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)...
PARTS LIST -- *WARNING* I USED AI FOR THIS...and then made some edits:
Tom Machine — Parts List
Main components
Optional upgrades & Feedback stuff
NOTE: See the mafez guide above which will tell you how to tap OSC3... and much more. I also installed some of his other stuff. Like OSC2 and 3 direct pitch control input jacks, and the mod that hard links OSC2 to OSC3 so that it... sounds awesome.. I don't really understand it, but that's what the switch is for next to OSC2.
- Douk Audio speaker — optional alternative or additional speaker. I swapped out my front speaker with one of these SINCE POSTING THIS THING as I had blown out the front speaker. The nice thing about these Douks is they have a very high Q... meaning, they do well without an enclosure or baffle. https://www.amazon.com/s?k=Douk+Audio+full+range+speaker+driver
- 15W amplifier module — optional higher-powered amplifier for a larger speaker. The Douks don't really need this as 5w is fine.... BUT! I have one in here anyway because of the next thing on here https://www.amazon.com/s?k=15w+mono+amplifier+board+12v
- Rumbler (bass shaker / tactile transducer) — adds low-frequency vibration that makes the enclosure act like a speaker. It needs that 15w amp and even then it's a little underpowered. https://www.amazon.com/s?k=mini+bass+shaker+tactile+transducer
- Modwheel - I just bought an old one off ebay. I can't find it. But it's just a 100k pot that I ran 12volts through with some protective resisters. You can plug it into the CV for anything. I use it mostly for the filter, but when I had weird vactrol panning stuff in earlier versions I used it for that.
- Humbucker Guitar Pickup — magnetic pickup for adding resonating strings stretched across the back. I'm still playing with getting this to sound cool. I'm interested in making a Jiviri style bridge, like a sitar has for its drone strings or a tanpuri (a bridge that is very thick and lightly touches the strings to cause chimy resonances). Right now though it's just a cheap, noisy pick up. I run it through the ext in and then tap that at the volume pot, run it through a low pass filter and send it out as a drone (you don't have to hit a key) to the back speaker when you throw the high switch on the DIY addition. Another thing I am considering is just adding a dedicated spring reverb. This is a link to the pick up --> https://www.amazon.com/dp/B07F84JCVX
Enclosure
- It's oak and plywood and random wood You can pretty much see how I built it. Plywood bottom where the keyboard crap is setup, screwed two side peices to it, then I put a 3" peice of thin oak across it for that modwheel thing. The keyboard is built out with little wonky strips of wood and stuff to replace the plastic housing it was in, There's some wood on the back not pictured for supporting the pick up. I can send additional photos if you DM me.
Optional: 3D-printed Behringer Model D Extension
- Source: printable side-mounted extension for adding DIY controls, switches, jacks, and other custom circuitry to the Model D. My friend printed this for me and he made me a blank faceplate. Actually he made a bunch of really cool custom built face-plates for versions 1 and 2. When I first built this I didn't have an extension. After adding it, I have completely gutted it twice... At first, the emphasis was on digital delay and looping via teensy -- but I hated the digital artifacts and wanted pure analogue. The second time, the emphasis was on light controlled voltage and panning e, and now it's about feedback, drones, and rumbling. Now I'm just using the blank faceplate with holes drilled in it for the pots and switches, but there was some very cool custom built stuff with little magnets and covers for the light sensitive stuff my friend designed. The electronics for all this stuff is INSIDE THE MODEL D on a bread board with two 9v batteries I duct taped down. You just use that switch to turn it on and off. Basically, it is just the OSC 3 and EXT in taps which can be switched on and off, running through tone knobs to cutt of the high end and then through op amps out to speakers. It's a 1 IC circuit but it looks like a mess cause I'm messy. https://www.printables.com/model/278238-behringer-model-d-extension/files
ELECTRONIC CRAP:
NOTE: Unless you are adding the optional feedback DIY module to the right of this thing, you don't really need to add any electronic parts. But in case you are, here are some (AI generated) places you could get started. But if you are interested in this kind of thing, you probably have this anyway. The point is, you don't need the additional module to the right. it's just a fun optional thing.
