r/synthdiy

I built this mainly for myself, to make circuit-modelled plugins for a browser DAW I’m working on (daw.synthcity.org). I figured others here might find it useful, so feedback is very welcome, here or via the feedback button in the app.

https://circuit.synthcity.org/

You draw an analog circuit and play it like a synth. It isn’t modelled curves: it’s component-level simulation every sample, so the knobs are actual pots in the circuit. Under the hood it’s MNA with trapezoidal integration and Newton iteration for the nonlinear parts, written in Rust and running in an AudioWorklet as WASM.

• 22 classic filters at component level: MS-20, Moog ladder, 303, SEM, Polivoks, Wasp, Steiner-Parker, Juno’s IR3109 and more. There are also pedals like the Tube Screamer, Big Muff and Uni-Vibe.
• Plays in real time. Use the keyboard or MIDI, patch VCO → filter → VCA, and swap the filter while it’s playing. It works on a phone too. You can make macro level synth blocks and play those - it's like a modular synth/Reaktor. When you double click on a macro block, it zooms into the editable circuit.
• Lots of modelled nonlinear parts: OTAs (CA3080, LM13700), tubes, JFETs, BBD chips for chorus and flanger, vactrols for LPGs, and transformer hysteresis. Swap an MN3009 for an MN3007 and hear the difference. Let me know what’s missing!
• Plugs into your modular. With a DC-coupled interface (ES-8/ES-9, a DC-coupled MOTU or similar) you get calibrated CV in and out, including 1 V/oct tracking.
• The simulator is differentiable. It computes exact gradients with respect to every component value, so it can fit a circuit to a recording of real hardware, optimise part values to a target response, or search for new topologies. One of the presets is a filter the search came up with.
• Works with your tools and your agents: Docs: circuit.synthcity.org/agents
  • import .cir netlists and LiveSPICE schematics;
  • export to LTspice, ngspice and KiCad;
  • an MCP server and API, so Claude/Codex or another agent can design, simulate and fit circuits.

LMK if you'd like some more features, or something done differently etc.

You can also share your playable circuits with others, just click "Share" and copy the link!

Enjoy!

Hey all,

Can anyone recommend a good wood-working course or book etc that has helped you build wooden cases for your projects? I've been making cases for a while, but I'm completely self taught and would like to up my game a little. surprisingly I still have all of my fingers :-)

Here a little project that i did a view months ago…i think it turned out really cool!

Howdy folks- I was hoping I could get a sanity check on this 1970s instrument that’s been in a storage unit for an indeterminate number of years.

Dare I plug it in? Is it a bad idea to mod or service it myself? My pal and I are moderately handy and educated in electronics

I got so frustrated trying to build the Blasser circuits and running into issue after issue: esoteric parts, missing documents, difficulty troubleshooting.

I decided to make a better paper circuit for beginners: the Old Faithful, our beloved Atari Punk Console.

I based the design it on a previous build I've already made a guide for, my dead-bug style Mosquito. You can find the guide here

Paper Mosquito Guide

I'm currently working on an upgraded version which includes polarity protection and an indicator LED.

Hi Nerdz,

I'm building a line in to eurorack converter using the Befaco In Amp schematics and I want to add a Sallen Key Highpass filter to remove 50 hz rumble

I've taken the Befaco INamp schematic and deleted the 2nd input

Basically the Befaco inamp is 2 stages:
The first opamp stage is doing a 2.2 gain,
Through the potmeter
to the second opamp stage to output

Where would it be best to add the filter:
1 Before the inamp
2 In between the first and second gain stage
3 After the whole inamp

Where would you integrate the Highpass filter, and could opamps be shared?

I definitely overwhelmed myself with projects and I need to clean house for my own sanity. I'm going to focus more on the projects I'm interested in.

I have the Klee sequencer which is almost 100% finished (of course minus the absolutely huge task of wiring lol)

And a Tellum Corporation Doomsday Machine that's mostly populated but will need some more components and ICs.

Just shoot me a fair offer and cover shipping.

(Not sure if this is allowed here mods but not really sure where else people would appreciate these)

Thanks for looking and message me if you have any questions.

Based on patmcbennets code. Expanded to 8 steps via 4051.Added tempo control via knob. Added 3 vc out plugs and vc in

Sounds really good for arduino

:)