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 Forum index » DIY Hardware and Software
SUPER SIMPLE 12db RESONANT LOWPASS FILTER-with AUDIOSAMPLES!
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tokyomatik



Joined: Jan 20, 2011
Posts: 170
Location: berlin
Audio files: 6

PostPosted: Tue Jan 24, 2012 2:00 am    Post subject: SUPER SIMPLE 12db RESONANT LOWPASS FILTER-with AUDIOSAMPLES! Reply with quote  Mark this post and the followings unread

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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Last edited by tokyomatik on Wed Jan 25, 2012 3:27 pm; edited 2 times in total
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tokyomatik



Joined: Jan 20, 2011
Posts: 170
Location: berlin
Audio files: 6

PostPosted: Tue Jan 24, 2012 2:03 am    Post subject: Reply with quote  Mark this post and the followings unread

here also the pcb layout
ready for press n peel


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Last edited by tokyomatik on Tue Jan 24, 2012 2:05 am; edited 1 time in total
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tokyomatik



Joined: Jan 20, 2011
Posts: 170
Location: berlin
Audio files: 6

PostPosted: Tue Jan 24, 2012 2:04 am    Post subject: Reply with quote  Mark this post and the followings unread

parts placement


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kaputtpanzer



Joined: Nov 02, 2009
Posts: 68
Location: Cologne
Audio files: 2

PostPosted: Tue Jan 24, 2012 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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vladosh



Joined: Aug 02, 2010
Posts: 463
Location: macedonia
Audio files: 8

PostPosted: Tue Jan 24, 2012 8:10 am    Post subject: Reply with quote  Mark this post and the followings unread

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 Smile
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tokyomatik



Joined: Jan 20, 2011
Posts: 170
Location: berlin
Audio files: 6

PostPosted: Tue Jan 24, 2012 6:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

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..... Embarassed ???
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
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tokyomatik



Joined: Jan 20, 2011
Posts: 170
Location: berlin
Audio files: 6

PostPosted: Wed Jan 25, 2012 12:54 am    Post subject: Reply with quote  Mark this post and the followings unread

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


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Dego



Joined: Apr 22, 2008
Posts: 139
Location: Sweden

PostPosted: Wed Jan 25, 2012 9:34 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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kaputtpanzer



Joined: Nov 02, 2009
Posts: 68
Location: Cologne
Audio files: 2

PostPosted: Fri Jan 27, 2012 4:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



Joined: Jan 28, 2012
Posts: 3
Location: germany

PostPosted: Sat Jan 28, 2012 12:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



Joined: Sep 04, 2015
Posts: 4
Location: ua

PostPosted: Mon Sep 07, 2015 1:56 am    Post subject: Reply with quote  Mark this post and the followings unread

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!
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tokyomatik



Joined: Jan 20, 2011
Posts: 170
Location: berlin
Audio files: 6

PostPosted: Tue Sep 08, 2015 5:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

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
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predok



Joined: Sep 04, 2015
Posts: 4
Location: ua

PostPosted: Thu Sep 10, 2015 5:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, it sounds very warm and good for a low bass sound. Filter cuts high frequencies too much but anyway I like it.
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gasboss775



Joined: Jan 02, 2016
Posts: 149
Location: Scotland

PostPosted: Fri Nov 17, 2017 6:26 am    Post subject: Super simple LPF Reply with quote  Mark this post and the followings unread

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.
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gasboss775



Joined: Jan 02, 2016
Posts: 149
Location: Scotland

PostPosted: Fri Nov 17, 2017 8:18 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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gasboss775



Joined: Jan 02, 2016
Posts: 149
Location: Scotland

PostPosted: Fri Nov 17, 2017 12:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

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



Joined: Jan 02, 2016
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PostPosted: Sun Nov 19, 2017 5:28 am    Post subject: Reply with quote  Mark this post and the followings unread

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



Joined: Sep 23, 2012
Posts: 124
Location: Hamburg, Germany
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PostPosted: Mon Nov 20, 2017 2:53 am    Post subject: Reply with quote  Mark this post and the followings unread

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) thumb up
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gasboss775



Joined: Jan 02, 2016
Posts: 149
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PostPosted: Mon Nov 20, 2017 8:18 am    Post subject: Reply with quote  Mark this post and the followings unread

L´Andratté wrote:
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) thumb up


Simplicity is always very seductive, but on closer inspection there are often limitations that are unavoidable without the addition of more complexity.

I had thought about adding series resistors as personally I don't like the misbehaviour of this circuit that occurs with high cut off and high resonance settings.

Do you think there is merit in using an expo converter to drive vactrols, as they are inherently non linear in nature?

Last edited by gasboss775 on Yesterday, at 4:07 am; edited 1 time in total
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Yangushii



Joined: Dec 09, 2017
Posts: 3
Location: Leiden NL

PostPosted: Sat Dec 09, 2017 1:42 am    Post subject: Reply with quote  Mark this post and the followings unread

tokyomatik wrote:
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


Cutoff doesn’t seem to do anything for me. I suspect I got the dual pot wiring wrong Smile

I connected like this:
Bottom lug 1 to 1k res/bc547 emitter
Top lug 1 to bottom lug 2 to 100nf cap
Top lug 2 to 10k res /100nf cap
Both lug 3 disconnected.

Pretty much like here:
https://1.bp.blogspot.com/-223y4GiQ2-I/WFF8cslxvHI/AAAAAAAALk4/PosVsJ7NhAcI1QWELd8cd1uk8Ud8_6pkgCKgB/s1600/IMG_20161214_164054.jpg


It does seem different on the pcb picture...

Anyone could tell me if I got it correct?

Thanks !
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gasboss775



Joined: Jan 02, 2016
Posts: 149
Location: Scotland

PostPosted: Yesterday, at 4:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Yangushii wrote:
tokyomatik wrote:
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


Cutoff doesn’t seem to do anything for me. I suspect I got the dual pot wiring wrong Smile

I connected like this:
Bottom lug 1 to 1k res/bc547 emitter
Top lug 1 to bottom lug 2 to 100nf cap
Top lug 2 to 10k res /100nf cap
Both lug 3 disconnected.

Pretty much like here:
https://1.bp.blogspot.com/-223y4GiQ2-I/WFF8cslxvHI/AAAAAAAALk4/PosVsJ7NhAcI1QWELd8cd1uk8Ud8_6pkgCKgB/s1600/IMG_20161214_164054.jpg




It does seem different on the pcb picture...

Anyone could tell me if I got it correct?

Thanks !


It should have worked, although the cut off would get lower as the pot is turned clockwise rather than increasing with clockwise rotation which is the usual convention. What value of pot did you use?
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gasboss775



Joined: Jan 02, 2016
Posts: 149
Location: Scotland

PostPosted: Yesterday, at 9:17 am    Post subject: Reply with quote  Mark this post and the followings unread

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]
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Yangushii



Joined: Dec 09, 2017
Posts: 3
Location: Leiden NL

PostPosted: Yesterday, at 10:24 am    Post subject: Reply with quote  Mark this post and the followings unread

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?
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gasboss775



Joined: Jan 02, 2016
Posts: 149
Location: Scotland

PostPosted: Yesterday, at 1:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yangushii wrote:
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?


If you can find regular bc547 rather than bc547c, as the c at the end means that the transistors have the highest hFE / Beta. Do you have a meter that let's you measure hFE?

Try to find something around 250 or less, doesn't have to be bc547 as long as its npn and with hFE less than or around 250.
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Yangushii



Joined: Dec 09, 2017
Posts: 3
Location: Leiden NL

PostPosted: Today, at 1:56 am    Post subject: Reply with quote  Mark this post and the followings unread

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 Very Happy

Thanks for the help!
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