketed them so I can swap them if needed.

Any suggestion on what I can use?

[gasboss775]

[Yangushii]

I tried with a bc547a (should be 220 HEF max)

I do get very faint variation at the end of the cutoff pot. By the way, I used a lin pot, could it be this?

Otherwise, i guess it's my layout... It's the first I made so I might need to have a second look

Thanks for the help!