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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  Voltage controlled filter for 10 bucks 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: Voltage controlled filter for 10 bucks  (Read 3098 times)
mongo
Posts: 247


Andy Soto - Paris France


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Voltage controlled filter for 10 bucks
« on: March 05, 2011, 11:44:08 AM »

 Just found this, it looks and sounds amazing!

 This could be awesome matched with an uglyface

 http://ericarcher.net/devices/diy-lpf/

 Andy.
« Last Edit: March 05, 2011, 11:46:31 AM by mongo » Logged

R.G.
more
Posts: 16206


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Re: Voltage controlled filter for 10 bucks
« Reply #1 on: March 05, 2011, 11:54:32 AM »

Yep. Classic voltage controlled state variable filter with OTAs.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
Earthscum
Posts: 1932


David Edgar


Re: Voltage controlled filter for 10 bucks
« Reply #2 on: March 05, 2011, 12:48:22 PM »

I tried a couple filter configurations with the 13700, and I could not get them to work right, but I could plug in a 13600 and they would sweep and filter beautifully... I was reading on some site that the 13600 can sweep easily 6 octaves, but the 13700 struggles to sweep 3-4 octaves. Is this true, or just bad design? I'm still learning (and read an article you linked about OTA's about 3 or 4 times). And, why such a difference?
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Give a man Fuzz, and he'll jam for a day... teach a man how to make a Fuzz and he'll never jam again!

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R.G.
more
Posts: 16206


WWW
Re: Voltage controlled filter for 10 bucks
« Reply #3 on: March 05, 2011, 01:11:08 PM »

I tried a couple filter configurations with the 13700, and I could not get them to work right, but I could plug in a 13600 and they would sweep and filter beautifully... I was reading on some site that the 13600 can sweep easily 6 octaves, but the 13700 struggles to sweep 3-4 octaves. Is this true, or just bad design? I'm still learning (and read an article you linked about OTA's about 3 or 4 times). And, why such a difference?
The only difference (at least that National Semi admits) between the LM13600 and LM13700 is that the bias current for the output buffer on the LM13600 is modulated by the bias current to keep it working best for the operating point of the OTA, and on the LM13700 it's constant. The constant version is better for low control signal feedthrough in audio applications. There is NO difference in the OTA, which is what does the sweep in the filters.

I'm sure you did read that somewhere. However, the internet has made everyone an expert as long as they say "I'm an expert" three times and click their ruby slippers together. I'd be willing to bet that person is telling the truth - for the very limited test they ran. Things like "um, how many of those did you test, and does every LM13600 beat every LM13700, or did you just get a bad one?" and "was this a sub in the same circuit board (and circuit, and parts...) or did you build two different circuits/boards and test them side by side, or test new designs sequentially?" and "was there a mistake in the LM13700 circuit? or the LM13600 circuit?"

Finding consistency takes more than a few test circuits.
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R.G.

Every single NASA manned mission starting with the Gemini series has carried a roll of duck tape.
Yes, really. Look it up.
T-Flex
Posts: 27



Re: Voltage controlled filter for 10 bucks
« Reply #4 on: March 05, 2011, 02:06:54 PM »

Would love to get a layout for this and give it a go
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It's more fun to compute.
artifus
Posts: 1742


dare to be na´ve


Re: Voltage controlled filter for 10 bucks
« Reply #5 on: March 05, 2011, 08:46:58 PM »

THE LM13600/LM13700 STORY
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