The heart of an analog synthesizer its the Voltage Controlled Oscillator ( or VCO ), so logically the first module I am going to start working with is the VCO.

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Front Panel

The synth cabinet is going to be based on the eurorack form factor, so the size of the front panel must comply with the "standard".

A typical synth enclosure is 6 HP units high, accommodating two rows of modules, each 3 high, and 84 HP units wide, so if we want a rack enclosure with 4 VCOs they should be 10 units wide, so they only take up half of the top row.

Following this guidelines, the aluminum front panel is 128.5mm high by 50.50mm width and the PCB in order to fit in normal fabhouse board size limits will be 100x50mm with a few mm of margin if we need the space.

A SVG of the front panel design has been made, so it can later be transfered to a piece of aluminium with the toner transfer method

The PCB will be mounted to the front panel with the potentiometers and audio jacks, so no holes for mounting are needed

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Schematic Transcription

The original VCO schematic are two pictures on the MFOS website, so I've made them again in KiCAD, in order to be able to layout a new board.

The original design specifies  a temperature compensator, witch after some research turns out to be synth lingo for a thermistor, a PTC thermistor to be more exact. The one used in the original design is a 2k with a very low tolerance. These have been proven difficult to find in the usual distributors, so two 1k .5% PTC thermistors in a 1206 and very close proximity to the matched transistor package will be used

The PCB layout will be done in the following days, and after the PCB is sent to the fabhouse, the KiCAD project will be uploaded to the project page.