As predicted, none of the exams I've had this week went particularly well. But maybe I'll surprise myself like last year when results come out.

This week

Not much progress this week due to exams. As mentioned in last week's update, I hope to start building from around mid-May.

When I haven't been in Laplace transform jail, this week I've been thinking about project timelines and also about possible designs for my VCO. I'll start with discussing project timelines first.

If I can get to having a good VCO, VCF and VCA by the end of July, I'll be happy, as this will give me a solid two months to add interesting improvements. I have an assessed university project from May-June, and an internship during July, both of which should come first, so I've given extra time to some of the earlier deadlines.

This plan almost definitely will change during the course of the project. This is my first build at this scale, and my first time making a synthesizer, so I'm prepared to anticipate and embrace delays.

Designing a VCO

A voltage controlled oscillator takes in a constant DC voltage known as a control voltage, and synthesizes an alternating wave with frequency directly proportional to the control voltage. The majority of musical synthesizers follow an exponential CV scheme known as "one volt per octave", where control voltage increases by one volt for a doubling in frequency. From a musical perspective this is a sensible control scheme, as doubling the frequency of any note results in the same pitch, but an octave up.

A VCO should also be able to generate multiple different waveforms; types commonly found on classic synths are square, sawtooth and triangle waves. Sine waves are not generally used, as they can be easily derived from filtering other waveforms.

Designing a reliable analog VCO is incredibly challenging, and there are several common types used in early analog synths. I'll discuss these more in a future update.

In the post

The CV-12 is a remarkable chip, which is capable of converting digital MIDI signals into a CV (control voltage) and a trigger (a short pulse that tells an envelope generator / amplifier when a MIDI Note On event is detected).

Many MIDI to CV/Trig converters are very expensive, with good ones costing around £100 each. These are intended more for the Eurorack market rather than for ground-up electronics builds, so don't really fit my requirements or budget.

What makes the CV-12 special is that it is capable of polyphonic MIDI to CV conversion, meaning it is capable of outputting many control voltages (corresponding to many different notes) at once. This means it becomes possible to play chords from the get-go. It's also fully configurable with various mode changes. Polyphony can be sacrificed for additional MIDI parameters like note pressure and pitch bend, and even VCF parameters like cutoff / resonance. Considering what this thing can do, £17 is an absolute bargain.

I also bought an SMD soldering practice kit, if not for learning how to solder SMD components for this project then just for a bit of fun. This consists of a small, and a variety of SMD resistors, capacitors and chips in different sizes to practice with.

I don't think I quite realised just how small SMD components really are - whilst the 1206 and 0805 size look manageable to solder with my iron, the smallest 0402 size ones are absolutely tiny.