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 Forum index » DIY Hardware and Software
Building the Polivoks Filter
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julianw



Joined: Jul 30, 2007
Posts: 78
Location: UK

PostPosted: Sat Sep 06, 2008 2:48 pm    Post subject: Building the Polivoks Filter
Subject description: Mods needed when building the Polivoks using the Papareil Synth Labs PCB
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There is a lot of information (written in German) within various threads in the www.sequencer.de forum detailing the many mods people have had to do in order to get their polivoks filters working with the correct range/input impedances, and also info on how to get the filter working on +/- 12v supply.

Most of this stuff doesn't show up on google, and I had to search pretty hard to find it, so I have attempted to summarize the alterations needed and overlay these alterations on top of the diagram from the Papereil Synth Labs website, this is included below as an attachment, hopefully it will be of use to somebody.

Marc Bareille wrote:
R26 and R24 are signal input resistors ( two inputs... ) . Each one for one input --> they define the input impedance of the filter ... Usualy it is 100k for a most of modular systems

R9 is the 'fixed' CV input ... It is usualy better to use a 100k resistor . You can increase it ( 220k , 470k...) if you find this input is too much efficient or if you use +/-10V CVs ...

R8 should also be adjusted (tweaked ) ... The unusual 162k value i propose on the schematic should be replaced by a 220k or even a bit more to get a correct cutoff range . Well this depend a lot of the programmable op-amps in fact and my vary from a brand or a model to another ...

Other rather important thing , valid with the LM4250 ( and may be the NTE888 too) :
I suggest you to solder the cutoff pot between -15V and +15V and not GND and +15V ... The filter will close much better! It is also important to tweak R8 ( generaly increase it 220k up to 1M... ) to get a correct cutoff range ... You can also increase R10/R11 up to 1M or even more ...


For more info, read these threads, they are formatted so that clicking these links will automatically translate them into english using google translate:

http://www.sequencer.de/synthesizer/viewtopic.php?f=13&t=7744
http://www.sequencer.de/synthesizer/viewtopic.php?f=13&t=9285
http://www.sequencer.de/synthesizer/viewtopic.php?f=13&t=5634
http://www.sequencer.de/synthesizer/viewtopic.php?f=13&t=2198
http://www.sequencer.de/synthesizer/viewtopic.php?f=13&t=6348
http://www.sequencer.de/synthesizer/viewtopic.php?f=13&t=8078
http://www.sequencer.de/synthesizer/viewtopic.php?f=13&t=5750

Cheers Guys, Julian


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Last edited by julianw on Mon Nov 08, 2010 6:16 am; edited 2 times in total
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fluxmonkey



Joined: Jun 24, 2005
Posts: 696
Location: cleve

PostPosted: Sat Sep 06, 2008 3:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Julian--

wow, thanks a ton for posting this, and for doing all that legwork!! my polyvox has been at the top of the Sad Unsuccsesful Project pile for a while now; i will pull it down tonite and see if i can get her going. much appreciated!!

bbob

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numbernone



Joined: Aug 16, 2006
Posts: 477
Location: new york city

PostPosted: Sat Sep 06, 2008 3:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yeh excellent to see this summed up.

Mine is also semi DOA stuck in a panel of otherwise fulling functioning modules. Cant wait to hear it roar.
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fluxmonkey



Joined: Jun 24, 2005
Posts: 696
Location: cleve

PostPosted: Sat Sep 06, 2008 7:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

fixes applied, and it works!! thanks a million.

this was one of the first modules i made an FPD/Shaeffer panel for, and i was always kind of bummed to have jumped the gun and bought a panel before i had a working module. and every once in a while someone would post something nice about their polyvox, and i'd get bummed out again. so it's nice to have this one squared away.

after only a few minutes of playing with it, this is obviously a very agressive filter w/ a lot of snarl to it, biting but not brittle. it's a definate add to the arsenal.

a good note to end the day on. thanks again!


bbob

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julianw



Joined: Jul 30, 2007
Posts: 78
Location: UK

PostPosted: Sat Sep 06, 2008 8:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

bbob wrote:
fixes applied, and it works!! thanks a million.


Nice one, glad you got it rippin' thumleft

bbob wrote:
this is obviously a very agressive filter w/ a lot of snarl to it, biting but not brittle. it's a definate add to the arsenal.


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Funky40



Joined: Sep 24, 2005
Posts: 875
Location: Swiss
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G2 patch files: 5

PostPosted: Sat Sep 06, 2008 11:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm a part of that community there and built my Polivoks following these threads.
I built after these threads and my Polivoks is NOT adjusted good.
The CV input has way too much modulationamount .
the audio input Gain is extreme, but this i like.

Serenadi has lots of experience with the Polivoksfilter.
he has made his own Le Bernard Polivoks filter
He has a Breadboard with pots and jacks and runs modules in dvelopment for Weeks or months in front of the modularsynth.
very very accurate working what he is doing ! Very !

If you go after these threads, follow serenadis suggestions !
but i think he built hes own after that time, so i'm not shure if he was really active about that topic then

btw.: you Guys are allways free and invited to choin that community there and ask in english Wink
for not so good english speaking folks it would be less pressure to answer there in english Wink
funny translations Laughing
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crashlander42



Joined: Oct 21, 2006
Posts: 292
Location: Orlando, FL (US)

PostPosted: Sun Sep 07, 2008 1:02 am    Post subject: Reply with quote  Mark this post and the followings unread

I built the Polivoks off of the schematic on the Papereil Synth Labs, but did not use the board. I dont know if there is much of a difference, although looking at the pic of the PCB layout I can spot a couple small ones right off, and that makes me think there are others.

I'm running off of a +/-15v power supply and did find that I had to change some resistor values at the pots to get things the way i like (I guess it's a good thing I breadboarded it first). I can't remember exactly what I changed, but the biggest one was at the frequency pot.

As for the gain, it is definitely necessary to attenuate your input, and I love the sound of the filter over driven. The output is a tad high, but I didn't really mess with it.

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haxster



Joined: Feb 01, 2006
Posts: 244
Location: MONTEREY PARK, CA 91754
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PostPosted: Sun Dec 07, 2008 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

I recently have fooled around with the polivoks design.
here is a schematic of the values I have used on 12v power supply. I added a 100k trimmer for the cutoff range fix.

http://electro-music.com/forum/viewtopic.php?highlight=polivoks&t=23246

I made pro pcb's off this design and it works.
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davebr



Joined: Jun 09, 2007
Posts: 181
Location: portland, or

PostPosted: Mon Feb 04, 2013 8:24 pm    Post subject: Polivoks Filter Reply with quote  Mark this post and the followings unread

I just finished building a Polivoks filter on a breadboard. I ended up using NTE888M parts and kept the stock resistors values of 162K for the CV and 110K for the current control. The filter has a nice range, good cutoff, and no dead zone. I did find that the resonance wasn't very interesting being just rail to rail square waves. I added some clipping diodes using the current limit feature in the programmable op amp to drop it to a lower output and a very nice sine wave. A switch will enable or disable that feature. I did significantly increase the input resistor to eliminate the need for input attenuation and get close to unity gain.

[EDIT - I just got some УД1208 Russian parts and did frequency plot comparisons between the NTE888M and УД1208 parts. There is a slight frequency and output amplitude difference but they look very similar. Scope images have been added to my website for comparsion.]

I have scope images of some waveforms on my site at http://modularsynthesis.com/kuzmin/polivoks/polivoks_vcf.htm.

Dave

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davebr



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Posts: 181
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PostPosted: Sun Mar 10, 2013 8:54 pm    Post subject: Re: Polivoks Filter Reply with quote  Mark this post and the followings unread

davebr wrote:
I just got some УД1208 Russian parts and did frequency plot comparisons between the NTE888M and УД1208 parts. There is a slight frequency and output amplitude difference but they look very similar.


I got some uA776 parts and added a comparison of those as well as a couple of videos and sound samples to my Polivoks filter page.

http://modularsynthesis.com/kuzmin/polivoks/polivoks_vcf.htm

Dave
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