If anyone wants to join in finalizing the code for our community, I have opened a new discussion : Hagiwo 6ch drum sequencer + 4x4 matrix keypad.
4 Likes
My latest build is a compact speaker module to have a quick way to monitor what’s going on in my eurorack system.
Also I build my test power supply into a plastic housing with additional space to add some testing utilities later (manual trigger, variable voltage source, etc…)
PS: Can you guess what circuit is currently set up on my breadboard? 
7 Likes
That’s pretty, a bit ARP2600-ish.
By coincidence, this week I also built a speaker amplifier using a ready-made TPA3118 module:
It runs off the DC supply to the power board, 15V or 19V.
3 Likes
Very nice and certainly much more powerful, than my little LM386-based module 
i fashioned this today with the worst reclaimed lumber i could find, a jigsasw, a drill, 3d prints, and no measurements whatsoever. 2×148hp. Open air design to make sure you can admire my art.
5 Likes
Colour me inspired!
Brilliant!
1 Like
Back to building again, made a double Analog Output power supply. Thanks @analogoutput !!
8 Likes
I just watched the YouTube vid. Loved it!
Although… I spent too much of the video with my eyes glued to a strange golden object, though just a shiny LED shroud, I’d managed to convince myself that this was going to be the capacitive interface for a Tap tempo or Tap lfo extension. Still, it’s a great build. Encore!
1 Like
Is it a noise generator? A 4 tone drone?
Yes! Its a voice from the MFOS Weird Sound Generator. Two sound oscillators and one modulator
1 Like
I kinda cheated. I zoomed in on the chip. Still had to guess the circuit tho. Cool.
1 Like
I didn’t recognize it, and should have.
2 Likes
Long time no build posts - my neurological delights mean I have fits and starts of a billion things at once. I’m back in the fold for now, so here we go.
Quadfadage. What started as an attempt to fix the wet/dry pot on an FX board ended up with me building a PCB based on the design by Laurent Chaté, and I accidentally made a Dieter Rams-inspired frontpanel for it.
Straightforward PCB. I may or may not add the diodes later - my power connectors are good at ensuring that the polarity is correct - but I put in a Eurorack power connector footprint so it felt wrong not to. Only real change to Laurent’s design is that I added capacitors for the op-amp power. The artwork is the Protect and Survive logo, which I’ve been putting on things for a while and now seems oddly fitting again 
(If you’ve never seen Protect and Survive, the logo and jingle at about 4m15s are incredible and probably where I started obsessing about synths, many years ago…)
9 Likes
1x1 meter Kosmo case. First idea was to make a polyphonic synth with four rows being identical and one to have modules to control all of them at once. So that everything would work as separate modules and/or voices if wanted. But that’s maybe a bit too ambitious and stupidly costly, in money and space, that I’ll just fill this with random modules and think about the polyphonic thing some time later. Half of the things there now are just empty panels that I need to build modules for and couple of digital things that have code in semi-working condition. And in the lower left corner there’s island for Eurorack-modules.
9 Likes
Time to poke at this for hours to figure out why it makes no sound
PT2399 experimentation board with pretty much every circuit variant i found online, using jumpers to confirm the circuit
4 Likes
Back on an old circuit bending box made a long time ago
and make a new version of it
all the build process here
7 Likes
Hey everyone 
As I gradually try and get my head back into this space I’ve revisited what I’d started last year, the drum sample player. It’s frightening to see my first post is 51 weeks old, I still feel like it’s what I was ‘just doing’, which shows how much my head hasn’t been in this space. (Links for the earlier posts at the bottom of this one.)
I decided to completely redo the panel, making it slimmer, while adding a screen and a rotary encoder to make it possible to have a proper menu. As far as I’m concerned it’s hardware complete now, so it’s ‘just’ a case of writing better firmware, which I’ve started. And along the way I accidentally made it look vaguely professional as well, which isn’t like me at all.
The OLED here is showing the CircuitPython command line. (I still think CircuitPython is the greatest thing I’ve ever found for microcontrollers.) I’ve added LEDs to show the state of the voices and made the most of the dual-colour capabilities of my printer to do a bit of labelling.
I didn’t have a knob that would fit the D-shaped shaft of the rotary encoder so I whipped up a matching two-tone knob which I’m more pleased with than I expected.
Electronically not much has changed compared to last year. The jumper at the top right is added so that I can plug in with USB and just power the 3.3V and 5V bits from my computer; in the other position it stops trying to pull power from the RP2040 board and feeds it the 5V it needs instead. It stops power circuitry getting hot and angry when I’m working on it.
The audio comes out of the PCM5102 audio chip at 2.1V RMS, which is 5.94V P2P. To get it to the Eurorack 10V P2P requires a gain of 1.68x, which makes it 9.98V P2P. Non-inverting op-amp using common resistor values - 10K and 6.8K - gets us bang on. The board’s 3.5mm jack is still there so, when not plugged into synth power, I can still get sound out
The red wire going to the purple I2S audio board is a late addition. If there were a lot of changes being made to the OLED then it would make audible squeals and chirrups when it was getting refreshed, where the I2C data transfer was getting in the way of sending the I2S audio data for a few milliseconds. After considering a lot of options I realised the answer was staring me in the face - the board has a soft-mute pin broken out, which is normally set with a solder jumper to always be unmuted. Removing that I’ve got the muting controlled by a pin on the RP2040 so, when there’s a need to use the screen, I can mute things beforehand. The chip does a really nice smooth transition between states, so there’s no pops.
The downside is that, obviously, I can’t have audio playing and do things on the screen at the same time, so I’ve decided there’s two modes - edit and play. That also makes programming for the rotary encoder that bit easier.
Anyway, that’ll do for today!
7 Likes
aaaaand he’s back!
I love the simplicity, please don’t worry about labels, perhaps find a way to have the OLED scroll through the outputs in play mode when bored. OR
take a tip from synth builders of the 80’s and add a sheet of white plastic to a slot in the base of the faceplate; then you can pull it out and write your set-up with a pen.
Can you recommend a good learning source for circuit python and audio.
Ps. I adore your case. Is it your own design?
2 Likes
Thanks very much!
I’m planning on having the current voices and their modes listed onscreen when in play mode. There’s one-shot/loop and trigger/gate already and I’m going to see if I can do round-robin without eating all the memory in the process. I want to be able to load and save kits (which is why I added the OLED and rotary encoder to the original) and my test code works so I’ll be working on that after getting the display to display something other than the Python command line.
For learning this stuff, I’ve mainly been pulling together various bits from the Adafruit learn guides and adapting them for my hardware: Adafruit Learning System - Liz Clark and John Park have written some great articles.
There’s also a very smart guy who I stumbled across and who got me interested in it in the first place: todbot (Tod Kurt) · GitHub
But to be honest, just messing around with CircuitPython is the best way to go. Its file system is presented to your computer as a flash drive, and by default it reloads the code automatically when you save. There’s a VS Code extension (which could be great if the author maintained it a bit better) and that has the library management and a serial terminal built in - a lot of what I’ve picked up has been from trying stuff out through the terminal and then saving what works.
And the case - the grey mini eurorack stand? That’s one of mine. I find it handy to have on my desk if I’m doing something. It gives me 20HP to work with, and I made a USB C to isolated ±12V adaptor, so I have a decent development rig!
3 Likes