Synthfox Custom Stuff

Hi there, welcome to my synthesizer corner!

My name's Astro, and i present online as this name and the audiogear microbrand Synthfox. I have been making DIY gear since around 2015, and have made big progress since then! Most of all i like creating original new circuits out of cheap common components, as well as enhancing and elaborating on some particular pieces of other devices' circuitry. So i decided to create this site, so people could come by and find some nice circuits to build!

You won't find super-beautiful stable VCOs and lush sounding VCFs here. What you definitely WILL find, though, is some experimental circuitry that makes your waves a funny mess. I especially love making CV sources and, most of all, sequencers of all kinds. Everybody is welcome to build, modify and re-document my stuff, but ONLY for personal build (not for sale!). Also include obligatory attribution to me (as Astro or Synthfox, preferably linking to this website) and everyone else mentioned in credits on all documents for the device that is a fork of something you found here.

Building a synthesizer system is not too hard or expensive, and is a lot of fun! It's a never-ending odyssey into weird interesting sounds and events. Join me and all other Synth DIY people on this trip, and start soldering already!


  • 20 JUN 2021: made a new firmware for the VC Sampler that is a very, terribly bad implementation of a karplus strong algorithm with a sawtooth initial buffer. It turns VC Sampler into a tiny glitching synth voice of its own. Give it a try. Also: working on more DIY modules but i'm all out of parts and neither of them is complete enough to be called ready.
  • 23 MAY 2021: the thesis defense is nigh, but i made a voltage controlled audio delay with a PT2399. Crunchy lo-fi delays, nom!
  • 09 MAY 2021: made a little LPG mixer for my soul. It's not perfect but it works and sound lush.
  • 05 MAY 2021: oh god, the university ain't treating me well! Didn't have any time to finish any DIY project. Loaded up the Dual Utility Summator at least, if you don't have something like this in your rack - you should. I have a bunch of amazing modules on the backburner, someday you will see them, i promise!
  • 20 MAR 2021: Busy with internship, but still managing to do stuff! My VC Sampler blew up, so i fixed it (and the schematic), a person pointed out i had some suspicious places on my Step Phrase Programmer schem - and yes, it did, fixed it, too. Lastly, i built a new module - it's a quadruple discrete core resonant filter, 3 bandpass and 1 lowpass in 1 bundle. Take a look at it, the new Quad VC Resonator!
  • 18 FEB 2021: Finished an extremely complicated (in my scale) build - the dual VC Sampler! It's my first hybrid module for my system. The firmware is also available on the module page, along with shcematics and all. It's crude and 8-bit and i LOVE it.. Check this thing out!
  • ?? FEB 2021: I made an X-Y controller and forgot to post the update about it. It's a neat joystick thing!
  • 16 JAN 2021: wow, what a huge break. I was away and was up to stuff, i guess. Anyhow, i made ANOTHER 4017 STEP SEQUENCER. Last one this time. I promise! It's so buff and overfeatured i might even consider it a shitpost. Anyhow, check it out here!
  • 19 NOV 2020: revived my first paperface eurorack module documented for this page from the dead - now it functions better than ever, and has a slightly different schematic. Updated its page for the case!
  • 13 NOV 2020: built another module - a cool logic thingy for gates mostly. Take a look at it here. Also, loaded up a new album called "Thoughts Scribbled Down" - it was kinda waiting for its hour for a while!
  • 25 OCT 2020: craved some sort of a dynamics control and/or fading device for the newly built VCO, so i threw together a neat simple vactrol crossfader circuit, and then made two of them in one plank. check it out!
  • 21 OCT 2020: i was procrastinating from doing this forever, but i finally pulled myself together and did it: the actual, full, dual VCO module, that's not a full ripoff of someone's design, has my soul and blood in it, and actually works surprisingly well. Would you please welcome - the 40106 Dual Oscillator!
  • 30 SEP 2020: took a huge break from modules. Didn't announce it right away, but i made a dual passive LPG but better, for a trade with a friend. Today, i also put out a new album called STATION T-16-10 @ 8824133, 2963667 right there - check it out! I expanded my eurorack by another 3u*84hp box, so finally i have some space for new DIY modules.
  • 02 AUG 2020: made a little utility slew limiter module cause i really wanted one. there it is, come take a look.
  • 27 JUL 2020: took a breather with the modular, travelled a bit, then lost an acution on another doepfer module and compensated by designing and building my own replacement for it. Check out this neat digital noise generators combo!
  • 04 JUL 2020: added a project i was slowly pushing and finally finished, the Musicomputer, to the other gear tab! Also, finished an article on making eurorack module panels -- you can read it here.
  • 27 JUN 2020: finally, i finished the SFP17 Dual Pluck Envelope! It was a pain in the back to make it working - because of not having a correct kind of flux, i used a very powerful and gunky one, leaving me with a very esotherically behaving board. Had to wash and scrub and reflow and repeat, repeat, repeat. But it's done, it works, and it's great!
  • 02 JUN 2020: university has been pure hell for last 14 days, but tomorrow's my last exam for this term and i'm back to making stuff. I totally forgot to write here, that i released a new album called mainframe memories over on the music tab. Be sure to check it out! Also i added those dumb buttons down there, how cool is THAT.
  • 14 MAY 2020: Finally got my spirit together and made myself some simple, but working VCOs! They're linear, so no cool beautiful melodies from CVPal or anything, but they're still nice, and they are 4 of them for the cost of two chips! It's a variation of a cool VCO schematic by Hendrik Göttling i found here.
  • 12 MAY 2020: The previous build was sticking out to the side, so i had to build something that could fit right next to it.. and i did! Made myself a cool nerdy utility adder with a digital-aimed taste, but purely analog at its core: the R2R Antialiased Summator!
  • 10 MAY 2020: the madness goes on and progresses! I thought of a cool not-so-random voltage warble thing, and decided to try it out. this happened, and it is wonderful.
  • 07 MAY 2020: Made another probabilistic thingy, the small sister of my Shift Core Generator - the On-Call Binary Random. Adds a whole new world or probabilistic rhythmic experience (and much more yet to explore) to the thing!
  • 24 APR 2020: My soldering iron broke down, but i got another one and am bacc on the tracc. With this, i finally built one of my dream utilities - this Arithmetics thingamagicky! I screwed up a minor part of it, but it was a last-time design decision anyways, and i will realise it in a better, more sophisticated way in another module someday.
  • 06 APR 2020: Late update - added a new device to the Other Gear page. Fixed some tiny typos here and there as well.
  • 01 APR 2020: New module - the full clone of Buchla 208 with added features, such as APRIL FOOLS. Ahaha. Funny. Anyways, there's a new module - my most complex build of recent months, the Shift Core Generator. It is a randomesque stepped random voltage generator, but also - much more than that. Check it out!
  • 31 MAR 2020: New module - the Subharmonic Divider! A nice tool to enhance a voice AND a field for weird sound experiments.
  • 27 MAR 2020: As promised, two new modules are up on my website: the Stacked Adder and the Master Output! This duo forms a nice stereo output mixdown combo, which was my primary goal with them. Although, the modular nature of this stuff will always bring you new usages for simple usual things. Go check it!
  • 25 MAR 2020: Wrapped up and uploaded two new albums to Music - one is a slightly psychedelic tale about a mountain, the other is impressionist garbage (i guess, i'm not that good at art!). As always - FLAC and MP3s available on an external hosting through links, and a sampler is right there. Side note: 3 new modules have been made so far, 1 has a bad chip which i can't find a replacement of right now, but 2 others are getting their module pages at Modules soon enough. Side side note: quarantine time, stay inside and make some synths! Or not. But stay strong!
  • 15 MAR 2020: New module: the Discrete Slope + Hysteresis Comparator combo. Go check it out here!
  • 01 MAR 2020: Loaded up the new module i designed and finished the same day (yesterday), the Compact Clock Source! It's a really neat little complex rhythm generator. Also i touched up the Other Gear page and made the first entry about my Korg Volca Bass breakout box.
  • 28 FEB 2020 [2]: Finished and digitized my experimental tape of weird music called Sounds With Less Meaning. It's now up with the download links at the music page!
  • 28 FEB 2020: Finally more or less back on my synthesizer making duties! Finished and documented a rebuild of my old times module - the Eight Step Sequence Programmer. Simple, but not as simple as you may think!
  • 13 JAN 2020: Put up 3 out of 5 (6?) CrapRack modules to the modules tab - the ones i was making a show about, called SYNTHCRAP. It feels awful to watch it now, but the modules are fun and should be archived and documented.
  • 04 JAN 2020: finally sharing this website online and kind of "publishing" it to the real world. Hope you have a blast! Some updates coming up soon, hopefully.
  • 19 DEC 2019: new album, Processed Noise and High Frequency Oscillations, added to the music tab. More updates soon - the month has been terrible university-wise.
  • 01 DEC 2019: new module SFP04 Directional VC Slew Limiter, reorganized the modules page a bit. Minor fixes.
  • 21 NOV 2019: added a 'my first audio electronics project' page, as well as polished up some other pages. Site to be announced to public soon enough.
  • 15 NOV 2019: added SFP03 to modules. Minor bugfixes.
  • 14 NOV 2019: initial setup of the website! Did a whole bunch of stuff.

Apart from making modules for various systems and sharing the circuits here, i make a lot of other stuff as well. Some of my non-modular things are displayed here in a non-logical and non-standardized format, as well as the music corner where i plan to host my modular music releases. In the 'stuff' section, you can find a bunch of useful how-to's and info's. I tried making it beginner friendly, even though - as always - i ask y'all to be careful and take care of yourself and your workspace. And yeah, never solder live synthesizers. (more on that in this disclaimer)

Also be sure to check out the abouts and my way more personal and less technical neocities webpage here.

p.s. also, as you might've noticed, this website isn't really mobile-friendly: it won't ever be, cause i am that nerd who is for actual usable computers' usage, + making it so requires a lot of relatively heavy javascript, and this place should have as much plain stuff phylosophy as possible. Sorry!

Peace Love Unity Respect, and synthesizers!