I’ve also had my eye on this one which uses 3xLM358 op-amps to generate triangles:
Only issue is that it’s at 9v, don’t know what will happen it if I power it with 12…
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Pop it between Eurorack 0V and +12V rails and see what comes out.
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Add two resistors as a voltage divider to reduce the voltage to 9v. One between gnd and the 9v trace and the other between the 9v trace and the +12v wire. Sorry, I’m too medicated to do the maths so jfdi badge to the first with values
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The design I’m working on only needs TL082 and transistors, but the 1V/oct input only works for 2 octaves (for now), and it’s not temperature compensated (but that’s an easy fix).
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https://electro-music.com/wiki/pmwiki.php?n=Schematics.VCO555ByThomasHenry
Has anyone ever given Thomas Henry’s 555 VCO a go? Always thought the sync on it sounded awesome. It was one of the first DIY projects I remember seeing but at the time I was scared off by it being +/-15V, and I couldn’t find a PCB anywhere. These days I would think about doing it on stripboard, but there’s too many projects in the way already
EDIT: didn’t see @BlackDeath post this first - regardless, would be good to know if anyone tried it.
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Haven’t, no. But there’s a Eurorack PCB and panel available.
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Ah no way! I think I was only looking at UK/EU dealers. Might have to pick that up
Thonk has it listed too, though out of stock.
In fact they have the main panel only listed, but also out of stock.
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Out of stock! Three words to inspire DIY
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Yeah, unfortunately it’s been out of stock for a few years, so I’ve given up on it coming back 
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Is the Eurorack adaptation of the Thomas Henry 555 VCO published? You really only need to change the values of a few components to make it work on a 12V rail system. I believe there are already some tested PCB or veroboard layouts that can be copied.
555 circuits without v/oct are super simple:
Bang a few of those together and you’ve got a cool drone voice.
With v/oct, I think it’s a different issue…
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Never saw a 555 circuit using only pins 1 to 4.
The 555 will astonish us for ever… 
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This is a bit above my pay grade, but it seems like this is the circuit to turn v/oct voltage into current values the 555 needs, and I’m guessing what the TH-555 uses:
Even without that, the simple 555 circuit is useful as a clock source if you don’t have a Keystep or something like that.
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Somebody just posted another thread about this, using the CD40106:
Kristen Blåsol (who has an awesome YouTube channel) also used that here: https://www.youtube.com/watch?v=DtUCzzjHhgM
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Not sure tbh! Been a long time since I looked around. I vaguely remember seeing a couple stripboard layouts but I don’t think any of them were confirmed working and all that
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Check out the ohmsynth videos on the CD40106 as well!
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Cd40106 is such a straightforward oscillation setup. Perfect for drones.
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I looked around and here’s what I found. A 2012 forum post on electro-music in which Thomas Henry introduces the schematic for the 555 VCO.
Fonitroniks’ DIY page which gives parts lists and assembly instructions for several Thomas Henry designs adapted for Eurorack:
The two PDF files to download the are TH-555VCO-10HP.pdf and TH555VCO-BuildNotes.pdf.
This ought to be sufficient to enable somebody to build a copy on veroboard.
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Well volunteered @Bitnik
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