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Pittsburgh Modular Microvolt 3900

Semi-modular Synthesizer
Published February 2019
By Gordon Reid

Pittsburgh Modular Microvolt 3900

Pittsburgh's desktop semi-modular has its eye set firmly on the experimental.

The Microvolt 3900 is a monophonic synthesizer in a chunky steel desktop box that also sports a lump of wood at the front to reassure you of its analogue credentials. It comprises a single 1V/oct oscillator, a low-pass filter and an unusual VCA section, all controlled by an LFO, a random CV source, a looping AD 'Function Generator' and an ADSR contour generator. It also includes an arpeggiator that offers a limited 16-step sequencing capability. All of this is sensibly pre-patched within the synth, but a 39-socket patchbay elevates it to semi-modular status, particularly since you can interrupt the signal path to create new audio routes as well as new modulation possibilities. The sockets themselves are all 3.5mm, which makes it physically compatible with most Eurorack equipment, and the CVs and gate voltages are chosen so that you should have no problem hooking it up to such as system. For clarity, inputs are shown by a box around the text, while outputs are shown using plain text.

The Signal Path

The single VCO generates four underlying waveforms: sine, sawtooth, pulse and 'fold'. The unadulterated sine wave is a little brighter than a pure tone, while switching on the Harmonic Sine function creates a considerably brighter waveform that, on the 'scope, looks much like an unrectified half-wave. The sawtooth is closer to the ideal, and is bright and raspy. The pulse wave has a minimum static duty cycle of around 6 percent, and a maximum of around 94 percent, but you can drive it down to 0 percent and up to 100 percent using pulse-width modulation. Fold is interesting because this starts with a sine wave and (as the name suggests) increases the amplitude and folds the waveform into more complex shapes as you increase the Fold Timbre level. Without...

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Published February 2019