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# TH-VCO1
(For more Background Details have [a look at the TH-VCO1 Wiki Article](https://code.hfbk.net/t6/sdiy/wikis/th-vco1))

**NB: All rights to the basic schematic design rest with Thomas Henry. We do not claim or grant any copyright or license to this design. His policy is to only distribute printed PCB boards via fonik. He granted us a one time chance to sell our run.**

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<img src="images/th-vco-1_1.jpg" height="500px">  
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The VCO-1 is a triangle core [VCO](https://code.hfbk.net/t6/sdiy/wikis/vco) designed by Thomas Henry. Thomas Henry made the original ±15V available on [birthofasynth.com](http://www.birthofasynth.com/Thomas_Henry/Pages/VCO-1.html). Because Eurorack Modules use a supply voltage of ±12V and the CA3080 OTA is harder to get amd use, [Tom Whitwell](https://github.com/TomWhitwell/TH-VCO1) from [Music Thing Modular](http://musicthing.co.uk/modular/) made an Adaption for Eurorack. This is our fork of Toms design, with improved routing, added a voltage reference and a completely new panel.
In the 2016/2017 Synthesizer Workshop at Computerei we decided to build the TH-VCO1 in Tom Whitwell's adaptation. We needed to order the PCBs ourselves which required a fresh export of Gerbers because our PCB manufacturer had different DRC rules than Toms. However there were a few things that we wanted to change (including the panel layout). One thing lead to another and nearly every bit of Tom's original traces have been rerouted. This had mainly to do with the different requirements we had doing a workshop with students of which some never touched a soldering iron before and others didn't had much to do with synthesizers before. Other changes had been implemented on Toms advice ("add a voltage reference") to make it an even more versatile VCO.

The triangular core of the VCO-1 is a Schmitt Trigger Integrator Circuit. If you're interested read more about it on [birthofasynth.com](http://www.birthofasynth.com/Thomas_Henry/Pages/VCO-1.html) or [here](https://code.hfbk.net/t6/sdiy/th-vco1)

Most of the used components are pretty standard.  The only non-standard (harder to get) components are a [2K 3300ppm Tempco](https://www.thonk.co.uk/shop/tempco-resistor-anakeohm-1-3300ppm-x3/) as R2, and a Polystyrene (or Mica) 1nf cap as C3, which should improve frequency stability. If no Polysterene cap is found one could potentially also use a (more expensive) Mica capacitor (German: Glimmerkondensator). You may also use an alternative value of 2.4nF here, to lower the Frequency range.

Look at Toms Quick demo here: https://www.instagram.com/p/_etQT6DmdM/

## Changes

Compared to Tom's Layout many things changed:

- The panel got a complete redesign (making it both fancier and easier to understand).
- Because of the changes in the panel the the Pots PCB had to be rerouted. Nearly everything could be routed on the top layer, leaving a nice undivided groundplane.
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- Due to Toms and J3RKs advice [on muffwiggler](https://www.muffwiggler.com/forum/viewtopic.php?p=2401495#2401495), a LM4040-10.0 Reference has been added to stabilize the pitch from voltage fluctuations happening in the potentially rough Eurorack environment. Look at the simulation results [here](simulations/LTSpice/LM4040_massive_fast_noise.jpg) and [here](simulations/LTSpice/LM4040_massive_slow_noise.jpg) (both showing a noisy rail on the top plot pane and the resulting buffered voltage after the LM4040 Voltage regulator). This change can be left out by adding jumpers instead of R1, C2 and SHU1 (LM4040)
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- This addition made it necessary to reroute the boards
- Two 1x5 Header Pin Strips have been added (to add stability even without adding screws), sadly we ordered the wrong pins ಠ_ಠ
- Most Pads have been swapped for bigger, easier to solder square pads.
- The PWM CV Attenuator Pot now is a 9mm Alpha trimmer (the small ones with the plastic head, commonly used for attenuverters). This however is downwards compatible to the 9mm Alpha pots: if a "normal" 9mm Alpha Pot is desired, it can still be used. You can get these Pots at Thonk if you want them.
- Cleaned up traces and silkscreen where necessary

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## images
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### PCB Boards
#### Components PCB (Top)
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![](manuals/Components_Top.png)
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#### Components PCB (Bottom)
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![](manuals/Components_Bottom.png)
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#### Pots PCB (Top)
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![](manuals/Pots_Top.png)
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#### Pots PCB (Bottom)
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![](manuals/Pots_Bottom.png)
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### Power Cable
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![](manuals/Powercable.png)
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#### Known Issues with PCB Rev 1.0
- Panel: Circle of Lin FM Attenuator not perfectly centered on hole
- Components: Power Header could get more space
- Components: Trimmers could get more space
- Components: Short circuit between -12 and -10 Volt Trace at U4. Remove Trace between JP1 Pin 8 and U4 Pin 4
- Diameter of Component holes could be bigger for easier soldering