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 Forum index » DIY Hardware and Software
Discrete Transistor 2040 SVVCF
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Scott Stites
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PostPosted: Fri Apr 12, 2013 5:22 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Glad to know im not going mad!


Well, if you are, I beat you to it. Laughing

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Scott Stites
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PostPosted: Fri Apr 12, 2013 5:29 am    Post subject: Reply with quote  Mark this post and the followings unread

StephenGiles wrote:
Scott Stites wrote:
Hey Dan,

I've been playing with BBDs lately. Lotsa fun, those too.

Cheerio,
Scott


Through zero flanging perhaps? Are you aware that Mike Irwin (where is he now?) designed a TZF using just one BBD?


Hey Stephen,

I missed this - sorry I didn't reply sooner. Is it the phase delay design that Mike based his on?

Mine is through zero, but it uses more than 1 BBD (it uses 8 ). I'm working on a pitch shifting application now.

Cheerio,
Scott

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Scott Stites
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PostPosted: Fri Apr 12, 2013 5:32 am    Post subject: Reply with quote  Mark this post and the followings unread

comrade_zero wrote:
First off, Mr. Stites, a hearty "thank you" for taking the time and energy to share this with us. This filter sounds good (I am a sucker for filters.) Secondly, any idea if or how it would behave on -12/+12v?
Especially if someone is looking to a Euro-format board? Thanks again.
c_z


Dang - how did I miss this one, too? Anyway, I've never tried it with +/-12V - I'm sure it could be made to work at that level if it doesn't out of the box.

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Scott Stites
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PostPosted: Sun Apr 14, 2013 1:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

My THAT transistor version was still on the breadboard - after four years, it still actually works. I recorded a short sample of it and posted it to the THAT FB page just to put a bug in their ear that maybe, some day, the analog resurgence will make it viable for them to make a similar IC as the 2040.

Here's the sample I recorded (LP output):

http://soundcloud.com/scott-stites/that-transistor-svvcf-lp-out

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vtl5c3



Joined: Sep 08, 2006
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PostPosted: Thu Jul 11, 2013 10:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Just found out about this thread.

Nice Job, Scott! I'm impressed how fat the filter sounds with only two poles.
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negativspace



Joined: Dec 25, 2010
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PostPosted: Thu Jul 11, 2013 12:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

comrade_zero wrote:
Secondly, any idea if or how it would behave on -12/+12v?


It works well on +/-12v with no changes. I imagine someone with a better grasp of transistor circuits could tweak a few resistor values, but based on my first build I don't think it's critical. It certainly sounds great and behaves as expected with no adjustments.

I did change two resistor values: R37 to 39k and R32 to 5.6k. That gives very usable self-oscillation (R37) and eliminates some 'thumping' in the audio that was occurring at high CV values (R32). I also connected the frequency pot between +12 and ground, not +12 and -12, which gives a much more comfortable range.

This really is a thick filter... excellent work, Scott, and thank you for sharing!

For those of you interested in a PCB, I'm working on one now with Scott's blessing. I'll offer it over at Muff's, but I'll do my best to keep this thread updated as it comes to fruition.
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vtl5c3



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PostPosted: Thu Jul 11, 2013 1:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Awesome! You just saved me a ton of work.

negativspace wrote:


For those of you interested in a PCB, I'm working on one now with Scott's blessing. I'll offer it over at Muff's, but I'll do my best to keep this thread updated as it comes to fruition.
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crashlander42



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

PostPosted: Thu Jul 11, 2013 10:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is awesome, because just a few hours ago I was Googling discrete VCF designs.
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negativspace



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PostPosted: Fri Jul 12, 2013 12:24 am    Post subject: Reply with quote  Mark this post and the followings unread

I love it when a plan comes together... Cool
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KnobHell



Joined: Jan 28, 2012
Posts: 58
Location: SLC

PostPosted: Wed Jul 24, 2013 9:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Scott

Qestion about the caps.

Should the 1nf be poly?

How about the 2.7nf?

I assume the 220's can be ceramic.
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Scott Stites
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PostPosted: Fri Aug 23, 2013 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

I had to think about that answer for a month Laughing

I used 1 nF polystyrene caps; the 2N7 was a mylar cap.

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Scott Stites
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PostPosted: Fri Aug 23, 2013 12:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

And, yep, 220s can be ceramic.
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KnobHell



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PostPosted: Sun Aug 25, 2013 9:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Cool, thanks Scott.

Hey, a month in synth time didn't even give me time to drop my build queue by one... Shocked

Thanks for the follow up.

Len
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