Music Tech.Synthesizers, effects.
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USB MIDI to CV Host Controller
I thought that in theory, it might be fun to build an analog music synthesizer. The circuits themselves seem fairly simple and use low cost components. But when you actually get into it, it becomes apparent that it involves A LOT of hand wiring! I discovered this after I ordered some PCBs from the late Ray Wilson’s Music From Outer Space. I built the Sound Lab Mini-Synth Mark II and the 16 Step Analog Sequencer. The PCBs are 2 layer and not too complicated. But after you build the PCBs, it turns out that you are much less than half the way there. Making the front panels and wiring up all the pots, switches, and connectors to the PCBs are easily two to four times the labor. And Ray didn’t make this easy because all the connections to the PCBs are located randomly wherever they were needed by the circuit rather than running them to common connector points. So you can’t put on-board connectors between the PCB and the controls.
Here’s what I mean:
I thought that in theory, it might be fun to build an analog music synthesizer. The circuits themselves seem fairly simple and use low cost components. But when you actually get into it, it becomes apparent that it involves A LOT of hand wiring! I discovered this after I ordered some PCBs from the late Ray Wilson’s Music From Outer Space. I built the Sound Lab Mini-Synth Mark II and the 16 Step Analog Sequencer. The PCBs are 2 layer and not too complicated. But after you build the PCBs, it turns out that you are much less than half the way there. Making the front panels and wiring up all the pots, switches, and connectors to the PCBs are easily two to four times the labor. And Ray didn’t make this easy because all the connections to the PCBs are located randomly wherever they were needed by the circuit rather than running them to common connector points. So you can’t put on-board connectors between the PCB and the controls.
Here’s what I mean:
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So after building all that, the Sequencer and the Sample and Hold controllers end up being somewhat limited in what you can do with them. I thought, I need a keyboard for this project. But then I thought, ugh, I don’t want to build one, that sounds like too much work. I knew that MIDI keyboards for digital and soft synths are readily available in many sizes and price points from many vendors. It used to be that MIDI controllers used a 5 pin DIN connector with a sort of RS-232 like serial protocol. That would be easy to decode with a microcontroller which would then output triggers and the control voltages via a few DACs. But most modern keyboards use a USB connection instead. Today’s MIDI keyboards are USB downstream devices, they expect to be plugged into an upstream USB Host, like a PC for example.
So after some research, I came across a project that was a USB host shield for the Arduino that used the Maxim MAX3421E along with driver code. This shield was from Circuits At Home, but a recent check shows that it doesn’t seem to be available any more. I see that Sparkfun and several others are selling them now. I hand prototyped up several Adafruit MCP4725 mini-DACs along with some regulators, a voltage reference, and some op amps onto a prototyping shield. After some coding experiments with Arduino sketches, I had a USB MIDI to analog controller up and running.
Here is the three layer stack Arduino prototype plugged into a Korg Nanokey.
So after some research, I came across a project that was a USB host shield for the Arduino that used the Maxim MAX3421E along with driver code. This shield was from Circuits At Home, but a recent check shows that it doesn’t seem to be available any more. I see that Sparkfun and several others are selling them now. I hand prototyped up several Adafruit MCP4725 mini-DACs along with some regulators, a voltage reference, and some op amps onto a prototyping shield. After some coding experiments with Arduino sketches, I had a USB MIDI to analog controller up and running.
Here is the three layer stack Arduino prototype plugged into a Korg Nanokey.
I then re-did the schematic and combined what was needed from the Arduino, the USB Host Shield, and my analog circuitry and put it all onto a single PCB. To get it to work, you have to first program the Arduino boot loader into the processor as explained on the Arduino website. Then I used an Arduino Uno with its DIP processor removed and ran ground and the in-circuit programming pins over to the processor in my PCB in order to program the Arduino sketch into it. It seems to work well, however the Microchip MCP4725 DACs are not very linear. If I re-do this design, I will find a better DAC part. Here’s the final result.
Following the note on the MFOS website, I hand modified the two VCO’s in the Sound Lab and they track reasonably well over a few octaves.
When I started this back in 2016, as far as I could tell, a USB MIDI Host Controller to Analog Control Voltage module was not available from anyone. Today they are available from Expert Sleepers in the UK for a few hundred bucks.
28-December-2019
28-December-2019
MFOS
Coming sometime!
Coming sometime!
Theremins
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Coming sometime!
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