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Showing posts from September, 2022

Eurorack VCO Module - AS3340

Update 2023-02-18: There's a new version of this design: v2.1 I don't consider this design done; but, I've gotta start writing it down because I'm carrying too much diagnostic info in my head regarding this thing. One of the early kit's I built was this AI011 VCO . Despite the website saying it uses a Curtis chip (CEM3340) mine came with a clone AS3340A. At the time I didn't know anything about either chip, I just wanted a VCO to build and play with. Overall it is a fine VCO, it sticks to the datasheet's circuit for trimming. I also built four Befaco Even VCO s to use with the polyphonic envelop generator . I was initially on the fence about building my own, but I eventually decided it would be a nice accomplishment to do an entire signal chain from keyboard to output all of my own designs and an oscillator was gonna be necessary. So I bought some AS3340's from Electric Druid and set about making my own design. The AS3340 has a triangle, falling sawtoot

Eurorack VCF Module - Low Pass Filter - AS3320

This is my first filter design for Eurorack. I seem to always use my multi-mode filters (built from kits) in lowpass mode so that's what I've designed for myself. I didn't want to jump into a multimode filter yet, it just complicates things I don't have a good grasp on yet. The module uses 8HP. For this filter I'm using the AS3320 filter chip which I picked up along with various other chips in that series from Electric Druid . When I went to figure out the circuit I ran into the biggest road block which is that the data sheet is nearly useless. It shows a sample circuit for low pass, high pass and other use cases but they are a tangled mess of wires, very poor layout for helping anyone understand the chip. In an age where the data sheet doesn't need to fit in a single page, there's no excuse for providing such bad documentation. Rant over. These chips are clones of CEM3320 and the full data sheet for that is somewhat better. Here's where I found it . In

Eurorack 4:1 Mixer Module

This is a Eurorack Mixer module with four inputs in 6HP. It's quite simple and only uses an op-amp and a handful of passive components. There are four inputs and one output. The inputs pass through independent potentiometers for attenuation and the all the inputs are summed and output. Here's what it looked like on the breadboard: There's also a simulation . This type of mixing allows a strong input to effect other inputs (crosstalk) so it's not optimal for an input that needs to be routed to some other place pre mix. Other than that limitation it seems to work just fine. The potentiometers used to attenuate the signal can be audio (logarithmic) or linear depending on how it's getting used.  I'm glad the design works because after panelizing these I got 30 in the first order which is more than enough for me. I haven't found any issues yet with the v1 circuit, but I haven't used them much either. Time will tell. If I make another mixer it will probably ha

Eurorack VCA Module - AS3360

Every synth needs a VCA. Since I've been making a few modules around Alfa chips that are largely clones of Curtis chips I picked up some AS3360 's to use for this module. The AS3360 has two VCAs in it. It's fairly simple to use compared to the VCF and VCO in the same series of chips.  Much of the design is straight from the data sheet with some bits borrowed from the Look Mum No Computer VCA  but I've changed some elements to deal with CVs in my system going 0-10V and for various component differences. As usual I put this thing together on the breadboard first. In this case it's pretty much a complete mockup of what I have in the PCB.  The PCB design goes quite smoothly when I can work out the details on the breadboard. The best part of looking at the LMNC design before going into the PCB design was realizing that that design inverts the input and inverts the output for a net non-inverted output. That's a nice simplification I wish I had thought of myself, it

Eurorack MIDI to 16x16 CV Gate Module

This is a big one. I have been pursuing an idea to make all the modules in a full Eurorack signal chain and to be able to do polyphonic voices in it. The first thing in the that chain is a midi module that can take midi from the computer or keyboard and turn it into signals for other modules.  Early on I needed a module like that so I bought a Befaco Midi Thing  kit from Thonk and started using it, but I wanted to have the ability to drive even more outputs. So this module has 16 CV outputs and 16 Gates. It consumes 18HP. It has MIDI input and output. the brains of the operation is an Arduino Pro Mini which I've written firmware for to handle polyphonic input (more on that later). There's a single button on the front which for now lets me set a MIDI channel. This thing doesn't have nearly as much configurability as the Midi Thing but I don't have to open a manual to change the main thing I need to configure. Design Process This design is much more in my comfort zone tha