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 Forum index » DIY Hardware and Software » Thomas Henry designs
CA3080 VCO's
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crashlander42



Joined: Oct 21, 2006
Posts: 292
Location: Orlando, FL (US)

PostPosted: Sat Jul 26, 2008 11:40 pm    Post subject: CA3080 VCO's
Subject description: questions I thought of while playing pool.
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I had originally thought that I couldn't even attempt one of the triangle to saw wave shapers from the VCO Cookbook with the CA3080 VCO since the only square wave was a PWM square off of the triangle. I was looking at "Making music with the CA3080" and noticed that you can tap a square wave off of Q1 and Q2 in the CA3080 VCO.

Could I use that square wave buffered off of Q1 & Q2 to do a similar triangle to saw shaper as say the XR2206 "Top-notch ramp wave output" in the VCO cook book? Maybe one of the other Triangle to ramp schematics in the VCO cookbook?

I'm guessing I could also run that square through one of the 4013 sub octave circuits as well right?

I guess I'll be warming the breadboard tomorrow!!

Can I do the 3080 VCO with a LM 13700 and use the spare OTA as a... oh I forgot. use the spare OTA for something else...

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Last edited by crashlander42 on Sun Jul 27, 2008 2:06 pm; edited 1 time in total
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Tim Servo



Joined: Jul 16, 2006
Posts: 924
Location: Silicon Valley
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PostPosted: Sun Jul 27, 2008 11:32 am    Post subject: CA3080 VCOs Reply with quote  Mark this post and the followings unread

Hey Crash,

Although I haven't breadboarded the 3080 VCO, my guess would be "yes" in answer to all of your questions. Wink

Thomas' tri to saw waveshaper will work as long as the transitions in the square wave coincide with the reversals of the triangle wave. The square you'll get from the VCO core should be correct, whereas the square you'd get from running the triangle through a comparator will be 90° out (the comparator output is usually set to make a transition when the triangle crosses 0V). I used this same approach to get the saw out of the 566 VCO. BTW, if you take the square wave from the VCO core and the square from running the triangle through a comparator, you'll have two squares 90° out of phase. Plus you can do PWM with the square that comes from the comparator.

And yes, you should be able to use the 4013 to divide down the square wave. Note that you should have a diode on the input of the 4013 to lop off the negative half of the square wave (since the 4013 only uses a +V supply, it won't like being fed negative voltages). Again, I used the same trick on our 566 VCO board, and it works grooviciously ©.

And finally, you should be able to do the same tricks with the 13600 and the 13700. It may require a bit of tweaking (the 13700 has predistortion diodes on the input IIRC), but the basic setups should be very similar. The 13700 is a good candidate because A) it's easy to get and B) it has that second half that could be used as an output VCA, or an FM input VCA, or ?

Let us know what you find out on the breadboard, although you should try to avoid warming it up TOO much... Shocked

Tim (doesn't like being fed negative voltages either) Servo
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