V/Hz state variable filter

nicolas3141 · Posted: Tue May 19, 2009 4:06 am Post subject: V/Hz state variable filter

Here is a filter to match the VCO http://electro-music.com/forum/topic-32689.html and ribbon controller http://electro-music.com/forum/topic-32651.html

This circuit is pretty much the standard state variable design from the LM13600 datasheet, but with a Q pot and diode clippers added that allows it to oscillate reliably so that it can be used a sine VCO as well as a filter. It has bandpass and lowpass outs.

A fairly basic circuit that sounds okay and is simple enough to understand and be built in a couple of hours on stripboard. It runs off +/-9V (ie two batteries). It expects a CV in the 0-6V range. The output is about a volt or so which won't blow anything up if you run it directly into effects pedals, etc.

It is V/Hz which means that if you set it up to give you C at 1V, you should get C an octave higher at about 2V and an octave higher again at about 4V.

I built mine last year, but have only finished tidying up the drawing, so if you notice anything amiss, please let me know.

Cheers,
Nicolas

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drapdap · Posted: Tue May 19, 2009 4:46 am Post subject:

Thank You for sharing this Nicolas, these circuits are really nice work.
I haven't got round to building any of them yet, but this filter was the last straw, im gathering parts now...

i'm not shure i understand the +6v switch on the input tho. Is it just to boost the signal so the resonance behaves well?

Does it tolerate +/- 12 volts, or do i need to raise some resistors?
(Of course i'll try it, but a firsthand answer really won't hurt my ego.)

is there more of these? Smile

thank you a gain

róbert

nicolas3141 · Posted: Tue May 19, 2009 3:07 pm Post subject:

That switch to +6V is my crude way of showing a switched socket that sees +6V when nothing is attached. It doesn't really need to be +6V, any stable +ve voltage would be fine.

To run it on higher voltage up to +/-15V should be fine, but increase the value of R4, R15 and R17 proportionally (say 6k, 14k and 14k or similar).

Cheers,
Nicolas

loss1234 · Posted: Sun May 31, 2009 7:14 am Post subject:

thanks so much for these great circuits!!!

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

Built the filter today. But ran in to some problems.

The q pot does not work properly Sad

It just work a little bit of the pots axel. I use a 100k pot just like in the schematics but should it be 10k?

What could else be wrong?

nicolas3141 · Posted: Thu Jun 11, 2009 2:14 pm Post subject:

I am not quite sure what you mean. When I turn the Q pot to 100% my filter rings (oscillates if there is no input). If I back it off a bit to around 70-90% the filter has that resonant wah type sound. Then as I turn it down further it loses the resonance and becomes more like a tone control type filter. Between 0-70% the changes in the sound of the filter are not very dramatic.

Perhaps a log pot would be better here so that we could get better control over the high resonance end and waste less rotation on the low resonance end.

This general type of filter is quite common, but what distinguishes one from the next is the feedback arrangement to provide Q control. So I encourage you to experiment with different pots and types of feedback. Let us know what you find that works.

Cheers,
Nicolas

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

It works now. I have the same result when I turn the Q pot now. I think that was what puzzled me was that there was not much action until you get to 70% turned Q pot. After 90 it goes crazy... Smile

I will try later on with a log pot....

So that is number 4 of your designs Very Happy

ADSR
LFO
VC-LFO
FILTER

Now I look forward to the Sample & Hold and VCA. Is there a ringmodulation as well? Wink

Thanks for your educational and fun designs!

ogg · Joined: Sep 30, 2009 Posts: 10 Location: UK

Hello, I've put an interactive simulation of this filter online at Music circuit simulations. It seems to be working but not entirely, I'm not sure which input is which and I don't think I have the op-amp voltages right. Thought you might like to see it, please send me corrections if you can see any mistakes.

I've credited you, nicolas3141, and linked to this discussion.

Cheers,

Ollie

v-un-v · Posted: Fri Oct 02, 2009 8:25 am Post subject:

Hey Ollie! welcome

to electro-music.com! Very Happy

I'm afraid this isn't working here (Safari on a MacIntel running OSX). Says it can't read a text file- although I'm getting a screen. A black screen I should add Smile

blue hell · Posted: Fri Oct 02, 2009 8:47 am Post subject:

ogg · Joined: Sep 30, 2009 Posts: 10 Location: UK

nicolas3141 · Posted: Mon Apr 12, 2010 3:02 am Post subject:

Hi Dego

one more uploaded. Sorry for the delay, but it has been summer down here and I have not been indoors so much Smile

http://electro-music.com/forum/topic-41277.html

Cheers,
Nicolas

Project_2501 · Joined: Jan 31, 2018 Posts: 68 Location: Los Angeles

New to the party Smile

Does anyone have the wiring layout? Stripboard layout has only one potentiometer (Q pot) which is P3, in schematic, they're 3 total pots right? I am missing something?

Once again, thank you nic for you layouts. I'm slowly building my rig. Ordering a MFOS psu soon Smile

gabbagabi · Posted: Wed May 02, 2018 10:50 am Post subject:

dude, u should know it better by now Wink

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Project_2501 · Joined: Jan 31, 2018 Posts: 68 Location: Los Angeles

I'm learning Smile

slowly but surely

To apply that +V, can i just hookup the +V from the power supply to give it a stable voltage? Where's the easiest place to find that +V to that switch socket. Thats the only confusing part for me.

gabbagabi · Posted: Wed May 02, 2018 9:57 pm Post subject:

we need to know on what voltage u run
and
the resistor-value of the pots u use

Project_2501 · Joined: Jan 31, 2018 Posts: 68 Location: Los Angeles

I'm going to be using a +V/-V 12 wall power supply by mfos. For pots, I guess 100k lin, but I have 10k, 25k, 50k lin available.

tinfoilcat · Joined: Apr 16, 2019 Posts: 8 Location: Stockholm, Sweden

This thread deserves a bump!

I built this filter and added sockets for the diodes. Then I tried red LED:s Twisted Evil

Crude video, second part with LED:s (close to max resonance all the time, it is pretty well behaved at lover settings! But slightly more agressive overall): https://www.youtube.com/watch?v=Ig_0-0Mmv3s

Thank you Nicholas!