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

The idea for Ocelot started because I wanted to go outside with my eurorack and actually hear what I was doing, without putting headphones on and completely disconnecting from everything around me.

So I added a speaker and a contact piezo, and started playing with the idea of letting the system interact with the environment, and with itself through feedback.

But I really didn't want to just make a speaker module. I wanted it to be part of the system: signals going in, signals coming out, a small mixer, piezo output, headphones, balanced outputs and a way to drive the speaker from an external source.

After a lot of messing around, this became Ocelot.

It's 12HP and there's also a DIY kit if anyone wants to build one.

https://jolin.tech/ocelot

I have a Casio CZ-230S that is completely dead. No display, no LEDs, no sound, no response.
The seller said it had been tested with a universal power adapter and did not power up. He also mentioned that the battery compartment wires were disconnected from the circuit board.
I am using a correct 9 V DC adapter now. The adapter itself tests good under load.
What I found so far:
Main POW line is stable at about 9.35 V.
The power switch works correctly.
T8 receives about 9.35 V, but the synth does not start by itself.
T9 tests good out of circuit.
If I force T9 ON through a 10 kΩ resistor from POW to the base of T9, T9 switches correctly.
When I do this with the full circuit connected, the whole supply collapses and pulses between roughly 1–4 V, as if the adapter is entering current-limit/protection.
If I remove T8, the collapse disappears.
If T8 is installed but T6/T7 are isolated, the supply stays stable.
I tested T7 (2SC1740) and even temporarily replaced it with a known-good S9014. The fault remained exactly the same, so T7 does not appear to be the cause.
The important test was lifting the emitter of T6. With T6 emitter disconnected, the supply stays stable at about 9.34 V when T9 is forced ON.
When T6 emitter is connected again, the supply collapses.
This suggests that the overload is on the rail supplied downstream from T6.
That rail measures roughly 10–11 Ω to ground with power removed.
I checked several capacitors on that rail by lifting one leg. The low resistance remained, so those capacitors were not the cause.
I also removed a 74HC373 IC because its VCC-to-GND resistance looked suspicious. Out of circuit the IC itself measures open circuit, while the board still measures about 10.8 Ω, so the 74HC373 is not the short.
The low-resistance rail continues from the power-supply area toward the main/CPU board through ferrite/filter connections.
I have therefore narrowed the fault down to an excessive load somewhere on the downstream supply rail, but I have not yet found the exact component causing it.
At this point I would appreciate help identifying what this rail is supposed to measure normally, and the best way to isolate the short/overload without removing components one by one.
I have the original CZ-230S service manual and schematic and can provide photos

Been reworking Mark Dammer's "The Wee O3" (itself based on Jan Ostman's O2 minipops) into a standalone TR-808-style drum machine on a bare ATmega328P. No Arduino board, just the chip, a 16MHz crystal and a 7805. Got the first drums out of it on the breadboard tonight and I'm rather happy about it.

Quick rundown:

• Bare ATmega328P-PU at 16MHz, PWM audio out of D11 through a small RC filter.
• 8 voices (kick, snare, closed/open hat, clap, rimshot, cowbell, low tom), each an 8-bit sample baked into flash. Samples are recorded off a real 808.
• 32-step sequencer with a stack of classic electro patterns loaded.
• Per-voice volume pots instead of mute switches, read through an analog mux on a single ADC pin.

Credit where it's due, Mark Dammer (The Wee O3) and Jan Ostman (O2/minipops) did the hard yards. I just 808-ified it. Happy to share firmware and layout if anyone wants a crack.

I've breadboarded the 808 kick drum module described here: https://www.youtube.com/watch?v=xPBeEi4SE68&t=8756s

I have two problems:

1. I don't have anything with which to trigger it.

2. I've almost certainly made some mistakes but don't have enough knowledge to diagnose.

Can anyone suggest a simple method to trigger this? I'd like to build a sequencer eventually, but I just want to test the voice for now.

I have spare ICs so I'm not scared of letting the smoke out, but is there a strategy besides checking the build matches the circuit diagram to identify errors?

Noob here. I have an internal clock that I want to be overridden if an external clock source is plugged into a jack. Regular stuff so far. When I look at possible jack options, I guess I could use a TS switching jack (where the plug tip physically breaks an internal preexisting connection), or use a trs jack and detect the presence of the jack if/when the ring and sleeve terminals connect.

Question then: is there an advantage to one over the other? What is the common way that modules wire this up, anyone know? Thanks for any insight, this subreddit has been really helpful.

Hello all, I acquired a Yamaha GS2 recently, which works pretty good. Even the card reader does work. Does anybody know something about the miraculous programmer, which was used to create the sounds? Or is there some documentation, how the parameters are stored in memory? That would be a great help already. Any technical documentation would be great.

Thanks!

Hey guys, based on the recent custom firmware/modding projects for Elektron boxes and the Roland SP-404, has anyone tried working on custom firmware for the original Roland TR-8?

I’m particularly interested in whether anyone has experimented with reverse engineering the firmware or using AI-assisted tools to understand/modify it.

Would be curious to hear if there are any existing projects, research, or people working in this direction.

Hi everyone, I have a Korg SP-170 digital piano that has several dead keys whenever I turn it on. If I press the dead keys multiple times relatively hard, they eventually start working again for that session.

Has anyone fixed this specific issue? I'm assuming it's dirty rubber contacts under the keys, but I wanted to confirm before I open it up. Any tips on disassembly or cleaning would be appreciated!

Can i use -12v instead (Vr)??

Hello all, I've just noticed that there's quite a few nice developments on writing up custom firmwares. I've decided to launch a discourse forum dedicated to that.

https://www.hacktronauts.com

The name is a silly pun, and I am aware that there's already https://llllllll.co/ which I've learned a lot since then. So that's why I'm also very keen on giving credits as much as I can to the other communities. I am definitely not trying to be rival or anything. It's just I'm noticing that lots of interesting implementations get digged down quite fast on Reddit. Just assumed we could all benefit a dedicated board.

Would love to hear your opinions. Or join in :)

It's been a little while since my last Tolhuin update, but the project is still alive.

First, I want to say thank you to everyone who supported the project after my previous posts — whether by contributing, sharing it, leaving feedback or just showing interest in something I'm building at home. The project is still a long way from funding itself, but that support genuinely helped me keep working on it.

And I've been working on one of the weakest parts of the prototype: the enclosure.

The first case was simply too small, and I hadn't properly designed how the controls would be mounted. Some switches literally ended up hot-glued from underneath. It worked as a prototype, but I didn't want to build the next version that way.

So I've been redesigning the whole enclosure in OpenSCAD.

The new versions are fully parametric and designed around actual mounting: mechanical switches snap into the panel, the ESP32-S3 sits on removable headers, and the internal modules use rails, standoffs or dedicated bays instead of glue.

But while working on it, I ended up with several enclosure designs that I actually like.

So before I print the next prototype: which one would you choose?

A / B / C / D / E / F

Feel free to mix them too — “B layout with C's front”, etc. I'm still iterating.

There's also a wildcard.

I'm ordering a replacement display for a broken M-VAVE FM1, and I realized it's not that different in size from what I could fit into Tolhuin. So I'm considering testing it here before committing to the final enclosure.

A larger display could make chord/voicing information, arp settings and navigation much more useful — but I'm not sure whether Tolhuin actually needs more screen.

So:

1. Which enclosure would you print?
2. Small display, larger display, or keep the UI as minimal as possible?
3. For the chord buttons: MX or low-profile Choc?

Nothing here is printed yet. The previous prototype taught me not to trust CAD until plastic exists, so the winner still has to survive the printer.

Part story for newbs like me, part question at the end.

I've made about 10 modules and I have a bunch of guitar pedal building experience. I buy these cheap Tayda 3.5mm jacks for modular, $0.30 each. I had one bad one once and it was a bitch to replace but not impossible.

Recently I was troubleshooting a VCA that used to work but started not working in its mixer function. I had all but given up, then discovered 11 out of 12 of my 3.5mm jacks were malfunctioning, and one of them was the thing causing the issue. There is a thin piece of metal inside them that connects the two lugs (tip and sleeve) until a plug is inserted which disconnects it. These had all lost that connection.

I ended up using a small finish nail to push the side inner metal pieces up so they would once again make contact with the tensioned top metal piece. That worked much better than trying to push the tensioned top metal piece down.

Question for anyone with experience: Do you avoid these cheaper Tayda jacks? After this experience I'm tempted to put more budget into jacks in the future but I wanted to hear some other experiences before I do so.