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 Forum index » DIY Hardware and Software » Thomas Henry designs
VCF for the 21st Century
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elmegil



Joined: Mar 20, 2012
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Location: Chicago
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PostPosted: Fri Aug 17, 2012 4:03 pm    Post subject: VCF for the 21st Century
Subject description: Is it supposed to self oscillate?
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As a relative Noob, I have never worked with filters (other than in the WSG Smile ) and so have never gotten them to self-oscillate.

I get a nice filter response on the VCF for the 21st Century; I've corrected the resonance pot (which had been backwards) and realized I hadn't hooked up coarse & fine controls (they went to the input resistors and then nowhere) but I have corrected that as well.

I am assuming, since there is a 1V/Oct trimmer, that I should be able to get oscillation out of this so I can actually adjust that response. However, I have been unable to find a way to make it oscillate.

Just to be sure:

I have coarse & fine set on the high side of mid range. I have a CV plugged in, but set to zero. I have the resonance all the way up. I have tried bumping the input with triangle and ramp waves of various frequencies with the input attenuation all the way up and nothing happens.

I did play with the V/Oct trimmer, but since it's not in the feedback loop of the filter I didn't expect much from that, and of course I didn't get much.

I do have the input switch in AC mode, not DC mode. Envelope attenuator is all the way down.

I've tried both a proper SSM2164 (as labelled anyway...on cursory examination it doesn't *appear* to be a fake) and a cool audio 2164.


So questions:

1) is it supposed to self-oscillate?
2) if not, how do I calibrate the 1V/Oct?
3) if so, what are the key things I'm missing to get it going?
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v-un-v
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PostPosted: Fri Aug 17, 2012 4:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

All decent analogue filters self oscillate. It still amazes me that digital clones still can't do this.
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elmegil



Joined: Mar 20, 2012
Posts: 1534
Location: Chicago
Audio files: 14

PostPosted: Fri Aug 17, 2012 6:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

So I would presume it's a decent filter given it's provenance, so the obvious assumption is that I've done something wrong Smile.

Anyone have any pointers as to what components are most crucial in this? Is it something that's going to be specific to the particular design? I'm digging in references, but so far not finding much....
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v-un-v
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PostPosted: Sat Aug 18, 2012 3:33 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd try and PM Thomas if you can. (If he doesn't reply here). But yes, it would seem odd if it didn't self oscillate? Smile
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ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN.
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