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FarmVCO 4069


Simple VCO


Upper temperature coefficient resistor(TCR)
Lower is Negative TCR
Generally,temperature coefficient resistor (TCR) is said to be hard to get. But I could get it easily in my country (Japan) in cheap price. Just that time, I had been asking some question about circuit diagram of analog synth to Rene Schmitz. His page is so great! I have been learning so many things here. Thanks a lot!
So I send mail him about TCR. I can get TCR so easily but I should get it so many pieces at a time. And he said, let's trade TCR with Negative TCR. It's so hard to get NTCR in Japan, so I said OK.

I got both NTCR and TCR. About TCR, see other page that I wrote in Japanese. And if you want to see the detail about using NTCR, see this page .
To testing NTCR, I wanted to build VCO or something. So I chose Rene's C-MOS VCO. Now I'm learning how to design circuit. I still can't design circuit from scratch, But I know that I can't use NTC (47k) that he send me directly. So I redrew circuit diagrams. And Rene checked them. (Thanks!)
In his circuit diagram, he used 4 NTCs, so I changed them as 1. And I change their values as he taught me. And I add soft sync input on it.
It's like this
He used European standard transistors, so I changed them to Japanese standard one. My PCB Pattern is this.Pin structure of transistor is different from European standard. Check it out! And he recommended that to use transistor buffer as saw out put, but I think that it must be used. Because the tune of this VCO will be drafted by the circuit connecting after this.
And for compatibility with my other modules, I change pulse convert circuit's VR to pot on a PCB. If there is without notice, all PNP transistors are 2SA1015 and all NPN transistors are 2SC1815

Arp's NPN-PNP Matched antilog circuit


Where is the OPAMP!
Q1 and Q2 in circuit diagrams must be matched pair about values of their Veb. And you must paste them together. Both transistor should be drifted together for temperature changing. Although my PCB pattern don't do them, but R6(NTC) also should be pasted with them together.

This circuit didn't use active parts for summing stage for getting simple. It causes something bad for CV inputs. It will going to make a gap of an octave or something. This type not matches for modular type. But it should OK for IN-BOX type.

Tune


Hot VCO?!
When you turn it on, C-MOS get hot. Don't worry about it. It should be.

There is no trim for hi area tune. but you must tune for pulse width. first, you set knob of PWM/PW anti clockwise then check output by oscilloscope and check it. If you don't have it, use your ear. if you hear the sound like "cheeee" it's pulse wave. "poooo" means square wave. Set it as you like.

About scale pot, play octave phrase. if it's narrow for octave (upper tone is downer than real tone) then turn your pot to hear tune downward. it will spread octave. Use initial tune pot together and set as you like.

Outputs


Saw wave

Squre Wave
Saw wave has a curve like the back of a cat. We call that "NEKOZE". "neko" maens cat and "ZE" means "back".
And Squre wave have also round courner.

About 4069

Reader of this page send me some message about 4069. I use "TC4069UBP" for this experiments. But he said that 4069 should have the versions and it should be "B" and "UB", He said that "B" type may need more current to work.
I think 4069 VCO is hot (I mean double in this word) and good, but if it use more less current to work, then I like it more.
As the other C-MOS logic IC's naming rule, they should mean "Bufferd" and "Un-bufferd". I check the web, but I can't find data sheet about 4069B.
And I can't get "B" type 4069 actually yet and I don't test with it. So if you want to build this and want to add to your system, Even if you can get "B" type, I recomend to use "UB" type. (added 2003/03/06)


This is my first try writing page in English .I may had mistaken. Point it out for me.
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"VCO 4069" Copyright 2002,2003 Motohiko Takeda, Crow Hill Laboratory
Motohiko Takeda Mail:takeda@aleph.co.jp