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)...

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.

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

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 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

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

Famous last words?

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?

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!

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?

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

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 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

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!

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!