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 Forum index » DIY Hardware and Software » Thomas Henry designs
x-4046 timing capacitor options? Does it affect tuning?
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Hashtag Octothorpe



Joined: Jun 11, 2017
Posts: 50
Location: Grand Rapids MI

PostPosted: Sun Jul 02, 2017 5:03 am    Post subject: x-4046 timing capacitor options? Does it affect tuning? Reply with quote  Mark this post and the followings unread

Hey!

I've breadboarded (well... paper for one, plywood for the other) a couple X-4046 VCOs and they sound incredible! I use a lot of used parts, and I only have one 100pF film capacitor. So one X-4046 has two 220pF caps in series for 110pF. I've got the triangle shaped well, and the sine looks amazing, and on my 2nd version, I broke out the "sine round" 100K variable resistor to a pot on the front panel, so I can glide from square to triangle-ish with sine in between! I'm pumped about that.

I haven't started tuning them yet, but wonder, can I build my next couple with 220pF timing caps or larger, or will that mess up the 1V/oct tuning? The range on the pair I've built goes ultrasonic, and I don't need ultrasonic notes coming from my modular. Smile

Instagram link of the1st build
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wackelpeter



Joined: May 05, 2013
Posts: 453
Location: germany
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PostPosted: Mon Jul 03, 2017 6:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Please correct me someone if i'm wrong but the timing cap is as far as i know the 10nF cap lurking between pin 6 and 7 of the 4046 chip.
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gdavis



Joined: Feb 27, 2013
Posts: 359
Location: San Diego
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PostPosted: Mon Jul 03, 2017 12:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yep, C3 between pins 6 and 7 of the 4046 is the timing cap. The 100pf C1 is simply there for stability of the opamp servo circuit. The value isn't critical but you don't want to vary it too much or it might affect the performance of the circuit. I'd guess 220pF is OK.
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