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# TH-VCO1
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(This is the TH-VCO1 Wiki Entry, for the [TH-VCO1 Project Repository look here](https://code.hfbk.net/t6/sdiy/tree/master/th-vco1))
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#### (This is the TH-VCO1 Wiki Entry, for the [TH-VCO1 Project Repository look here](https://code.hfbk.net/t6/sdiy/tree/master/th-vco1))
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![20170321_173027__](/uploads/78765b329e94deaac886b66ad9cc4450/20170321_173027__.jpg)
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## Basics
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The Thomas Henry VCO1 is a [Voltage controlled Oscillator/VCO](vco) for the Eurorack modular system. It has a coarse and fine frequency control and can output 3 different waveforms (PWM, Sine and Triangle). The pulse width of the PWM-output can be controlled via knob or control voltage. The output of the oscillator is constantly on – this is typical for oscillators in modular synthesizers. This is why it might be a good idea to pair them with a [Voltage controlled Amplifier/VCA](vca) or a [Voltage controlled Filter/VCF](vcf), which enables us to play the oscillator with different volumes, envelopes and timbres.
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... | ... | @@ -13,7 +14,7 @@ The TH VCO-1 is a relatively simple [VCO](vco) designed by Thomas Henry. Thomas |
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The frequency of this oscillation is controlled by an LM13700 OTA which works a bit like a [VCA](vca), but is actually controlled by current. One of the harder parts of designing an accurate [VCO](vco) circuit is getting a good linear (evenly "tuned") exponential voltage control which is achieved in our case by the use of an monolithic matched pair of NPN and PNP transistors in one chip (THAT340) and by using Tempco resistors which have a temperature characteristic opposite to other parts of the circuit in order to "cancel out" temperature drift. By using these Tempcos we can avoid big changes in tuning when eg. the room temperature changes.
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For a more thorough insight on this refer to [temperature compensation theory](http://ijfritz.byethost4.com/sy_cir7.htm) and [dial-a-tempco](http://ijfritz.byethost4.com/sy_cir9.htm?i=1).
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The TH-VCO1 uses btw. a discrete Schmitt Trigger circuit built around two transistors [http://www.diystompboxes.com/smfforum/index.php?topic=99939.0](explained here). This could be replaced by an dedicated Comparator IC or by an opamp based Comparator, but should actually be faster than a opamp based Comparator (produces cleaner waveforms at higher frequencies).
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The TH-VCO1 uses a discrete Schmitt Trigger circuit built around two transistors [explained here](http://www.diystompboxes.com/smfforum/index.php?topic=99939.0). This could be replaced by an dedicated Comparator IC or by an opamp based Comparator, but should actually be faster than a opamp based Comparator (produces cleaner waveforms at higher frequencies).
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## Build Manuals
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- A simple [User Guide](https://code.hfbk.net/t6/sdiy/blob/master/th-vco1/DIY_Manuals/TH-VCO1_User_Manual.pdf)
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