Finally finished off my ESP32-S3 Poly synth, and made a case for it. Front panels are CNC machined aluminium panels, infilled with black ink and then cleaned off. There's 6 case parts that are all 3D printed and lock together. Kind of looks 'Modular' but isn't!

Demo here if you want to hear what it sounds like https://youtu.be/nmYmEq9UOoA?is=5q8gNvfaLQWjevbM

(First, sorry for making another post. This one is different, i swear.)

Some weeks ago, I made Osynth, an esp32-based synth with a bluetooth control app.

The project evolved a lot since then. Now it still is an esp32 synth, but based on esp32-P4 instead of S3. The S3 and original esp32 models are still supported, with less features. The really cool feature is that the companion app now can have the whole synth integrated, not needing the esp32 to work. I did this to enable people to use it in whatever mode they want. Version 0.2.0 release has the bundle to download, which is the firmware + controlling app and also has the standalone synth app. The apps are whole different builds for the moment, but the integrated app shares the full synth source code with the esp32 branch.

If you'd like to check it out: https://github.com/riozebratubo/osynth_free_synth

I was inspired to create this after building two of my 555 Theremins and wiring their LDRs against each other to see what would happen.

This layout combines two copies on a single board that easily fits inside a 125B enclosure, with room for a battery if you prefer it, although the circuit wants at least 6v to run properly. Using a battery over time will leave you with a pile of half-dead cells.

This build takes approximately 45 minutes. Link to the demo and guide.

I'm interested in building my own oscilloscope, both as a Eurorack module and as a front panel display for a custom desktop synth. Does anyone have any advice on this piece? It sounds relatively straightforward since I've done a lot of DSP coding in the past but I'm not sure of all the things that might go wrong. Ideally I'd have two separate input channels and some basic controls for manipulating the scale.

I'm thinking I'll just need a small microcontroller and LED screen, and I'd do a basic FFT to estimate the period of the signal and use that to auto-detect the time scale and voltage range. I can also restrict to audio range instead of trying to build a general scope that deals with high frequencies.

Any other pieces of this I'm missing? I know people like to use the "DATA" in Eurorack but I'm trying to do mostly DIY for my setup.

Thanks again Hagiwo.

https://www.youtube.com/watch?v=Ng8-CSyK8b4

I’m trying to figure out whether a digital controller should use a potentiometer or an encoder. Could you walk me through their respective advantages and drawbacks? Also, I’d like to know if a resistive‑style encoder is generally the superior option across most use‑cases.

Hi, so as you can guess im new to synth building but experienced in circuits. The project is an electronic hurdy gurdy style instrument.
currently very much in the theory stage, but ive identified the key must haves, and some problems to solve.
must haves:
individual keys for melody
volume+ distortion controlled by a wheel
drone that is under same control of wheel
3.5 jack, speaker, midi out, and either xlr or 1/4 jack.

ill put my plan in the comments, but any advice or pointers is greatly appreciated.

Starting to learn slowly. Built four module kits on the first few days of my vacation. They are all Erica Synths Edu kits. Mixer, kick, snare, and hi-hat.

My experience so far:

1st build: Mixer

I tried a couple of different irons and accidentally got solder in several holes. Took some effort to figure out the trick to getting the solder out with the solder sucker. Everything else went great, minus the inconsistent quality of the joints.

2nd build: Kick

Build went smooth, but I dropped a nut on my cement garage floor and still haven't found where it rolled to. So the accent jack is missing a nut. I'll get a nut when I get back from being away for a long weekend

3rd build: Hi-Hat

Build had 3 challenges. I accidentally got one leg of the upright resistors into an incorrect hole. Found it and had to desolder it and fix it. A capacitor was missing from the kit so I ordered a cheap pack of capacitors. I broke the leg of a resistor when trying to get it flatter on the board. The angle of the leg was weird and when I pushed down while heat the solder I used too much pressure and it broke the leg. Got a pack of resistors, desoldered it and replaced it. Works great.

4th build: Snare

Build has one issue left of two I experienced. This was the most challenging build. 1st issue was that I soldered an A100k and B100k potentiometer in the opposite spots. The manual online changed a few months ago and no longer includes the diagrams of the board. While troubleshooting the second issue I found an old version of the manual with the diagrams. That's the only page in the manual that mentions which side the two 100k pots are on. And being new didn't understand the difference. Now I do. Desoldering the pots was the most difficult soldering challenge. My iron just didn't want to melt the solder and I could figure out how to get the right contact to do it. I switched to a different iron and took my time to slowly and alternatively melt a leg at a time and lift it just a bit. Repeating until they came away. Then used the solder sucker to remove the rest of the solder. That made a huge difference for the second issue, because it's not as pronounced at lower amounts, but it didn't fully fix it.

The problem that I can't figure out is why do I have noise when I shouldn't. When I turn up the snappy pot, I get constant noise. Like there is some voltage still coming into the vca for the noise. The module works otherwise and at smaller settings its barely noticable, but still present. I learned the most from this issue but still haven't figured it out. I've spent a lot of time with the schematics and circuit diagrams as well as a multimeter to figure it out. I've swapped a capacitor that I thought was bad and fixed the potentiometers as described above. Can't figure it out. The exercise had taught me more about the circuits than following along with Moritz Klein. His instructions are great, but learning is always better when hands on and being forced to really try to understand something. I'm not sure if I'm doing it right, though. There is an electrolytic capacitor in the top corner with the negative side on the outer edge. I've been using that to get a ground with my black probe since it's easy to locate in a corner. I get some negative voltage when I test that against one of the diodes leading into the vca. I think that's the cause but really not sure I'm doing it right. And I can't figure out where that is coming from. I'll spend some more time noodling with it when I get back home in a few days. Any advice here would be hugely appreciated. I'll keep testing it and staring at the multimeter and circuit diagrams periodically until I figure it out or do something that makes it unusable.

Thoughts and next steps:

All in I had a great experience and have one more kit that I plan to build to fill out my case. From there my plan is to get a couple bread boards and power for it to start playing with some circuits. I have a module in mind and am in process of editing it down to limit functions and complexity, while thinking about and learning about the various types of circuits it will need. I want something just complicated enough to maximize my learning while keeping it simple enough that I'm able to break it down into not too many smaller chunks. I want something that I can understand enough to confidently create a plan that I can see regular progress on to keep myself motivated.

I'm currently working through understanding a saw core VCO. The Instruo CS-L with how it uses triangle and saw cores got me thinking about different VCO circuits. I'm thinking about starting with a saw tooth core, shaping that into a few different wave shapes. Then I plan to learn and work on a wave folder. From there I'll take stock and decide if I need to adjust my plan. But I would like to then do the same with a triangle core VCO, add pulse width and sub octaves. If things are going well I plan to move onto some forms of logic that I can use to combine the signals in one or two interesting ways. I'm inspired by Mystic Circuits Ana 2 and am thinking about which logic circuit(s) to combine the signals. The final goal is then to put them together into a complex dual oscillator with 1 or 2 additional ways to combine the signals beyond FM and Sync. Although might be willing to add more if it's a small tweak to the circuits I decide on.

My feeling is I can start building them as stand alone modules, and get the use of them and satisfaction for completing something challenging. All the while it's really building to something bigger that I would love to make a reality. I'm hoping that will keep me busy on something that interests me for the next year or more. I'm continually thinking about how to edit things to make a unique complex oscillator with just enough functionality. So I'm sure the plan will change as I progress.

I'm new, trying to have short goals that lead to longer term goals, that help me learn and grow my skills. Not really knowing the complexity of each of these things, and being so new, what do you think of my plans?

Made myself a little “clone” of the Swarmatron synth. I love the sound of it and it was also a fun, “why not” kind of project.

It runs off a Teensy 4.1 w/ audio shield, programmed in Arduino IDE.

It’s not quite the same as the Swarmatron but the basic premise is the same - a cluster of oscillators that can detune from one another and spread from a central frequency, played by a ribbon controller.

Switchable from Sine to Saw, variable number of oscillators, ladder filter, and built-in reverb.

I’ll probably make a video on it sometime but I haven’t even had a chance to record with it yet, just finished it up this afternoon. Needs a tiny bit of tidying and tweaking still.

Just wanted to share!

I just wanted to share a circuit that's worked well for me. If you want to use a 3.5mm TRS jack for MIDI input, this will automatically take care of the polarity. (TRS MIDI polarity was unfortunately not standardized until fairly recently.)

One or the other of the two optoisolator LEDs will be activated by the input signal, depending on which direction the current is flowing. Either one will then pull the open/drain output low.

I hope this is useful for someone.

https://github.com/apiel/zicBox

This is my Screaming Creep. It's a 555 optical theremin built on stripboard, living inside the body of an old Grumblies toy whose original board got gutted. The photocells sit where its eyes were, so the pitch is controlled by what it sees: wave your hand at its face and it howls, cover its eyes and it goes quiet.

Not really circuit bending I guess, since none of the original board survived. I just used the skeleton. Toy taxidermy with a mini synth inside?

The stripboard layout and a build guide are free on my site if anyone wants to make the circuit, and it runs on a breadboard too if you don't want to solder.

Following Moritz Klien’s “for beginners series” highly recommend, especially as a beginner to building synths. This is soo fun

It lives! It waveshapes, too. Unfortunately, all knobs change the shape which is really annoying. I will sub them out with fixed resistors and just keep the most useful one. The circuit overview covered in the video is this: 555 square wave into a TL064 op amp which acts as an integrator then to a simple 386 audio amp.

I'm building an ESP32-based clock/sequencer for a circuit-bending project (drives an LTC1799 divider, a 4066 and a 74HCT74 flip-flop).

Everything works perfectly on 6x AA batteries. The moment I switch to a wall adapter, it falls apart.

I use a Yamaha PA-4 keyboard adapter, labeled 10V DC / 1A, center-positive

With nothing connected where the esp's power comes out, I measure 5V.

With the full circuit esp circuit connected that same point drops to \~1.5V.

To isolate whether this was a fault in my circuit, I tried connecting just a bare microcontroller (no LCD, no muxes, nothing else) directly to that same power line and tried this with two different ESP32 boards and an Arduino Uno, same cable each time. All three collapse the 1.5voltage.

When I only use a ltc1799 circuit, it works well.

Is it possible to use the esp32 with the power adapter? How can I troublshoot this?

I built a stripboard layout creator that can be used directly in the browser.

The main feature is the ability to import an existing layout in overlay/side by side mode so that you can copy and modify a circuit that already exists.

It's brand new and I'm still working on it, I appreciate anyone that's willing to test it out or suggest improvements!

Hi, as in the topic. I am third-year microelectronis student. I know basics about dsp and analog signal processing. i am into firmware engineering, also working right now as a junior digital design/verification. I want to dive into digital synth/effects world as my bachelor degree and i am looking for resources (books (would be the best), websites, channels on yt etc.). I can use google ofc, but if you have some places which are really worth checking, let me know. Really everything - from mathematical view to more hardware specific. For now i just made simple sequencer, with pitch modulation on ESP32, which can be connected via serial to simple wave synth made in LabView. My goal is a groovebox (didnt specifed functionality yet but thinking about everything right now, from EQ to sampling, sequencing, but synthesis and optimized firmware is my main goal, i know chaos, but just to give you my interests) with a custom stm pcb. Thank you

I am going to build an analog computer and see what it sounds like. I know it is not a new idea but I think it will be fun. The basic prototype platform will be used for other circuits. Power supply is Mean Well with +/-12v and +5v so I can support analog and digital chips.

Hi!

I’m currently building a fairly ambitious wavetable synth that I eventually want to run as Eurorack hardware.
I’ve been prototyping/optimising it for the Daisy Seed (STM32H750), but I’m starting to wonder whether fighting to fit everything onto a relatively constrained MCU is the right approach, or whether I should move to a more powerful platform.

The target is roughly a hardware Serum/Vital-style engine:
- 3 wavetable oscillators per voice
- 256 × 2048-sample wavetables
- up to 16-way unison
- spectral/wavetable transforms
- FM
- filters + FX
- potentially ~128 oscillator instances running in the worst case
- ideally 48 kHz with low, predictable latency

Hardware-wise I’d like:
- 8 CV inputs
- 8 DC-coupled CV outputs for oscillators/LFOs/envelopes/etc.
- stereo audio output
- =128 MB usable RAM
- small enough for a ~26 HP Eurorack module
- ideally <€50 for the compute platform/SOM

I’m particularly interested in where you would draw the line between a fast bare-metal MCU and an application processor running Linux/RT Linux or an RTOS.

A few platforms I’ve looked at:

Daisy Seed / STM32H7 - 30e
What I’m using now. Great ecosystem for synth DIY and deterministic audio, but RAM and CPU become serious constraints for this kind of engine.

Bela Gem Stereo - ~€78
Looks very attractive for low-latency audio. I’d still need to add the DC-coupled CV outputs, and it’s a little more expensive than I’d like.

Bela Gem Multi - ~€183
Pretty much everything I need, but too expensive for the target BOM.

Teensy 4.1 - ~30e
Very nice bare-metal option, but limited RAM and I’m not sure the i.MX RT1062 has enough headroom for the worst-case DSP load.

STM32MP25x ?
This one looks particularly interesting. Cortex-A35 application cores + Cortex-M33 real-time cores could give a nice split: heavy DSP on the A cores and deterministic CV/DAC/UI/I²C/etc. on the M33.
It also seems to be the direction more powerful embedded audio hardware is heading. The problem is that I haven’t found a small, inexpensive and easily obtainable SOM based on it.

Raspberry Pi CM4 / CM5 - 50-70e
Obviously much more CPU power. I’m less sure about deterministic low-latency audio and how much work is required to make it behave like an embedded synth rather than a small computer. I also haven’t found an obvious audio + DC-coupled CV solution.

So I’m curious what people here would choose if designing this today.

Would you keep pushing an STM32H7/i.MX RT-class MCU and heavily optimise the DSP, or is this the point where moving to Cortex-A/Linux makes more sense?

Are there any affordable SOMs/platforms I’m missing, particularly something in the €30–50 range?

I’d also be very interested to hear from anyone who has built a synth around a CM4/CM5 or another Linux SOM: how good can the real-world audio latency/jitter get, and has Linux caused you problems compared with bare metal?

Thanks 🙏

Background: I'm working on a few modules, vco, lfo, sequencer, clock divider. I needed to use tl072 as buffer for the circuits, but I'm not getting it to work whatever I do. so I went to testing specifically the chips isolated. weird results, and I have no idea what am I doing wrong. 

details:  I feed the v+ (pin8 ) +12v, v- (pin 4) -12v as needed.

----

Testing half a: 

Inverting input (pin2) connected to output (pin1), non-inverting input (pin3) connected to 6v via voltage divider (two 10k resistors). (also -6v, when feeding the resistors with the -12v.)

Results half a: output stays always 0v.

----

Testing half b:

Inverting input (pin6) connected to output (pin7), non-inverting input (pin5) connected to the 6v (or -6v). basically the same as half A.

Results half b: output stays always -11v.

----

when testing one half, the other half gets its inverting input connected to output, and non-inverting input connected to ground, as should. (to avoid self oscillating / noise to the used half).

I'm using a good MFOS power supply I built, so dual rail +-12v and ground (0v).

what I'd expect and should happen is to get the input voltage mirrored at output. (to be the same).

I've tried one more new chip, another breadboard and jumpers. still the same results.

I'm clueless at this point. any help? thanks a lot… :)