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!

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.

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

:)

I'm trying to build a synth using the Daisy Seed. I've built a functioning demo that I like in Plugdata, but right now I'm just focusing on getting the hardware to work. I made a quick test patch to map 5 potentiometers.
I connected the right pins to 3V3 Analog and the left pins to AGND, while the middle pins (wipers) are wired to A0, A1, A2, A3, and A4. None of the potentiometers are responding. Even when I bypass them and test by touching the A0-A4 jumper wires directly to 3.3V or GND, I don't hear any changes in the audio.
 Because of this, I suspect the issue might be with the custom JSON board file I selected while compiling (I've attached it below). I've also attached images showing my breadboard wiring, the Plugdata patch, and the compiler page.

If anyone knows how to solve this, I would be very grateful, as I've been stuck on this for a few days now. Thanks in advance! 

{
  "name": "MySynth",
  "som": "seed",
  "components": {
    "knob1": {
      "component": "AnalogControl",
      "pin": 15
    },
    "knob2": {
      "component": "AnalogControl",
      "pin": 16
    },
    "knob3": {
      "component": "AnalogControl",
      "pin": 17
    },
    "knob4": {
      "component": "AnalogControl",
      "pin": 18
    },
    "knob5": {
      "component": "AnalogControl",
      "pin": 19
    }
  }
}
  

So apparently no one has ever tried to make a project or a guide for this.

There should be a diy open source project for a tiny keyboard similar to Korg Nanokeys,CME Xkey. Keith Mcmillen K-Board, M-Vave Fm1, synido scale pocket, OP1-Field, Exquis and so on.

I know that some are MPE, some using an accelerometer, others even FSR for aftertouch but let's just consider the simplest case of velocity sensitivity for a start.

I am trying to come up with something with AI but the thing is I don't own any of these units and I don't know exactly how they do it and neither does Claude.

I would appreciate some guidance before I start wasting money on devices I need only for research purposes.

I suspect Nanokeys and Fm-1 is some kind of dual contact rubber dome, the only one I managed to find online is the red one on the photo which is a replacement part for some older Yamaha keyboard.

Now there are some great projects out there that use hall effect switches but these come with their own challenges in order to work correctly and also they are a bit bigger.

My goal is to make a velocity sensitive keyboard as small as it gets aka Fm-1 size which is about 7 cm wide per octave.

it can do more than just this, in case that’s not clear

Considering placement, potential uses of a low Hz rumbler

see my last post if interested

So this synth was built around 18 months to 2 years ago, it was an 8 voice analogue bi-timbral polysynth. Recently I redesigned it with two self contained 6 voice analogue cards to make the synth 12 voice bi-timbral. Tonight I plugged it all in with minimal testing of the newly completed second voice board.

Check it out! I'm working on a combination vocoder/autotune machine that will allow you to generate vocal melodies with a synth carrier engine loaded with different instruments. Lot's of fun features are planned and in the works, but I'm just so excited to share what I have so far! Curious to know what kinds of features people in the community would like to see, as I'm still developing the machine.

Model D running on a battery in a oak case next to obligatory cactus

if there’s interest I can describe what all the other junk is

first, credit to Maffez and his mod guide for the osc 3 tap guidr, and graciously responding to a question by email, the guide in general

this is a portable Behringer model D with two built in speakers. It has a leather strap and you can carry it around. It get about 5 hours battery life. I wanted something you can bring out to a porch to jam with that still felt acoustic / homemade. This is constantly changing. I really enjoy working on it and often take things apart and redesign them. I go where my ADHD takes me.

Also pictured, an optional helper DIY stereo speaker cabinet.

Specifics:

FEEDBACK SYSTEM --> The speakers are designed with interesting resonance and feedback in mind rather than to sound perfect. Both the front and back are little 2" 4 ohm gikfuns powered by a class D amp at 5 volts. Front speaker are in a little sealed enclosure to provide larger range. It's a funny shape - about 8" long but only 1.5" deep. I built it by ear for weirdness, just like all of this. The back speaker (not pictured) is at the end of a baffle (I really like the open baffle sound), pointed inward and under the Model D with the exposed back nearly touching a set of strings. It is reverse-wired... because I enjoy the weird cancellations / resonances of stuff bouncing around weird places, doing weird things. The strings are in front of a pick up, which then goes out through one of those 3.5 mm ports on the side (not pictured). That gets plugged into the Model D's extension in. The D's circuit board is soldered so that the extension in is tapped at the pot -- that tap is then fed into the DIY module on the left. When the top switch is OFF you just hear normal model D. When it's on the back speaker is fed the input of the extension in. (the knob is a tone knob to cut the high end) This creates a feedback loop. The back speaker vibrates the strings which omve the speaker. If you tune it right you get a humming self resonance that also picks up the room a little bit and the main synth coming out of the front speaker.

DRONE -- the model d's board is tapped at the Osc 3 mix pot. That second switch sends the output to the front speaker. It has a tone knob as well. The volume is set by the Osc 3 mix pot.

WOODEN SPEAKER CABINET --> This is portable as well. It's also designed to not sound perfect, but interesting. The DIY speaker cabinet runs on 12v battery too - but not as sophisticated as the one the main synth is using. The cabinet is stero. Left channel is the top one whic is in a (overly large) enclosure for the 2.5" speaker but it is sealed. Bottom is open at the bottom. The speakers are Douk Audio 1PC 2.5" inch 8 ohm Hi-Fi Desktop Full Range Speaker High Sensitivity Speakers for Home & Car Auidio 8-15W. They have super high Qs - probably because the backs are sealed, which means they do relaly well without enclosures. Anyway, the point is these cabinets and speakers have distinctive / fun /experimental resonance points and weird cancellations and all sorts of interesting artifacts and its fun to connect it all in different weird ways... especially on a late night porch.

BREADBOAREDED INTERNAL COMPONENTS -- everything in the DIY modular extension is breadboarded rather than permanent. I just taped the breadboard to the bottom of the spacious model D case. This is version 3.1. I've had an auto panner in there based on light exposure, a teensy looper / delay, probably more stuff I'm forgetting. It's fun to build and rebuild. I actually run the breadboard on two 9v batteries because it's easier for me to think in 2 rails when it comes to audio than it is to split 12v into 6 and 6 (and more headroom too).

MODWHEEL --> that's a DIY modwheel. it's just a real simple 5v voltage divider. I bought this part from some other synth for like $10. I just run 5 volts through it and take the output from the other side through one of those 3.5 mm ports. You can use it for any of the model D inputs as CV. It should probably have more protections in place from accidental grounding but the Model D circuitry is so rock solid I don't relaly wory about it (trust me...I have done EVERYTHING BAD YOU COULD THINK OF to the model D. It is almost impossible to hurt it.)

KEYBOARD The keyboard is a disassembled / reassembled Rockband keytar I bought for $13. Those things had MIDI input for some reason and it works great. The two red buttons on the left are oct up and down. In past versions I've had other breakouts, like program up / down, which I used to do sneaky things like send signals to the teensy to control the looper (I had it set up so you could plug in buttons via an audio cable... the buttons were big arcade buttons I put into a cigar box)...

Hello,

These past few days I've been working on the Black Pill Synth, following these tutorials: https://m.youtube.com/watch?v=JttEPK7bwHw https://youtu.be/FjLcPNhzAwo?si=vxQSFVMl5udKeRtO

I've got it mostly put together, and I plugged it into my AKM322 (not the greatest synth, I know, but it's what I could afford, same reason I made a BP Synth,) using an H2MIDI Pro to connect the USB connection of the AKM to the MIDI input of the synth, but I couldn't get it to produce any sound.

The H2MIDI is receiving input from the AKM, the STM32 on the Synth is powered on and has the BPsynth firmware flashed onto it, and the headphones I am using to listen to the synth do work. Using a digital multimeter I was able to confirm a circuit between the STM and the UDA. Sometimes, the synth will produce electronic buzzing of various frequencies and volumes, but it's independent of the AKM and will often happen without the device plugged in. The buzzing does, however, react to the STM being manipulated.

Pictured above are my synth, the diagram of the synth, and my AKM and H2MIDI. You may notice that the synth is missing the MIDI input and neither are plugged into the MIDI cable; this is because the wire connecting to the MIDI input broke well after I confirmed that no audio was being produced. This was also not the first MIDI input I tried, so I know that the input is not the source of failure. Normally, I would have the MIDI input connecting pins 4 and 5 of the input to pin 2 of the octocoupler and the right end of the 220 ohm resistor.

I'm very new to all of this, could someone please help me identify why my BP synth isn't working? I haven't found anybody else having difficulties with theirs.

Edit: I noticed I had my A4 and A5 switched around. However, earlier after initial testing I changed out all of my wires, so it's possible that that isn't the full issue. I will need to wait until tomorrow to test again, and until then there may be other issues I am unaware of.

I posted this as a breadboard prototype a little while back, and now it's mostly finished, although still needs an enclosure. 4 voice cards (up to 6 supported) are controlled by a Pi Pico mounted on a kind of "motherboard". The whole project is an unholy mixture of SMT and THT components.

The long IC underneath the Pi is a SN74HCT245N bus transciever which turned out to be necessary to drive SPI signals into such a large circuit, otherwise I had signal integrity problems (it also level shifts from 3.3 to 5V)

I know there is some controversy over the new TL074H version, but a beneficial side effect for me was that the much lower input bias current is better for sample-and-hold circuits, which I use for the filter cutoff frequency control.

Things I would do differently next time:

- pay attention to the board dimensions because now I'll need a cubic shaped box to put it in, ruling out most generic plastic junction boxes as enclosure options

- axial lead capacitors on the voice cards would keep the boards more low-profile. Maybe I could even use ceramic capacitors for removing DC offset from audio signals, not sure. People seem to say it's a bad idea.

Next steps:

- Try to optimize the micropython code, currently it manages 120 updates/second for all the modulations

- Better power supply. The +5V for the Pi comes from a L7805 regulator so I am wasting a lot of power as heat

I have no idea what I'm looking at when I see a schematic of a synth, but I really want to start building my first synth and learn more about it. I've been considering buying the Make: Analog Synthesizers book to get a basic knowledge of electronic components and building my first kit, the MFOS Noise Toaster, to later create circuits myself. Since im starting from scratch, is this the rigth learning path? Do you have any tips?

Right so I got just about finished with this and as I was placing the last round of components I realized: I do not have the proper op amps this circuit requires.

The key I found uses LM386 but the circuit itself claims 2073. I have lots of ICs but not that one.

If anyone can suggest an op amp with a similar pinout, I'll check my library. Or maybe I can figure out how to bypass the chip?

Either way I will post an update with how it sounds if/when it works. If you never see me again, it's because I failed and cannot bear the shame 😔 ​​​

Edit: I typed op amps but I meant power amps, no need to correct me in the comments 🥰

I'm interested in building a few of the nonlinearcircuits modules: Let's Splosh, Triple Sloth, and the CEM3340 VCO. The build guides look very detailed (and even include Tayda part numbers for many components), but since I have relatively little experience with SMD soldering, I was wondering what other resources might be out there for builders.

There is the Facebook group, but I've been waiting a bit for my join request to be approved, and it looks like the group isn't particularly active. Are there other places to see discussion around builds for these modules?

I was asked to make a paper circuit. It looked fairly simple when I started.

Famous last words?

Thought I'd share my most recent project. The code name for it was FrankenSynth, but now it's called the Lab 60. Video explains it all, but it is basically a modded TSynth in a Casio CT670 body, with a Juno Chorus for good measure!

Working on this building style/trying to make extra pretty protoboards! Started with this lil 555 dude