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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
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comrade_zero
Joined: Mar 05, 2009 Posts: 66 Location: arizona
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Posted: Fri May 30, 2014 1:13 am Post subject:
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I am assuming you want single supply? Eric Archer has a 13700 9v vcf that sounded pretty good on the demos. You could cook up a low-parts count Sallen-Key filter with a single op-amp and some LED's and LDR's. You could adapt some of the Wasp filter clones that are floating around (based on the CD4069, I seem to recall a 13700 version to replace the 3080's of the original.) Probably the simplest resonant filter on a single supply is the WSG filter from Ray Wilson (musicfromouterspace) it's a little "weak," but for a workshop synth it may fit the bill...
Good luck, hope this helps.
c_z |
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Fri May 30, 2014 2:57 am Post subject:
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hey c_z,
yes single-supply with virtual ground.
Like I mentioned the op-amp based filters start to hum, when I get close with my hand.
But thanks for the hint with the eric archer vcf... |
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Fri May 30, 2014 3:11 am Post subject:
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I had a look at the eric archer ota vcf. Looks nice and simple. But I was wondering about the op-amps, do i really need them? The one at the output is just an amp, I guess I can cut out this part. But what about the CV input section, I don't really understand what the circuit does there. Isn't it possible to build it like the ms 20 vcf and cut this part out, too?
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
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Posted: Fri May 30, 2014 6:10 am Post subject:
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The amps do two things
1) provide a wet/dry signal mix
2) buffer the output.
If your intent is to just have raw filter as normal for modulars, you could omit the first op amp and the pot that does the wet/dry mix, but I don't think I'd recommend unbuffering the output, otherwise loading will affect the behavior of the filter. |
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Fri May 30, 2014 6:48 am Post subject:
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elmegil wrote: | The amps do two things
1) provide a wet/dry signal mix
2) buffer the output.
If your intent is to just have raw filter as normal for modulars, you could omit the first op amp and the pot that does the wet/dry mix, but I don't think I'd recommend unbuffering the output, otherwise loading will affect the behavior of the filter. |
Guess my question was not clear enough, the opamp questions were related to the eric archer vcf... But thank you anyway |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
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Posted: Fri May 30, 2014 7:58 am Post subject:
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Sorry I was confused because there's a schematic right there in the post you asked your question in
Edit:
So to Eric's schematic; the first op amp is part of the expo converter, that's required. The second amp is doing the same thing as the two op amps in the schematic I replied to before -- it's providing a wet/dry mix (you could omit some of the resistors and the pot) and a buffer for the filter. Again: if you omit the buffer, and you plan to hook the output to anything arbitrary, you could have a load change the characteristics of the filter. If the filter output goes to one fixed place, and you know the load *doesn't* alter it from your desired response, then you could omit it (though you shouldn't omit the decoupling cap). |
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Fri May 30, 2014 12:44 pm Post subject:
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Thanks for your help.
I think I will modify the ms20 schematic a little bit for our needs and use this. I was wondering why the ms20 filter is working with out a expo converter and the eric archers vcf needs one. |
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elmegil
Joined: Mar 20, 2012 Posts: 2177 Location: Chicago
Audio files: 16
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Posted: Fri May 30, 2014 2:23 pm Post subject:
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The MS-20 was a V/Hz device not a V/Oct one.... Probably the cause |
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