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OneBoard Farm VCO
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acidblue



Joined: Jun 26, 2009
Posts: 226
Location: The Darkside

PostPosted: Sun Feb 22, 2015 3:08 pm    Post subject: OneBoard Farm VCO Reply with quote  Mark this post and the followings unread

I found this while cruising the internet.
http://www.aleph.co.jp/~takeda/radio/OneBoardFarm.html

Looks pretty interesting like to use the VCO on one of my projects but I
cant find any documentation on how to tune it.

Any one use this ?


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Broadwave



Joined: Feb 16, 2007
Posts: 347
Location: Manchester UK
Audio files: 6

PostPosted: Mon Feb 23, 2015 2:09 am    Post subject: Reply with quote  Mark this post and the followings unread

I've built a couple of them, they're ok-ish (you'll get about 3 octaves before the scaling starts to give out).

I'm not sure what you mean by "tuning"... TRIM3 is used to set the basic VCO frequency and VR1 is your manual tune pot, TRIM1 sets the scaling to 1V/Oct, and TRIM4 is for Hi Freq scaling.

The resistors on the octave switch are 1k (1% or better will do)
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acidblue



Joined: Jun 26, 2009
Posts: 226
Location: The Darkside

PostPosted: Mon Feb 23, 2015 1:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

It was my understanding that all analog VCO's had to be tuned before
they could be used.

Other VCO schems I've seen come with a text comment on how to tune them as the procedure is sometimes different from VCO to VCO, although I could be wrong.

Thanks for your input any way, I 'll play with the TRIM's till it sounds good to my ears.
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Broadwave



Joined: Feb 16, 2007
Posts: 347
Location: Manchester UK
Audio files: 6

PostPosted: Tue Feb 24, 2015 12:04 am    Post subject: Reply with quote  Mark this post and the followings unread

This should get you up & running Wink

1. Connect the square wave output to an amplifier to listen as you go.

2. Set the Octave Selector switch to mid position

3. Set TRIM4 fully clockwise for the time being.

4. Attach a 1v/Oct source (CV keyboard or MIDI>CV Converter), and play the lower "C0"

5. Adjust VR1 and TRIM3 so that the oscillator frequency is around 200 Hz.

6. Play the lower "C0" key followed by the "C3" key three octaves higher... keep doing this while adjusting TRIM1 (Scale Adjust Trimmer) until the octaves are in tune.

7. Now play "C3" followed by "C5" (repeat as above) but this time, adjust TRIM4 to scale the higher frequency - To be honest, you'll probably only be able to scale the VCO to around 4 octaves max.

You will probably have to go back and repeat 5 & 6 until the VCO is scaled correctly, it'll eventually come together.

8. Adjust TRIM2 (LM431Ref Voltage) until each position on the Octave switch is precisely one octave apart.

Hope this helps.
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