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 Forum index » DIY Hardware and Software » The layout factory
Polivox VCF layout
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LFLab



Joined: Dec 17, 2009
Posts: 198
Location: Rosmalen, Netherlands

PostPosted: Mon Jan 13, 2014 3:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Busy troubleshooting this, I built one, but it doesn't work.
I am suspecting the programmable opamps I bought on ebay, but found a couple of other things as well:

The Q pot is actually cutoff, and cutoff is Q

Don't use 741's for the single opamp, since there is no compensation or supply bypassing, it oscillated in my build. TL071 is ok (haven't checked the scope yet, but it doesn't get hot, contrary to the 741 I used).

R8 is marked as 82k but in marc bareille's schematic this is 162k.

Checked all component designators against Marc Bareille's schematic, and they are the same, R2 and R3 are swapped, but both 100k. C3 and C4 are C5 and C6, but that's clear as well.

The trimpot is a cutoff range adjuster.

I am going to get ua776 opamps and retry (or, if I cannot get those, I'll plonk in LM4250's and change R10 and R11).
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LFLab



Joined: Dec 17, 2009
Posts: 198
Location: Rosmalen, Netherlands

PostPosted: Thu Jan 30, 2014 4:10 am    Post subject: Reply with quote  Mark this post and the followings unread

So, plugging in ua776 it works somewhat, the resonance control seems to work, but cutoff range doesn't do a whole lot, and the FM knob also isn't functioning correctly.
All in all, not sure what I'll do, better roll my own, methinks.

There are some people who have built the VCF from this layout correctly, but I don't feel like fiddling with it anymore, especially since there are some issues with it, and it is a simple enough schematic to plonk it into Eagle myself.
From what I did hear, playing with the resonance knob, it can properly scream, so I'll certainly build a couple of these.
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airfrankenstein



Joined: Jan 10, 2010
Posts: 44
Location: france

PostPosted: Sun Mar 09, 2014 11:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the update. I was on the point of building this but perhaps will go back back to bareille's version or hackster's (which seems to be the blue lantern version).
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LFLab



Joined: Dec 17, 2009
Posts: 198
Location: Rosmalen, Netherlands

PostPosted: Mon Mar 10, 2014 5:22 am    Post subject: Reply with quote  Mark this post and the followings unread

There's also a PCB by Girts on Muffwiggler, seems to work well (and you can order the original semicons to go with it (transistor, programmable gain opamps).
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airfrankenstein



Joined: Jan 10, 2010
Posts: 44
Location: france

PostPosted: Mon Mar 10, 2014 11:51 am    Post subject: Reply with quote  Mark this post and the followings unread

yeah i know looks very nice tight budget after euro excess spending
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vladosh



Joined: Aug 02, 2010
Posts: 422
Location: macedonia
Audio files: 6

PostPosted: Tue Mar 11, 2014 5:51 am    Post subject: Reply with quote  Mark this post and the followings unread

this is how this polivoks sounds ,the lpf is useless so this is the bpf ,built two of these ,it needs alot attenuation on all inputs and outputs as i read somewhere else too,so a bit cleaner version of this filter would be great

https://soundcloud.com/synthacks/polivoks-vcf-demo
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airfrankenstein



Joined: Jan 10, 2010
Posts: 44
Location: france

PostPosted: Wed Mar 12, 2014 7:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Vladosh! Most useful.
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Snaper



Joined: Feb 28, 2014
Posts: 71
Location: Hungary

PostPosted: Fri Jun 27, 2014 2:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

LFLab wrote:
There's also a PCB by Girts on Muffwiggler, seems to work well (and you can order the original semicons to go with it (transistor, programmable gain opamps).

Built 2 of those. They are stable and great sounding!
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