DoublePlusBass

 Yo, it's the first PCB I designed!

This circuit, the DoublePlusBass, represents the culmination of a LONG journey starting with my first complex point-to-point success (a TR-808 kick drum) and wanting a 909 style kick drum. Couldn't get it. Failure after failure.

Thomas Henry's Bass++ is a miracle of minimalist complexity, wringing a very capable and versatile kick drum voice out of a single LM13900 and a dual op amp. Quick note: there's a .pdf on that website that is AMAZING you HAVE to see it okay fine here's a link my god it's a thing of beauty.

So, I got massive kicks out of Thomas Henry's excellent work, but I wanted more flexibility and less "crosstalk" between settings. Which involved more parts. I wanted a pitch envelope that made the kick pitch more similar to the 808, which sags right at the end vs. the 909, which spiked downward fairly quickly after the attack.

Feature creep crept in, with every problem being solved with more buffers, so my own kick drum diverged significantly from the Bass++ inspiration, so the DoublePlusBass was born.

All my schematics had been hand-drawn up to this point, but the DoublePlusBass was super complicated, so I was struggling fitting all the schematics neatly on one page. Yes, I resorted to cutting and pasting. But then I started investigating electronic design applications, and after much frustration, landed on EasyEDA, which runs in a browser, which kinda rules.

After getting the schematic drawn, my mouse crept up to the "create PCB" menu item so with much trembling and quaking, I clicked it. POW!!!!! All my parts were there, on a blank field, ready to organize and trace. Incredible. Mind-blowing.

I've never had success with any kind of 2 dimensional prototyping. 3D is where my brain lives, where my circuitry took shape and gained life. BUT!!!! The 2 dimensions of a PCB somehow did click, so ...

... to make a long story not any longer, this is my first PCB. The current prints are a lot better in layout and whatnot, but the ELEVEN potentiometers are still laid out like they were, and the functionality is basically the same.

Okay, I'm actually NOT going to list everything that each pot and jack does, I'm in a hurry, but here's the biggest surprise: the 808/909 envelope moves the fundamental pitch up a great deal when turned toward the 808 side. The 909 starts high and drops to the fundamental pitch. The 808 hits its fundamental pitch right away, and sags down from there. So my least solvable problem was this: that knob fades between two theoretical fundamental pitches, but there's only one pitch CV, which ... the user has to turn lower when choosing a more 808-style pitch envelope.

Okay, that's all for now.

PlusSnare, an 808 snare with a twist!

 This little fellow is a basic snare voice module that accepts a trigger, and outputs a snare. It's a modern copy of the Roland 808 snare voice, snappy volume, two different "body" bridged-T circuits that make a "bong" sound, and a knob that fades between the two. It sounds like a reasonably accurate synthesized snare drum, and exactly like some* 808 snares.

*the OG '80s and '90s Roland drum machines are mostly analog, with 5% carbon film resistors and (aging) electrolytic or (high-tolerance) ceramics and maybe even (SCARY) tantalum caps. So, every one of those machines will sound slightly different, sometimes you'd even be able to tell by listening. But they all sound like 808s or 909s or 707s or whatever.

Anyway, this module ALSO has a delay circuit. It uses the ubiquitous PT2399 chip, with the parameters shoved way past where they're supposed to go, we've all heard the runaway delays and the CRONCHY delay times that happen when a designer wrinkles up the datasheet .pdf and drags it into the recycle bin.

Also also, you can inject whatever sound you want for the "snappy". Kinda fun to experiment with a random audio track, say, Carly Rae Jepsen's hit pop anthem Call Me Maybe? The input will be getting the same filtering and VCA'ing that the white noise gets, just so you know.

Okay lemme seeeeeee... hmm, instead of trying to remember what this module can do, and how to get it to do it, allow me to send you to a Youtube video of it:

 

 

Okay there it is! Quick rundown if you don't want to watch a video:

Jacks:

Trig triggers, MixCV controls the wet/dry mix, with high voltages injecting the snare voice into the delay circuit. The delay tails, so a low voltage won't cut off the delays. It's fun to have the 3rd snare per phrase have a dump of delay... this module was inspired by King Tubby's use of this technique. Acc is basically CV control over the amplitude of the snare. The 808 machine has two levels, but this is infinitely variable. Out is out.  Alt is for alternative "snappy" sound inputs.

Knobs:

Tone fades between the two "body" resonant voices. Snap adjusts the volume of the white noise or the alternate signal. Delay controls the length of the delay repeats. Reps controls how much of the repeated signal gets passed back into the delay circuit. These last two controls will crunch and degrade, and repeat into very loud runaway feedback. Mix is the initial wet/dry control of the output between the snare voice and the delay circuit. Vol is output volume obviously, with a twist: the first two thirds or so of the volume are straightforward amplitude, but the last third soft-clips against a pair of diodes, making for a nice saturated snare sound.

Huh, I guess that's a pretty complete rundown, not as quick as I'd thought. Okay enjoy!

POWER to the People

Here's a module that's got +12V, -12V, optional +5V, and a headphone amp. It charges via USB-C, and seems to work pretty well... my multimeter shows confusing numbers when I try to measure millamps, hopefully some actual stats will be forthcoming.

So here's the placeholder for the build document. I'll hurl some

 SAFETY WARNINGS

 here because lithium ion batteries can be hazardous.

• Never short a lithium ion battery. They will die, possibly by bursting, possibly by lighting on fire. They are very difficult to extinguish, since they often have oxidizing chemicals built in, as though they're DESIGNED to be rocket fuel or something.
• If you do have a battery light on fire, put it in a bucket of sand and move the bucket to a well-ventilated area. Wait for the battery to stop being on fire. Wait even longer for it to cool. Then take the goo to a qualified battery disposal site in your area.
• Pay extremely close attention to the polarity of the battery you're plugging in to this module, and the polarity of the pads or connectors you're connecting to. I can't guarantee that your battery will be correctly labeled or built, so please check that stuff. This module has reverse-polarity protection, but try not to test it.
• Avoid shorting the outputs rail-to-ground, or rail-to-rail. The module is built with short-circuit and over-current protection, but again, try not to test it.
• Use boxed-style IDC headers for the Eurorack cable headers. This is important because you don't want to plug your cables in wrong, but even more importantly, they'll provide the physical foundation for the cable ends that the 13650 battery you might be zip-tying to your module. This module will work with any single (1S, in battery lingo) lithium ion battery, but there's holes to make it easy to zip-tie a cylindrical cell there.
• Please secure whatever battery you use in a safe way inside whatever enclosure this module will live in. Lithium ion batteries should never be rattling around inside anything, so seriously, folks, don't goof around with this stuff.

Features of the M4TM POWER to the People

• Rechargeable and portable bipolar power for Eurorack modules
• Optional 5V power rail 
• ? mA of power with ? voltage sag ??
• Overcharge, undercharge, overcurrent, and short-circuit protection
• Headphone amplifier! Stereo, with the top input sending signal to both channels if nothing is plugged in to the bottom input
• The cheapest battery-capable +/-12V power supplies out there will abuse the battery if you charge the battery while using it. This one has a little mosfet that allows for use WHILE charging. Neat.

Okay that's it for now. I'll probably make a build-guide which will hopefully be here, or at least I'll link to it.